Homebrew PCBs

Now I have never built a CNC anything and I am not overly mechanical.  
Right that is my qualifications out of the way...

I was thinking about high torque motors to drive a linear thread and I 
thought about those really cheap cordless drills.  That is idea pt1.  

Now of course you need some sort of feedback for the position, the 
normal way would be to put a shaft encoder on the drive.  My thinking 
is that if you used a linear encoder then you would get absoulte 
positioning thereby negating the need for backlash compensation.  Now a 
quick look around ebay reveals that linear encoders are not cheap.  So 
has anyone used optical mice for a linear encoder? (idea pt b)

Here endith todays musings.

Mike

On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20 <mikegw20@...> wrote:

> Now I have never built a CNC anything and I am not overly mechanical.
> Right that is my qualifications out of the way...
> I was thinking about high torque motors to drive a linear thread and I
> thought about those really cheap cordless drills.  That is idea pt1.
> Now of course you need some sort of feedback for the position, the
> normal way would be to put a shaft encoder on the drive.  My thinking
> is that if you used a linear encoder then you would get absoulte
> positioning thereby negating the need for backlash compensation.  Now a
> quick look around ebay reveals that linear encoders are not cheap.  So
> has anyone used optical mice for a linear encoder? (idea pt b)
> Here endith todays musings.
> Mike


cordless drills usually use a motor what the model-vehicle builders would  
call similar to a "speed 600".
Not a bad motor, and you can get replacements really cheap as well as  
better motors the same size.

I would try to find drills with metal gears for this purpose. I recently  
bought a very cheap one with plastic gears, it is still working, but i'm  
always expecting it to fail any time. It was cheaper than a replacement  
battery for a better drill.
There are often ebay lots of many drills.


As for linear encoder, there are those striped plastic strips in printers,  
but a much easier solution would be to use digital calipers and use the  
data-out, 'cause you would get absolute position not only relative.  
Probably more expensive than shaft encoders and certainly more expensive  
than steppers.


ST

While I don't fully know the exact details, I can tell you right 
away, you cannot rely on software to eliminate the backlash within a 
CNC system.  For basic positioning, perhaps a little, but in 
practice, no.

While software can compensate for the static deviation between where 
it told the motor to position and where it really is based on 
encoder feedback, the "Slop" is still there.  During cutting, the 
dynamic cutting forces will cause the axes to move around within the 
mechanical slop.  When drilling, the position will be off and the 
holes will not be on size.  When milling, all sorts of dimensional 
problems pop up and in the end, you will have wished you took the 
time the eliminate the mechancial backlash.

While there is backlash compensation within all CNC systems I have 
used in the industrial world, it is primarily only used to 
compensate for a very samll amount of backlash .001" or less 
usually. Beyond that and it is time to correct the mechanical 
problems.

So, don't waste your time or effort in thinking of a software 
solution to backlash - backlash is a mechanical problem and must be 
designed out of the system for even the most basic of machine 
performance.








--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
<stefan_trethan@g...> wrote:
> On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20 <mikegw20@h...> wrote:
> 
> > Now I have never built a CNC anything and I am not overly 
mechanical.
> > Right that is my qualifications out of the way...
> > I was thinking about high torque motors to drive a linear thread 
and I
> > thought about those really cheap cordless drills.  That is idea 
pt1.
> > Now of course you need some sort of feedback for the position, 
the
> > normal way would be to put a shaft encoder on the drive.  My 
thinking
> > is that if you used a linear encoder then you would get absoulte
> > positioning thereby negating the need for backlash 
compensation.  Now a
> > quick look around ebay reveals that linear encoders are not 
cheap.  So
> > has anyone used optical mice for a linear encoder? (idea pt b)
> > Here endith todays musings.
> > Mike
> 
> 
> cordless drills usually use a motor what the model-vehicle 
builders would  
> call similar to a "speed 600".
> Not a bad motor, and you can get replacements really cheap as well 
as  
> better motors the same size.
> 
> I would try to find drills with metal gears for this purpose. I 
recently  
> bought a very cheap one with plastic gears, it is still working, 
but i'm  
> always expecting it to fail any time. It was cheaper than a 
replacement  
> battery for a better drill.
> There are often ebay lots of many drills.
> 
> 
> As for linear encoder, there are those striped plastic strips in 
printers,  
> but a much easier solution would be to use digital calipers and 
use the  
> data-out, 'cause you would get absolute position not only 
relative.  
> Probably more expensive than shaft encoders and certainly more 
expensive  

> than steppers.
> 
> 
> ST

>When drilling, the position will be off and the
>holes will not be on size.

I don't agree with this. Perhaps with a light table and a high runout 
drill such as the ubiquitous Dremel one may have an issue. With a 
heavy table (the X axis and saddle in my setup weighs over 40 lbs) 
and a low runout drill this is not an issue. Backlash compensation in 
software is very effective when it comes to precision drilling IMO 
provided you know what you're doing. Milling and routing is another 
story.

--- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
<lcdpublishing@y...> wrote:
> While I don't fully know the exact details, I can tell you right 
> away, you cannot rely on software to eliminate the backlash within 
a 
> CNC system.  For basic positioning, perhaps a little, but in 
> practice, no.
> 
> While software can compensate for the static deviation between 
where 
> it told the motor to position and where it really is based on 
> encoder feedback, the "Slop" is still there.  During cutting, the 
> dynamic cutting forces will cause the axes to move around within 
the 
> mechanical slop.  When drilling, the position will be off and the 
> holes will not be on size.  When milling, all sorts of dimensional 
> problems pop up and in the end, you will have wished you took the 
> time the eliminate the mechancial backlash.
> 
> While there is backlash compensation within all CNC systems I have 
> used in the industrial world, it is primarily only used to 
> compensate for a very samll amount of backlash .001" or less 
> usually. Beyond that and it is time to correct the mechanical 
> problems.
> 
> So, don't waste your time or effort in thinking of a software 
> solution to backlash - backlash is a mechanical problem and must be 
> designed out of the system for even the most basic of machine 
> performance.
> 
> 
> 
> 
> 
> 
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
> <stefan_trethan@g...> wrote:
> > On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20 <mikegw20@h...> 
wrote:
> > 
> > > Now I have never built a CNC anything and I am not overly 
> mechanical.
> > > Right that is my qualifications out of the way...
> > > I was thinking about high torque motors to drive a linear 
thread 
> and I
> > > thought about those really cheap cordless drills.  That is idea 
> pt1.
> > > Now of course you need some sort of feedback for the position, 
> the
> > > normal way would be to put a shaft encoder on the drive.  My 
> thinking
> > > is that if you used a linear encoder then you would get absoulte
> > > positioning thereby negating the need for backlash 
> compensation.  Now a
> > > quick look around ebay reveals that linear encoders are not 
> cheap.  So
> > > has anyone used optical mice for a linear encoder? (idea pt b)
> > > Here endith todays musings.
> > > Mike
> > 
> > 
> > cordless drills usually use a motor what the model-vehicle 
> builders would  
> > call similar to a "speed 600".
> > Not a bad motor, and you can get replacements really cheap as 
well 

> as  
> > better motors the same size.
> > 
> > I would try to find drills with metal gears for this purpose. I 
> recently  
> > bought a very cheap one with plastic gears, it is still working, 
> but i'm  
> > always expecting it to fail any time. It was cheaper than a 
> replacement  
> > battery for a better drill.
> > There are often ebay lots of many drills.
> > 
> > 
> > As for linear encoder, there are those striped plastic strips in 
> printers,  
> > but a much easier solution would be to use digital calipers and 
> use the  
> > data-out, 'cause you would get absolute position not only 
> relative.  
> > Probably more expensive than shaft encoders and certainly more 
> expensive  
> > than steppers.
> > 
> > 
> > ST

Considering that most of the drill bits used for circuit boards are 
so small, they probably would bend or break before they cause the 
table and part to move.  A 40 pound table would not move, the drill 
bit would break.  

There will be others here that will be using dremels and will be 
using very lightweight tables with loose construction.  So, while 
you may not agree, fact is fact, software backlash compensation is 
not the "Solution" to poor machine design and construction.  
However, sometimes you can get away with it.

Furthermore, you make the statement "If you know what you are 
doing", well, considering that most of the people considering making 
a CNC machine will be their first CNC (and probably machine), it's a 
bad assumption.  Again, "trickery", is not a good solution to poor 
machine design and construction.





--- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
<derekhawkins@y...> wrote:
> >When drilling, the position will be off and the
> >holes will not be on size.
> 
> I don't agree with this. Perhaps with a light table and a high 
runout 
> drill such as the ubiquitous Dremel one may have an issue. With a 
> heavy table (the X axis and saddle in my setup weighs over 40 lbs) 
> and a low runout drill this is not an issue. Backlash compensation 
in 
> software is very effective when it comes to precision drilling IMO 
> provided you know what you're doing. Milling and routing is 
another 
> story.
> 
> --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
> <lcdpublishing@y...> wrote:
> > While I don't fully know the exact details, I can tell you right 
> > away, you cannot rely on software to eliminate the backlash 
within 
> a 
> > CNC system.  For basic positioning, perhaps a little, but in 
> > practice, no.
> > 
> > While software can compensate for the static deviation between 
> where 
> > it told the motor to position and where it really is based on 
> > encoder feedback, the "Slop" is still there.  During cutting, 
the 
> > dynamic cutting forces will cause the axes to move around within 
> the 
> > mechanical slop.  When drilling, the position will be off and 
the 
> > holes will not be on size.  When milling, all sorts of 
dimensional 
> > problems pop up and in the end, you will have wished you took 
the 
> > time the eliminate the mechancial backlash.
> > 
> > While there is backlash compensation within all CNC systems I 
have 
> > used in the industrial world, it is primarily only used to 
> > compensate for a very samll amount of backlash .001" or less 
> > usually. Beyond that and it is time to correct the mechanical 
> > problems.
> > 
> > So, don't waste your time or effort in thinking of a software 
> > solution to backlash - backlash is a mechanical problem and must 
be 
> > designed out of the system for even the most basic of machine 
> > performance.
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > 
> > --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
> > <stefan_trethan@g...> wrote:
> > > On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20 <mikegw20@h...> 
> wrote:
> > > 
> > > > Now I have never built a CNC anything and I am not overly 
> > mechanical.
> > > > Right that is my qualifications out of the way...
> > > > I was thinking about high torque motors to drive a linear 
> thread 
> > and I
> > > > thought about those really cheap cordless drills.  That is 
idea 
> > pt1.
> > > > Now of course you need some sort of feedback for the 
position, 
> > the
> > > > normal way would be to put a shaft encoder on the drive.  My 
> > thinking
> > > > is that if you used a linear encoder then you would get 
absoulte
> > > > positioning thereby negating the need for backlash 
> > compensation.  Now a
> > > > quick look around ebay reveals that linear encoders are not 
> > cheap.  So
> > > > has anyone used optical mice for a linear encoder? (idea pt 
b)
> > > > Here endith todays musings.
> > > > Mike
> > > 
> > > 
> > > cordless drills usually use a motor what the model-vehicle 
> > builders would  
> > > call similar to a "speed 600".
> > > Not a bad motor, and you can get replacements really cheap as 
> well 
> > as  
> > > better motors the same size.
> > > 
> > > I would try to find drills with metal gears for this purpose. 
I 
> > recently  
> > > bought a very cheap one with plastic gears, it is still 
working, 
> > but i'm  
> > > always expecting it to fail any time. It was cheaper than a 
> > replacement  
> > > battery for a better drill.
> > > There are often ebay lots of many drills.
> > > 
> > > 
> > > As for linear encoder, there are those striped plastic strips 
in 
> > printers,  
> > > but a much easier solution would be to use digital calipers 
and 

> > use the  
> > > data-out, 'cause you would get absolute position not only 
> > relative.  
> > > Probably more expensive than shaft encoders and certainly more 
> > expensive  
> > > than steppers.
> > > 
> > > 
> > > ST

lcdpublishing wrote:
> So, don't waste your time or effort in thinking of a software 
> solution to backlash - backlash is a mechanical problem and must be 
> designed out of the system for even the most basic of machine 
> performance.

In practice it is rarely a problem.  The static friction
of the ways combined with the cut being driven against
one extreme of the backlash removes the opportunity for
the movement to rattle around within the backlash slop.

In the case of drilling where the force being exerted does
not oppose the movement backlash, static friction present
in the ways is usually sufficient.  Otherwise if not you can
add an automated gib/ways jamb nut to lock the movement.

-- 
uhmgawa@...        www.gnu.org

>A 40 pound table would not move, the drill
>bit would break.

LOL! Where is the force trying to move the drill bit coming from? 
Assuming such a force existed, why would this force suddenly 
disappear with a perfect zero backlash setup and not break the bit 
then also? Both a 40 pound table and a zero backlash setup would have 
the same thing in common "THE TABLE WON'T MOVE".

Any slop would be manifested as spurious **movement of the table** in 
the backlash dead zone since the X and Y screws are "fixed" at drill 
time by the holding torque of the motor. You seem to be confusing 
drilling and milling in the same random thought.

>There will be others here that will be using dremels and will be 
>using very lightweight tables with loose construction.

With the right size hole the bit will be piloted to some extent in a 
lightweight setup just as in manual drilling. Most of us are alrady 
familiar with that trick. Long story short....You're making a 
mountain out of a mole hill. However, I would agree with you 100% if 
discussing milling or drilling.




--- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
<lcdpublishing@y...> wrote:
> Considering that most of the drill bits used for circuit boards are 
> so small, they probably would bend or break before they cause the 
> table and part to move.  A 40 pound table would not move, the drill 
> bit would break.  
> 
> There will be others here that will be using dremels and will be 
> using very lightweight tables with loose construction.  So, while 
> you may not agree, fact is fact, software backlash compensation is 
> not the "Solution" to poor machine design and construction.  
> However, sometimes you can get away with it.
> 
> Furthermore, you make the statement "If you know what you are 
> doing", well, considering that most of the people considering 
making 
> a CNC machine will be their first CNC (and probably machine), it's 
a 
> bad assumption.  Again, "trickery", is not a good solution to poor 
> machine design and construction.
> 
> 
> 
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
> <derekhawkins@y...> wrote:
> > >When drilling, the position will be off and the
> > >holes will not be on size.
> > 
> > I don't agree with this. Perhaps with a light table and a high 
> runout 
> > drill such as the ubiquitous Dremel one may have an issue. With a 
> > heavy table (the X axis and saddle in my setup weighs over 40 
lbs) 
> > and a low runout drill this is not an issue. Backlash 
compensation 
> in 
> > software is very effective when it comes to precision drilling 
IMO 
> > provided you know what you're doing. Milling and routing is 
> another 
> > story.
> > 
> > --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
> > <lcdpublishing@y...> wrote:
> > > While I don't fully know the exact details, I can tell you 
right 
> > > away, you cannot rely on software to eliminate the backlash 
> within 
> > a 
> > > CNC system.  For basic positioning, perhaps a little, but in 
> > > practice, no.
> > > 
> > > While software can compensate for the static deviation between 
> > where 
> > > it told the motor to position and where it really is based on 
> > > encoder feedback, the "Slop" is still there.  During cutting, 
> the 
> > > dynamic cutting forces will cause the axes to move around 
within 
> > the 
> > > mechanical slop.  When drilling, the position will be off and 
> the 
> > > holes will not be on size.  When milling, all sorts of 
> dimensional 
> > > problems pop up and in the end, you will have wished you took 
> the 
> > > time the eliminate the mechancial backlash.
> > > 
> > > While there is backlash compensation within all CNC systems I 
> have 
> > > used in the industrial world, it is primarily only used to 
> > > compensate for a very samll amount of backlash .001" or less 
> > > usually. Beyond that and it is time to correct the mechanical 
> > > problems.
> > > 
> > > So, don't waste your time or effort in thinking of a software 
> > > solution to backlash - backlash is a mechanical problem and 
must 
> be 
> > > designed out of the system for even the most basic of machine 
> > > performance.
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
> > > <stefan_trethan@g...> wrote:
> > > > On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20 <mikegw20@h...> 
> > wrote:
> > > > 
> > > > > Now I have never built a CNC anything and I am not overly 
> > > mechanical.
> > > > > Right that is my qualifications out of the way...
> > > > > I was thinking about high torque motors to drive a linear 
> > thread 
> > > and I
> > > > > thought about those really cheap cordless drills.  That is 
> idea 
> > > pt1.
> > > > > Now of course you need some sort of feedback for the 
> position, 
> > > the
> > > > > normal way would be to put a shaft encoder on the drive.  
My 
> > > thinking
> > > > > is that if you used a linear encoder then you would get 
> absoulte
> > > > > positioning thereby negating the need for backlash 
> > > compensation.  Now a
> > > > > quick look around ebay reveals that linear encoders are not 
> > > cheap.  So
> > > > > has anyone used optical mice for a linear encoder? (idea pt 
> b)
> > > > > Here endith todays musings.
> > > > > Mike
> > > > 
> > > > 
> > > > cordless drills usually use a motor what the model-vehicle 
> > > builders would  
> > > > call similar to a "speed 600".
> > > > Not a bad motor, and you can get replacements really cheap as 
> > well 
> > > as  
> > > > better motors the same size.
> > > > 
> > > > I would try to find drills with metal gears for this purpose. 
> I 
> > > recently  
> > > > bought a very cheap one with plastic gears, it is still 
> working, 
> > > but i'm  
> > > > always expecting it to fail any time. It was cheaper than a 
> > > replacement  
> > > > battery for a better drill.
> > > > There are often ebay lots of many drills.
> > > > 
> > > > 
> > > > As for linear encoder, there are those striped plastic strips 
> in 
> > > printers,  
> > > > but a much easier solution would be to use digital calipers 
> and 
> > > use the  
> > > > data-out, 'cause you would get absolute position not only 
> > > relative.  
> > > > Probably more expensive than shaft encoders and certainly 
more 

> > > expensive  
> > > > than steppers.
> > > > 
> > > > 
> > > > ST

>discussing milling or drilling.

That should have been milling or routing.


--- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
<derekhawkins@y...> wrote:
> >A 40 pound table would not move, the drill
> >bit would break.
> 
> LOL! Where is the force trying to move the drill bit coming from? 
> Assuming such a force existed, why would this force suddenly 
> disappear with a perfect zero backlash setup and not break the bit 
> then also? Both a 40 pound table and a zero backlash setup would 
have 
> the same thing in common "THE TABLE WON'T MOVE".
> 
> Any slop would be manifested as spurious **movement of the table** 
in 
> the backlash dead zone since the X and Y screws are "fixed" at 
drill 
> time by the holding torque of the motor. You seem to be confusing 
> drilling and milling in the same random thought.
> 
> >There will be others here that will be using dremels and will be 
> >using very lightweight tables with loose construction.
> 
> With the right size hole the bit will be piloted to some extent in 
a 
> lightweight setup just as in manual drilling. Most of us are alrady 
> familiar with that trick. Long story short....You're making a 
> mountain out of a mole hill. However, I would agree with you 100% 
if 
> discussing milling or drilling.
> 
> 
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
> <lcdpublishing@y...> wrote:
> > Considering that most of the drill bits used for circuit boards 
are 
> > so small, they probably would bend or break before they cause the 
> > table and part to move.  A 40 pound table would not move, the 
drill 
> > bit would break.  
> > 
> > There will be others here that will be using dremels and will be 
> > using very lightweight tables with loose construction.  So, while 
> > you may not agree, fact is fact, software backlash compensation 
is 
> > not the "Solution" to poor machine design and construction.  
> > However, sometimes you can get away with it.
> > 
> > Furthermore, you make the statement "If you know what you are 
> > doing", well, considering that most of the people considering 
> making 
> > a CNC machine will be their first CNC (and probably machine), 
it's 
> a 
> > bad assumption.  Again, "trickery", is not a good solution to 
poor 
> > machine design and construction.
> > 
> > 
> > 
> > 
> > 
> > --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
> > <derekhawkins@y...> wrote:
> > > >When drilling, the position will be off and the
> > > >holes will not be on size.
> > > 
> > > I don't agree with this. Perhaps with a light table and a high 
> > runout 
> > > drill such as the ubiquitous Dremel one may have an issue. With 
a 
> > > heavy table (the X axis and saddle in my setup weighs over 40 
> lbs) 
> > > and a low runout drill this is not an issue. Backlash 
> compensation 
> > in 
> > > software is very effective when it comes to precision drilling 
> IMO 
> > > provided you know what you're doing. Milling and routing is 
> > another 
> > > story.
> > > 
> > > --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
> > > <lcdpublishing@y...> wrote:
> > > > While I don't fully know the exact details, I can tell you 
> right 
> > > > away, you cannot rely on software to eliminate the backlash 
> > within 
> > > a 
> > > > CNC system.  For basic positioning, perhaps a little, but in 
> > > > practice, no.
> > > > 
> > > > While software can compensate for the static deviation 
between 
> > > where 
> > > > it told the motor to position and where it really is based on 
> > > > encoder feedback, the "Slop" is still there.  During cutting, 
> > the 
> > > > dynamic cutting forces will cause the axes to move around 
> within 
> > > the 
> > > > mechanical slop.  When drilling, the position will be off and 
> > the 
> > > > holes will not be on size.  When milling, all sorts of 
> > dimensional 
> > > > problems pop up and in the end, you will have wished you took 
> > the 
> > > > time the eliminate the mechancial backlash.
> > > > 
> > > > While there is backlash compensation within all CNC systems I 
> > have 
> > > > used in the industrial world, it is primarily only used to 
> > > > compensate for a very samll amount of backlash .001" or less 
> > > > usually. Beyond that and it is time to correct the mechanical 
> > > > problems.
> > > > 
> > > > So, don't waste your time or effort in thinking of a software 
> > > > solution to backlash - backlash is a mechanical problem and 
> must 
> > be 
> > > > designed out of the system for even the most basic of machine 
> > > > performance.
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
> > > > <stefan_trethan@g...> wrote:
> > > > > On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20 
<mikegw20@h...> 
> > > wrote:
> > > > > 
> > > > > > Now I have never built a CNC anything and I am not overly 
> > > > mechanical.
> > > > > > Right that is my qualifications out of the way...
> > > > > > I was thinking about high torque motors to drive a linear 
> > > thread 
> > > > and I
> > > > > > thought about those really cheap cordless drills.  That 
is 
> > idea 
> > > > pt1.
> > > > > > Now of course you need some sort of feedback for the 
> > position, 
> > > > the
> > > > > > normal way would be to put a shaft encoder on the drive.  
> My 
> > > > thinking
> > > > > > is that if you used a linear encoder then you would get 
> > absoulte
> > > > > > positioning thereby negating the need for backlash 
> > > > compensation.  Now a
> > > > > > quick look around ebay reveals that linear encoders are 
not 
> > > > cheap.  So
> > > > > > has anyone used optical mice for a linear encoder? (idea 
pt 
> > b)
> > > > > > Here endith todays musings.
> > > > > > Mike
> > > > > 
> > > > > 
> > > > > cordless drills usually use a motor what the model-vehicle 
> > > > builders would  
> > > > > call similar to a "speed 600".
> > > > > Not a bad motor, and you can get replacements really cheap 
as 
> > > well 
> > > > as  
> > > > > better motors the same size.
> > > > > 
> > > > > I would try to find drills with metal gears for this 
purpose. 
> > I 
> > > > recently  
> > > > > bought a very cheap one with plastic gears, it is still 
> > working, 
> > > > but i'm  
> > > > > always expecting it to fail any time. It was cheaper than a 
> > > > replacement  
> > > > > battery for a better drill.
> > > > > There are often ebay lots of many drills.
> > > > > 
> > > > > 
> > > > > As for linear encoder, there are those striped plastic 
strips 

> > in 
> > > > printers,  
> > > > > but a much easier solution would be to use digital calipers 
> > and 
> > > > use the  
> > > > > data-out, 'cause you would get absolute position not only 
> > > > relative.  
> > > > > Probably more expensive than shaft encoders and certainly 
> more 
> > > > expensive  
> > > > > than steppers.
> > > > > 
> > > > > 
> > > > > ST

Again, as I have stated before, using software backlash compensation 
is not an excuse for poor machine design and construction.  I agree 
completly that a small circuit board drill would not move the table, 
however, the larger the drill, the greater the problems.  I really 
don't care to debate this with you. We obviously have different 
standards of right and wrong - I can back my statements up with 
machine tool design in industrial applications, you cannot.




--- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
<derekhawkins@y...> wrote:
> >A 40 pound table would not move, the drill
> >bit would break.
> 
> LOL! Where is the force trying to move the drill bit coming from? 
> Assuming such a force existed, why would this force suddenly 
> disappear with a perfect zero backlash setup and not break the bit 
> then also? Both a 40 pound table and a zero backlash setup would 
have 
> the same thing in common "THE TABLE WON'T MOVE".
> 
> Any slop would be manifested as spurious **movement of the table** 
in 
> the backlash dead zone since the X and Y screws are "fixed" at 
drill 
> time by the holding torque of the motor. You seem to be confusing 
> drilling and milling in the same random thought.
> 
> >There will be others here that will be using dremels and will be 
> >using very lightweight tables with loose construction.
> 
> With the right size hole the bit will be piloted to some extent in 
a 
> lightweight setup just as in manual drilling. Most of us are 
alrady 
> familiar with that trick. Long story short....You're making a 
> mountain out of a mole hill. However, I would agree with you 100% 
if 
> discussing milling or drilling.
> 
> 
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
> <lcdpublishing@y...> wrote:
> > Considering that most of the drill bits used for circuit boards 
are 
> > so small, they probably would bend or break before they cause 
the 
> > table and part to move.  A 40 pound table would not move, the 
drill 
> > bit would break.  
> > 
> > There will be others here that will be using dremels and will be 
> > using very lightweight tables with loose construction.  So, 
while 
> > you may not agree, fact is fact, software backlash compensation 
is 
> > not the "Solution" to poor machine design and construction.  
> > However, sometimes you can get away with it.
> > 
> > Furthermore, you make the statement "If you know what you are 
> > doing", well, considering that most of the people considering 
> making 
> > a CNC machine will be their first CNC (and probably machine), 
it's 
> a 
> > bad assumption.  Again, "trickery", is not a good solution to 
poor 
> > machine design and construction.
> > 
> > 
> > 
> > 
> > 
> > --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
> > <derekhawkins@y...> wrote:
> > > >When drilling, the position will be off and the
> > > >holes will not be on size.
> > > 
> > > I don't agree with this. Perhaps with a light table and a high 
> > runout 
> > > drill such as the ubiquitous Dremel one may have an issue. 
With a 
> > > heavy table (the X axis and saddle in my setup weighs over 40 
> lbs) 
> > > and a low runout drill this is not an issue. Backlash 
> compensation 
> > in 
> > > software is very effective when it comes to precision drilling 
> IMO 
> > > provided you know what you're doing. Milling and routing is 
> > another 
> > > story.
> > > 
> > > --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
> > > <lcdpublishing@y...> wrote:
> > > > While I don't fully know the exact details, I can tell you 
> right 
> > > > away, you cannot rely on software to eliminate the backlash 
> > within 
> > > a 
> > > > CNC system.  For basic positioning, perhaps a little, but in 
> > > > practice, no.
> > > > 
> > > > While software can compensate for the static deviation 
between 
> > > where 
> > > > it told the motor to position and where it really is based 
on 
> > > > encoder feedback, the "Slop" is still there.  During 
cutting, 
> > the 
> > > > dynamic cutting forces will cause the axes to move around 
> within 
> > > the 
> > > > mechanical slop.  When drilling, the position will be off 
and 
> > the 
> > > > holes will not be on size.  When milling, all sorts of 
> > dimensional 
> > > > problems pop up and in the end, you will have wished you 
took 
> > the 
> > > > time the eliminate the mechancial backlash.
> > > > 
> > > > While there is backlash compensation within all CNC systems 
I 
> > have 
> > > > used in the industrial world, it is primarily only used to 
> > > > compensate for a very samll amount of backlash .001" or less 
> > > > usually. Beyond that and it is time to correct the 
mechanical 
> > > > problems.
> > > > 
> > > > So, don't waste your time or effort in thinking of a 
software 
> > > > solution to backlash - backlash is a mechanical problem and 
> must 
> > be 
> > > > designed out of the system for even the most basic of 
machine 
> > > > performance.
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > 
> > > > --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
> > > > <stefan_trethan@g...> wrote:
> > > > > On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20 
<mikegw20@h...> 
> > > wrote:
> > > > > 
> > > > > > Now I have never built a CNC anything and I am not 
overly 
> > > > mechanical.
> > > > > > Right that is my qualifications out of the way...
> > > > > > I was thinking about high torque motors to drive a 
linear 
> > > thread 
> > > > and I
> > > > > > thought about those really cheap cordless drills.  That 
is 
> > idea 
> > > > pt1.
> > > > > > Now of course you need some sort of feedback for the 
> > position, 
> > > > the
> > > > > > normal way would be to put a shaft encoder on the 
drive.  
> My 
> > > > thinking
> > > > > > is that if you used a linear encoder then you would get 
> > absoulte
> > > > > > positioning thereby negating the need for backlash 
> > > > compensation.  Now a
> > > > > > quick look around ebay reveals that linear encoders are 
not 
> > > > cheap.  So
> > > > > > has anyone used optical mice for a linear encoder? (idea 
pt 
> > b)
> > > > > > Here endith todays musings.
> > > > > > Mike
> > > > > 
> > > > > 
> > > > > cordless drills usually use a motor what the model-vehicle 
> > > > builders would  
> > > > > call similar to a "speed 600".
> > > > > Not a bad motor, and you can get replacements really cheap 
as 
> > > well 
> > > > as  
> > > > > better motors the same size.
> > > > > 
> > > > > I would try to find drills with metal gears for this 
purpose. 
> > I 
> > > > recently  
> > > > > bought a very cheap one with plastic gears, it is still 
> > working, 
> > > > but i'm  
> > > > > always expecting it to fail any time. It was cheaper than 
a 
> > > > replacement  
> > > > > battery for a better drill.
> > > > > There are often ebay lots of many drills.
> > > > > 
> > > > > 
> > > > > As for linear encoder, there are those striped plastic 
strips 
> > in 
> > > > printers,  
> > > > > but a much easier solution would be to use digital 
calipers 

> > and 
> > > > use the  
> > > > > data-out, 'cause you would get absolute position not only 
> > > > relative.  
> > > > > Probably more expensive than shaft encoders and certainly 
> more 
> > > > expensive  
> > > > > than steppers.
> > > > > 
> > > > > 
> > > > > ST

> We obviously have different 
> standards of right and wrong - I can back my statements up with 
> machine tool design in industrial applications, you cannot.

I'd be a fool to even try since these homebrew projects were never 
intended to be industrial applications? Maybe you should add "fool" 
somewhere in the subject line.

--- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
<lcdpublishing@y...> wrote:
> Again, as I have stated before, using software backlash 
compensation 
> is not an excuse for poor machine design and construction.  I agree 
> completly that a small circuit board drill would not move the 
table, 
> however, the larger the drill, the greater the problems.  I really 
> don't care to debate this with you. We obviously have different 
> standards of right and wrong - I can back my statements up with 
> machine tool design in industrial applications, you cannot.
> 
> 
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
> <derekhawkins@y...> wrote:
> > >A 40 pound table would not move, the drill
> > >bit would break.
> > 
> > LOL! Where is the force trying to move the drill bit coming from? 
> > Assuming such a force existed, why would this force suddenly 
> > disappear with a perfect zero backlash setup and not break the 
bit 
> > then also? Both a 40 pound table and a zero backlash setup would 
> have 
> > the same thing in common "THE TABLE WON'T MOVE".
> > 
> > Any slop would be manifested as spurious **movement of the 
table** 
> in 
> > the backlash dead zone since the X and Y screws are "fixed" at 
> drill 
> > time by the holding torque of the motor. You seem to be confusing 
> > drilling and milling in the same random thought.
> > 
> > >There will be others here that will be using dremels and will be 
> > >using very lightweight tables with loose construction.
> > 
> > With the right size hole the bit will be piloted to some extent 
in 
> a 
> > lightweight setup just as in manual drilling. Most of us are 
> alrady 
> > familiar with that trick. Long story short....You're making a 
> > mountain out of a mole hill. However, I would agree with you 100% 
> if 
> > discussing milling or drilling.
> > 
> > 
> > 
> > 
> > --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
> > <lcdpublishing@y...> wrote:
> > > Considering that most of the drill bits used for circuit boards 
> are 
> > > so small, they probably would bend or break before they cause 
> the 
> > > table and part to move.  A 40 pound table would not move, the 
> drill 
> > > bit would break.  
> > > 
> > > There will be others here that will be using dremels and will 
be 
> > > using very lightweight tables with loose construction.  So, 
> while 
> > > you may not agree, fact is fact, software backlash compensation 
> is 
> > > not the "Solution" to poor machine design and construction.  
> > > However, sometimes you can get away with it.
> > > 
> > > Furthermore, you make the statement "If you know what you are 
> > > doing", well, considering that most of the people considering 
> > making 
> > > a CNC machine will be their first CNC (and probably machine), 
> it's 
> > a 
> > > bad assumption.  Again, "trickery", is not a good solution to 
> poor 
> > > machine design and construction.
> > > 
> > > 
> > > 
> > > 
> > > 
> > > --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
> > > <derekhawkins@y...> wrote:
> > > > >When drilling, the position will be off and the
> > > > >holes will not be on size.
> > > > 
> > > > I don't agree with this. Perhaps with a light table and a 
high 
> > > runout 
> > > > drill such as the ubiquitous Dremel one may have an issue. 
> With a 
> > > > heavy table (the X axis and saddle in my setup weighs over 40 
> > lbs) 
> > > > and a low runout drill this is not an issue. Backlash 
> > compensation 
> > > in 
> > > > software is very effective when it comes to precision 
drilling 
> > IMO 
> > > > provided you know what you're doing. Milling and routing is 
> > > another 
> > > > story.
> > > > 
> > > > --- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
> > > > <lcdpublishing@y...> wrote:
> > > > > While I don't fully know the exact details, I can tell you 
> > right 
> > > > > away, you cannot rely on software to eliminate the backlash 
> > > within 
> > > > a 
> > > > > CNC system.  For basic positioning, perhaps a little, but 
in 
> > > > > practice, no.
> > > > > 
> > > > > While software can compensate for the static deviation 
> between 
> > > > where 
> > > > > it told the motor to position and where it really is based 
> on 
> > > > > encoder feedback, the "Slop" is still there.  During 
> cutting, 
> > > the 
> > > > > dynamic cutting forces will cause the axes to move around 
> > within 
> > > > the 
> > > > > mechanical slop.  When drilling, the position will be off 
> and 
> > > the 
> > > > > holes will not be on size.  When milling, all sorts of 
> > > dimensional 
> > > > > problems pop up and in the end, you will have wished you 
> took 
> > > the 
> > > > > time the eliminate the mechancial backlash.
> > > > > 
> > > > > While there is backlash compensation within all CNC systems 
> I 
> > > have 
> > > > > used in the industrial world, it is primarily only used to 
> > > > > compensate for a very samll amount of backlash .001" or 
less 
> > > > > usually. Beyond that and it is time to correct the 
> mechanical 
> > > > > problems.
> > > > > 
> > > > > So, don't waste your time or effort in thinking of a 
> software 
> > > > > solution to backlash - backlash is a mechanical problem and 
> > must 
> > > be 
> > > > > designed out of the system for even the most basic of 
> machine 
> > > > > performance.
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > --- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
> > > > > <stefan_trethan@g...> wrote:
> > > > > > On Tue, 28 Jun 2005 08:36:23 +0200, mikegw20 
> <mikegw20@h...> 
> > > > wrote:
> > > > > > 
> > > > > > > Now I have never built a CNC anything and I am not 
> overly 
> > > > > mechanical.
> > > > > > > Right that is my qualifications out of the way...
> > > > > > > I was thinking about high torque motors to drive a 
> linear 
> > > > thread 
> > > > > and I
> > > > > > > thought about those really cheap cordless drills.  That 
> is 
> > > idea 
> > > > > pt1.
> > > > > > > Now of course you need some sort of feedback for the 
> > > position, 
> > > > > the
> > > > > > > normal way would be to put a shaft encoder on the 
> drive.  
> > My 
> > > > > thinking
> > > > > > > is that if you used a linear encoder then you would get 
> > > absoulte
> > > > > > > positioning thereby negating the need for backlash 
> > > > > compensation.  Now a
> > > > > > > quick look around ebay reveals that linear encoders are 
> not 
> > > > > cheap.  So
> > > > > > > has anyone used optical mice for a linear encoder? 
(idea 
> pt 
> > > b)
> > > > > > > Here endith todays musings.
> > > > > > > Mike
> > > > > > 
> > > > > > 
> > > > > > cordless drills usually use a motor what the model-
vehicle 
> > > > > builders would  
> > > > > > call similar to a "speed 600".
> > > > > > Not a bad motor, and you can get replacements really 
cheap 

> as 
> > > > well 
> > > > > as  
> > > > > > better motors the same size.
> > > > > > 
> > > > > > I would try to find drills with metal gears for this 
> purpose. 
> > > I 
> > > > > recently  
> > > > > > bought a very cheap one with plastic gears, it is still 
> > > working, 
> > > > > but i'm  
> > > > > > always expecting it to fail any time. It was cheaper than 
> a 
> > > > > replacement  
> > > > > > battery for a better drill.
> > > > > > There are often ebay lots of many drills.
> > > > > > 
> > > > > > 
> > > > > > As for linear encoder, there are those striped plastic 
> strips 
> > > in 
> > > > > printers,  
> > > > > > but a much easier solution would be to use digital 
> calipers 
> > > and 
> > > > > use the  
> > > > > > data-out, 'cause you would get absolute position not only 
> > > > > relative.  
> > > > > > Probably more expensive than shaft encoders and certainly 
> > more 
> > > > > expensive  
> > > > > > than steppers.
> > > > > > 
> > > > > > 
> > > > > > ST

Now, now, don't start the name calling.  Just accept the facts and 
learn from them.




--- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
<derekhawkins@y...> wrote:

> > We obviously have different 
> > standards of right and wrong - I can back my statements up with 
> > machine tool design in industrial applications, you cannot.
> 
> I'd be a fool to even try since these homebrew projects were never 
> intended to be industrial applications? Maybe you should add "fool" 
> somewhere in the subject line.

In a message dated 6/28/2005 7:15:54 A.M. Central Daylight Time,  
lcdpublishing@... writes:

So,  don't waste your time or effort in thinking of a software solution to 
backlash  - backlash is a mechanical problem and must be designed out of the 
system for  even the most basic of machine performance.<<
 
I have been doing home-brew CNC for decades, and I agree with  Chris here!  
If it doesn't "work right", no amount of software cleverness  will "fix 
it"!!!!!!!!!!
 
Jan Rowland






[Non-text portions of this message have been removed]

Thanks all for what turns out to be a lively dicussion.  However, as a 
follow on assuming that I have backlash compensation (by whatever 
means) Do you know of anyone using an optical mouse as a linear 
encoder?  They way I figure it is indeed possible to communicate to the 
ps/2 port and optical mice have resolutions in the 400lines/inch (some 
much better).  

Has anyone used an optical mouse for postion sensing?

Mike

mikegw20 wrote:
> Has anyone used an optical mouse for postion sensing?

Your term of "optical mouse" is a bit confusing here.
If you are referring to a ball-driven mechanical mouse
with x/y photo interrupters, yes that is a possible
solution with a few constraints.

The interrupter wheel segments mark off 10* or
36 divisions per revolution for run of the mill
units.  To achieve a resolution in the ballpark
of 0.001" a lead screw having a pitch of 24-28TPI
is required.  This will likely be a conventional
60* cut screw thread rather than a more durable
acme thread which has a broader profile and is
not normally available in this fine of a pitch.

Fabricating a higher resolution photo interrupter
disk is possible via laser printing to transparency
film.  Other sources of quick and dirty photo
interrupters are reclaimed high tooth count gears
from electro-mechanical devices.

A PC mouse is a good starting point in any case
as it furnishes two dual-channel IR quadrature
detectors and emitters which provide a means to
sense rotational displacement as well as direction.

-- 
uhmgawa@...        www.gnu.org

--- In Homebrew_PCBs@yahoogroups.com, uhmgawa <uhmgawa@m...> wrote:
> mikegw20 wrote:
> > Has anyone used an optical mouse for postion sensing?
> 
> Your term of "optical mouse" is a bit confusing here.
> If you are referring to a ball-driven mechanical mouse
> with x/y photo interrupters, yes that is a possible
> solution with a few constraints.
> 

No, I refer to what we would call an optical mouse, no ball only a 
light.  Ripping the guts out of one would be difficult but strapping a 
small mouse alongside an axis such that in moves in harmony OR pointing 
the sensor at a wheel connected to a shaft.  Both would give the 
distance traveled via the ps2 port.  There are a few designs around to 
interface a micro controller to the ps2 port.  Maybe in the guts of the 
mouse there is a quadrature output avoiding the need for the ps2 
interface.

To me it seems an easy way to get around the difficulty of producing 
high resolution graduated slides (the kind that would otherwise be got 
from an inkjet printer)

Mike

On Wed, 29 Jun 2005 07:12:09 +0200, mikegw20 <mikegw20@...> wrote:

>
> No, I refer to what we would call an optical mouse, no ball only a
> light.  Ripping the guts out of one would be difficult but strapping a
> small mouse alongside an axis such that in moves in harmony OR pointing
> the sensor at a wheel connected to a shaft.  Both would give the
> distance traveled via the ps2 port.  There are a few designs around to
> interface a micro controller to the ps2 port.  Maybe in the guts of the
> mouse there is a quadrature output avoiding the need for the ps2
> interface.
> To me it seems an easy way to get around the difficulty of producing
> high resolution graduated slides (the kind that would otherwise be got
> from an inkjet printer)
> Mike


In those mice is basically a low-res camera, like 16x16 dots or so.
Stripping the guts would not be too hard, the buttons might be useful for  
zero switches.

ST

Agilent makes the internals for optical mice. 

http://www.home.agilent.com/USeng/nav/-536893644.536905699/pd.html

--- In Homebrew_PCBs@yahoogroups.com, "mikegw20" <mikegw20@h...>
wrote:
> Thanks all for what turns out to be a lively dicussion.  However,
as a 
> follow on assuming that I have backlash compensation (by whatever 
> means) Do you know of anyone using an optical mouse as a linear 
> encoder?  They way I figure it is indeed possible to communicate to
the 
> ps/2 port and optical mice have resolutions in the 400lines/inch
(some 

> much better).  
> 
> Has anyone used an optical mouse for postion sensing?
> 
> Mike

>If it doesn't "work right", no amount of software cleverness  
>will "fix it"!!!!!!!!!!

What does "work right" mean? There are tolerances in dimensions and 
targeted positions after motion. Do you consider 10 mils of backlash 
in a foam cutting CNC setup the result of a poor design for example?


--- In Homebrew_PCBs@yahoogroups.com, JanRwl@A... wrote:
> In a message dated 6/28/2005 7:15:54 A.M. Central Daylight Time,  
> lcdpublishing@y... writes:
> 
> So,  don't waste your time or effort in thinking of a software 
solution to 
> backlash  - backlash is a mechanical problem and must be designed 
out of the 
> system for  even the most basic of machine performance.<<
>  
> I have been doing home-brew CNC for decades, and I agree with  
Chris here!  
> If it doesn't "work right", no amount of software cleverness  
will "fix 

> it"!!!!!!!!!!
>  
> Jan Rowland
> 
> 
> 
> 
> 
> 
> [Non-text portions of this message have been removed]

On Wed, 29 Jun 2005 17:36:34 +0200, derekhawkins <derekhawkins@...>  
wrote:

>
> What does "work right" mean? There are tolerances in dimensions and
> targeted positions after motion. Do you consider 10 mils of backlash
> in a foam cutting CNC setup the result of a poor design for example?


As soon as you need to compensate something isn't right ;-)

10mil in a foam cutter is probably below what you consider too much.

ST

As I stated before, I really don't care to debate with you the 
difference between right and wrong, either you get it or you don't.

Chris





--- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
<derekhawkins@y...> wrote:
> >If it doesn't "work right", no amount of software cleverness  
> >will "fix it"!!!!!!!!!!
> 
> What does "work right" mean? There are tolerances in dimensions 
and 
> targeted positions after motion. Do you consider 10 mils of 
backlash 
> in a foam cutting CNC setup the result of a poor design for 
example?
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, JanRwl@A... wrote:
> > In a message dated 6/28/2005 7:15:54 A.M. Central Daylight 
Time,  
> > lcdpublishing@y... writes:
> > 
> > So,  don't waste your time or effort in thinking of a software 
> solution to 
> > backlash  - backlash is a mechanical problem and must be 
designed 

> out of the 
> > system for  even the most basic of machine performance.<<
> >  
> > I have been doing home-brew CNC for decades, and I agree with  
> Chris here!  
> > If it doesn't "work right", no amount of software cleverness  
> will "fix 
> > it"!!!!!!!!!!
> >  
> > Jan Rowland
> > 
> > 
> > 
> > 
> > 
> > 
> > [Non-text portions of this message have been removed]

> As soon as you need to compensate something isn't right ;-)

What is the lead accuracy of the best ball screw you can find? What is 
the typical diameter of a homebrew PCB pad? What is the hole diameter 
in that typical pad? Truth is, you won't even have to compensate for 10 
thou backlash unless aesthetically dead center means a lot to you.

> 10mil in a foam cutter is probably below what you consider too much.

I'm willing to bet the farm (if I had one) that more than 50% of all 
industrial CNC setups have backlash > 10 thou. Either because greater 
accuracy was never required or due to lack of maintenance. Whatever, 
provided the end product isn't being impacted, nobody cares. Search 
Google on >milling backlash thou< to get a better feel of what is 
tolerated in milling circles where backlash is most important.




--- In Homebrew_PCBs@yahoogroups.com, "Stefan Trethan" 
<stefan_trethan@g...> wrote:

> On Wed, 29 Jun 2005 17:36:34 +0200, derekhawkins <derekhawkins@y...>  
> wrote:
> 
> >
> > What does "work right" mean? There are tolerances in dimensions and
> > targeted positions after motion. Do you consider 10 mils of backlash
> > in a foam cutting CNC setup the result of a poor design for example?
> 
> 
> As soon as you need to compensate something isn't right ;-)
> 
> 10mil in a foam cutter is probably below what you consider too much.
> 
> ST

> As I stated before, I really don't care to debate with you the 
> difference between right and wrong, either you get it or you don't.

Can't recall addressing you unless you're also JanRwl@A... The only 
thing I got from you was that you're an idiot who simply didn't 
understand backlash as it applies to the real world. Couldn't care 
less how much experience you **claim** to have. Your ability to 
regurgitate established norms is nothing more than "preaching to the 
choir" in my case.

--- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
<lcdpublishing@y...> wrote:

> As I stated before, I really don't care to debate with you the 
> difference between right and wrong, either you get it or you don't.
> 
> Chris
> 
> 
> 
> 
> 
> --- In Homebrew_PCBs@yahoogroups.com, "derekhawkins" 
> <derekhawkins@y...> wrote:
> > >If it doesn't "work right", no amount of software cleverness  
> > >will "fix it"!!!!!!!!!!
> > 
> > What does "work right" mean? There are tolerances in dimensions 
> and 
> > targeted positions after motion. Do you consider 10 mils of 
> backlash 
> > in a foam cutting CNC setup the result of a poor design for 
> example?
> > 
> > 
> > --- In Homebrew_PCBs@yahoogroups.com, JanRwl@A... wrote:
> > > In a message dated 6/28/2005 7:15:54 A.M. Central Daylight 
> Time,  
> > > lcdpublishing@y... writes:
> > > 
> > > So,  don't waste your time or effort in thinking of a software 
> > solution to 
> > > backlash  - backlash is a mechanical problem and must be 
> designed 
> > out of the 
> > > system for  even the most basic of machine performance.<<
> > >  
> > > I have been doing home-brew CNC for decades, and I agree with  
> > Chris here!  
> > > If it doesn't "work right", no amount of software cleverness  
> > will "fix 
> > > it"!!!!!!!!!!
> > >  
> > > Jan Rowland
> > > 
> > > 
> > > 
> > > 
> > > 
> > > 
> > > [Non-text portions of this message have been removed]

Okay, Now you are just talking stupid.  The reason you would bet the 
farm that you don't have to bet, is that you don't know what you are 
talking about. Manual mills may have upwards of .100" backlash.  

Industrial CNC machines (and most hobbiest CNC machines) that use ball 
screws have less than .002" backlash on the screws.  An even greater 
majority of precision metalworking machinery (industrial machine 
tools) have less than .0006" of backlash.  Most machine tools using 
ball screws go so far as to even put two nuts on with a tab between 
them to further eliminate backlash to near zero (usually .0002" or 
less).  When a machine tool get's excesive mechanical backlash, you 
would adjust the two ball nuts to remove it, the software compensation 
is only there to take care of .0003" or so.

Now drop this discussion and quit demonstrating your ignorance on the 
subject mater.






 
> I'm willing to bet the farm (if I had one) that more than 50% of all 
> industrial CNC setups have backlash > 10 thou. Either because 
greater 
> accuracy was never required or due to lack of maintenance. Whatever, 
> provided the end product isn't being impacted, nobody cares. Search

All you are doing is quoting the specs for the **better** CNC 
machines out there. Something any idiot can do by going to the 
manufacturer's websites. It's like quoting the specs on Benzs, BMWs 
etc. and then giving the impression that these are the only cars that 
exist.

If a manual mill can have a backlash of .100" (I certainly wouldn't 
want to have one such as this but these are your words) and the owner 
was satisfied with it then why wouldn't he be satisfied after 
converting to CNC with backlash compensation in software? Why would 
his products suddenly be any worse?

Now here is where you're really foolish...Didn't you say this;

"While there is backlash compensation within all CNC systems I have 
used in the industrial world, it is primarily only used to compensate 
for a very small amount of backlash .001" or less usually. Beyond 
that and it is time to correct the mechanical problems."

Great! So you've used some of the better CNC systems out there. But 
you seem also to be suggesting that if any of us have backlash 
over .001" then it's a poor design.... How many in this group even 
have the capacity to measure .001" backlash? When drilling PCBs using 
a home setup, at least one reference point has to be arrived at 
manually, who the hell can do that with .001" accuracy? Do you even 
know the size of a typical PCB pad? Trust me, most of the guys here 
will be happy if the bit hits the pad...ANYWHERE!!! LOL!


--- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing" 
<lcdpublishing@y...> wrote:
> Okay, Now you are just talking stupid.  The reason you would bet 
the 
> farm that you don't have to bet, is that you don't know what you 
are 
> talking about. Manual mills may have upwards of .100" backlash.  
> 
> Industrial CNC machines (and most hobbiest CNC machines) that use 
ball 
> screws have less than .002" backlash on the screws.  An even 
greater 
> majority of precision metalworking machinery (industrial machine 
> tools) have less than .0006" of backlash.  Most machine tools using 
> ball screws go so far as to even put two nuts on with a tab between 
> them to further eliminate backlash to near zero (usually .0002" or 
> less).  When a machine tool get's excesive mechanical backlash, you 
> would adjust the two ball nuts to remove it, the software 
compensation 
> is only there to take care of .0003" or so.
> 
> Now drop this discussion and quit demonstrating your ignorance on 
the 
> subject mater.
> 
> 
> 
> 
> 
> 
>  
> > I'm willing to bet the farm (if I had one) that more than 50% of 
all 
> > industrial CNC setups have backlash > 10 thou. Either because 
> greater 
> > accuracy was never required or due to lack of maintenance. 
Whatever, 
> > provided the end product isn't being impacted, nobody cares. 
Search

This disagreement is getting abusive. I think it's time to end this
thread.

Steve, listowner Homebrew_PCBs

In a message dated 6/29/2005 10:41:40 A.M. Central Daylight Time,  
derekhawkins@... writes:

Do you  consider 10 mils of backlash in a foam cutting CNC setup the result 
of a  poor design for example?<<
Surely somewhat sloppy, if not "poor design".  Half that  backlash should be 
routine for competent machinists.   However, a  foam-cutter might "tolerate" 
that much slop.  A metalworking machine such  as a lathe or mill 
almost-certainly not.





[Non-text portions of this message have been removed]

"Most machine tools using ball screws go so far as to even put two
nuts on with a tab between them to further eliminate backlash to
near zero (usually .0002" or less)."

That's exactly what I am doing to reduce the inherent
slop in ordinary long screws & nuts; 1/2" 13-TPI.

Robert
:)


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>However, a foam-cutter might "tolerate"
>that much slop. A metalworking machine such as a lathe or mill
>almost-certainly not.

Horses for courses. Why would someone in the foam cutting business 
want to pay for machines meeting lathe or mill standards if they 
weren't required? He's more interested in his product than the 
specifications of the machines used to make them. 


--- In Homebrew_PCBs@yahoogroups.com, JanRwl@A... wrote:
> In a message dated 6/29/2005 10:41:40 A.M. Central Daylight Time,  
> derekhawkins@y... writes:
> 
> Do you  consider 10 mils of backlash in a foam cutting CNC setup 
the result 
> of a  poor design for example?<<
> Surely somewhat sloppy, if not "poor design".  Half that  backlash 
should be 
> routine for competent machinists.   However, a  foam-cutter 
might "tolerate" 

> that much slop.  A metalworking machine such  as a lathe or mill 
> almost-certainly not.
> 
> 
> 
> 
> 
> [Non-text portions of this message have been removed]