Homebrew PCBs

James,

Didn't see the link yet, but usually you trade one source of error 
for another. The probnlem with rotary-used-linear machines is that as 
the distance from the pivot changes so does the mech. 
advantage, "step" size, etc. And trying to make a linear move near 
one of the pivots requires a nearly instantaneous change in direction 
and requires acceleration far in excess of what most inexpensive 
drives can achieve...

There's more, but these are the bigge's

Ballendo 

In Homebrew_PCBs, "James Newtons Massmind" wrote:
>As far as "error components" goes, has anyone looked at reducing the 
>number of joints required as a means of reducing error? And 
interesting idea is that of using only two joints in a radial system 
rather than the 4 or more required in a linear system.
> http://www.massmind.org/techref/idea/lccam.htm scroll down
> http://freeandeasy.sourceforge.net/ at the end of the paragraph 
about
> "prototype XY table"
> http://freeandeasy.sourceforge.net/rotary.php
> 
> Roller-skate bearings top and bottom on the main shaft were sloppy 
(as
> expected) but when they are pressed towards each other, the 
compression
> takes all the slop out and the result is very good. It reminded me 
of what
> you were doing, but I don't think it is really the same.
> 
> ---
> James Newton, massmind.org Knowledge Archiver 
> james@m... 1-619-652-0593 fax:1-208-279-8767 
> All the engineering secrets worth knowing:
> http://techref.massmind.org What do YOU know?
> 
> 
> 
> 
> Message: 21
>    Date: Mon, 14 Jun 2004 01:53:10 EDT
>    From: JanRwl@A...
> Subject: Re: bit cleaning while drilling PCBs
> 
> In a message dated 6/13/2004 7:52:33 PM Central Standard Time, 
> dg140@f... writes:
> How did you account for backlash in your homebrew CNC rig?<<
> 
> You DID see the photo in the PHOTO section under "Jan Rowland"?  
> 
> I built that in '84, and was feeling CHEAP, so I did NOT spring for 
the 
> preloaded Turcite nuts sold by Ball Screws and Actuators, San Jose, 
CA.  I
> bought 
> the "Single" Turcite nuts which have a 15/16"-16 threaded end for 
fastening 
> into the carriage or flange or whatever.  I then carefully 
bored/tapped a
> hole 
> for 6-32 cap-screws through one side, and then I band-sawed through 
that one
> 
> side with the screw-hole so that inserting and tightening the screw 
would 
> "reduce" the I.D.  This would tighten-up on the screw nicely, and 
obviously
> a "feel" 
> for HOW-tight was necessary.  It worked, and has not been a problem 
needing 
> re-adjustment.  These nuts are also more than twice as compact as 
the
> (spring-) 
> preloaded nuts, and MUCH less expensive.  These screws are 7/16" 
dia. 
> 1/8"-pitch, 4-start.  Thus, one turn = 1/2" movement.  So each step 
of the
> axis 
> steppers is 0.0025".  Thus, I had to write my "Coordinate recording 
program"
> to 
> round-off each X and Y typed in to the nearest 0.0025" (not 
0.001").  I
> realized 
> how cumbersome this would be (got USED to it!), but wanted the 1/2" 
lead for
> 
> SPEED of operation between holes. 
>   What about those PCB drilling machines, what do they do for 
backlash and 
> other error components?<<
> Of course, all lead-screws on such professional CNC $100,000 
machines are 
> covered with bellows ("way-covers", etc.), so they are not viewable 
by a
> visitor 
> not willing to exhibit violence.  I am however POSITIVE they are 
preloaded 
> ball-screws!  AND, the screws are surely "precision ground", not 
the ROLLED
> type 
> also available.  
> 
> "Other error components?"  There are MORE?  Uh . . .  I'd guess 
MUCH care
> and 
> careful workmanship by folks who can READ (if you get what I mean!).