Homebrew PCBs

--- In Homebrew_PCBs@y..., Steve Greenfield <alienrelics@y...> wrote:

[edited for size]

>Accuracy is not just repeatability or linearity. It
is also important that if the calculations say X steps move the
head 4 inches, that it not be 3.9 inches.>

Hi Steve,
Dialing in that 4.0" = 4.0" is done in the driver software. So that 
parts easy.


>Boeing Surplus... Yeah! I live about 30 minutes from Boeing
Surplus. What they don't have, there are metal sheet suppliers all
around them.<

I see a new project in you future. ;)


> http://www.smallpartsinc.com for new stuff.<

Did you mean http://www.smallparts.com ?

>What makes you think they are using 60 oz-in, besides the size of
the steppers?<

Just the size, from the movie I can tell their NEMA23 size and from 
the pics I can see they are the shorter single stack. The largest 
rated ones I have (or found ) in that size are 60 oz/in, the ones I 
mentioned before are all longer and or square frame. If they were 
that size and square they might be 83 oz/in, and if they were 
octagonal, they would probably be PacSci and even higher rated. I 
think 60 oz/in is giving them the benifit of the doubt. Of course if 
their being driven dual coil then that might increase to abt 75-80 
oz/in. 

As smooth as the boards curves looked they might be driven with 
microstepping drives. I dont really want to dedicate my Gecko 201s to 
driving this project but I might. ;)

Also if you watch the movie you'll see their in no hurray either to 
mill the board. It doesn't take a lot of power to move that slow, and 
that slow the steppers are going to have a lot of power.

Also, 60 oz in steppers, through a 10:1 drive (10tpi Acme) will have 
a holding force of over 200lbs... 

60 oz/in X 10 (drive ratio) X 2pi (6.28) / 16 (oz/lb) = 235.5 lbs of 
holding force. 


>Don Lancaster <http://www.tinaja.com> has a great idea for
lightweight milling heads- dental turbines. Tiny flexible air hose,
tiny dental turbine, and you have a cutter head that is extremely
lightweight. Very high speed but the cutting head is small so
cutting speed isn't quite as high as it might seem. Maybe something
that could even be retrofit to an HP flatbed plotter? Very cheap so
when they wear out you just toss the turbine and install another.
Perhaps use the exhaust air to make a vacuum system to suck the
particles up. <

Interesting, and I have 2 - HP 7475A's collecting dust in the 
closet. :)
I might try that later, this project can double as a light duty CNC 
Router, Signmaker... :)

Thanks
mike