Re: Help?? CNC PCB Drilling Machine

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@n...>
wrote:

> Depending on what machine tools you have I would go for:
>
> Mdf frame construction (or Ali if you have the skill/tools)
>
> Silver steel or ground steel linear rails (not so expensive)
>
> Home made Delrin (acetal) slides (basically reamed rod to fit rail)
>
> 1mm pitch 6mm threaded rod for a leadscrew (assuming ultra accuracy
> not needed)
>
> Nylon/Delrin Lead nut, long enough to elliminate backlash.
>
> Nema23 steppers, you don't need 100oz-in even because of what you

are

> doing. Get bipolar and don't get high voltage ones.
>
> Good three axis driver kits include camtronics and Xytolex these

run

> from the parralel port and use free driver software such as

TurboCNC.

>
> Alternately you could use ebay to get some better mechanical
> components. Either way you may find it the cheapest place to buy

the

> steppers.

Thanks Graham !

you took my 'merican 'nglish and turned it into words Sammy can
understand.

drill rod is harder than standard cold rolled steel, but easy to
work, Silver Steel is the more common term on that side of the pond.

all-thread in the U.S. is threaded rod over there.

I'm not going to approach the mm to inch, but just not the fine pitch
is good for this work.



One thing about steppers. It seems that on the PCB drilling machine,
all one has to do is move the table, or move the gantry. for those,
the only drag is the screw thread and any drag on the slides. so the
50 oz-in steppers with a ledscrew will be at least 10:1 on threaded
rod or ACME or drag will be greatly reduced on ball screws.

on the Z axis, a corse pitch screw will still transfer pleanty of
power with a 50 oz-in unit.

I didn't find a spreadsheet in the files section that included
calculating force on a leadscrew based on motor power, but a
leadscrew will transfer much higher forces than a belt.



as far as a belt drive, this may be complicating things a litte as a
gear reduction is needed to get any accuracy without a microstepping
motor (a stepper driver chip that sends 10 steps to the motor so
instead of it's normal 200 steps per revolution it takes 2,000 steps
per revolution)

Also, a belt drive gets into a little more complicated mouting vs. a
direct drive. and a belt drive requires a higher power motor as
rotion of steps to table movement is much lower.

hope this helps a little.

Dave