RE: [CAD_CAM_EDM_DRO] Re: Opinions on $250 cnc machine

Hi John,

I've built up an XY table using MDF and 1/2" DEC printer rails. For the
leadscrew it uses standard 1/4-20 allthread and tapped teflon inserts. A
more complete description is on message 289 with photos posted in the photo
section at EDMHomeBuilders.

I built this to hold a frame of 12 circuit board so I could move each board
under a programming head and program rfPIC micros and then test them
automatically. It's got enough power that I had to add braces to the end
plate after I inadvertently ran the stepper up against it and broke the glue
joint. The Teflon nut has zero backlash (for now) and very low friction.

But: The moving table is heavy and when I move to one end it flexes the
rails on the bottom. A lighter bent sheet aluminium arrangement would have
been better. (or maybe your poly).

As a pick and place type unit or circuit board drilling system or perhaps
even for engraving, it may work fine. But having also built a Gingery
Lathe, I can tell you there is no substitute for mass mass mass in a mill or
a lathe. If you want precision you can't use allthread. Just put two
pieces beside each other and see if all the threads interlock. They won't.
It's what a friend calls the drunken thread syndrome and it's a side effect
of how they are manufactured.

A decent set of threaded leadscrews will end up covering most of your costs.
Just look at the Sherline. Mostly extruded aluminium with lots of CNC
operations to reduce human involvement in manufacturing. I've seen the work
done people using one of those and it's nothing short of outstanding but
enlarging a machine usually means you have to cube the mass to get the same
level of performance.

Regards,

John Dammeyer

> >
> > Yahoo! Groups Links
> >
>
> I've
> been using easily replacable "snap-in" polyethylene nuts -no backlash
> on the only one I've had to use...It's just a 1" cube drilled &
> tapped.
>
> Before I get in any trouble let me say that I'm here to share
> and get experienced opinions on something I'm positive will
> benefit all. I haven't seen this stuff used and it should be.
>
> I built a disc finisher (polishing machine) 10 years ago out of it
> and have used it 15 hrs a week every since.
>
> My first lathe was cast on the end of an old blower motor.
> I made actual usable roller bearings out of the stuff.
>
> I,d like to make a sortof "snap-together" customizable
> cnc kit and I have.
>
> I do want my idea critiqued, critisized, and taken apart
> because the thing HAS to work.
>
> Thanks -John