Re: [CAD_CAM_EDM_DRO] Build my own CNC lathe - possible?

Alan Rothenbush wrote:

> Lazy Sunday morning, drinking coffee, daydreaming and a crazy plan starting to coalesce.
>
> 1. I've CNC'd my old Sherline lathe and have been playing with it in earnest, to get my head around the use of a CNC lathe. (Long time user of a CNC'd mill).
>
> This pretty cool!
>
> I took the trouble of adding manual handwheels to it (just in case) but I can see that a nice MPG will completely obviate the need for these.
>
> Problem is, there's some backlash in the system and due to the age of the Sherline, it's not easily removed. (Uses the OLD style leadscrew nuts). I'm compensating in software, but of course that's not the same thing.
>
> Still, a CNC lathe is cool.
>

Actually, the backlash can be taken out! Assuming you can make a nut
which fits on the leadscrew, screw it to the original nut (the new nut
can be thin, but it will wear more quickly.) Drill the pair for two
roll pins parallel to the lead screw. Now, get some Belleville washers
(the cone shaped washers), put them between the nuts inside the roll
pins until you can almost compress the washers. Add shims so the holes
line up and there is real tension between the two nuts. Suddenly there
is zero backlash if the washers remain compressed and the washers
provide enough force to heep the leadscrew pressing on the original nut.

Now for the bad news.

1. the original nut will wear more quickly
2. it will require higher forces to move things
3. this IS NOT more accurate, just more repeatable
4. preloads can easily be applied other ways, this is just one method
5. if the original bearings/bearing surfaces are worn, the backlash
may be there.

Find the source of the backlash before you try to fix it. Replacing a
worn part, or adjusting clearances may be cheaper than modifying things
to fix something not broken.

> <snip>4. Staring at the McMaster Carr online site and peeking at eBay, I keep looking at all these linear rails and I've got to wonder; couldn't a guy build his own CNC lathe for a WHOLE lot less?
>
> Some stout linear rails fastened to a suitable base (the ground flat bed of an old lathe, for example). Standard linear slide for the cross slide. Ball screws.
>
> Use an existing spindle out of something, maybe even another Southbend so all the existing attachments can be reused.
>
> Fab up a headstock and line bore it right on the machine itself; same thing for a tailstock.
>
>
>
> Sunday morning on the couch, this SEEMS doable. Am I dreaming? Hallucinating? Any opinions (including "you're nuts") appreciated.
>
>
> Alan

Go to the Open Source Lathe group!

You are not discussing something as cheap as you thought. Start with
the PROPER, high precision headstock bearings and wince. Then look at
the slide costs. It ain't cheap!

Also look at the e-leadscrew group for a semi-CNC lathe conversion.
Pretty neat. Also pretty cheap!

Consider getting a commercial CNC lathe with blown electronics and
starting from there. New industrial electronics may be more than the
machine is worth, it may be available for less than it will cost you to
build your own. Once you start to design the chucker, the tool changer,
coolant feed system, etc. you are talking a LOT of work. If you start
with those in place, but needing control electronics, you may be FAR
ahead of the game.