Re: My take on lathe conversion

> From: Joe Vicars <jvicars@...>
>
> I have thought about Lathe conversion for my 12" atlas and have
> decided to leave the acme lead screw in place and replace the half nut
> with a machined anti backlash acme nut. There are several ways to do
> preload/backlash compensation with acme screws that will be adequate for
> my needs. I also am of the opinion that the carriage really doesnt need
> backlash compensation any way. 95% of the time I am cutting towards the
> headstock, and reversing the direction of the carriage under load is
> just not that common.

Generally I would agree, with two reservataions. The first is that I
don't really want to use the threading leadscrew and half nuts for
power feed. They have too much slop, might wear quickly, and I don't
want to modify the gearbox so as to be able to turn the screw with a
stepper or servo. Therefore I want to put an extra feedscrew on the
lathe somehwere, and with 1" rolled ballcsrcews only about twice the price
of 1" threaded rod, might as well go with one.

The second reservation has to do with cutting nonlinear tapers in the
normal large-end-towards-headstock orientation (which is the reason I
might do the conversion) Feed towards the headstock and the cutting
force may tend to push the crosslide ahead of the feed. Therefore I'm
tempted to take finishing cuts towards the tailstock. But then the
cutting force might feed the carriage ahead of the screw. Given the
weight and friction of the carriage, I'm not too worried, but it is
still a consideration.

> The cross slide is another story and that will be a small 1/4 or 3/8"
> or ball. Very cheap and not too difficult to replace.

I worry about excess flex on those little guys. Also note that at
least at McMaster, the 5/8, 3/4, and 1" sizes are cheaper than the
little ones.

> The compound rest is removed and placed on a shelf.

Something I should probably do. Have to machine a replacement to hold the
Phase-2 toolpost though.

> Here's the real gem though. The large spindle back gear is replaced
> with a timing belt drive so that the spindle becomes the third axis for
> thread cutting and for two axis milling. I have used a small router on
> my lathe for several jobs machining aluminum. The spindle pulley can
> also be disengaged to run at full speed with the original v pulley/motor
> setup.

Interesting.

Chris

--
Christopher C. Stratton, stratton@...
Instrument Maker, Horn Player & Engineer
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