Re: [CAD_CAM_EDM_DRO] Re: Cost estimate for machining of acme screws

JanRwl@... wrote:

>In a message dated 11/17/2002 1:10:55 AM Central Standard Time,
>elson@... writes:
>
>
>
>>On my Atlas lathe, it would probably take a half hour for the first one, and
>>maybe 15 minutes for each after that. With a 'real' lathe, it might get
>>closer to 5 minutes each. It would take a bit longer if you wanted the
>>ends ground instead of a turned finish.
>>
>>
>>
>Assuming you would just "chuck up" on the O.D. of the screw as simply as you
>would with any length of CR rod, I would totally agree with your numbers,
>here. But if you fiddle with some brass sleeve (I have made those for my
>own similar applications in the past) to slip over the O.D. of the screw to
>protect it from the chuck-jaw-teeth (even a "smooth" collet has three grooves
>which COULD make "nicks" in an otherwise-very-smooth screw-O.D.!) it can take
>more! None of us (or few, anyway) have mentioned "tolerance" for this
>operation. Assuming you would want to press-on a ball-bearing, we would want
>-0 to +0.0005", so the screw-end will press-into the ball-bearing without
>"hydraulic force" required. But more than just an "interference fit"! It's
>reaching, measuring, and ENSURING that rather precision O.D. that is the
>time-consumer here!
>
>

If you really want a slight interference fit for the bearings, then
you'd better be prepared for
grinding it with a toolpost grinder. There's no way to repeatably get
.0005" tolerance with
a pointed cutting tool!

>Now, if you have a dozen or more such ends to do, with professional
>experience in setup, and a very fine Hardinge, etc., lathe, you could do
>these in only a couple minutes, each, perhaps even including "last-pass
>measurement", but I still assert that "first one" would, as you say, take at
>least a half-hour!l
>
>But, wow! This is SURELY far-off-topic, particularly, by now! And in the
>past when we've gotten off on "machine-shop tangents" like this, Bill has
>jumped in our [deleted] and spanked us heartily! Wonder why THIS topic has
>been tolerated for so long????
>
>

Machining retrofit screws for CNC applications is pretty much on topic.
Some people can buy
new kit-level screws, some people will just replace handwheels with
pulleys, but machining
a ballscrew is a pretty common task when converting to CNC.

Jon