On Sunday 09 October 2005 01:28, Jon Elson wrote:
>Gene Heskett wrote:
>>On Saturday 08 October 2005 22:18, Jon Elson wrote:
>>Lucky dog. These look like a better quality of 20 tpi ready-thread
>>similar to what I can buy at Tractor Supply, but without the cad
>Huh? On my Bridgeport, I have some 5 TPI ballscrews from an Excellon
>PC board drilling machine. The screws are something like .0005"/3 Foot,
>and then had corrector cams to improve the accuracy to something insane
>like ten times better than that. I never even bothered to hook up the
>cams, on a milling machine, I'd never see the difference.
It certainly wouldn't be something I'd spend any time on unless I was
carving a new mirror for the hubble.
>> But my dial indicator seems to have wibbbles of up to a thou plus or
>>minus in any 2 adjacent .010" movements. As its a cheap ($30) dial
>>indicator, it could be as much a problem as the leadscrew.
>I use gage blocks and a dial test indicator to do leadscrew tests. The
> dial test indicators have much less force to deflect the dial, so lack
> of stiffness
>in the indicator mount is less of a problem. I also have a Federal
> Maxxum electronic indicator that reads out to .00005" with a low force
> and no hysteresis. Your description doesn't make it clear whether you
> have a problem with non-repeatability or cyclical errors in the screws.
> Making .010"
>moves may be deep in the stick-slip friction zone of the machine. You
> might try making the same up one inch, then back, several times, and
> see if you get a consistent reading from each cycle. If not, then
> there is something like motor settling that may not be very precise.
I could measure the settling point of one end of the move, only one dial
indicator, its one of the little ones with the finger sticking out the end
and pivoting, only a 1" dial. I originally bought it for centering up
the wibbles of using a 4 jaw chuck on the lathe. My 3 haw seems to
have about a .010 built in off-center, even after I ground the jaws
with a dremel. Got it from grizzly, along with the universal arm mounting
on a 70 lb magnetic base.
As to the src of what I'm seeing, I'm inclined to blame much of its error
over a .010 move on the precision of the gears in the indicator. Its
been abused some by watching a workpiece with the chuck drive engaged
at 30-60 rpm many times.
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Copyright 2005 by Maurice Eugene Heskett, all rights reserved.