From: Robert Bastow <teenut@home.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: Why is leads crew jerky???
Date: Sat, 16 Oct 1999 06:01:00 GMT

Simply a bit of "Stiction"..Stick-slip..which CANNOT be avoided on sliding
surfaces (which includes your acme leadscrew and nut) Your mill sounds as though
it is as well set up as any I have ever met with!

If you had been using a REALLY sensitive DTI (Not a DRO) you would see the
table, as you turn the screw, would HOLD for a moment (thats the "stick") then
JUMP a wee ways (Thats the "slip")  Then you would see it CREEP a tiny amount
before coming to rest..that last bit is the oil film settling down after being
squeezed.

See what you miss with a DRO!!  (O.0005" or even 0.0002" is way too coarse to
see this happen)  8^)

teenut

Kpnorm wrote:

> I was double checking my 0 with the edge finder today. I"m .002 away and cound
> a series of 9 small jerky movements as I go those .002. Now I've noticed this
> many times but why isn't it smooth when I dial over in slow small amoonts on
> this mill? Lead man said it was because mill is old but I don't believe it.
> I've used maybe 20 mills but no new ones. I tiink it has more to do with
> friction.
> Ken