In article .com,
John Martin wrote:

Pete wrote:
This machine also has .30 backlash on the X axis. Any tricks to repair or
improve this?

If you really mean .30" backlash, there's something seriously wrong
with the machine. If you instead mean .030", that's not bad. There's
always backlash, you just have to learn how to compensate for and work
with it.

Agreed. If it really is 0.300" backlash, that is more than one
turn of the leadscrew, which means that at least *some* of that backlash
has to be somewhere other than the fit of the nut to the leadscrew. I
could see something like that *possibly* happening if the screws
mounting the nut to the saddle are loose. If so, tighten them and
re-check. Also, the leadscrew may be loose in the bearings at the end
of the table, allowing end float. That should be controlled by a nut
between the bearings and the crank.

However, I suspect that it is more a case of reading "30" on the
dial when checking for backlash and thinking that it represents 1.000"
full turn. That would really be only 0.030", as the dial is either
0.100" for a full turn, or 0.200" for a full turn, depending on the
leadscrew pitch.

When I got my well used 12x24" Clausing lathe, the cross-feed
leadscrew had a backlash of 0.070" (with 0.100" being a full turn of the
leadscrew. In that case, both the nut and the leadscrew were badly
worn. Instead of the leadscrew looking something like this (Acme
thread) (View with a fixed pitch font, like Courier. Proportional
pitch fonts will distort the image, because the spaces are a different
width than the '_', '/' and '\' characters.


Un-worn leadscrew (thread crests should join the sides, but not with
ASCII drawing):
_ _ _ _ _ _ _ _ _ _
_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \_/ \

Badly worn leadscrew:

_/\__/\__/\__/\__/\__/\__/\__/\__/\__/\_

If the "flaking" is worn off the ways (not really the scraping,
but special deeper scrapes designed to make scattered reservoirs for
waylube, to allow it to be distributed on the mating ways as the machine
moves), then it is likely that the leadscrew and nut have already been
replaced once -- so you could have 0.030" backlash in the replaced
leadscrew and nut, and *lots* of wear on the ways. On my Series-I
Bridgeport, the ways are chrome plated and *ground* flat, not scraped.
The flaking looks at though it might have been put in with an angle
grinder at a shallow angle. Chrome ways are too hard for normal hand
scraping.

Note that if you try to tighten the nut so as to eliminate
backlash in the middle of a worn leadscrew, you won't be able to run the
leadscrew to the ends, as the nut will be too tight in the relatively
unworn section.

Good Luck,
DoN.

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