Author Topic: Worn cross-slide leadscrew?  (Read 1001 times)

Offline AdeV

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Worn cross-slide leadscrew?
« on: June 08, 2020, 01:46:40 PM »
Afternoon chaps!

I've finally finished(ish) fitting a DRO to the old Edgwick lathe - well... two of the four anyway... but most importantly I've got the cross slide one on now. Which has lead to some "interesting" comparisons....

After a bit of fettling, I think  the DRO is pretty much dead nuts on; at least, cuts on a test bar agree, to within a couple of tenths, of the DRO reading... So next I figured I'd compare the DRO to the handwheel. Starting at the furthest outward position, wind in a few thou, set handwheel & DRO to zero. Wind in an inch. Handwheel now over-reads compared to the DRO by about 1 thou. Go another inch; 2 thou. Go another inch or three; 5 thou. In fact, by the middle of the travel, there's a 10 thou discrepancy. Keep going, and it closes up again to around 5 thou difference when the leadscrew nut hits its end stop.

Since the DRO *appears* to be OK, within the small range of cuts I've tried, would this rather large discrepancy across the travel suggest a worn leadscrew (and, quite probably, nut)?

If the DRO is right & the handwheel is wrong, this would go some way to explaining why I was having so much difficulty chasing down tolerances...

Oh, and while I'm here, and on a partially completely different subject: The DRO "rattles" between numbers when the lathe is running - obviously, the vibration is sufficient to cause the encoder to toggle. Now, I *could* fix that by hiding the 10ths digit  :lol: but I'm wondering, is there a better way? Maybe shim the readers with rubber sheet? Or is it just something Chinesium DROs do, and I just learn to live with it?

I'll do a build log soon, promise... I want to get the carriage readout mounted before I do the write-up.

Ooh - another question: What's the typical axis designation for a lathe? IIRC Carriage is Z, Cross-slide is X, there is no Y... As I've gone for 4-axis: Carriage, Cross-slide, Compound-slide, Tailstock, what would be the "normal" way to set those up?  Won't matter once DIY-DRO is a bit further advanced, of course, as you'll be able to name the axes  :thumbup:
Cheers!
Ade.
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Location: Wallasey, Merseyside. A long way from anywhere.
Or: Zhengzhou, China. An even longer way from anywhere...
Skype: adev73

Offline Sea.dog

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Re: Worn cross-slide leadscrew?
« Reply #1 on: June 08, 2020, 04:26:17 PM »
"Wind in an inch. Handwheel now over-reads compared to the DRO by about 1 thou. Go another inch; 2 thou. Go another inch or three; 5 thou. In fact, by the middle of the travel, there's a 10 thou discrepancy. Keep going, and it closes up again to around 5 thou difference when the leadscrew nut hits its end stop."


Absolutely typical of an old lathe, Ade. My Boxford was exactly the same. You'll probably find very bad wear on the centre of the feed screw, tapering away to good thread at either end. The nut is likely to be badly worn as well.

Offline Pete.

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Re: Worn cross-slide leadscrew?
« Reply #2 on: June 08, 2020, 05:25:58 PM »
You could use gauge blocks and a dial indicator to verify the DRO is reading correctly, then forget about the dial numbers.