Author Topic: Odd wear on the mill....  (Read 2410 times)

Offline AdeV

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Odd wear on the mill....
« on: April 06, 2020, 12:58:15 PM »
The other day, I finally got a Round Tuit for a project I've been meaning to do for yonks - a two-dial-indicator tramming tool. Nice easy build, got it done in a couple of hours, which was nice. It revealed what I thought - the mill was waaay out of tram (it's been moved to the "new" workshop, 4 years ago, and not trammed since).

So, a bit of wiggly-woggly, and within 20 mins I'd got it dead nuts (to the vice), which made me immensely pleased. Only when I tried a cut, it was all over the place... like I'd screwed my tramming tool up or something....

So, break it all down, make sure the tramming tool is properly calibrated, etc., and eventually I got it all sorted. But now I've taken the vice off the mill.... so, did a couple of test cuts on the X-axis, all good. Mounted the vice back on the mill (after deburring the bottom of it, and thoroughly cleaning it of every chip I could find).... way off again! So, obviously a slightly wonky vice (not a surprise - it's made of 10 year old Chineseium). Adding paper shims to suit has got me pretty close to level and flat in X and Y... but whilst working at it, I've discovered an annoying (and, I think, uncorrectable) problem: When I crank the Y-axis back, it rises - about 0.04-0.07mm over 5" of travel. Whilst this won't be too much of a problem in normal use (and, obviously, I've already been suffering with it for this long); but what's causing that? I assume it's wear somewhere... Can I shim my way out of the problem somehow? Or do I need to break the mill down, learn to scrape, and re-scrape it flat and true all over?
Cheers!
Ade.
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Location: Wallasey, Merseyside. A long way from anywhere.
Occasionally: Zhengzhou, China. An even longer way from anywhere...

Offline djc

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Re: Odd wear on the mill....
« Reply #1 on: April 06, 2020, 01:32:42 PM »
What sort of mill is it?

If it were a standard knee mill, it could mean the angle between the Y and Z is not 90 degrees.

It could mean your top Z-gibs are a bit loose.

If it is a column machine, round or square, you can shim the back of the column.

On a knee mill, I think they aim on a new machine for the front to be slightly high so that as it wears it improves before it worsens.

Offline AdeV

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Re: Odd wear on the mill....
« Reply #2 on: April 06, 2020, 04:59:36 PM »
What sort of mill is it?

Oops, I guess that's a fairly important piece of info....

It's a standard Bridgeport knee mill.


If it were a standard knee mill, it could mean the angle between the Y and Z is not 90 degrees.

It could mean your top Z-gibs are a bit loose.

...

On a knee mill, I think they aim on a new machine for the front to be slightly high so that as it wears it improves before it worsens.

Ok, that could make some sense - the Z-axis is a little sloppy (there's about 0.05mm difference in tram with the Z-axis locked vs. unlocked). I'll investigate the gibs (need to do the X-axis one as well, as the table's a bit loose in the centre).

This definitely isn't a new mill though - it's only 11 years younger than me!
Cheers!
Ade.
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Location: Wallasey, Merseyside. A long way from anywhere.
Occasionally: Zhengzhou, China. An even longer way from anywhere...


Offline AdeV

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Re: Odd wear on the mill....
« Reply #4 on: April 08, 2020, 03:32:41 AM »
Thanks for those links! :headbang:

I shall investigate the Z-axis gibs... Since I've not touched them in the mumbleteen (over 10!!) years I've owned the mill, they're probably well overdue a coat of looking at....  :palm:
Cheers!
Ade.
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Location: Wallasey, Merseyside. A long way from anywhere.
Occasionally: Zhengzhou, China. An even longer way from anywhere...