Leveling a CNC lathe

Spent the day leveling a Daewoo Puma today. We have an import quality
"master precision" level. Apparently graduated to .0002" over
10" (sounds like bullshit to me, but that's what the tool says).
The long and the short of the situation is that the X axis is no
problem. Can get it entirely within 1/4 graduation of level.
The Z is not so easy. The best we can do is the bed low in the middle
(zero), with the headstock being 2 graduations high, and the tailstock
being 2 graduations high as well.
The Puma has basically four pads under the headstock, and two under
the tailstock. There are no pads in the exact middle so we can't
simply jack the middle up to get rid of the "smiley face". Of the four
pads under the headstock, two are about 12" closer to the middle than
the other two, but they're certainly under the headstock.
Despite our best efforts and at least three distinct approaches to
this situation, we were unable to get the Z axis any closer than high
2 at each end.
So - should we stop there and start making chips, or is our (half-way
expensive) time worth the effort of fighting with the last +2
graduations? If the lathe is actually .0004" out over 14" travel, I'm
inclined to leave it as the longest part is only about 5" long and we
have no tolerances below about +/-.002" for this machine.
Naturally my boss is not only interested in tolerances, but also
premature machine wear.
Thoughts would be appreciated!
Reply to
Robin S.
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Robin, You can check the level by rotating 180 degrees. You should get the same reading when rotating the level regardless of how far out it, or the surface your rotating it on is. Most levels have an adjustment screw to make corrections.
Best, Steve
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Do you have the Daewoo manual? My YCI manaual for my VMC states the machine must be level within 1mm/M or 0.012"/ ft. You're at 0.0004/ft at the ends. See if you can find a Daewoo spec for that. I would think you're good. The sag sort of bothers me, but maybe someone here knows if it really is important or not.
Thank You, Randy
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if I'm understanding correctly, the ways have a smiley face? That might be a bad thing, especially if your trying to turn something long between the center and the chuck. But if the ways are true to the center and chuck, I'll have to agree with one of the other posters, you could have it on a 20 degree tilt and see no problems.
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If the owner of the shop doesn=92t have confidence in his precision level why can't he check his precision level against another level in the same position on whatever and compare readings? Should he feel confident in his precision level if both levels are calibrated the way you describe above and both give the same reading making sure that neither level is off the scale... I think he should.
Jon Banquer San Diego, CA
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You don't trust the level and you don't know for sure if the surface is even flat/straight. Run an indicator across the surface and check it to verify/reject the levels readings.
Are you placing the level on a critical surface, one that the turret/bed actually rides or is this some other?
-- Tom
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you can get the z axiz of the bed straight by using the four adjustments at the headstock end. To move the middle of the bed up you would evenly take a slight amount of pressure on the far left two adjustment bolts.When you back off on the outside bolts the bed will slightly bow up and take out the error you have. You could alternately tighten the middle set of bolts and get the same effect. For that error that you have, dont move the bolts more than a 1/16 of a turn at a time, and move them both the same amount.
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Robin, A couple of things. Yes your precision level very well is that accurate, and easy to check. If you flip it 180 degrees and get EXACTLY the same reading then it is properly calibrated. Mine has a cross vial also. It has to be level side to side as well in order to be really accurate. The 0.0002" per 10" is actually an indication of the sensitivity of the bubble. Someone leveled a machine for me recently with a 4 foot carpenters level, dead nuts on. My 0.0005" per ft. level indicated it was 4 gradations off. Flipping my level 180 gave the same 4 gradations of error, indicating that my level was in fact accurate, and the machine was not level.
BIG question here. How thick is the concrete floor/foundation? What does the manufacturer recommend? I tried leveling a lathe once, and gave up trying to get it really close when I realized it was the FLOOR moving, not the lathe! In the same shop I went to do some repair work on the 60" Toshiba Blanchard style grinder. I noted in the manual that it required a foundation at least 6 FEET thick. It was on a floor only 6" thick. I asked the operator if the machine was accurate and stayed that way. He told me that he had to stop grinding when the forklift was moving around! This on a grinder with a 200 HP motor! $200,000 for a grinder and they save money by not installing the foundation!
Gary H. Lucas
Reply to
Thanks for the thoughts. After testing it, the level seems to be accurate.
We can't tell how thick the floor is as it's not ours to drill. However, given how the machine moved over night, we're pretty sure the floor is "settling". Given the size of the shop and the lack of electrical infrastructure for heavy machines, I'd assume the floor is relatively thin.
We did indeed try to remove the low in the middle by backing off the far left screws. They simple loosened completely leaving the weight of the headstock on the "middle" screws, but not adjusting the bow.
The manual specifies +/-0.00025" over 10", which we did (and had previously) achieved. When all else fails, RTFM.
We will continue to re-level the machine in a week, a month after that, and every six months there after (or until there is some significant stabilization).
Reply to
Robin S.
There is nothing unusual here, Gary. This is the typical machining job shop mentality. If you wish to be successful in this trade you learn to accept this kind of mentality and deal with it. If you can't deal with it you move on.
I've worked in shops where they didn't have the proper footings under the machines and we leveled the machines every 6 months.
Jon Banquer San Diego, CA
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I put an entire shop in near Portland, assured by the architect that the floor was good. I wanted the floor cut and poured so the machines settled on a foot of proper concrete.
I had it cored anyway.
3" of first layer with a second layer of 6" of very course cement separated (basically lubricated) by a layer of thick tar paper.
They planted the machines anyway, but I was able to argue for 24" square pieces of 3/4" plate under the feet to spread the load.
Amazingly, it didn't hold up.
Document everything so that when it comes apart like a cheap suit, all know what happened.
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