Leveling

[KevinV_MEI]

Did a search on leveling and found partial answers to a problem I'm having. I have a 1997 VMC1000/30. Holds accuracy extremely well but not very precise. Dimensions in X direction are spot on, repeats +/- 0.0002 and as precise. Y axis dim's repeat within 10ths but are off the mark by about 0.002.
I conferred with the repairman, thinking tram issues, who said no it's a leveling issue. Level on the table front to back and left to right reads within the 0.0005"/10" mark on a precision level. Tram measures within 0.0008 in a 10" circle.

How should I be checking level?
What adjustments can I make?

Anybody else have a similar problem

[underthetire]

Truthfully, actual level to the world makes little difference. You need to put the level on the table and move the axis to different spots, should stay the same. If it moves , you have either a leveling problem or an axis problem. Y axis is the one that can be affected by the center pads of the machine, they can concave the Y if too loose, or convex if too tight. Your tram numbers seem ok, maybe slightly high for my taste, but reasonable. I'm guessing you have thrust bearing issues in Y, or possibly a screw or pitch error comp is wrong.

[KevinV_MEI]

The concave/convex issue is what I thought too. How would I check that?

As for thrust/backlash comps etc. here's what I did to rule those out or at least point to tram level issues.

Drilled, end milled hole (circle cut), reamed a hole on center 0,0 indicated ground (6) six side block of CR. X measured withing 10ths of center TIR. Y measured almost 0.004" TIR.(don't recall which direction it was in the vise, will note next time.)

Friend and I looked at each other, said ok let's double check everything and do it again.
Exact same results.

Did it again on a different block with a change in process. Since the hole is 8mm, I zeroed the C/L of the block, changed Fixture offset to reflect that, put a 5/16 EM in, drilled and chased a hole with that, then reamed it. The X/Y axis then was never moved from the indicated position of 0,0, only Z moved for obvious reasons. Exact same error in position.

[underthetire]

Place level on center on table, parallel to the Y axis. Note where the bubble is. Move Y back, note bubble. Move Y out, note bubble. Any change indicates a sag in the Y, adjust for that. Once done, check tram. Tram WILL change doing this.

[KevinV_MEI]

Thanks I'll look into that now.

[underthetire]

Post back with results. I usually don't do tests like that with everything in the picture to narrow down problems. What you may be seeing is spindle head growth, especially if the machine has a cooler for the spindle. I once tried helping a customer out years ago on a old Mori. Same thing your describing, but the maintenance dept had already changed the Y axis ballscrew and bearings for this problem. I was out of ideas over the phone, so I made a trip out there. Sure enough, Y axis was changing .002"+. After about an hour of testing, I had found someone changed the thermostat on the cooler. It was marked 0 then +15,-15. Someone had decided colder must be better, so they moved it to -15. 0 is ambient shop temp, -15 was actually -15deg C. as the head got colder and colder, it pulled closer and closer the the column. Set it back to 0, and problem solved.

Moral of my story, never overlook the simple stuff.

[KevinV_MEI]

Thank UTT
We just checked level. Center to back bubble didn't change. Center to front bubble moved to show the front of the machine 0.0002/3 per 10". Is that significant to warrant changing the level. We did switch the level end for end with exactly the same results.

Machine is relatively cold, no significant cutting before or after tests. Spindle is new, just professionally rebuilt by Precision Spindle and reinstalled by DB2 Machine repair.

Tested the Z axis alignment this way. 1/10th Interapid indicator, indicated a jig ground hole in a block with the indicator as short as possible and the spindle as close to the hole in Z as possible. Ran the spindle up, extended the indicator arm to it's full reach and re-swung the hole. within 1 tenth.

Puzzled.

[underthetire]

Doesn't sound too bad. Your gonna get some movement on that kind of machine. Has this machine lost parameters in the past?

[KevinV_MEI]

No no loss of parameters as far as I know, it's 6 months new to me.

Change of previous statement. Tram is out 0.0035 in a 13" circle, heavy in front as the indicator on the level indicated.

[underthetire]

WAAAY to far out IMO. I usually sweep entire table width ( unless the machine is huge ) and old machines dialed within .001 or better. new machines as close as time will allow, usually a couple tenths. I would start with that and re-test. Keep in mind some older box way machines will never come in, without re-turcite and fitting, but if thats like our VMC1000, should be linear guides. Ours was never very square from the beginning, since Hardinge bought Taiwan machines.

[KevinV_MEI]

it's a 97 so I assume box, never had the way covers off. I know should inspect them but the thing cuts so nice I had to get it up and running, customers screaming for more capacity. Table is 20" just that's as far as my indicator holder will go without adding a new rod.

We're going to try and change the level now to compensate. Will report soon.

[KevinV_MEI]

Update, went through level several times. No significant change. Had Advanced Machine out on another issue on another machine yesterdayand picked his brain on it. He's not a Bridgeport guy (Fadal) but is an excellent mechanic. We looked a few things over and found the Z axis gibs were out of adjustment just enough and the head was sagging slightly. A few tweaks later and it's now less than 0.002" over the full width of the table. We could have tweaked it to get it closer but he didn't feel the amount of work was worth the gain.