Maching subplate flat

[jbexplorer]

I work on a 1999 Fadal 30 x 16 hs 88 CNC. I've run this machine since new. The other day I did the table push pull test with an indicator and got .004 - .005 movement in Y axis. I called the repair man to do a service. He tighten the gibbs and changed the Z axis bearings. When he got done he called me out to the machine and indicted the top of the table. Well the table goes from 0 at the right back to +.004 at right front to -.004 at left front to +.009 at the left back corner. So the turcite is worn on the ways. My boss wants me to put on a subplate and cut it flat. I don't think this will work, maybe some of you have a better idea. Thanks for any input.

[little bubba]

With all due respect, your boss is an idiot. It won't work.

You are just going to mask a problem and create a non-flat table, which will lead to more problems, this will snowball into a bunch of money and time spent on nothing which will result in fixing it right eventually.

Edit, I would double check the techs #s. Was he getting these variations by running the table around, or swinging an indicator in the spindle? I've seen a manual machine with a twist in the table, but nothing approaching what you are describing. Is the machine level, or is it sitting on 3 feet? I would do some serious investigating before I even threw a penny at it.

[jbexplorer]

The machine is level. That is the first thing the repair man did. We just don't have the money to fix it right right now. Just need to get by for a couple months.

[scadvice]

...is an important question. little bubba is right...You need to tell us that bit of information to have an idea what is wrong.
If you hand turn a indicator in the spindle and it is high or low on one side, relative to the other, that indicates that the spindle is tilted more or less than 90 degs from the tables flat. The causes I know of for this are:
1) The spindle cartridge is not aligned 90 deg to the z axis relative to the tables axis flat.
2) The Gibbs are not adjusted correctly or loose.
3) The machine is not level.
If you are using an indicator stationary (not rotating the spindle) and moving the X & Y axis to get those readings then I would suspect the turcite is worn mostly on the X & Y. The table is rising and falling.
If you can rotate the indicator and it is reasonably flat to table, the spindle cartridge alignment is probably ok.
If what you described was from hand rotating the spindle (which I hope it is) then a spindle alinement for now may help (Continued on next message...)

[scadvice]

, but not be a complete fix. It bears looking into. Uneven turcite wear could be an effect and not the cause of the problem.
The effect may be poor lubrication so the lube and oil metering system. It should be checked. Also, try moving the z axis up and down while rotationally indicating the table. Mark the table with the differences at their locations. See if these change at the far end and in betweens of the z travel. This would suggest Z axis problems such as gibbs slop or uneven turcite wear. BTW- rarely, but sometimes, worn out gibbs will not adjust. you will need to rig up something to hold the indicator that far away.
Other stuff I can think of to add - move your vise or vises around each and month also to the ends of the table travel, so that wear on the ways and turcite is evened out. A pain I know, but worth it. My guess is that if this shows up when you rotate the indicator in the spindle, its the spindle alinement. But not being there, it is hard to tell. Even a minor crash can cause that. A subplate will not help. Sorry boss... Steve

[jbexplorer]

After the repair man left, I mounted a indicator to the spindle. Then moved x y with the hand control to the 4 corners to take the readings. Then I moved the table to the center and sweep a 14" dia. X+ I set at zero X- read +.005 Y- read +.004 and Y+ read +.004. I know the turcite is worn. The spindle is ok. This machine has never been "crashed". Thanks for your comments. Just trying to get buy for a couple months.

[scadvice]

...the only thing I can suggest is to fine the most stable ( least amount of change) area on the table that your part or parts fit on and mount/rotate /fit your vise or vises there. If you have larger parts that may not work and the best I could suggest is some creative programming to compensate as best you can. I have at times made fixtures with bends on the face to compensate for parts that stress relieve while machining but that is a completely different issue from yours. I think that was what you boss was thinking of, but as I said they are not the same issue.
Let us know if you come up with a solution... I'm always interested in this sort of thing. Steve