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Studer s40-2 siemans control grinding problem


Jun 22, 2018
We have a new to us Studer s40-2.
The problem we are having is when Traversing parts. The center of the shafts. (26 inches long) go .0002 to .0003 smaller than the ends. The centerline of the shafts are within .0002 from Center to center. The only thing I have found is to let the ends dwell for 4 seconds each and the more free passes the worse it gets. I feel we are losing to much time this way. We have not run into this on any other of our grinds. But the rest of our grinders this length are manual.
Any ides
If your tailstock center line was higher that the wheel head center line and the workhead lower that the wheel head center line you would have a hour glass shaped part.
Thank you for the response. I checked that it is within .0003 on the 28 inch shaft from end to end
My understanding is that the S40 grinder is made with a polymer granite base supported on three feet. With the three support feet the frame cannot be twisted even if the machine is not level.
So you will need to look elsewhere for the problem.

The difficulty is that the machine is new to you and its previous work history is unknown..

Would it be possible to shift the positions of both the headstock and tailstock to the right of the table and see if the error in the part geometry changes?
On much older grinder designs it was possible to float the table carriage and change its height with respect to the wheelhead if the way lubrication pumps were not set up correctly. A bent ball screw might also lift the table.

The machine rebuilding forum on this website will be a better place to ask for help. The forum participants will want to know the condition of the machine ways. If your machine has the cast in place plastic dots on the ways the wear pattern may not be apparent. If you mounted a dial indicator on the wheelhead and ran a known good test bar mounted on centers past the wheelhead you could get an idea if the problem is in the ways. You will need to account for the test bar gravity sag when doing the measurement.

Some manufacturers of machine tools increase the accuracy of their machines by doing a optical survey of the carriage motion and then creating a look up table in the controller that compensates for the measured error.

So, for example, if there was a small out of plane error in the grinder carriage longitude motion it could be corrected by moving the wheel head slightly to cancel out the error.

It might be worthwhile checking if the controller has such a look up table set up for the Studer. The table entries may have become corrupted.