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madman
11-24-2007, 11:52 PM
Ive just spent near a week fiddling with my surface grinder. I redressed changed wheels ect. I can hold .0003 on a 10 inch part but i thought after grinding the (shars) new magnetic chuck i would have super accuracy perhaps a .0001 on the entire face that was ground. What am i doing wrong. ?? I thought if a grinder was dialed in surface grind magnetic chuck that theoretically it should be darn near perfect???? Mike PS I was trying to grind in a special centerless grinding cam for a friends machine. I am having troubles keeping it to .0002 tolerance?? Thanx

Carld
11-25-2007, 12:22 AM
How big is the part you'r grinding?

What kind of metal is it?

Grinding dry or wet?

Are you measuring flatness or thickness or both?

What brand of grinder are you using?

What wheel and grade are you using?

oldtiffie
11-25-2007, 05:24 AM
There are quite a few possibilities for lack of accuracy on a surface grinder.

It would help if you could put some pics up of the job and the grinder.

Dimensions of the job will help as well.

As your mag chuck dials in withing 0.0001" all over then your chuck should be OK and the job should be as accurate as your chuck top surface.

The chances are that the problem is to do with the chuck distorting the job as it "grips" before you start grinding and having the job return to normal when the chuck is released.

Heat and wheel wear are sometimes a cause as well.

JoeFin
11-25-2007, 09:04 AM
Sorry – Dumb question

When you installed the new chuck, you did surface the chuck.

You should have also stoned the mounting on the table too, to make sure there are no little burrs holding it up on the ‘T’ slot.

By the time the coolant tank is cleaned, any chipped paint is touched up, ‘T’ slot cleaned out and stoned, and then Mag chuck resurfaced it is an all day job. Pretty good idea to wire wheel the threads of the mounting bolts to make sure a small burr doesn’t give you a false reading when you torque it down.

wierdscience
11-25-2007, 11:14 AM
Sweeping the chuck is a slow process taken in .0001" passes running front to back,.0001" downfeed back to front,.0001"front to back all while running coolant and making passes no wider than half the width of the wheel.

Cooling is important,the side being ground will heat and cause the chuck or part to expand,but only on the side being ground which causes it to bow.This bow gets ground out and after the part or chuck cools it will relax to a cupped state.

All of that said,have you tried reversing the part in process? If the part has internal stress removing all of the material from one side will cause it to cup or bow.Taking equal amounts from both sides may help.

Lou
11-26-2007, 12:49 PM
A magnetic chuck that has been ground will only reflect the accuracy of the grinders ways. Running an indicator over the surface after grinding will indicate what appears to be a flat surface. The only way to test is by grinding something ( both sides) and then mic it, or use a known good parallel
on the chuck and sweep it with a indicator.