When surface grinding a part, you are usually looking for a nice finish, close tolerance, flatness, a precise planar relationship to a specified datum or any combination of these features. I have found that getting a nice surface finish depends a lot more on the grinding procedure than having a perfectly matched wheel for the material (although this never hurts-see Machinery's Handbook). When dressing the wheel, get aggressive on the first couple of passes .002 - .004 per pass with a relatively fast crossfeed, then take a .001 pass at the same crossfeed followed by 3-4 zero passes at gradually slower crossfeeds. I put my hand behind the wheel on my final dressing passes to make sure there is no more grit coming off the wheel. When I begin grinding the part, I set my longitudinal feed (x-axis) at just about full speed. I set my crossfeed (y-axis) at no more than .050 per step (less is better). For some reason this seems to give an excellent surface finish regardless of z-depth. Another item that will affect surface finish is having clean coolant. If your coolant is full of grit and swarf, it will cause problems. Keep it clean! Flatness is pretty straight forward. If your chuck is not flat, it needs to be ground in. I usually rough grind the chuck with the magnet off, then I finish with the magnet on taking no more than .0001-.0002 d.o.c. on my finish passes. Stay on top of the finish operation because the chuck will hold the iron filings and possibly stall out the wheel. Other things that will affect flatness have to do with workholding and heat.

Here are some ideas you can try out:

1) Shim the part if your mag. chuck is bending the part,

2) hold the part in a vise or other fixture.

3) If you have an electro-magnetic chuck, you can gradually release the magnetic force as you get to spark-out.

4) Thin parts should be blocked in on the chuck with parallels, banding strap, or similar materials.

5) Don't discount double back tape, it works amazingly well as long as you are not too aggressive with your grinding operation. I have also used double back tape as a workholding tool to grind aluminum, plastic, ceramic and rubber.

As far as holding a tolerance, you are just going to have to do it the old fashioned way. Measure the part with a depth micrometer from surface to surface or pull the part off the chuck and measure with a micrometer, then use the z-axis dial to reach finish size.

Here are some tricks to get the part off the chuck without scratching the part or the chuck:

1) If you have a large part with thru holes, a little compressed air in the hole will float the part right off the chuck. Place one hand around the blow gun tip and the hole.

2) No holes? Blow air in from the side. Cover the end of the blow gun and edge of part with your hand to keep from spraying coolant all over the place.

3) If your parts are more rectangular or square than flat, they can be easily removed without scratches or damage with a crescent wrench. Simply cinch down on the part with the wrench and rock it toward or away from you.

Never get greedy when grinding non-ferous metals: aluminum, brass, copper, etc. Rather than using coolant on these materials, it is recommended to use lard or shortening (apply with acid brush). Again, don't try to take off too much material.

When finished grinding, let the wheel run dry for 3-5 minutes. This will throw out any coolant left in the wheel. Coolant embedded in the wheel will cause it to go out of balance and create problems.

Click back arrow on your tool bar to return to Helpful Hints page.