Grinding Non-magnetic Plates in a Surface Grinder
This method of holding non-magnetic plates on a surface grinder is a precise way of grinding when the workpiece is too large or cumbersome to be held in a vise or cradled w/ steel plates. I used molten sulphur & mixed it w/ lard oil. The mastic was then applied in a bead all around the bottom of the workpiece & allowed to harden. Light cuts were then taken on the work surface with a 36-F or G silicon carbide wheel. It will produce a nice finish & also grind the work flat. Of course melt the sulphur outside unless you have a strong exhaust system. When finished grinding, use a sharp flat chisel to break up the bead & clean up your mag chuck.
The old timers used paraffin wax before magnetic chucks were common, or at least I was told so.
I have used double sided tape before.
Put a ferrous sheet thinner than your final ground part, with some surface area to it, on the mag vise next to your part, as a backstop. Then use one of the techniques that experts have advised. This reduces the shear seen by whatever fastening method you use.
Seems like paraffin might melt if you surface grind...
I've used ferrous stops as Jim suggested above and held the parts to the surface of the chuck with hot glue from a common hot glue gun. Weight the parts down until the glue cools. This was using coolant so no problem getting the glue heated up during grinding. It peals off nicely when the grinding is finished.
Another method that works well for appropriate parts is to bond them with cyanoacrylate glue to a suitable steel plate and mount that on the mag chuck. The bond can be broken by elevated temperature or a solvent.
I block parts in front, as has been mentioned. Then just use regular, what look like "combs" for non-magnetic materials. Paper or crayon mark shims if necessary under the work.
In cases where the ~1/8" thickness of the "combs" is too much, spring steel saw stock (about .032 x a "couple" inches wide) can be used in front & back for blocking, and sprung agains the sides to get the same effect as the combs.
Have heard of using melted shellac, but never tried it. Would seem difficult to get to flow out on a cold chuck, unless maybe ironed on, or a good heat gun.....Then what, let the chuck cool for a while?
As far as caulking the sides, I might try a hot melt glue gun before stinky sulpher. Then again, didn't they used to light sulpher & smoke up the room for pulmonary ailments, so maybe it would do a person good from time to time.