Hi, I'm a fitter and turner from way back in the late '50's and machinery has always been my passion......... still is in retirement.

The vertical grinder I mentioned did a very creditable job as I used it for a lot of tool making jobs, and the surface finish depended a lot on how you dress the stone.

The important bit is to have the vertical head dead square with the table or like a mill with a flycutter you will get back cutting and hollowing of the surface.

It's a very quick machine to use and is similar to a wash grinder in action......it doesn't compare to a horizontal type surface grinder.....that one can give a mirror finish.

I would say that for lack of a surface grinder, a DIY one is better than none at all.

Perhaps all it takes is some linear rails for the X axis as that's where the fast motion occurs and dovetails for the Y and Z axis as they only move slowly......they're very precise machines but you "could" build one if you really must have one.......the mag chuck is the most expensive bit, but you can cobble one up too with the electro magnets I mentioned.......anything is possible.

If you went the DIY path, then a motorised head would be the way to go....... that is a 1/4 hp 3,000 rpm single phase electric motor...... as it would be a complete package just waiting for the body to mount it on etc.

The bearings would be OK for the small amount you'd need it for.
Ian.