An extremely accurate granite surface plate might seem superfluous in a woodworking shop but I find my 9″ x 12″ x 2″ 30 pound rock to be very handy. It is simply a smooth and very flat slab of black granite, with a phenomenal surface tolerance, even on this economy model, of 0.0001 inch, which is about 2.5 microns.

Its main use in my shop is to accurately flatten other tools, such as plane soles. I use aluminum oxide or silicon carbide abrasive paper adhered to the plate with only water, or just hand held or taped in place for working on small tools. I can flatten the sole of a 9″ smoothing plane, especially easily if it is a bronze plane, or even somewhat larger planes, though certainly not a 22″ jointer.

Used with a feeler gauge, it serves as a reference to verify the accuracy of layout tools, such as straightedges, and any other tool that is supposed to have a straight/flat surface. For those who like sandpaper sharpening, the granite plate can be used as a base for the abrasive paper when extreme accuracy may be desirable, such as when flattening the back of a new blade.

I like knowing that there are a few dependable references in the shop – the granite plate, a Starrett straightedge and square – with which to vet other tools. They’re like the Constitution of the shop and the woodworker is the Supreme Court. However, I then have only myself to blame for the inaccuracies in my work!

I bought my granite plate at a local industrial supply house for about $35. Woodcraft, Japan Woodworker, and Enco have good buys on them. A 12″ x 18″ x 3″ or a 9′ x 24″ x 3″ plate may be more useful but the weight goes way up to about 85 pounds. Obtaining your plate locally will save a lot of money on shipping.