HHIP 4401-1597 6" X 8" X 2" Granite Surface Plate, Grade B, 0 Ledge

Very flat. Cleaned the granite and floated a known flat lapped part across its surface. Measurements show it to be definitely better than +/- .0005" .Additionally, some of these photo/video reviews are a real hoot! Remember, this is a classB / toolroom grade rock...Most of the complainers are actually revealing the flaws in thier own set-up.... Seller should probably do themselves a favor and include a geometry book free with purchase!

This surface plate is more than sufficiently calibrated for a hobbyist or shop, and is absurd value at $20.

My set up has a base of solid 3/4" thick steel milled to .001" , then a 1/8" corrugated cardboard sheet with the A grade granite sitting on top of it. My test system is a ultra-precision block 3x4x1" accurate to .000003" in all directions with a Starrett surface gauge corrected and machined to same tolerance bolted to it. A Brown and Sharp .00005" indicator is attached to the set up. This unit can detect .000005" inch variations and easily measure accurately to .0001". The results were conclusive that there was less than 50 millionth inch variation and probably consistently measured within 10 millionth in the center.... With minor touch ups it is near perfect for me. Great piece

Came well packaged in a wooden crate that was boxed and with no damage to the slab. Using a 0.0005" gauge over the entire surface, I saw no deflection of the needle. Therefore, my granite slab appears to be at or near the stated flatness of 0.00005" Class A-0 as advertised. I am very pleased as it is what my home workshop needed for precise metal working.

very good plate, class B good price, will do for knife making.

I knew these would be cheap, but oh man I wasn't prepared for how much. They were *technically* in spec, but just barely, right up to the edge of the spec.I needed extreme quality, so I bought 3 to do the 3 surface method and I wanted 6 surfaces so I was going to do 2 sets of 3 surfaces to get pristine flats. Unfortunately the backs were rough saw cut, 2 of them weren't too bad, only varying by about .04" but the third was where cuts from 2 directions met and had a total variance of more than 1/8" which would've made it useless to set on something and get a flat measurement from in any case.In any case it took a few months of working them in my space time but eventually I got all 6 surfaces to flat within .00001" (my finest guage) but kept going with the process beyond that down to .0000001" grit worked with distilled water so they might be flatter. It's gorgeous rock. As I started, it became clear that the original surfaces were simply ground, not lapped, and polished to look flat, the grinding marks popped out very quickly in the process and took a while to work out, about 15 process steps, and to get where I was going took about 75 steps on the pre-finished sides and about 500 steps on the unfinished sides (a fair bit of which I did using sandpapers and even brought out sanders to just get into the ballpark).

Flat I guessI have no way to test its accuracy but it looks ok to me. On the just so so side the edging was a bit rough and the surface in one spot seamed not as smooth that was just in a 1/2 inch in on one side. I decided to use a 2000 grit sand paper on it and the edges. After that I was happy with it. only one side is good the other side is not it rough so if you need both sides accurate this is not for you.

This is a good flat stone for QC inspection.This one wont be calibrated, but it a good station spot check rock.Packaging was good.