How Do You Flatten Aluminum Oxide Stones?

[FortyTwoBlades]

Again, being a bit anal, but I wouldn't trust that a spare piece of granite is going to be perfectly flat. I've had pieces of marble that weren't particularly close, for example.

The degree of flatness of basically any polished granite tile (in my experience so far) will be close enough. If you really need more flatness than that you probably should be using diamond stones in a high-precision jig arrangement 'cause all the flatness in the world won't mean anything if you aren't getting consistent strokes on it. Even microtome blades don't actually need that level of precision.

The hardness of granite compared to other stones means that much of the finishing process is done with a focus on precision to minimize wastage and its slow rate of wear also lessens the severity of any variances in spot pressure or time during polishing. Tiles are generally made from slabs that were already polished via an arduous automated process and simply cut into smaller pieces from there. Bonded abrasives, by their nature, wear to expose fresh grit. In the process of doing so, the uneven wear pattern pretty quickly results in deviations greater than that typically exhibited in most granite plates. If you're really worried about it, take a steel straightedge with ya' to the home improvement store. Personally I bought mine sight unseen off the internet and it's dead flat.

 

[EngrSorenson]

The degree of flatness of basically any polished granite tile (in my experience so far) will be close enough. If you really need more flatness than that you probably should be using diamond stones in a high-precision jig arrangement 'cause all the flatness in the world won't mean anything if you aren't getting consistent strokes on it. Even microtome blades don't actually need that level of precision.

The hardness of granite compared to other stones means that much of the finishing process is done with a focus on precision to minimize wastage and its slow rate of wear also lessens the severity of any variances in spot pressure or time during polishing. Tiles are generally made from slabs that were already polished via an arduous automated process and simply cut into smaller pieces from there. Bonded abrasives, by their nature, wear to expose fresh grit. In the process of doing so, the uneven wear pattern pretty quickly results in deviations greater than that typically exhibited in most granite plates. If you're really worried about it, take a steel straightedge with ya' to the home improvement store. Personally I bought mine sight unseen off the internet and it's dead flat.

I’ve been spending a lot of time thinking about how flat is flat enough. Just a guess here, but I doubt +/- 0.0005 of advertised DMT lapping plate flatness is much more meaningful than +/- 0.005.

I bet even the best jig setup has enough slop in the system (setup, connections, etc) that it doesn’t matter.

 

[OLd_gUY]

Food For Thought - for flattening, I use THIS which is made of Tempered Glass (not float) with SiC powder and pencil marks. Although it is thick and hard, it will scratch and since it so cost effective I have 2 - for coarser and finer grits to forestall cross contamination. It comes with screw in legs for more height but I find them to be unnecessary. To get an idea if this might work for you, here's an in action YouTube vid with CBN stones - click HERE