Granite in the shop

[Dick Hutchings]

I just got a 1 1/4" X 12" X 12" piece from a friend. I had asked for it quite a while ago and I don't remember exactly what I wanted it for. Aside from sharpening with sandpaper, what are some other uses?

[sunburst]

If the surface is accurately ground flat it is a hard, stable, durable surface plate upon which you can check things for flatness. A flatness reference.

[Joe Mendel]

I have a 24" x 18" granite machinist's block. I use it for checking flatness, various clamping operations. I have self adhesive sandpaper attached for flattening saddles and nuts, etc. It's great for fretting, if you fret before attaching the FB to the neck. I probably have several more uses that aren't coming to mind right now.

[Dick Hutchings]

If the surface is accurately ground flat it is a hard, stable, durable surface plate upon which you can check things for flatness. A flatness reference.

I have no way of knowing how accurately it's been ground but I assume it's pretty good.

[sunburst]

Year, unless you buy an actual surface plate with published specs for flatness you don't really know. Observing reflections in the surface gives us a good idea, and besides, for most things a good flat surface confirmed by eye is all we need.

[bigskygirl]

Sounds like a good Old Time tune title...sorry, couldn't resist...

[Dick Hutchings]

I'll have to write that one :-)

[Richard500]

Dick, a piece that thick is too thin to be a machinist’s plate, likely countertop material, but since these things are ground and polished, plenty flat enough, and also you don’t destroy it’s value as a measurement tool.
So, you can also use it as a lap; that is, spread abrasive on it and flatten metal parts, like the bottoms of hand planes. In machinist use, it would be used with a height gauge, a scriber and other tools for doing accurate layout in three dimensions. I can’t think of any interesting uses on a mandolin. I keep the metal version at home, but hardly use it.
A 12x12 is a little small, but can also be used in the kitchen for bread and pastry manipulations, which is a new skill I’m working on. However, if it is countertop stuff, be aware that it may have a sealant coat that you might not want to eat.
The company I worked for, having a mostly optics history, liked to assemble large machines on these plates, which is pretty silly, but we bought at least a dozen that were around 8 feet square and more than a foot thick: pink granite, with flatness certifications. Expensive things, currently slowly sinking in the local rock and stone supply yards where they went after the auction. I suppose a wealthy person with a sense of humor might make a unique patio, or a 2001-style monolith.

[Dick Hutchings]

It's a little short for flattening hand planes, I may ask for another piece. Maybe and end cut, 4 X 24.

[amowry]

I have one that’s about 6” x 24” that always has 80 grit stuck to it for flattening neck surfaces and small parts.

[Dick Hutchings]

Is it easy to maneuver

[amowry]

Yep, mine's only an inch thick, but it stays plenty flat at that thickness. It spends most of its time on the floor under my bench, and I just lift it up and put it on the bench when I need it. It's much better than a belt sander for things that need to be flat. If you take a good 2' straightedge to a countertop manufacturer you can usually find free remnants that are plenty flat for our purposes (better than 0.001"). It's a little harder to detect winding with a straightedge, but that's usually not really an issue.

[Dale Ludewig]

I have a Starrett that's like 4" thick, maybe 18 * 24. It's on a cart with railroad like wheels (old factory work cart). I have sandpaper (80 grit or so) stuck to it. I probably mainly use it to level the rims on mandolins before I glue the top or back on. You have to have the rim in the form but it's great for that job. Other than that, it kind of sits there. And it's too heavy for one person to pick up.

[Dick Hutchings]

Yikes!

[Richard500]

I didn’t mention that the cast iron version has additional utility as the measuring tools have magnetic bases, and some plates have an accurate array of tapped holes that make clamping setups easier. Maybe also useful for some gluing operations?
By the way, poor maneuverability of granite is one of the reasons Russian entries in F1 racing were not competitive.

[MrMoe]

I learned to get things flat (or as close as I can) from watching Dan Gelbart`s you Tube series. I struggled with my procedure with the fret rocker for years. Turns out it had not been faced or polished and was not flat. I will try to link that video... It is part of one in this series of 18

https://www.youtube.com/watch?v=xMP_AfiNlX4

[tree]

I occasionally use the granite samples I have in the shop as weights when glueing, instead of clamps (or with clamps).

[MrMoe]

Mr Gelbart talks about flatness and displays some granite on episode 17

[Dale Ludewig]

I started watching that and could feel getting pulled down the rabbit hole. I'll finish watching later. But, that's amazing. Luckily, we're only talking about gluing parts together where they don't (hopefully) move.

[MrMoe]

He is inspiring. Using these techniques to get my fret rocker and other tools truly flat has greatly improved my fret work.