Sandstone Grindingwheels

Factual Questions
1

I’ve just sort of “inherited” a grindstone made of natural sandstone. It belonged to my wife’s grandfather, and her father just recently dug it out of the barn, refurbished the mechanical stuff, added a motor, and gave it to me.

He did a peachy job of matching the motor speed and the pulleys to get the turning speed down to something useful, and I used it today to sharpen a few things. A couple of lawnmower blades, the blades on my hand powered grass clippers, and I fixed up the blade on a lockback knife that he’d ruined on a bench grinder.

I’ve got a couple of questions about the stone itself.

First, I’ve noticed that the ground off stone tends to form a sort of mud, and that this mud can dry very hard. Is sandstone simply sand in a hard clay matrix?

The answer to next question could get kind of long and involved. How do you take care of a sandstone grinding wheel?

Besides the obvious not dumping it on the ground and shattering it, or grinding on the side and ruining it, what kind of things do you NOT do with sandstone? Is there anything in particular that you should do with one?

I expect I’m going to have to dress the wheel - it is out of round and has a (very minor) dip across the surface. Is there anything special I would need to do with it as opposed to how you would dress a typical corundum grindstone?

A few details:
The stone itself is 8cm wide and has a diameter of 40cm (3 1/8 " by 15 3/4".) There is a water tray below the wheel that you can raise by a lever to wet the wheel - the wheel does not run in the water, you have to watch and dip the lever when things get too dry.

2

I’ve stumped the dopers!

3

You’re right about what sandstone is, but the glue might be other material than clay.

If I read you right about the speed, you’ve addressed that, you don’t want to rev it up really high due to centrifugal force and lack of standardized manufacturing with certified tolerances that you get using a natural substance like sandstone.

My grandfather had a big grindstone, probably about 30" diameter, with a foot treadle. To wet it, there was a tin can with a nail-hole in it. (There was a hand-pumped-draft forge and a big anvil in the shop also. As a kid I would sometimes get to watch something being forged.)

I have a notion that you don’t press the item being sharpened hard against the stone, let it work at its own rate. Is there a ‘stop’ to steady the work against?

4

There isn’t much of a stop to hold stuff you’re working on. I found yesterday that I was better off working free hand rather than using the stop.

The speed is rather low - about what I’ve seen on treadle powered stones. It makes it a lot easier to work with compared to the highspeed bench grinders that you can buy for $20 at Wal Mart.

As for letting it work at it’s own rate, I’m reminded of my father’s instructions when using any power tool - don’t “crowd” the machine, just let it work.