Sandstone Rebuild

[John Chamorro]

I'm rebuilding a sandstone grinder as a gift for my son in law. It's a cobble job that had a funky stand and the mandrel had pvc pipe and spray foam for alignment. I'm thinking I'll plug the wooden mandrel with a wood dowel and redrill it. 

I'm wondering what the rpm should be? Is it set by surface speed, or is there a recommended rpm x diameter depending on intended use? Any info or suggestions are welcome.

[ThomasPowers]

How was it originally spun?  Hand, foot, powered? 

Unless it's quite large in diameter, (say greater than 3'), these were used more for touching up tools and not for heavy stock removal and were not run extremely fast.  Getting a good wheel can be an issue as well. If it was left with sections wet (in a trough, partially buried in the ground, etc) the wheel can degrade leaving you a wheel that quickly wears lopsided.

If it was hand or foot powered you should be able to figure out how many turns per minute would be sustainable for your power source.  If it was powered you still want to keep it slow to avoid exploding the stone. (So close to human powered speeds are suggested.)

In reality speeds were probably dependent on they type and coarseness of the stone and how it was being used.

[John Chamorro]

Thanks for the reply. I'll fill in the blanks best I can not knowing the origins of the stone.

I don't know how it was originally spun. It is 2 1/2" x 22' with a square wooden mandrel. When I got it, it was mounted in what looks like a high school welding project with sort of a tub, powered by an electric motor. It wobbled maybe an inch side to side and maybe 1/2" up and down. It was put together with pvc pipe and sealing foam with a chunk of all thread run through the middle, as the mandrel. I'm intending to plug and redrill the mandrel with a wooden dowel.

Cosmetically and physically it looks to be in very good shape with only very minor edge dings in it.

It's future use will be for sharpening hand made knives that my son in law makes as a hobby.

[ThomasPowers]

22' is definitely an industrial one that would have been run using water power! (In fact larger than any I have read about, 8-12' I have run across...)

(Yes a typo; but it's Friday, a day of silliness here!)

With hand or foot powered, these were very seldomly geared and so one foot depression would be 1 full turn of the wheel, you can figure out how fast you can pedal pushing the mass.  (For a traditional version. I'm surprised to not have seen more conversions using a 10 speed bicycle as the driver.)

[John Chamorro]

Hah! Yep I meant 22 inches,,,,,

[marcusb]

I hate to admit it but I had a nice homemade setup several years ago and junked it when I moved....... It was a stone about 2.5 feet in diameter set on a steel frame. They used a tire cut in half for the water tank. NOTE: I have been told to only fill the water when you are going to use it and empty when done or you will get a soft spot on the stone. The drive consisted of a small electric 110v motor that went thru a right angle gear reducer then to the stone via v belts. I kept the reducer and motor. I think it was 20:1 or something like that. Anyways as TP said it did not turn very fast, about as fast as you can imagine spinning one by hand would be about right. But man it sure put a nice grind on an axe. Some day I would like to build another with stone from here. Hope this helps.

[John Chamorro]

6 hours ago, ThomasPowers said:

With hand or foot powered, these were very seldomly geared and so one foot depression would be 1 full turn of the wheel, you can figure out how fast you can pedal pushing the mass. 

I come up with stone speed of about 200 rpm. The internet that's always right says a cyclist pedals about 100 rpm.