Sandstone disc for flat lap?

[Buttercup]

As Seachange is exploring in another thread :
http://www.warmglass.com/phpBB/viewtopi ... ap#p336952

I, too, am considering converting a potter's wheel to a flat lap. I can get a fine sandstone disc cut to size for a very reasonable price and wonder if anyone has experience using sandstone and could share the pros and cons. That would be much appreciated.

I realize it only comes in the one grit size and that I'll have to hand work as well, or can finer grit sizes be used loose on top of it with water without destroying it?

Thanks so much, Jen.

[Marty]

It should be good for a little while until the glass grinds the stone away. Think about relative hardnesses.

[Lauri Levanto]

Maybe I am wrong as usual.
Isn't the traditional chrystal cutting made with sandstone wheels?
-lauri

[Brock]

Maybe I am wrong as usual.
Isn't the traditional chrystal cutting made with sandstone wheels?
-lauri

You're not wrong . . .

[Morganica]

Yes--lathe cutters use sandstone wheels (among other things). Saw a Harcuba demo using them, very impressive--I was surprised at the softness of the cut and the amount of material he could remove. (Of course, it was Jirji Harcuba, so who knows if a normal person can do that)

I don't see why you couldn't use a sandstone disc on a potter's wheel, but you'd have to be even more careful to keep moving the glass all over the stone so that it wears down evenly. That's harder than you'd think, especially when you're focusing on a piece that needs a lot of grinding.

You could certainly try putting additional grit over the wheel but it would most likely cause more problems than it would solve. Wheels typically don't use a lot of grit, and I'd think it would be fairly easy for the sandstone to intrude or break off and contaminate the slurry. You'd also risk contaminating your wheel with a different-sized grit--it could get stuck in any pockets or spaces. Either way, a stray piece of the wrong-sized grit would scratch the glass, ruining the work.

You might be able to set up some kind of steel disc that snaps on over the sandstone when you want to use different grits. Personally, I really love the big grit wheels--they're slow-moving so you can control the cutting action, and SiC or Al grit gives a much softer finish than a fast-moving diamond lap.

[Jeff Wright]

Harcuba, and others, use the wheels in a lathe, i.e. spinning vertically. It is really hard to source these wheels now. The sandstone ones need to be re-profiled every few minutes. They do wear away. The reason for dressing/profiling is the pores get filled with glass waste slurry and stops the cutting action. I doubt that you'd get good results on a horizontal/flat lap, but it is worth a try.

[Buttercup]

Marty, Lauri, Brock, Cynthia and Jeff, thank you so much for all that thoughtful advice. I'd wondered about the porosity and relative hardness so it may be better not to spend the money on a sandstone wheel but to look for a cast iron or steel solution for greater versatility in grit sizes, or glass, if I can make it stick there.

If I do go with steel would that be mild steel or stainless, and what gauge?

The sandstone would probably have to be a good bit larger in diameter to avoid wearing a groove.

I'm trying to upload a photo of Jiri Harcuba engraving using a copper 1c. piece but the photo is not accepted as it has 'an invalid filename'. It's a JPEG. I couldn't find any info on how to upload, must be in the missing archives. Can someone point me to that info, or tell me how, please?

Thanks again for the input. Jen

[peter cummings]

I've put a 13 inch steel plate, 6 mm thick onto my pottery wheel. Drilled holes for the centre and drive pins. Bought diaamond wheels from His. Goes great.
I used an old steel lap, about 24 inch, with loose grits. You put grit and water in the centre and it works its way out. A beautiful singing noise. Loved it. Just too lazy or unconfident to build a bigger set up or I would have done that again.
Peter.

[Buttercup]

Thanks Peter. Guess it would have to be mild steel to take the magnetic discs as SS isn't magnetic, is it? I'm not ready yet to invest in diamond discs and am contemplating the suggestions on the other thread, including grit on float. Having had to replace most of my 110v equipment with 240V here I don't have a lot to spend.

Was the 24" wheel actually steel or would it maybe have been cast? Methinks steel would be a nasty rusty mess all the time??

If I did use steel I was thinking of getting a couple of 'pins' welded on to line up on and go down into the holes for the batts on the potter's wheel. That would avoid having a bolt in the middle, just a continuous smooth surface. That wouldn't work on cast, though. Guess one would have to be careful with downwards pressure in case the pins under the plate flipped out of the guide holes. Silicon it to the potter's wheel?

Would SS work with grit and water? I can get that fabricated locally. Thanks for the input. Jen

[peter cummings]

Yes Jen, the big wheel was mild steel and showed a fair amount of rust. A quick wipe with a pot scrubber cleaned it. Cleaning between different grits is a hassle. Nearly worth a few seperate plates.
My potters wheel has pins pointing up to hold the batts. Pins going down would be a bit trickier, but there's not that much pressure. If you push too hard the grit get pushed out the way and wont work. I made a 6 mm plate glass disc for finer grits and that works well. Cheap and flat if you can get scrap. Could be a good experimental option, a few dobs of silicon might fix it.I dont know if ss would work, the grit need to cut in a bit to grip, I think.
If you try hand work on a glass plate, you'll get a good idea how it all works, and it's still a good option at times. The book cold work without machines is great.
Peter.

[Buttercup]

Thanks again, Peter. Lots to digest. Just reread the appropriate parts of The Joy of Coldworking (I'd forgotten there was a paragraph or two about sandstone wheels) and will look into getting Cold working Without Machines. Then again, maybe I should stop reading about it and just jump in and do it using float! I have lots of good advice to consider, thanks to everyone who offered it. Jen