How to flatten a big green SiC stone?

[Fred Bryant]

Well, first some background. I am new to this handtool, and hence, sharpening stuff. Up till I moved last, I had a grinder and a2X8X1 King combo 1000/6000 waterstone. I was flattening by sandpaper on a piece of granite with the associated mess. When I move, the granite and grinder got packed away, but I got a DMT 4x10 duosharp course/fine diamond plate.

While traveling on the road for work, this worked great as it well small, compact, and a whole lot less messy. Being on the road, there was not much woodworking, but I was able to collect some vintage tools and worked on rehabbing them in the hotel at night. Things were fine, but I found I needed a grinding stone, so I got a generic big green SiC 220 grit waterstone ( 10x5x4 ). All was fine at first, but then my diamond stone gave up the ghost. I wrote it off to pour product quality or just the nature of diamond stone ( not sure which lie I told myself ).

Well in a previous thread it was mentioned that a coarse waterstone will eat a diamond stone in short order that normally would last a long time on finer stones ( 1000 & up ). A light went on; the abrasive on the coarse stone is large enough to reach the nickel bonding substrate on the diamond store. So, while the diamond store was flattening the coarse SiC stone, the coarse SiC stone was compromising the nickel substrate that was holding the diamonds. This match what I recall seeing on the DMT stone, yellow plastic showing through were the nickel was. An expensive lesson learned.


Currently, I have no diamond stone ( trashed a while ago ), and my only waterstone has worn to less than 3/8" thick before it cracked ( there was not allot of 1000 grit left on it anyways ). So, I am in the market for some new stuff. I think I am going to go with Stu's 3 stone kit with the Atoma diamond stone to replace my waterstone and DMT diamond stone. With that said, I still like my big green 220 grit SiC stone, as it is fast for hand grinding. What I need is a portable way to flatten it ( I can not afford to touch it with another diamond stone ).


My question is what do I use to flatten it?

One method I have heard of is to lap it with 90 grit abrasive power on a cast iron plate made for this purpose. If this is the best way, where do I get the plate to flatten a 10x5x4 stone and how to I keep the plate flat? Or is the plate expendable? If so, how long will it last?

Thx's, Fred ( jyblood@nwi.net )

[george wilson]

I flattened my stones on the side of an old sandstone wheel before I went to ceramic. Use water,and a sandstone(antique type) wheel would even shortly flatten a black Arkansas stone.

Some use a cinder block,which is easier to get,and still has sand in it. Use plenty of water.

[David Wong]

I use coarse SiC powder on a Shapton compact flattening plate to maintain my 220 and 500 grit stones. The plate has stayed flat after about 1 year of usage. I use the whole plate with both lengthwise and diagonal strokes of the stone on top.

[Jack Curtis]

Sidewalks and concrete blocks come in very handy for flattening those coarse stones.

[David Weaver]

Just get something flat, even a brick, and 60 or more coarse than that wet and dry (it can be generic, you're not using the abrasive to cut abrasive, you're just using it to plow away at the binder). It'll take care of it no problem.

Because it's a grinding stone, and because you'll constantly be dealing with some level of it being out of flat, you only need to get it reasonable each time. Even a flat block of hardwood to back the sandpaper would be fine. It doesn't need to be any bigger than something like 8x3 or 6x3.

[Trevor Walsh]

I find a good flat piece of concrete for flattening 220 and 1000 grit stones. 4k and 8k I do on 220 wet sandpaper bonded to something flat.

[Stuart Tierney]

Loose grit, on glass.

Any abrasive grit will do, and if you need it I'll send some. ;)

However...

Coarse stones don't always eat up diamond plates. Some coarse stones eat up some diamond plates in very short order. I have to assume the #220 stone you've got here is the generic, soft and muddy type stone and if it ate up the diamond plate very quickly, there is no lie to tell yourself, the diamond plate was of insufficient quality. Don't care who made it, if a diamond plate can't stand up to virtually any 'generic' stone, then it's crap. Some of the more modern, tough and durable stones, then the diamond plates should stand up to them well too, but some don't.

Some of the newer coarse stones which will either give a diamond plate a very difficult time or flat out kill it dead in very short order.

Now, even though a diamond plate can flatten a coarse stone (and I do it often), it's no real trouble to use some loose grit on glass or steel to flatten with and in some cases, it's the only real method that works effectively and economically. Heck, I sent out some loose grit yesterday specifically for flattening coarse stones. Just the grit, in a bottle, in an envelope, because the folks that the grit is being sent to are having trouble flattening the stones they have.

You don't need cast iron, anything moderately hard and flat will do. Glass is cheap and freely available. Steel is tough and durable but not always 'flat'.

And don't worry, unless your #220 stone there is hard and strongly dish resistant. Most coarse stones fall to pieces when threatened with flattening and aren't a problem.

It's quite difficult to gauge 'how difficult' the #220 you have actually is to flatten because we don't know for certain who made it unless you tell us. ;)

Stu.

[David Weaver]

I cannot figure out why the manufacturers would advocate the use of loose grit and then turn their noses up at using wet and dry paper.

Not that I use either, but this is a pair of pieces of advice together that make no sense to me. FTR, i've never had large loose grit get stuck in any stone where you could just wipe it off by hand, be it some loose impediment that got on the stone, or a piece of stray wet and dry that did the same.

[Stuart Tierney]

I cannot figure out why the manufacturers would advocate the use of loose grit and then turn their noses up at using wet and dry paper.



Because the way sandpaper works and the way loose grit is supposed to work is completely different?

I must admit, initially I had the cause of the problem incorrectly explained, so blame my Japanese translation more than anything else.

The sandpaper itself isn't the problem, it's that you're using a friable, consumable abrasive stuck to a less than durable substrate to act as an abrasive and 'grind' down the stone. Loose grit rolling around doesn't have much opportunity to embed into either the substrate or the stone because it's always in motion. Sandpaper, the abrasive is fixed in position and it can 'pick up' into harder stones. Softer stones, anything that gets picked up falls out pretty quickly when it's either still being flattened or when the stone is actually used.

It's frustrating for me because I know it happens, because I've actually used sandpaper to flatten a hard stone when I wanted to save grabbing a plate, and then spent extra time getting the sandpaper particles out of the stone. And yet, folks here and elsewhere say "I use sandpaper and never have a problem!" omitting that they're doing it with softer stones, which aren't (as badly) affected.

I then get the emails from folks asking "I use sandpaper to flatten, why am I having problems?" and then spend my time trying to point things out over and over and over again and I am quite frankly getting sick of it.

So, here it is in public one more time...

If you have softer stones, you can probably use sandpaper to flatten them and won't have a problem.

If you have harder stones and use sandpaper to flatten them, then you might get problems caused directly by the sandpaper.

And if you have harder stones, concrete, cinder blocks, etc. won't do the job either. I know, I've tried.

I don't even want to post this, but since I've written it out (AGAIN) I'll leave it.


Stu.

[David Weaver]

I wouldn't try a cinder block for long term use, it'll just get out of flat.

I don't know if I've ever used sandpaper on the finer shaptons, purely because hard stones are hard on sandpaper.

I have used 60 grit sandpaper on 90 and 220 grit hard ceramic stones and never had any of it stick, though. I would imagine people having problems with sandpaper and not loose grit aren't rinsing the surface of their hard stones off and running their hands off of them to wipe off the loose particles.

I'll take whack at it over the next couple of weeks, I guess. It still doesn't fly if cast iron or loose grit is one of the suggested surfaces, because bits of loose grit will definitely embed in cast.

[Fred Bryant]

A gentlemen is offering me one of these lapping plates. It is about 8" by 8" by 1", and he claims to have checked it on a surface plate and it is flat. Is this worth pursuing? If so, how much?

Thx's, Fred ( jyblood@nwi.net )

[David Weaver]

At that size, i wouldn't give a lot for it. There are granite plates much larger than that (and probably flatter) for $25.