120 grit Sigma Power Stone - the 'Black Beast'

[snafuspyramid]

So I've recently received a 120 grit Sigma power stone from Tools from Japan.

I want to use it to put new bevels on a bunch of chisels and planes.

I ground away at them for a few solid hours, and haven't yet managed to put a bevel on even a single #4 plane iron.

I'm clearly doing something wrong - I read that these things should take off a mm of steel every few minutes.

Once I realised that I'd managed to dig a decent groove into the stone with the roller on my jig, I went about trying to re-flatten it. As I learnt, that's not at all easy to do. The stone happily ate several sheets of WD sandpaper, and then snacked on the sad remains of an old diamond stone.

Then, I dug around in the packaging and discovered an information sheet from Schtoo, and a wee bottle of carbondurum medium grit powder. You sprinkle the powder on a hard surface (10ml plate glass for me), add a little water, and then grind the thing around for a while. This is a truly unpleasant experience - think of all the chalkboards in all the world at a manicure school. But lo, it disposed of several mm of stone pretty quick. Hopefully, it also removed any glazing the stone might have had.

Newly enthused, I went back to grinding. But, after fifteen minutes, I've still made virtually no progress - certainly no more than when using my 1000 King. What's going on? How long should the cutting take?

PS I'm putting a fair bit of effort into it, pushing down hard.

[Pac man]

More information please Are they new chisels and do your chisels have a flat bevel ( either never been used or always been ground on a flat surface) or hollow ground ( on a bench grinder)?

What steel are they made from?

[snafuspyramid]

I've been working primarily on the cutter for a no 5 Stanley, post Ww2 vintage. I was also working on old Marples and Titan chisels. They're all so blunt they're almost round...

[Schtoo]

How wet is the stone? It does need constant flushing, as in nearly submerged and always throwing water over it.

The stone should be chewing through that steel like it's butter. I've got several, and there is a slight variance between them all, but not enough to explain this.

There's a few guys here who've got them, hopefully they'll chime in with their experiences as well, since while I've used them quite a bit, I don't know everything about them, and perhaps never will.


Just wondering what I've got to sacrifice. Everything I have is already sharp!

Stu.

[Schtoo]

Ok,

Just found an old Record 2" blade, and completely reground the bevel on the thing since the last post. The stone definitely slowed down if I left the crud on there, but a rinse and it was to normal.

Just to give you a time reference as to how long it actually takes to do.

Not including the time to find the blade, tray and holder for the stone nor the minute to soak it.

Stu.

[snafuspyramid]

Mine is clearly not up to scratch then. I will grind it down more tomorrow. I'm running out of powder though, I use around two thumbnails each time and grinding to a flat paste on plate glass, then give an extra minute. I'll try a marble tile in a few days.

[stolar]

I have a said stone and did not have much time to play but litte i did use it it was all i exected it to be.
It does need constant splashing though, it is very porous and "thirsty" and i found that it needs a splash of water every few strokes .
I recently acquired few early 19th century american chisels is a sad state and although it did need some work this stone is like nothing else i've seen.
Certanly not comparabel to a 1000 stone, that description and comarison would indicate glazing.

Did you posibly manage to glaze it very quickly by not keeping it wet?

[Schtoo]

Hmm...

That's not even a reasonable facsimile of what they're supposed to be like...

Might be asking you to send that one back so I can get it to Sigma Power and ask what's going on.


They might throw it back at me and tell me "you wanted the dang things hard!".

The marble tile might not be such a hot idea, since it'll grind down faster than the stone.

And if there's stone been ground off, then any hard layer should also be gone.

I'll get some stuff off to you tomorrow, a known good stone and some more loose grit AND some finer grit that'll speed things up as well.

Looks like the instructions need revising, and I need to include some more grit with the stones. Odd, they've always been a pain to deal with, but tolerable and the performance was more than worth it. I'm upset you aren't seeing the same results, and more worried that I've sent out plenty of stones from the same batch, and they might be behaving badly as well...

We'll get it sorted, I promise.

Stu.

[Schtoo]

Branko, yours is a previous batch, maybe.

But what you described is exactly what they're supposed to be like...

Hmm...


Stu.

[enak]

My Sigma 120 works fine, fixed a minor chip on a 70mm Blue steel plane blade in about 5 minutes.

Regards,
Kane

[snafuspyramid]

I've been using the stone submerged by about 1mm of water, and swishing it around every few strokes. I also ran it under a tap every five minutes or so. So, not that.

I'll have to try grinding it down some more (sending it half way back around the world has to be the last resort). The fact that it's ridiculously hard might not be a bad thing, provided I can somehow wear it down to a good cutting surface.

I'll keep at it until the grit is all used up.

How long should I grind it down for? Just until the crunching ceases? Or should I keep working on the slurry for a few minutes?

[snafuspyramid]

Edit: just reread Stu's post. Thanks for the typically generous offer. Soon we'll see whether I'm the idiot after all (I suspect I am...)

[Schtoo]

I suspect that maybe you're deglazing it, and then going too far and clogging it with fine particles which is then glazing it again.

You should be washing away some pretty big chunks of material, not liquefied stone.

I've sent a couple bottles of grit and a known good stone. One bottle is the normal coarse flattening/conditioning grit, The other is #120 the same as the stone, which you can sprinkle on the stone and sharpen with to speed things up and make sure it's deglazed. The Sigma #120 is one of the very few stones that will allow you to do this, and the only known stone at this grit level.

(But maybe the Shapton Glass #120 will allow it too. Not tried it yet, and might make that particular stone actually work...)

Either way, we'll get it sorted out.

Stu.

[snafuspyramid]

You're probably right.

I've tried stopping as soon as the 'crunching' sound disappears, with better results. (Before, I was rubbing the thing about for another ten or twenty seconds after the grit had turned into slurry, no doubt clogging the pores).

Now, grinding a chisel against it gives a rather satisfying crunching sensation, and when submerged you can see a fine trail of steel particles float off. Certainly, it no longer feels like I'm using a 1000 grit King.

But despite the improvement, it's still much to slow to be much use in grinding new primary bevels. Also, I can't find any way of flattening it (the abrasive grit doesn't seem to do it). The stone is just so hard!

Of course, I'll have to wait until I get hold of the new one to compare the two and figure out what's going on. In the meantime, I'll try not to give up hope and buy a bench grinder - I'd hate to abandon the Dark Side...

I realise I'm asking a lot of a busy man, but might a video instruction or review be in order some time in the future?

[rsser]

What bevel angle are you going from and to? Ie. how much are you taking off?

Are you able to use most of the stone area consistent with the needs of the jig, inc. swapping ends? You said you got a groove; prob. a result just of working the centre?

Std high carbon steel? A2 or M2?

(Much as grinders are noisy nasty things, they are designed to do what you're trying to do by hand. You can grind easily almost to the tip and finish off with a 2ndary bevel on a coarse whetstone. That said I have a #120 Shapton Pro and I flatten backs with it; works pretty well).