Lapping chisel and plane blade backs - a few tips

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Update:

I'd been looking at getting an extra coarse diamond plate but opted for a #120 Shapton magnesia which was about $50 posted from Japan.

For the test I got out a couple of 1 or 1.25" Titan firmers both of which were flat except for one corner. Both had had a lot of work on the Coarse diamond plate and I'd got sick of continuing as they were only for rough work.

The Shapton cut quickly and in a few minutes both were flat. Clogging wasn't bad at all.

One prob with an extra coarse stone of course is that it may leave deep scratches.

I took the firmers straight to a #1000 Bester (ceramic stone) and in a few minutes more all the coarse scratches were gone. Got a similar result with another chisel of softer steel on a #1000 Shapton.

So far it's shaping up to be a cost-effective alternative to a DMT X/coarse. But a reliable way of flattening it has to be found.

[mic-d]

Hi Ern,
I've recently been doing the backs of some A2 blades on kingstones 1200 and 6000 and found they worked quite well and after 1600 strokes on the 1200 it was still quite flat (checked with a straight edge) if I worked the whole surface evenly. When I flatten the waterstones by lapping on abrasive paper on float glass they end up a little bit convex (IMO the old problem with lapping anything) but by rubbing them with a coarse DMT plate I can see that central high point wear down to the edge at which point I check them with the straight edge and they are f.l.a.t. (can see no light). Can you do this with the Shaptons?
FWIW I found that trying to lap backs on my cast iron lap with 3000 grit diamond powder also gave an untrue finish. The leading edge wore faster.

Cheers
Michael

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So were the Kings fresh out of the box initially?

No, I haven't been checking with a straight edge. Just checking the scratch pattern. With the 3rd chisel I mentioned, a 3/8 BE Berg, I went to #1000 Shapton, #4000 Shapton and then #8000 Sigma.

All had been flattened first with a coarse DMT steel backed stone.

At each stage I got different results. Used the same technique going in two directions.

Could be random variation.

Or we know that the DMT is not flat flat.

??

[mic-d]

Nope the Kings are the ones I've had for several years now. Even though my DMT is slightly concave along the entire length it works fine to just take the convex top out of the stone (I hold it at right angles to the kingstone and watch the wear pattern on the stone). Sorry just realised I may have misinterpreted what you meant in your penultimate post "but a reliable way of flattening it has to be found" by it I thought you meant the shapton, but perhaps you mean the back of a blade???

Cheers
Michael

So were the Kings fresh out of the box initially?

No, I haven't been checking with a straight edge. Just checking the scratch pattern. With the 3rd chisel I mentioned, a 3/8 BE Berg, I went to #1000 Shapton, #4000 Shapton and then #8000 Sigma.

All had been flattened first with a coarse DMT steel backed stone.

At each stage I got different results. Used the same technique going in two directions.

Could be random variation.

Or we know that the DMT is not flat flat.

??

[rsser]

Yes, the Shapton. The DMT is about 220 grit; the Shapton 120.

Maybe the Shapton 120 conditioning stone would do and it's cheap.

Added: For deglazing the Bester 120 Stu Tierney recommends #36 SiC grit on a steel or glass plate

[mic-d]

The DMT is about 220 grit; the Shapton 120.

Sorry Ern I don't understand the significance of this. Could you spell it out for me

Cheers
Michael

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Sorry Michael.

I flatten my waterstones with the DMT #220 diamond stone, but assume that to flatten a #120 stone a grit of that or coarser is required.

[mic-d]

Sorry Michael.

I flatten my waterstones with the DMT #220 diamond stone, but assume that to flatten a #120 stone a grit of that or coarser is required.

Oh I see, sorry a bit dozey this mornin. So whatcha going to use on the shapton if sandpaper is not allowed?

Cheers
Michael

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Would seem to be several options:

Naniwa flattening stone (comes in several grades)

Conditioning stone of #120 grit; looks like a hockey puck

Shapton's own stone flattening system (but not at USD 170!)

Coarse silicon carbide grit on a flat plate

Get a 2nd Shapton #120 and rub them together (views about whether this works well seem to vary).