Lapping chisel and plane blade backs - a few tips

Having dug out a few divots from the fingers I thought I'd share what I've learned.

I now wear rubber thimbles. Good with water lube; useless with oil though.

Use a thick rare earth magnet to improve grip. IIRC Derek has posted about using a magnetic dial gauge stand for plane blades. This is prob where my idea came from.

This magnet is a thick ring as you can see in the pic. Works well: fingers either side or one in the hole. Doesn't really stick well though with BE chisels under about 3/4".

It actually has enough pull to hollow a Stanley blade against a diamond on metal substrate. Not recommended.

I'm on a roll with some new stones and doing a deal of lapping and polishing.

In the pic is a 30mm wide Muji HSS blade out of a palm smoother. Again I found that their steel is darned hard, or should I say abrasive resistant. Took 300 strokes to flatten on a newish coarse DMT stone. More than double that to polish up to 8000 grit (fine diamond, then ceramic #1000, #4000, & #8000).

Some other impressions: the Hock A2 Cryo blades are more abrasion resistant (OK, sample of 2 only) than Veritas A2 (sample > 6). The 2 Hocks needed lapping; the V. only need polishing.

With exactly the same back and bevel polishing procedure, the Veritas O1 feel sharper to a finger stroke than their A2. Best guess is that the alloy grain is coarser so there's more resistance to the skin stroking over it. No diff in producing galoot pattern baldness that I can see but I'm getting to the stage of losing skin with this test :(

The ceramic #4000 (Shapton Glasstone) is a sod for stiction, even with a drop of liquid soap. Not impressed. Circular movements reduce it quite a lot though. The ceramic #8000 is a Sigma which also produces a deal of stiction. OK, this work should only have to be done once in my lifetime so no more whingeing :wink:

To speed the hard work up I've tried Scary Sharp and found it unreliable. Too easy to get more abrasion on one or both corners which just generates more work to take the rest down. If I continue with this obsession a very coarse diamond stone is what I'd go for.

Rsser
That is an excellent idea. I happen to have a couple of 1cm square by 12cm long magnets which I use for setting up my jointer blades so I will give them a go.
Thank you

Hi Ern,
myself and others have also found the sandpaper-stuck to-glass method always dubs corners. I use a coarse diamond stone if required followed by waterstones.

Cheers
Michael

Yeah, I can see the logic in why it might and sometimes does fail. That said, I've had some quite good results. Can't explain the diff. Whatever, while I've gained patience and will do a thousand strokes if need be I have no tolerance for a chance outcome any more.

Well done Ern.

I avoid thinking about lapping blade back when thinking about a new plane or blade... if I thought about the stroke, stroke, stroke x 1000, I'd never get one! :rolleyes:

Yeah, it's taken me a while to learn the patience.

For distraction I count to fifty (that's one count per return stroke) and start over.

The fun really starts once the back is flat cos there's nearly always minor variation in the flatness of the waterstones and getting a polished tip requires changing the sides, extent of overlap and stroke weightings. A back that is spot on at 1000 won't be at 4000 and so on.

Ern, I saw you ask about the life of diamond stones in another thread... did you get one, and if so, what do you think of it?

I've had an 8x3" DMT Duo coarse/fine for some time Clinton and it's done a lot of work. When with one blade I stopped counting at 500 I started to wonder whether it was getting tired or I was :(

This is one of the perforated jobs and increasingly swarf wasn't being washed off at clean-up so just last night I took to it with Jiff - a liquid abrasive cleaner for kitchen use - and a nail brush. That's removed some but not all of the gray stuff. I've yet to give it a run.

In any case I got another C/F but in 10x4 and am debating about the obsessiveness of getting an 11" extra coarse from Jim Davey. Every time I think I've got all the chisels and blades that could be needed somehow some more manage to creep into the shed :rolleyes:

An alt. would be to live with Scary Sharp for rough flattening and just joint the cutting edge beyond the dropped away corners. I did this with one Muji HSS blade, reground the bevel on a dry grinder leaving about 1.5mm of vertical, and then went to form the 2ndary bevel on coarse diamond with jig. Even just that took hundreds of strokes. That Muji steel is something else!

Edit; sorry, I didn't quite answer your question. If I had my time over I'd forget Scary Sharp, get a big extra-coarse diamond and a C/F duo and then some good waterstones. The diamond stones give you a lapped back more reliably and quicker than other methods I've tried. K, there are cheaper methods like the alt. above but frustration has a price too.

Yes Ern, frustration and 1000's of strokes do have a price.

I'm pretty decided on a extra-coarse/coarse combo, but the life of 'stone' is a seperate issue, however I'd like to know the difference/ease/life/speed/cost comparisons between diamond paste, abrasive powder, diamond stones and jewlery makers 'diamond platens'. For me, I'd like to understand what makes the fastest, most cost effective method of flattening backs.

Ern - I have a full set of the 10 x 4 CMT DuoSharps, and I have to say that the Extra Coarse side hasn't found much use. I tried it a few times, but didn't find the material removal rate to be much different to the Coarse plate. Having said that, the Coarse plate is fantastic for changing bevel angles, etc., even on A2 blades.

As an aside, I reckon the Extra Fine (after a bit of use to wear it in) is roughly equivalent to a 1000 grit waterstone. This allows me to do all my primary bevel forming on the diamond plates (which are flat, and STAY flat through the sharpening process), then I just go straight to an 8000 waterstone to form a microbevel.

Probably against all the laws of good sharpening, but works really well.

I note that LN seem to push this "dual grit" process now, using just 1000 and 8000 stones.

Clinton, good questions.

Diamond paste: IIRC the coarsest I've seen around is about 50 micron. For serious lapping starting at something like 120 grit (coated or FEPA rating or about 135 micron) wouldn't be too coarse in my book.

Silicone carbide loose grits on plate glass as per the Veritas kit is something else I'm going to try; Michael warns of the same risk of corners over-abrading as with SS but it may work differently.

A rotary jeweller's lapping plate is worth a look of course, but they're not cheap once you've got one for each grit. Again to quote Michael, he's managed to get two fine diamond paste grits to work on one plate with cleaning in between, but at a guess coarse grits would be harder to control this way.

Mr B., thanks for that info about the small diff btwn extra coarse and coarse. Darn it.

Yes, more folk are talking about jumping from 1000 to 8000. Standards are a bit tricky here of course. I've been talking about JIS in which 1000 is about 700 ANSI or 15 micron; 4000 JIS is 4 micron. 8000 is rated as one micron.

To add: just been doing more clean-up with Jif and reckon this should've been done sooner rather than later.

Also Woody, if you go to use the magnets with diamond stones, just beware there's not too much pull as light pressure is recommended with these.

Quote:

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Originally Posted by rsser

Silicone carbide loose grits on plate glass as per the Veritas kit is something else I'm going to try; Michael warns of the same risk of corners over-abrading as with SS but it may work differently.

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Not quite Ern, what I warned of, in relation to loose SiC on glass, is preferentially wearing the glass, instead of the cast iron, steel etc.
See this post by Forest Addy, about half way down:
How to flatten a plane sole... - Practical Machinist - Largest Manufacturing Technology Forum on the Web

To test this, try lapping a piece of glass on a diamond stone instead of steel, you'll quickly see it goes a lot faster than the steel.
I have no idea why Veritas recommends this method.

I suppose you would wear a hollow in the glass which then might lead to rounding of the metal thing you're lapping...

Cheers
Michael

Apologies for mis-reporting you Michael.

Yes, the risk you identify sounds perfectly plausible.

To be fair to V. they recommend you put a mylar sheet on the glass but I understand this to be aimed at holding the loose grit; just my memory though, increasingly fallible.

I've never been tempted by the loose silicon carbide grit. Lots of messing around, and logic says that it will wear away most reference surface materials about as fast as it flattens your steel. So that granite surface plate flat to 0.0001" certainly won't stay flat for long

Granite Surface Plate : CARBA-TEC

I'd buy one of the Carbatec granite plates if they ever had them in stock :((

I vote diamond plates as far into the sharpening process as possible (thereby keeping the ground edge pretty much straight), with only the final microbevel formed on fine waterstones or (preferably) ceramic stones a la Shapton. Use your coarse DMT diamond plate to keep the waterstones/ceramic stones flat. The only thing I'm likely to change in my process is to replace my 8000 waterstone with an 8000, and possibly an additional 12000, Shapton ceramic stone

For substantial material removal, I'd start with a really coarse wet & dry sheet on the granite surface plate (thereby avoiding damage to your reference surface), then finish up with the Coarse CMT diamond plate to correct any slight rounding introduced by the paper. From there its into the progression of diamond plates, and so on....

Remember, we have to leave some time to actually USE the tools........:D