A major problem trying to flatten the back of expensive Japanese chisels

[Joel Gelman]

I recently purchased a set of expensive Japanese chisels. I previously had several less expensive Japanese bench chisels from Japan Woodworker, and no problem flattening the backs. For this expensive set, I took them to a workshop with Garrett Hack. I only needed 1 for the course. He suggested I flatten the back with a not so course water stone to start, but then I showed him how it was not evenly reaching the edge across, and so the plan was course to fine. It was a fairly narrow chisel and I got is nice and sharp, but it took awhile. No time to work on the other chisels during the workshop as I was kept busy.

When I came home this weekend, I went to sharpen the rest with my NanoHone waterstones. Goal was mirror finishes and sharp. As I started to flatten the backs, especially the wider chisels, I noted that I was not getting the scratch pattern to reach across. This is shown in the pictures. I got nowhere with grits less than 200 (70u) and with that course grit it seemed to take forever. More problematic was that although with time the surface area not getting touched got smaller and smaller, I was removing quite a bit of material on the other side. However, I know that I must get the back flat all the way across and if that does not happen with a courser grit, the finer grits will not make that happen. I never had problems like that with other chisels or plane blades.

To be sure, I was very frequently flattening my stones, and I was very aware not to put uneven pressure, especially since I noted the low spot tended to be to the left when viewing the back. I even tried to vary how I was moving the chisel across the stone, and as I suspected, it did not matter. It did not matter if I tried to flatten the entire back or limit to the area more towards the edge. It was flat on the flat stone, and with the wider chisels in particular, not so hard to keep the bottom in contact.

I really think these chisels came not so flat unless someone can suggest something I could have done to cause this. To be sure, I was using flat stones and not applying uneven pressure.

Thoughts?


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[Mark Hennebury]

Looks to me like the chisels were not flat to start, as you seem to be resting on the tang at the back and the front cutting edge, but not touching the back edge. I would grind the tang down a bit, so that you can rest the chisel back completely flat on the stone, instead or riding up on the tang.

I recently purchased a set of expensive Japanese chisels. I previously had several less expensive Japanese bench chisels from Japan Woodworker, and no problem flattening the backs. For this expensive set, I took them to a workshop with Garrett Hack. I only needed 1 for the course. He suggested I flatten the back with a not so course water stone to start, but then I showed him how it was not evenly reaching the edge across, and so the plan was course to fine. It was a fairly narrow chisel and I got is nice and sharp, but it took awhile. No time to work on the other chisels during the workshop as I was kept busy.

When I came home this weekend, I went to sharpen the rest with my NanoHone waterstones. Goal was mirror finishes and sharp. As I started to flatten the backs, especially the wider chisels, I noted that I was not getting the scratch pattern to reach across. This is shown in the pictures. I got nowhere with grits less than 200 (70u) and with that course grit it seemed to take forever. More problematic was that although with time the surface area not getting touched got smaller and smaller, I was removing quite a bit of material on the other side. However, I know that I must get the back flat all the way across and if that does not happen with a courser grit, the finer grits will not make that happen. I never had problems like that with other chisels or plane blades.

To be sure, I was very frequently flattening my stones, and I was very aware not to put uneven pressure, especially since I noted the low spot tended to be to the left when viewing the back. I even tried to vary how I was moving the chisel across the stone, and as I suspected, it did not matter. It did not matter if I tried to flatten the entire back or limit to the area more towards the edge. It was flat on the flat stone, and with the wider chisels in particular, not so hard to keep the bottom in contact.

I really think these chisels came not so flat unless someone can suggest something I could have done to cause this. To be sure, I was using flat stones and not applying uneven pressure.

Thoughts?


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[Eric R. Smith]

I too had a problem with a very expensive set of nomi. I decided it best to flatten the lower half and not remove too much material. Flattening went quicker and I did not loose a bunch of expensive steel.

[Mark Hennebury]

This is what i did to a very cheap set of chisels, not Japanese, not expensive, but the same issue that you, in the chisel back will lift up from the stone if you lap up onto the shank/ neck part. So I ground a clearance area. NOT suggesting that you do anything quite as drastic, but you could grind a few thou clearance on the neck/shank, so that you can flatten the back without the problem that you are having. I ground them such a lot as I used them for paring and it made a nice grip close up for good control.

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[Andrew Hughes]

I think you shouldn’t try to flatten the entire back.
It’s unnecessary concentrate on the first 3rd.
When you started did you check what you had to work with from the maker ?
I have a couple of Japanese chisels that rest on the small landing at the tang but most of mine started flat near the edge.
I like saving as much of the hollow as possible.
Here a look a my mortise chisel it almost half way but started near the edge.
Good Luck

[Joel Gelman]

After seeing this issue I tried focusing on the front end but that did not seem a solution as still a problem. I think if the issue was front to back, a lesser issue since what matters is only the front part of the back but my issue is on one side

[Richard Coers]

It is a real task, cheap or expensive. That's why I bought a knock off of the Makita horizontal water grinder. It came with a course stone and helped out a lot. But on those wheels you still have to pay attention since the outside of the wheel grinds faster than the inside surface.

[Cameron Wood]

I would not use anything like a 200 grit stone- too easy to go away from flat. The wide chisel looks like the scratches go lengthwise- should be parallel with the cutting edge, except maybe on very narrow chisels.
In your situation, I would use a kanaban and carborundum powder, and a stick laid across the end of the chisel to put more pressure near the cutting edge- illustrated p. 153 of "Japanese Woodworking Tools..."

[Mark Hennebury]

If you look at my $10 chisel you can see that it is hollow ground and flat all around the perimeter, the tang, shank, neck ...whatever you want to call it does not interfere with me lapping the back flat, perfectly flat over the entire back surface, because it has been ground to provide a relief from that surface. A chisel back should be flat, the whole back. Remove any metal that interferes with you doing that, it's not complicated. A tool of any price range can work if you understand the geometry. The is no point having an expensive tool that doesn't work, or that you are afraid to modify to make it work. If it doesn't work it is worthless. Your chisel is not working. it is expensive and pretty. Observe what you have done and you will see that the back has not touched the stone, only the front and the shank, and you have pressed more on on side of the front wearing down one side far more than the other. You need to do a little, stop analyze and understand what is wrong and what to correct, you can't just keep doing the same thing when it's not working. The scratch patterns tell you what is touching the stone....if what you say about the stones being flat is correct. Observation and analysis is the key. Grind down the shank and lap the chisel back flat. you will them be able to lap a perfectly flat polished back on a beautiful and functional tool.

After seeing this issue I tried focusing on the front end but that did not seem a solution as still a problem. I think if the issue was front to back, a lesser issue since what matters is only the front part of the back but my issue is on one side

[Joel Gelman]

I did not start with 70u. I started with much finer and when it appeared one edge was not seeing the stone, I then went to more course. I was very frequently stopping to check flattening often. With time I would in every case see the area not touched on one side get smaller and smaller, indicating the back was becoming flat. The pictures were when almost flat, not early on.

[Derek Cohen]

Joel, an expensive chisel should not require that much work. Okay, you don't have a choice now (unless you send the bloody thing back). Walk away from the stones and, instead, glue a 1m/3' length of 80 grit sandpaper on a flat surface (jointer table). Paper from a belt sander works well. Work the 80 grit along the full length. That will keep the blade flat. Mark with layout fluid to keep track of the lower spots. Also, this will help determine if you are skewing the grind more to one side. Move to 120 grit when done, then 240 grit, 400 then 800. Only at that point you can go to your stones.

Regards from Perth

Derek

[Jimmy Harris]

Derek has a good solution. One thing you'll notice in the world of fancy kitchen knives, which you don't see too often with woodworking tools, is that certain steels react to certain stones differently. You can some Japanese kitchen knives in the Rockwell 65-67 range. So you might have one stone that works better on harder steels and another stone that works better on softer steels, and they can both be the same grit. It might grind it down eventually, but either the stone will be too soft and you'll effectively be polishing the stone with your steel (instead of the other way around), or the stone will be too hard, and you'll just be scratching the steel with your stone, and never get a sharp edge. With Japanese chisels and their laminated steel, they can put a much harder steel back on the chisel than you could get away with with western chisels. So you might be in a situation where your stone isn't hard enough effectively lap the back, and is just crumbling in the attempt. Upgrading to a good diamond stone would probably fix the problem or, as Derek mentioned, just going to sandpaper might be a cheaper and equally effective alternative. Then once you move up the grits, you might find that your higher grit stones handle the steel fine where your lower grit stones struggled. Which wouldn't surprise me, as it's usually the lower grit stones that exhibit this problem most often. Probably because we're asking more of them.

[Reed Gray]

I lucked into some great old hand plane blades a month or so ago. They had been abused. I stretched some 80 grit belt from my drum sander over my table saw and went to work. It took an hour or two for each of the blades. Now that they are done, I shouldn't have to do that ever again. In theory anyway....

robo hippy

[Cameron Wood]

80 grit sandpaper? Ouch. I'm feeling bad for these chisels and their maker.

I looked at the NanoHone website. They make a big deal of flatness measured in microns. That's not working so go to a sanding belt about 3/64" thick laid on a saw table?

Try different stones, as noted by Jimmy Harris above. Sounds like the steel is very hard. Another point is don't expect to get it all done in one session. Work at it until your hands get tired, then come back later for more.

[Mark Hennebury]

One of my old Japanese chisels ground for clearance, I did a crude job on the grinding, but the chisel is functional,, and can easily and quickly be lapped flat.

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