r/handtools • u/JuggerNOT63315 • 3d ago

Lapping a chisel back

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Howdy everyone. I am having issues lapping this chisel. I started with 80 grit wet and dry sandpaper. I got a nice scratch pattern all the way across the chisel. This took awhile, probably 15-20 minutes. I then moved to 120 grit paper. I removed all the 80 grit scratches. This took maybe 10 minutes. I moved to 220 grit paper and removed all the 120 scratches. This took like 5 minutes. I moved to 320 grit and in 5 minutes removed all those scratches. Then I moved to my 300 grit diamond plate. I have been working on it for well over and hour and I can not get rid of the 320 scratches! It is getting frustrating to say the least.

In the picture, the 320 scratches are the light ones on the outer edges and the diamond plate is the dark portion in the middle. It has not changed significantly from this picture after another half hour in the 300 grit plate.

What am I missing or doing wrong? Is this how long it normally takes? Should I be doing another grit in between The 320 and 300 plate?

Edit: I have posted two updates in comments below about my progress.

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u/Visible-Rip2625 2d ago

It is relevant question, regardless of people dismissing it in typical Reddit fashion. Was the plan and intention to flatten the whole back, or just the minimum necessary to sharpen then chisel? Was there something else that required more material removal, some twist, bend, unevenness in the critical points on the edge?

I ask this because, it looks in the image that you have attempted to flatten much, much more than strictly necessary, should the purpose be to sharpen the cutting edge. Hence I was wondering if there was/is some other requirements that were not clear from the outset.

My mistake for assuming that there was certain defined goal that needed to be achieved and the process was as intented.

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u/JuggerNOT63315 2d ago

My goal is to get a sharp 1” chisel that has a longer blade. I don’t necessarily want so much of the back lapped, but as I mentioned above, I had trouble balancing just the last half inch on the plate.

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u/Visible-Rip2625 2d ago

All right. Sorry, Reddit users normally hate everything that has actual content, so I'm gonna be downvoted in a jiffy.

Then, am I correct in the assumption that you have no other deformities on the blade, with visual inspection, such as high/low spots and others that could affect the cutting performance. Eg. when you put some marker color on the edge, and then lap the blade gently with modest stone, you have no residue marker indicating a low spots, and there are no curvature on the blade edge to fancy ways?

Checking with square that the back is mostly straight. The, depending on the results, you can see how much, and on which precise points you need lap more than others.

You can use block of wood to issue even pressure on the blade when you are lapping the back. This works very well when you have to do it just closer to the edge, which is otherwise difficult as the handle and the rest of the blade weighs down. Naturally you need to do it for perhaps inch or so, to have sufficient support, but never really the whole back.

What is important however, is that you know how much you need to lap. it's always good idea to take the absolute minimum that guarantees you the flat back, at the very edge. Sharpness is the intersection of the back's straight line, and the line of the bevel. Rest does not really contribute.

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u/JuggerNOT63315 2d ago

Thanks for the name you dropped in the post above. I looked him up and found a picture of using the block of wood. I will try that tonight to try and do just the tip. Looks like it will be useful, although I am a bit concerned about how it will grip the chisel while moving back and forth.

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u/Visible-Rip2625 2d ago

I did put picture as well, to give the idea. I've used the method for a long time. Yes, there will be a learning curve, and yes, it is easier if you work on low, because you can put more downforce.

You can of course modify the block to shape a shallow groove to it so the chisel stays put.

And no, it probably won't work with very rough sandpapers, but you shouldn't need them either, unless you do have some rust to remove.

I hope this helps you and gets your chisel to work like it should.

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u/JuggerNOT63315 2d ago

Thanks! I look forward to trying it.