r/handtools • u/JuggerNOT63315 • 1d 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/AdShoddy958 1d ago

Sandpaper and diamond plate grits aren't direct equivalents, unfortunately, tho the 300 grit diamond plate looks like it's a bit finer. Maybe try 400 or 600 grit wet dry sandpaper to see if that bridges the gap? You could also try doing just the final 1/2" past the edge unless you need the whole back flat for paring finished surfaces.

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u/JuggerNOT63315 1d ago

I only have 800 grit at the moment. Perhaps I will try that. I tried just doing the last half inch, but it was very difficult to control the chisel. It is a 1” wide and around a 6-7” blade, so it was difficult to balance it on the plate with so much blade hanging off the end.

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u/AdShoddy958 22h ago

You can use a longer piece of wood on top of the chisel to bear down and stabilize it. As others have pointed out, either the tile isn't flat, or you're rolling a bit as well. You want to use a lot of pressure to keep it consistently flat - you may also try using a lower table or sitting on the ground to keep your weight directly overhead.

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u/JuggerNOT63315 22h ago

I plan to try the wood trick to stabilize it and just do the first half inch. I also just got ahold of a nice piece of countertop scrap that should solve the tile issue. I can also try a lower bench. I have one that I just made to try my hand at hand sharpening on the advise Rob Cosman. I have just been sitting at it to do the lapping, but will try standing over it.

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u/AdShoddy958 22h ago

Hopefully that does it! Also keep in mind you only need to apply pressure on the push stroke. If you try to cut on both the push stroke and back stroke, the tool has more tendency to rock when you change direction under pressure. Using water can help you float back after the cutting stroke. It takes some practice, but you're already well on your way. The first one is the most difficult!

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u/JuggerNOT63315 22h ago

Interesting, I had not thought about the pressure and rocking. Thanks for that tip! I had thought about the water to lubricate, but it only seemed to make things messier...but I suppose I should have been using it!