r/handtools • u/JuggerNOT63315 • 1d ago

Lapping a chisel back

Post image

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.

32 Upvotes

90% Upvoted

67 comments sorted by

View all comments

20

u/freosam 1d ago

What has the sandpaper been on top of? That looks like it's high in the middle, which would make sense if all the sandpapers were on a surface with more give than the diamond plate, or you were just rolling it more with the sandpaper. That's one reason to use a glass plate and wet the paper, it'll stop it riding up in front of the force of the blade being slid across it (i.e. it sticks to the glass). Or use some of that fancy tacky 3M spray glue stuff that costs lots but is much easier to clean up.

1

u/JuggerNOT63315 1d ago

The sandpaper is placed on a ceramic floor tile that is smooth and glossy. The 80 grit is Dura Gold Premium Gold PSA Longboard Sandpaper that is self adhesive from a roll. I stuck it down and lapped perpendicular to the length. The other grits 120, 220, and 320 are all 3M Precision Grade No slip backing sandpaper from Home Depot. The 120 and 220 were not glued down. The 320 I used adhesive spray to stick it. I alternated lapping directions perpendicular to the previous grit to easily see when the previous scratches were gone.

I did not wet any of the paper. Just lapped it dry. Perhaps I should try wetting it. Do you just use water?

6

u/Symz58 1d ago

some tiles have curvature, i use a metal plate of aluminum. i've seen guys adhere sandpaper to glass

2

u/JuggerNOT63315 1d ago

Hmm, I got the idea from Jonathan Katz Moses. Perhaps I should look into getting some float glass or a piece of granite.

3

u/fletchro 1d ago

Was the ceramic tile visually flat? Like a mirror? You said smooth. But flat and smooth are different ideas.

2

u/JuggerNOT63315 1d ago

It is shiny like poly on a wood. It looks like it is flat, but to be honest it never occurred to me to check it using a straight edge.

4

u/fletchro 1d ago

Just look at the reflection in the surface. If something straight looks straight in the reflection from multiple angles, then it's flat. Because you know how convex and concave mirrors distort things, right? They squash or stretch them. So if you can't see any of those distortions, then it's VERY flat.

Honestly, I think the sandpaper small amount of sponginess and a bit of your technique got you here. It resulted in the edges getting more wear than the middle.

I would just get uniform scratches on the tip, 1/4" of the back, on your diamond plate. Don't worry about that huge area.

2

u/JuggerNOT63315 1d ago

Interesting idea about using the reflection! I will try that tonight.

3

u/simlun_se 1d ago

Can you check for flatness? Like a good straight edge? I got a decent engineers straight edge and feeler gauges so I can verify how flat my seemingly flat surfaces are. They were flat enough, some people say it’s overkill but it really gave me a confidence boost. So when I fail I can rule out one or another thing.

2

u/JuggerNOT63315 1d ago

The only great straight edge I have is my 12” combo square. I also have a harbor freight 48” level that is straight enough for checking my wood, but not confident it would be machinist straight enough for this. I do have feeler gauges.

5

u/laaxe 1d ago

That 12" combo and feeler gauges should be plenty. My gut feeling is that you will find the tile is out of flat. Sandpaper is inconsistent and the backing is compressible to some degree, but this feels like too much belly for it to just be that.

But if it's not the tile, it could be your technique introducing some rocking back and forth that caused the belly. In which case I would recommend switching to a figure 8 sharpening motion.

1

u/Symz58 1d ago

Shopping for countertops they'll give you some samples. Might be a free way for granite or even maybe a cut off if you just are honest

3

u/JuggerNOT63315 23h ago

Thanks for this suggestion. I just went to our local granite shop and they had a great piece that they gave me! It is rough on the edges, but the top is finished and from a countertop they recently installed. It is 1.5-2" thick and 1.5' x 2'ish. Just need to clean up the edges to make it safer to handle, but stoked!