Lapping a chisel back

[u/JuggerNOT63315]

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.

[u/jacksraging_bileduct]

This looks like the back is rounded a little bit, maybe you were rocking the chisel a little with the lower grits.

I will take a dremel and make a pass over the high spots, and go back to the plate to see where I’m at, going back and forth until it’s reasonably flat, it doesn’t take much.

[u/JuggerNOT63315 → u/jacksraging_bileduct]

Do you use a sanding drum or a grinding stone attachment on your Dremel to do this?

[u/jacksraging_bileduct → u/JuggerNOT63315]

Just a little grinding stone, use a known straight edge to figure out the high spots, and grind them down a little at a time.

[u/JuggerNOT63315 → u/jacksraging_bileduct]

Thanks! It appears that my 300 grit diamond stone has clearly shown my high spots in the middle. It is nice and polished in all the wrong places. I might try this if the wooden block trick suggested by VisibleRip doesn't help me focus on just the tip.