Cant get this sharp

[Frederick Skelly]

Working on an old Keen Kutter plane blade. Its about 1/8" thick. Have tried all my normal methods (combination of sandpaper and stones, plus a mark 2 veritas jig) and it wont get or keep a sharp edge. After 6000 grit, the edge looks good and seems sharp.

So I used it on some pine. After a few strokes, the blade looks like it has fine chips in it which also show in the planed surface. So I flatten the edge to eliminate the chips, make sure the edge is square and start over. Still not sharp enough to take thin shavings. Chips again.

I have a 30* primary bevel and a 5* secondary bevel. The back is flat. I used the ruler trick on the back to get a mild backbevel. This approach has been working very well for me to date. The only thing thats different this time the thicker iron and the 30* primary bevel.

Got any ideas?

Thanks,
Fred

[David Weaver]

There was a post about this last week. If it's brand new, the edge may be starved for carbon. If it's not brand new and unused, then if it's chipping and not folding, put it in the oven at 300 degrees for 45 minutes.

Try it. If that doesn't work, try it at 350 for 45 minutes. Try it.

As soon as it's not chipping, stop. Once you're to 400, change the interval to 25 degrees.

[Jim Koepke]

I have a 30* primary bevel and a 5* secondary bevel. The back is flat. I used the ruler trick on the back to get a mild backbevel. This approach has been working very well for me to date. The only thing thats different this time the thicker iron and the 30* primary bevel.


David may have pin pointed the real problem.

For a bench plane when the bevel gets to be much more than 35º you can start to lose your clearance angle.

My thought on the ruler trick is that it must work since so many swear by it. Though if the blade is going back and forth while resting on a ruler there is a slight rounding from the change of angle.

You might also want to switch pieces of pine. Select one that is from a different batch. Sometimes there are contaminants in the wood. Especially it it was run through a surface sander with a new belt releasing its loose grit.

I have a few pieces of pine that are a dream to plane. Sub thou shavings all the time. then there are some pieces that wouldn't come smooth after a thousand sharpenings.

jtk

[Jim Matthews]

The dark annular rings and knots of Eastern pine are surprisingly hard.

Do you have the same chipping on something like Oak? The older plane blades were built to handle most any task -
they would not have been popular if there were lots of problems like you've reported.

Try another test block - long grain and see if the problem is persistent.

[David Weaver]

Jim 1 brings up a good point, too. If it's a piece of wood that's been laying around, make sure there's no grit in it, which would look like little tears in the wood surface after you ran a plane across.

[Frederick Skelly]

Thanks guys. Ill try your suggestions in the next few days and let you know what happened.

David - one question. If I put the blade in the oven, should I let it air cool, or quench it in oil or water?

Thank you!
Fred

[David Weaver]

It doesn't make much difference at the lower range, but I'd let it air cool. IT doesn't take long for it to get cool enough to handle if you just take it out and put it on a baking rack. You're only tempering, and not hardening (which is the only time you need to quench)

[Frederick Skelly]

Thank you!

[Chris Hachet]

Good luck, and keep us posted!

[Frederick Skelly]

Update for Sunday June 2.
I've had that blade in the oven twice now. Started at 300* for 45 mins, then 350* for 45 mins. Today, I decreased the bevel from 30* (primary) +5* (secondary) down to 25* + 5*. I took extra care to be sure I eliminated scratches and had a wire edge. I polished the back flat to 6000 grit. It looked and felt sharp (cut paper, not reflecting light, etc), but even on another piece of wood the edge chipped very quickly. The chips were smaller this time, but they were there - I can see them with my naked eye and feel the sawtooth edge with my finger. So it's back to the oven for 400* for 45 mins. We'll see.

Could be I'm kidding myself, but I'm starting to wonder if this old hardware store blade (E.C. Simmons "Keen Cutter") is just bad steel that never will hold an edge. Guess I'm going to find out, soon.

Oh well. Back to it. Take care all!
Fred