Plane Iron made of Pringles...

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J_SAMa

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Bought a pre-war, NOS J. Jowett plane iron for a plane build (small jointer). For some reason it is surprisingly brittle. It develops chips quickly, really quickly. Below is a shot of the edge after less than a dozen strokes on pine. Sharpening angle was a good 35 deg. I even added a back bevel.



Here's the weird bit: whilst I was flattening its back on a diamond stone, little particles started to fall off... They were extremely hard, hard enough to scratch the stone by knocking diamond off. It's a bit hard to put into words so pics:
Those short black lines:


And they did a number on the stone too:



Going by the way it feels on the stone, I think that if anything, it is overly hard, not soft. But then again maybe I'm just used to how quickly the Bailey-type irons sharpen. The burr is tough to hone off, not very typical of old steel at all. With my other old irons the burrs just jump off if I so much as point them at a strop.
Any ideas? Improperly tempered or wrong alloy content? If the former, should I pop it in the oven? At what temperature?

Lesson learned, don't buy NOS... There's a reason they were never used #-o.

Thank you,
Sam
 
I've got some chisels and gouges that don't seem to get sharp. When sharpening, the burr don't seem to break off cleanly and the edge is jagged. If i use a light pressure, I can get a smooth edge but they seem less sharp than my other tools. My guess is it's too soft.

I did some steel hardening and tempering at college. After hardening (heating then quenching), the teacher said we could test the steel hardness by trying to scratch it with a file, the file should skate off if the hardening was done correctly. Which reminds me that's what I should do my my problem chisels; test it with a file, a good chisel and something softer like a saw or scraper. Tempering was done at 200 degrees, which might be slightly on the hard side, maybe try 220.

i wouldn't automatically assume NOS or old unused tools as being no good or had manufacturing faults. There could be all sorts of other reasons why they were not used.
 
Carefully grind it back a further 1 mm or so. You might reach good steel at the correct temper.
 
J_SAMa":324ultzw said:
Bought a pre-war, NOS J. Jowett plane iron for a plane build (small jointer). For some reason it is surprisingly brittle. It develops chips quickly, really quickly. Below is a shot of the edge after less than a dozen strokes on pine. Sharpening angle was a good 35 deg. I even added a back bevel.


Ouch on the damage to your diamond stone.

Just to confirm - are you sure you removed the wire edge? ( would assume you did, but I'll ask anyway.

it's easy to get that ragged effect when a wire edge breaks down.

BugBear
 
bugbear":14n6z5te said:
J_SAMa":14n6z5te said:
Bought a pre-war, NOS J. Jowett plane iron for a plane build (small jointer). For some reason it is surprisingly brittle. It develops chips quickly, really quickly. Below is a shot of the edge after less than a dozen strokes on pine. Sharpening angle was a good 35 deg. I even added a back bevel.


Ouch on the damage to your diamond stone.

Just to confirm - are you sure you removed the wire edge? ( would assume you did, but I'll ask anyway.

it's easy to get that ragged effect when a wire edge breaks down.

BugBear

That's the thing... As I said, once raised the wire edge is quite tough to remove. I need to spend about 5 to 10 minutes stropping it. Even though I can't feel it with my fingertips it may still be there.
But I don't think it's the wire edge. The chips get much bigger with more use.
 
Under tempered.

As you have already tried increasing the honed angle (logical first step) I would assume that it is decent 1% ish carbon steel and pop it in the oven with your Sunday roast and see what happens.

If it all goes pear shaped give me a call, I've got a few spares knocking about.
 
matthewwh":3bd4ic1l said:
Under tempered.

As you have already tried increasing the honed angle (logical first step) I would assume that it is decent 1% ish carbon steel and pop it in the oven with your Sunday roast and see what happens.

If it all goes pear shaped give me a call, I've got a few spares knocking about.

At what temperature? Say 200 C? I'm not sure what the modern equivalent of "Sheffield cast steel" is so haven't been able to find a tempering chart.
 
J_SAMa":1tv2ygmz said:
matthewwh":1tv2ygmz said:
Under tempered.

As you have already tried increasing the honed angle (logical first step) I would assume that it is decent 1% ish carbon steel and pop it in the oven with your Sunday roast and see what happens.

If it all goes pear shaped give me a call, I've got a few spares knocking about.

At what temperature? Say 200 C? I'm not sure what the modern equivalent of "Sheffield cast steel" is so haven't been able to find a tempering chart.

One source (Tubal Cain's 'Hardening, Tempering and Heat Treatment') suggests 215 - 225 degrees centigrade for Wood Chisels, so plane irons should be somewhere about the same range. That will give a hardness of about 60 - 61 Rockwell 'C'.

Given that most domestic oven thermostats and oven thermometers are not noted for pin-point accuracy, it might be a good plan to temper a bit 'low' to start with, and if there is still any residual brittleness, temper again at a slightly higher temperature. Raising to temperature, soaking for 15 minutes or so, and allowing to cool slowly should do the job.
 

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