Plane Iron made of Pringles...

[J_SAMa]

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

 

[JohnPW]

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.

 

[MIGNAL]

Carefully grind it back a further 1 mm or so. You might reach good steel at the correct temper.

 

[bugbear]

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

 

[J_SAMa]

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.

 

[matthewwh]

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.

 

[J_SAMa]

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.

 

[Cheshirechappie]

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.