Union plane iron - Won't hold edge

[Strokes77]

Working on a Union plane iron right now.  It's the thick iron typical with unions.  Flattened the back, set bevel on tormek at 25 deg, microbevel at 30 degrees on stones.  Shave arm hair.

But after about 3 or 4 plane strokes in nice smooth walnut, the plane won't cut anymore, shavings turn to dust.  Take iron out, inspect it, and it feels like a butter knife with a burr on the wear bevel...


Can the iron be salvaged somehow?  I assume someone in the past drew the temper from it? Is that right?

[Admiral]

Working on a Union plane iron right now.  It's the thick iron typical with unions.  Flattened the back, set bevel on tormek at 25 deg, microbevel at 30 degrees on stones.  Shave arm hair.

But after about 3 or 4 plane strokes in nice smooth walnut, the plane won't cut anymore, shavings turn to dust.  Take iron out, inspect it, and it feels like a butter knife with a burr on the wear bevel...


Can the iron be salvaged somehow?  I assume someone in the past drew the temper from it? Is that right?

If there is enough, grind it back about 1/8”, then resharpen. If that doesn’t work, then re-harden. Hopefully Jack will be along to tell you how to do it. I’ve not been brave enough to try that.

[Timberwolf]

If there is enough, grind it back about 1/8”, then resharpen. If that doesn’t work, then re-harden. Hopefully Jack will be along to tell you how to do it. I’ve not been brave enough to try that.

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Rich's suggestion is spot on....Grind it back as he said., but keep the edge cool while doing so...Then try stroking the edge with a sharp file..If you can scratch the blade, it has been de-tempered....If you can not cut it with a sharp file, you are as good as you're going to get..If it is still not holding it's edge as long as you think it should, you can raise the bevel angle a couple degrees with a micro-bevel..That should solve the problem...

Re-hardening it is also a possibility, but should only be attempted if the other suggestions fail..because warping the blade is a real possibility when the steel is heated and then quenched without a proper clamping jig to prevent warpage from the shock of the quench.

[Strokes77]

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Rich's suggestion is spot on....Grind it back as he said., but keep the edge cool while doing so...Then try stroking the edge with a sharp file..If you can scratch the blade, it has been de-tempered....If you can not cut it with a sharp file, you are as good as you're going to get..If it is still not holding it's edge as long as you think it should, you can raise the bevel angle a couple degrees with a micro-bevel..That should solve the problem...

Re-hardening it is also a possibility, but should  only be attempted if the other suggestions fail..because warping the blade is a real possibility when the steel is heated and then quenched without a proper clamping jig to prevent warpage from the shock of the quench.

I put it back on the tormek.  Ground for 5 minutes or so.  Tried again.. The edge lasted longer.. maybe 3 to 4 times as long.. but it still failed after maybe 20 strokes...

Does that make sense?  am I getting closer to the harder steel... or is temper an all or nothing thing.  does it gradually return to hardness?

[barryvabeach]

I don't know anything about Union blades, but many times the suggestion is to grind it a little to see if a prior owner overheated it while grinding, and annealed it a bit.  Not sure how far you ground it back on the tormek, nor how long it is to the slot.  If you still have plenty of length to the slot, try grinding it a bit more.  I think an 1/8 of an inch would be plenty.   If that doesn't work, as long as it is ordinary 0-1,  I have heat treated them and they are pretty easy.    This is a detailed description by Ron Hock.  I use a magnet wrapped around a heavy copper wire to test for critical temp,  and have a few loose firebricks that I stack in a way to make a sort of oven, then a mapp torch or propane torch and a metal bucket with used oil and you are good to go.

[Timberwolf]

I put it back on the tormek.  Ground for 5 minutes or so.  Tried again.. The edge lasted longer.. maybe 3 to 4 times as long.. but it still failed after maybe 20 strokes...

Does that make sense?  am I getting closer to the harder steel... or is temper an all or nothing thing.  does it gradually return to hardness?

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"I put it back on the tormek. Ground for 5 minutes or so. Tried again.. The edge lasted longer.. maybe 3 to 4 times as long.. but it still failed after maybe 20 strokes..."

Have you tested the steel for hardness using a file??...What is the angle of your bevel?...If you can file it, the steel will not hold the edge long..I would grind it back more and test it with a file..If it is hard, the file will "skate" and not be able to cut the steel...Use a marking pen and put a witness mark on the blade to show how much steel you have removed. From what you said, I don't think you removed very much.
If you ultimately have to harden the blade, you can use a 4" diameter clay flower pot as a make-shift kiln..Just lay it on it's side and put a couple of charcoal briquets in it, lay the blade on the charcoal and use the torch to heat it cherry red {or test with a magnet} He heat will be concentrated and reflected back onto the steel, Making the torch more effective.

[Admiral]

I put it back on the tormek.  Ground for 5 minutes or so.  Tried again.. The edge lasted longer.. maybe 3 to 4 times as long.. but it still failed after maybe 20 strokes...

Does that make sense?  am I getting closer to the harder steel... or is temper an all or nothing thing.  does it gradually return to hardness?

The tormek with take you hours.  Take it to a bench grinder, just light touch and quench after each pass.  Draw a line on the back another 1/16 down, then use the bench grinder to roughly reset the bevel, then to the Tormek.  I always reset bevels on the bench grinder as you can spend too much time on the Tormek.

[Timberwolf]

The tormek with take you hours.  Take it to a bench grinder, just light touch and quench after each pass.  Draw a line on the back another 1/16 down, then use the bench grinder to roughly reset the bevel, then to the Tormek.  I always reset bevels on the bench grinder as you can spend too much time on the Tormek.

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Agreed...the Tormek is a poor "grinder" but a good sharpener...certainly not a good substitute for a bench or a belt grinder...They each serve a different purpose.

[JimReed@Tallahassee]

This is a good time of the year to work with O-1 steel. Turkey frying is still popular and large jugs of cooking oil can be had inexpensively. It work fine and smells great.

[blackhat]

When grinding it back, don't try and maintain the bevel the whole way.  Grind the edge square until you have removed as much as you want and then grind a new bevel.  This will reduce the risk of overheating the edge as you are grinding.  Grind the edge square until you have about a 1/16 flat.  Hold that flat on a file with moderate downwards pressure and draw it towards you. If the file cuts it easily grind a bit more, if it seems to slide easily, reestablish your bevel and sharpen.