Union plane iron - Won't hold edge

[Strokes77]

.............
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.

Update.  

a regular mill file easily cuts the steel at the bevel.  Very soft.  

I'll update later after I mess with it some more.  I will probably cut my losses on it.

[barryvabeach]

Since it is dead soft, I wouldn't mess with a grinder.  You can try to heat treat it, since it is a loss at present, you have nothing to lose.  Learning to heat treating can come in handy when you want to make a chisel for a particular job.

[Admiral]

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. 

Yes. I forgot to say that. 

[rwe2156]

A lot of irons are tempered just near the cutting end.

Any possibility the iron has been ground past that point?

I would try re-tempering.

[Souperchicken]

I don't know anything about Union irons, but another possibility is that it is (was?) a laminated iron and it's been used past the tool steel bit.  In that case it really won't harden even if you redo the heat treat because there's not enough carbon in the remaining alloy.

[Strokes77]

I don't know anything about Union irons, but another possibility is that it is (was?) a laminated iron and it's been used past the tool steel bit.  In that case it really won't harden even if you redo the heat treat because there's not enough carbon in the remaining alloy.

Last question.  

I have a new method of flattening the backs.  It works fast, but I don't have a lot of experience with it and not sure if it has caused this...  I built a jig that holds the iron, and really allows me to go pretty fast and put relatively heavy pressure down on the iron while lapping on 120 grit paper.  

Is it possible this creates enough heat to ruin the entirety of the iron?  It doesn't change color, but it is hot to the touch.  Probably longer than I would want to touch for 3-4 seconds.

[Steve Friedman]

I have no idea whether it's possible to destroy the temper by sharping on sandpaper, but I often get the blade so hot that I can't touch it for more than an instant and never had a problem with losing temper.  I have destroyed blades on a bench grinder, but never without some power sharpening.

You can use some water to cool down a hot iron while sharpening, but sometimes it's just as easy and effective to use something nearby as a heat sink.  Especially if it's cold outside.  

I am curious about your blade, so keep posting until you solve the mystery.  Or until you give up.


Steve

[barryvabeach]

You definitely did not destroy the temper by sharpening the back by hand -     Scroll down on this page and you will see the chart for tempering
http://www.threeplanes.net/toolsteel.html  

You would have to get the blade to 300 degrees to hit 63 RC for tool steel, which is still extremely hard.  We often temper to 400 to 500 F, and that is still fine.  Destroying the temper, which is near Blue is closer to 600, and  I don't think it is physically possible to get there by hand.

Even if it were possible to get above 400 degrees by hand sharpening, you would feel it as more than just a little hot to the touch, think about taking something out of the oven at 400.

 As has been suggested, it is possible that when the iron was made, they only heated the very end, or more unlikely, they laminated a hardened piece of tool on the end ( you would probably see some evidence of that.

[Timberwolf]

Last question.  

I have a new method of flattening the backs.  It works fast, but I don't have a lot of experience with it and not sure if it has caused this...  I built a jig that holds the iron, and really allows me to go pretty fast and put relatively heavy pressure down on the iron while lapping on 120 grit paper.  

Is it possible this creates enough heat to ruin the entirety of the iron?  It doesn't change color, but it is hot to the touch.  Probably longer than I would want to touch for 3-4 seconds.

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"Is it possible this creates enough heat to ruin the entirety of the iron? "

[Strokes77]

Thanks for answering my dumb question without making me feel dumb. That's why I like this place.

Appreciate y'all.