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Dave Slight

A2 vs O2 blades

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Does anyone know what the difference between the A2 and O2 blades is, other than the way in which they are quenched/cooled?
I know A = air, and that O = oil, but why the difference, and what properties do they give, relative to each other?

I'm not really interested in the newer PM blades, made from powdered unicorns and yeti toe nails or whatever.

I had asked this question in a topic on the luthiers bench, but it might be more appropriate here.

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O1 can usually be sharpened to a keener edge than A2 . A2 is a little tougher so the edge will usually last longer before sharpening.  They both make decent blades and it depends on how sharp you really need them. O1 has a finer grain structure so the edge can be sharper.

O1 can rust more easily than A2 (which contains around 5% chromium).

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When I first started making knives, a guy told me I needed a Ph.D. In metallurgy to get my questions answered. After 4 years, I agree with him. But on the practical side, you can follow the recipes of others and make good blades without having a Ph.D. Here is a link to some good reading. https://books.google.com/books/about/Steel_Metallurgy_for_the_Non_metallurgis.html?id=brpx-LtdCLYC&printsec=frontcover&source=kp_read_button

i also know a Ph. D metallurgist and he is worth every dollar I gave him.

Just curious, why no interest in PM steels?

john 

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A2 stays sharper longer than O1. A2 can fail miserably (edge chipping or pits). O1 gets sharper but wares more quickly. 

As John says PMV11 is fantastic. Not just saying that because I'm Canadian -- the lee valley / veritas blades are excellent. It gets almost as sharp as the best O1 or old steel and stays sharp much longer that A2.

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10 minutes ago, Melvin Goldsmith said:

How heat sensetive is pmv11 for re grinding etc?

Good question. I dont know off the top of my head. I have a white paper somewhere that Lee Vally published -- they did a ton of research  -- I'll try and dig it out

I use a Tormek grinder which runs cool. Some Lee Valley blades don't have parallel sides all the way through so lining them up in a grinding gig can be a bit tricky.  

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1 hour ago, Melvin Goldsmith said:

How heat sensetive is pmv11 for re grinding etc?

 

Tempering temperature is about 400 F, so, yes, heat sensitive.

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Thanks to FC, violins88 & Urban for your helpful replies and the links.

That makes sense since I have knives in the O steel, and plane irons in A2, which would need to be tougher. As they are used for different purposes, it's hard to compare directly, but both have been fine for me. Like a lot of things, I just use them without thinking too much about why they are different, but recently have been curious.

To John Schmidt & John C, I wasn't interested in PM blades, as I don't have anything made from it, and wanted to know more about the things that I have. If you are both impressed, then I'm sure they are very good, but I won't be buying any. At this point, I'm looking to have a clear out of tools.

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14 hours ago, Melvin Goldsmith said:

How heat sensetive is pmv11 for re grinding etc?

 

I use PMV 11 blades on all my planes and I have one PMV chisel that I bought at used tool show.  I don't have a tormek but rather just a plain Baldor grinder.  I don't have problems when grinding.  I'm conscientious about it ie water dips etc.  The PMV 11 is excellent and I attest to what the other above have said about it.

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