Thread: Buffing-generated heat ruining blade temper?

I just finished polishing on old 5/8 Wade&Butcher with my Dremel and it looks great! However, even after going through the honing and pasted strop process, it doesn't seem to shave like it used to even after thorough stropping. It very well could be my imagination, but is it possible to ruin a blade's temper by polishing using a rotary tool (circa 2500 RPM) such as a Dremel? I noticed there was a substantial amount of heat generated in the process, with the blade a bit too hot to touch at times.

Any ideas?

Thanks in advance!
Dan

It's very likely. I don't know the particulars, but I don't think it's more than a couple-three hundred degrees to de-temper carbon steel. IIRC, you can detemper a blade with nothing more than the heat of a normal kitchen oven. Bill Ellis...? Can't remember if Paul Bos does your HT on your ATS34 or you do it yourself. Anyway, I believe carbon steels, particularly the older steels, don't take as much heat as the newer stuff, such as today's knifemakers are using. The tricky part also is the edge is so thin, it doesn't take much to heat it up with a dremel or bench grinder style buffing wheel.

Damn it. Though it was the guinea pig and cheapest razor I have, it was such a nice shaver....

If you can touch it without burning a blister on your finger, the temper should be unaffected. Until the temperature tops 300 degrees, the crystaline structure of the steel does not change. Tempering steel is actually the process of bringing down the initial hardness to a usable level. Here is more information. Suffice to say that unless you really went nuts on your razor, the poor shaving properties you are experiencing are probably the result of inadequate honing. Working a blade over thoroughly usually blunts the edge significantly and I've found it all too easy to quit honing before the blade is actually sharpened completely.

Here's more on heat treatment, tempering and annealing:

To harden most steel it is heated to a medium red or slightly above the point where it becomes non-magnetic. It is then quenched in water, oil or air depending on the type of steel. The steel is now at its maximum hardness but is very brittle. To reduce the brittleness the metal is tempered by heating it to some where between 350°F and 1350°F. This reduced the hardness a little and the brittelness a lot. Most steels need to be tempered at about 450°F for maximum usable hardness but every steel is slightly different.

To soften steel so that it can be cold worked and machined is called annealing. To anneal steel is is heated to slightly above the hardening temperature and then cooled as slow as possible. Cooling is done in an insulating medium such as dry powdered lime or in vermiculite. High carbon and many alloy steels can only be cooled slow enough in a temperatue controlled furnace since the cooling rate must be only 20 degrees F per hour for several hours.

Originally Posted by PapaBull

If you can touch it without burning a blister on your finger, the temper should be unaffected. Until the temperature tops 300 degrees, the crystaline structure of the steel does not change.

Yes, but be careful. The cutting edge is very thin (i.e, has very little mass) so it takes very little friction to pruduce a huge temperature spike. This spike will be localized at the edge (i.e. there will be a large temperature gradient). You can easily burn the edge even if the average temperature of the blade remains low, especially with steel which does not conduct heat very well. That's why knife grinders are water-cooled & have low RPM motors.

With knives, you can remedy a burned edge by simply honing it into oblivion. Don't know if this is also true for razors but I can't see why it wouldn't be.

I think I ended up doing this to a W&B I picked up off of Ebay. Randy wasn't able to get an edge for the life of him on that blade after I'd buffed out the majority of pitting. I'm beginning to think dremels and razors are an extremely bad combination.

Unless you saw the steel change color, you did not lose temper. I suppose it would be possible to damage the edge if you kept the wheel in the same spot and waited for the rainbow, but as long as you keep the tool moving you will not have a problem. You can hide any damage by buffing out the discoloration once it has cooled below 500 degrees, so it is possible it was damaged before you got it.

For as long as I have been making knives, I have been told by my contemporaries that you need to generate heat over 500 degrees to cause any damage to the temper. Many knifemakers use a mini torch to generate heat at the guard area to apply silver solder to joints. This is more than you will do with a buff on a dremel. (As long as you keep it moving) After heat treat, most steels are baked for hours around 450 to set the temper.

Papa Bull... Some very good info. It would have taken me 4 pages to try to say the same thing.

I use a 1 horse Baldor buffer with a 10 inch wheel at 1750 RPM's with 6 to 10 pounds of pressure on my stuff. I haven't lost a blade yet. So, if the big daddy won't wreck a blade, your dremel won't. That would be eqivalent to running your rotary around 18,000 rpm's with much less pressure. As long as you keep it moving, you should be ok. Do not fear the buff...

Okay, let me rephrase that. I pulled an extremely stupid and ground out the pitting. Avoid the grinders and try to use the slowest speed possible on your dremel for buffing. Shouldn't take much for it to be effective.

Send me the razor and I'll put an edge on it. I have cleaned up hundreds of ebay specials and been able to get them shavable. I try not to use too high a speed on the dremel, but many have gotten "hot" in the process and turned out to be very nice shavers. Lynn

If Randy spent more than 4 hours trying to get an edge on it do you really want to bother? I got a nice King Kutter off of Ebay that has no pitting and I'm going to get that one honed up instead. I'm just writing the W&B off as a lost cause and a lesson learned.