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[Doug Lester]

I went to a knife show yesterday and took along a few knifes that I made. Got to talk to a couple of other knife smiths, one who lives about a half hour away from me. A little taken aback that they weren't quite as impressed with my knives as I was but I did get some good advice and that's what I drove six hours round trip to get. Time to crank my knife making up a notch.

The biggest problem that I have is in heat treating. I have a tendancy to warp the blades. I'm deffinantly getting the blades too hot and probably not heated evenly. I'm thinking about putting a piece of black pipe that I have into the gas forge and heating inside of it. These blades, the ones that were warped were edge quenched. I was also wondering if that might have contributed to the warpage. What are the feeling of edge quenching vs. full quench?

All in all, I'm glad that I went got some good suggestions, such as not trying to forge the blade as close to finish and got some pointers on how to possibly salvage the warped blades. I'm going to have to use something like a straight edge for right now to check straightness; I don't appear to have quite the eye to check visually.

Doug Lester

 

[SBuzek]

Uneven grinds and edges too thin will cause edges to warp.Also over heating.get a thermocouple and pid to check temps. You can get both for about 60 bucks.Also the muffle will help with even heating.
Stan

 

[ddavelarsen]

+1 on the iron pipe. That's how I worked to even the temps in my propane forge too, and it helped immensely. If you get pipe with galvanizing on it, stay away from the forge while it's burning off - poison! Best to avoid anything galvanized around heat, actually.

 

[JAWilliams]

There are ways to straighten the blades but you have to heat them back up. I tried to straighten one that was cooling down and snapped it. Lesson learned.

 

[EdCaffreyMS]

I suspect that much of your issues can be solved by changing a couple of things.

You mentioned about forging close to finished shape. That MAY have something to do with the warping, IF your forging those edges down close to finished thickness. Remember the old Blacksmith saying... "For the edge that wins, forge it thick and grind it thin". That is not to say grind that edge thin before heat treating!! After forging, rough grind the blades, leaving the edges about the thickness of a nickel. Then remove the excess material AFTER heat treating (during what I can "finish grinding". Something else that helps eliminate warping is to normalize 2-3 times just prior to hardening.

When I'm producing very thin blades such as folders and slipjoints, I will heat treat before grinding any bevels.

You asked for opinions on full versus edge quenching. I personally like the edge quench, not only because I can control many facets of the finished knife by using this method, but if a blade does warp, the edge quench method allows me to straighten it...where as a fully hardened blade won't afford me the same opportunity. Sometimes you have to think about methods that not only make a great blade, but also give YOU advantages in producing those blades....for me the edge quench does both.

 

[burchtree]

Always a full quench -- drawing the back or using clay will achieve the same effect. Edge-quenching tends to create more pearlite.

Like others have said, you don't want to finish it to perfection before HT. 1/16 thick or more will be fine. Things warp, that is all there is to it -- an arbor press set up will help you straighten things after a snap temper (about 30 minutes).

Straightening some titanium in this pic:

 

[Doug Lester]

I just reheated my warped blade and straightened it with a hammer and checked straightness with the edge of a square, then I just retempered it. I use the pipe closed off at one end; used furnace patch to do that. It even the heat out a lot better but still not perfiect. I immagine that I'll make a high temp salt tank for that task. I did toss a few pieces of charcoal into the pipe to heat the blade for quenching, and so far, that is the best thing that I have found for preventing heat scale. Not 100% still, but a whole lot better. I've got the blade in the oven now for the first tempering cycle so I'll see how it comes out later. Tomorrow I'll forge out another blade using some of the suggestions made.

Doug Lester