One brick warping?

M

MSCantrell

Knifemaker / Craftsman / Service Provider
Joined
Mar 12, 2005
Messages
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I hope someone can help me out with this- I'm slowly getting through the knifemaking process on my first couple of knives. This week, heat treating. So I built a one-brick forge (anybody in mid-Michigan... Lansing Refractory= great service, great prices). Long hole down the center, one small hole coming in from the side. Propane torch goes in the side.

Now, problem is, the center of the blade get hot quicker (and gets hotter) than the tip and guard area. So when I quench 'em... they warp! The first one, I thought it was just because I had tried three times before I got it hot enough (didn't have a magnet around, tried to go by color, whoops). But now it happened again. Got the blade plenty hot, and now it's hard all the way up and down the length, but it's warped pretty bad in the middle. What do I do?

There are a couple of things I need to know. First, are these warped ones salvageable? Next, did I do something wrong in constructing the forge? Last, is there something I can change about my technique?

Thanks, guys,
Mike
 
I have not had any use of a 1 brick forge so my replies are based on my larger forges.

I let my forge heat up until the whole inside is up to temperature before heat treating when all the forge is hot I still tend to have a hot spot but you can move the blade around until the whole thing is hot. That my be a problem if the blade is too big. I also tend to block the front entry hole of my forge to help the whole thing warm up If you have a opening at the back you may need to close that aswell. My forge is closed at the back and a small hole at the front and some bricks to put in front to blok it further.

If you re heat the blade you will be able to straighten it. Many way from just hitting it with the vertical hande end of the hammer It burns the wood but protects the blade. Anneal the blade and use a 3 pin method.

Concentrat more on getting the heat even rather than the fixing the warp.

I always rotate my blade in the heat and allow a little extra time after it is hot to even out all over. At the same time care needs to be taken to avoid over heating the tip and cutting edge.

Last with my larger forge I moved the gas inlet hole forward of center and angled it backwards. The flame swirles around and back evening the heat to some degree.

Good luck
 
That pretty much covers it.
I was thinking maybe the torch is coming straight into the center of the chamber.
I'd put it in at an angle like Reg suggested, so the flame swirls around the chamber, instead of heating just the center.
 
One question I would ask; how far along in the grinding of the blade, did you do the heat treat? People, when they first begin making knives, tend to almost complete the blade before they do the H.t. A thin blade is very difficult
to keep from warping. You will find, as you progress, where that "sweet spot"
is. Where do I stop grinding and do the H.T. Fred
 
Reg,
I did something like you did- the hole is toward the back of the brick, angled forward. The back hole is covered with another brick.

Howies,
I think what I may need to do is hollow the center hole out. Right now it's just barely bigger than the blade that's going in. Not much room for "swirling."

Fred,
Guilty as charged- I had ground it with the angle grinder then hand sanded to 120 grit when I started heat treating. How unfinished do you leave them? And while we're at it, what's the best way to get all the scale off afterward?
 
I read about the one brick forge but not tried yet.
I am also knew to knifemaking and I am wanting a forge
I got some info from the anvilfire site they also have links to home made propane burners and forges. I heat my blades at the botom of my wood stove
in the coals and the wifes fan. To prevent scale I use a brazing flux found in
all welding supply shops. This flux wont prevent all the scale from forming but whats left is easy to remove no major pits, also the flux max temp of usefullness is 1600 deg F. This product is no good for high aloy steels I just use O-1.
hope this helps Darrin.
 
Might help to normalize the blade a couple of times before the final HT.Grinding with an angle grinder has got to leave some kind of serious stress.As soon as you can ,make a little larger oven.Also make sure you fully heat the blade,that is why we soak the blade for about 5 minutes before quench (when you have a forge or oven that can be controlled).Uneven heating equals uneven cooling,thus warpage.If it warps upon quench ,(this sounds a bit scary), take the blade out of the oil while the blade is still around 300-400F put it on the anvil and gently work it flat with the hammer (this is where a brass hammer shows its worth).If all goes well it won't break.Temper twice and sand to finish.Leave the angle grinder alone after HT.Don't worry about the scale,it sands off while finishing.
Stacy
 
I have just made a 2 brick forge, as the bricks came in pairs. The only thing I can add from the above, since I have only made one dozen blades and the guys above have lots of expierience.
My forge is two bricks with a big C cut out of each one and wired together. I can get two small blades in it at one time. I have coat hanger holding a slice of brick on the back and I can slide it down to leave a slit to slide the blade or tang out the back. I can do two blades at one time and the biggest one I have made has a 5 inch blade, not counting the tang.
The most important thing with these small forges that I have learned is the basic cheapo burners will not heat well or evenly. I have a store bought venturie style burner that screws on to the propane can.The basic non venturie burner was a big disapointment and may be your source of grief. :barf: I also have made the burner hole larger so I can change the angle of the burner. The forge gets hot quickley but does become more uniformly hot with use. As a final note do not push the burner end vey far into the hole as the tip will get very hot if you do this
Cheers Ron
 
Really guys

Has anyone ever tried one of these powering a forge? Not a one brick, but larger, or does the flame spread to much?
 
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