Noobie ?, straighten a blank

T

Tune_up

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Sep 14, 2010
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I heat treated and tempered a blank from 1084, but when I began to hand finish I noticed that the point is off center about an 1/8" . I know I should have caught this right after HT. Question is How do I correct, start over with HT, try to straighten at tempering temp, normalize then repeat HT/temper?
 
I straighten right after the second tempering cycle. Has worked very well for me. Might try bringing it up to tempering temp again and then straighten.
 
For a small warp the best method is to shim it up so the warp is over corrected by about the amount of warp. Place the blade on a piece of 1/4" stock, with a shim under the tip that will move it the way you want. The shim should be about equal the warp amount, so for a 1/8" warp, try an 1/8" shim. Clamp the assembly tightly with a couple of C-clamps so the blade flexes to over-correct the warp. Put in the oven at 400F for 1 to 1.5 hours Take out and let cool for 30 minutes. Remove and check the results. Repeat with more or less shimming as needed. This should be the first try.

Another method:
Put it in the oven at 400F and let it sit for 30 minutes. Take out with heavy gloves and straighten. Clamp a wooden board with a thin slot cut in it in the vise and stick the blade in the slot. Bend or twist as needed to take out the warp. If it cools down much, put it back in the oven for 10-15 minutes and straighten some more. Repeat as many times as needed. When straight, put back in the oven for 30 minutes. Be aware that a blade tip is thin and fragile, and can snap off easily...so go slow and be gentle.
 
It's probably a good idea to run one tempering cycle to reduce stresses even if you notice the warp right after heat treat. starting with the second temper cycle you can use a three point rig in a vise or try the clamping method. I have had better success and no broken blades so far with the clamping method. I lost a few to the three point vise set-up. Keep in mind it may take more than one temper cycle to see successful results. You may also need to ramp up the temp in subsequent cycles a few degrees to get the steel to relax enough to take the correction.
 
Thanks, will attempt repair this evening.
Do most just "eyeball" it to check for straight or use a reference surface? I didn't notice until I placed the blade on a flat surface and noticed the tip was to low on one side and to high on the other. After realizing it wasn't straight I can see the slight curve.
 
In addition to lay flat...

When I:
eyeball - look at the edge from tip to heel.
computer - spine to edge, edge to spine lengthwise against an app window frame.
sharpie - mark the edge, then vertically roll the edge onto a piece of paper, then use ruler to see where exactly the bend/warp.
 
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