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AJ Chalifoux

Straightening Long Blades

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Hi All,

I'd like to see what other people do to straighten sword-length blades out of the forge. Correcting warps post-HT is simple enough and has been covered numerous times on this forum alone, but getting a long blade perfectly straight in the first place has always been a challenge to me. I find it especially hard on curved blades. My go-to is generally to find a flat surface, heat the blade up for normalizing, and either gently tap with the hammer down the length on the flat surface (flipping occasionally), or lay the sword down and press down on it with a heavy piece of flat steel (or thick board). Does anyone have anything better? On straight blades this works okay, but if I clamp the tang to a flat work surface afterward I'll still end up with more clearance between the surface and the tip on one side than on the other. Curved blades have been giving me trouble recently...

 

Best,

A.J.

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Pre-heat-treat I use the vise and a twisting wrench to get the kinks and curves out cold.  This is after forging and the post-forging normalization.  During HT I use gloves, a baseball bat, and a stump that's got a groove about four inches wide in the top.  I pull the blade from the oil and give it a quick look while it's around 600 degrees F.  If there's a gentle bend, heavy welding gloves will let you gently press it back straight over the stump.  If there's more of a sharp kink, the baseball bat used on the blade held over the slot in the stump works a treat.  Then it's back into the quench to finish transforming to martensite.  The whole pull-check-fix-back thing takes a second or two at the most, and it's not hurting the steel because you've passed the nose of the cooling curve on the way from quenching temp to the time you pull it out just below the Ms start temperature.  This means it is going to harden fully unless you hold it at that temperature for an hour or so.  Then back in the quench to hasten along the Ms finish point.

There are also ways to auto-temper a sword blade by repeated interrupted quenches, but I'm not brave enough to try it, plus I'm pretty sure it's not the best way to get a good blade.

If there's a warp left after it's cold, then I do the same things during tempering while it's at heat.  A corkscrew curve is the hardest to get rid of for me.  The vise and twisting wrench are the only thing that works for me when that happens.

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I'm thinking I'll have to take it one step at a time with a vise and torch/localized heat, but I just want to know if there's any neat tricks anybody picked up along the way to make the process less tedious.

I haven't been brave enough to straighten directly after quench while it's still hot. How long is the blade submerged in oil before you pull it out? I generally just let it go and take the warps out during tempering with a propane torch, a heavy vise, a steel tube, and a foul mouth. Worst I've tried to take out was sabering of a longsword. The worst I've actually been able to take out was excessive waviness on the edge of a messer by clamping the spine in a vise, heating the edge to blue/purple, and attacking it with pliers and my full body weight. Never could get it all out, though...

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Wait until just the point where the oil doesn't spontaneously combust (or stay flaming long, anyway) on contact with the blade.  Depending on the oil used, that's anywhere from ~450 to ~650 degrees F, well below Ms start.  Mineral oils usually have a higher flash point than veggie oils, but not always.  If you saw the Forged in Fire episode with Burt Foster you saw him do this on quenching.  He quenched, waited a second or three, pulled the blade, watched the flame sputter out (he was actually checking for warps as the flame sputtered out), then dunked it again.

If you're using Parks 50, don't do that.  Parks 50 does not like being set on fire.  Slows it down a bit.

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