I apologize if this is not in the right spot. I have a very fine sword that I had custom made on budget. As a result it had a few rough spots etc which is fine with me. One thing i noticed is that it has always had a bit of a warp in its straightness. Its very minimal and hard to spot unless your are looking for it. Now that I am in a better finacial situation I would like to get it refurbished, get a better polish on it and have the samll warp straightened out. So my question is this. Will the re-heat treating of the blade cause its length,width, or thickness to change? Its fine if it looses a little meat when being polished back up but would there be any significant change overall?

Does the warping affect the performance or is it merely an aesthetic flaw? Can it be rectified with cold work?

Re-heat treating the blade is as likely to reintroduce some warping as to remedy it.

If you decide to have any heat treatment done on your blade, at least contact the original manufacturer and ask what alloy he used. You cannot do a proper heat treatment without knowing the alloy.

Just to clarify its a type XIIIa made of marquenched 5160 with a take down assembly. I wouldnt say the warp effects its performance even though it is toward the end of the blades center of percussion. Mainly its more of a vanity on my part in wanting it to be as perfect as possible.

I was able to fix a set in an A&A blade--thanks to Craig's advice--by resting the blade between two blocks of wood with the set centered and standing on a third block positioned directly over the set. Of course, that probably won't work if your warp/set is in the same plane as the edge.

Is the sword sharp? If not, do you use it regularly? If it's a blunt, the warp might have come from usage. My own sword is warped quite a bit, since it has a ring on only one side and it gets most of the hits on one side of the blade. I'm not the only one either, so this seems to be a fairly normal occurence.

Dunno if it helps, so best of luck and regards!

Yeah its wayyyyy sharp and its my primary sword for everything from cuttting to florysh drills. the warp has been there since i got it though and is a result of warping from being tempered not from use, thanks for the input though.

Many historical swords are warped because of the heat treating. Except it as something historically accurate. ;)

I am a bit iffy about cold straightening a blade. It will, after all, stress it. I have handled and worked on many old swords (as in over 400 years old), and I have never seen one that was straight by modern standards. It is true, though, that if you cut something with a bit of resistance to it (like tameshigiri with green bamboo down the center) not quite true, it will bend your blade a bit, so that's always a possible part of the crookedness.

Depending on sword hardness it may be possible to cold-straighten it. Our blunts do sometimes get bent so that it starts affecting usability and we do have to straighten them. Of course doing it repeatedly will one day break the blade, but doing it once is not a big problem. Though if it is possible I would not straighten the blade. I have left a messer that I finished several months ago warped after heat treatment because it did not affect usability.

Now if you have sabering or "propeller" type of warp then annealing, straightening, normalizing and quenching again is the only thing that will help. Though I am afraid that in this case it would be easier to make a new blade from scratch.

One hint. If the blade got warped during heat treatment you could temper it ever so slightly (or skip this phase depending on steel hardness after the quench), tie the blade to a straight piece of metal and then temper to the final hardness. I have never done this myself, but one guy once heat treated steel blanks for me that way. The blanks came out perfectly straight. Straightening effect will probably depend on the final hardness. If you temper the blade to 55 HRC it may stay warped, bu if you temper it to 45 HRC it is more likely to become straight. This is my wild guess though.

EDIT: I just noticed that Aleksei gives similar advice above. I think he's correct that you'll probably have to temper at least as soft as the initial tempering to get a strong straightening effect, though multiple tries may work just as well.


You don't necessarily need to completely redo the heat-treatment to fix certain types of warpage, in certain types of blades. If the warp is far enough away from the handle, you may even be able to get away with not having to take the hilt apart. One trick that I've used to good effect is this:

-Find a steel bar at least as thick as the blade (ideally 1.25+ times thicker), and at least as long as the warped section of the blade.
-Get several metal c-clamps and clamp the blade flat against the bar.
-Put the clamped blade into the oven at ~450F for an hour.
-Let cool and remove clamps and check straightness.

Obviously, this is more difficult with a diamond sectioned blade. The flatter the blade section, the better this works.

That's it. It may take several times in the oven, but each time, your blade will come out a bit more straight.

You will have to re-finish the blade, though, as there will be some slight oxide coloration from the time at temperature.

This should not adversely affect the hardness of the blade, and if anything, might impart some added toughness (depending on how the blade was initially heat-treated).

Dustin

There have been some excellent suggestions so far and this technique is more or less a variation on Aleksei and Dustin's ideas.

One technique I have used for years for straightening blades is to clamp it in a well anchored machinist or leg vise with the point of the bend protruding. Using a propane or oxy-acetylene torch to slowly and gently heat the area of the bend until it changes to a metallic blue in the middle with a dark straw color along the edges, remove the heat and then gently flex the blade against the bend. Naturally be sure to use all appropriate safety equipment and precautions. After straightening I typically quench the blade in my trough of peanut oil. though you could also let it air cool.
If done carefully this will correct minor warpage without adversely affecting the integrity of the blade.
As I said I have used this trick for years and then thoroughly tested the blades. There was no compromise in structural integrity, edge-holding ability, or toughness.
I must point out that this technique requires patience, careful attention, and optimally, experience. If this is a prized sword and you are inexperienced or nervous about it, I would recommend against attempting to straighten the blade in this manner.
That's my two cents for whatever its worth.

Ok, I will toss in some more info on straightening warped swords. If a sword is not "saber" or "propeller" warped it can be straightened using the following technique.

One needs a hammer with a sharp but somewhat rounded edge. More or less like a blunted chisel. The blade is placed on an anvil/rail/whatever so that "inside" of the bend faces up (i.e. the bent middle part of the blade rests on the anvil while ends are raised). Now take the aforementioned hammer and using light but frequent blows start hammering the warp area. The hammer edge should dig into the blade just a little, "spreading" the steel on the surface. As the surface elongates the blade will become straight. After the blade has been straightened this way the area with hammer marks should be tempered and then hammer marks can be ground/polished off.

The guy who described this technique said that he used it to straighten thin shasqua blades and that around 200C is enough temperature for tempering. I tried this technique only once to straighten my messer that I mentioned earlier in this thread. The warped area was relatively thick (around 4mm) and I tempered it to around 320C after straightening. I am quite satisfied with the result. The messer is around 43-45 HRC. This technique will probably work best on thinner blades. And of course the harder the blade the more difficult it is to straighten. I also think that this technique can be used to straighten minor "propeller" twist for some blade cross sections.

If I made a sword from 5160 and it had a warp after heat treat, grinding, or any other situation I would heat it up to no more then 435F and apply pressure against the warp and 9.8 times out of 10 it will come right out. The material that I work with is harder to get warps out and unless something is really warped out of heat treat I can get the warps out and the edge straight.

There are many ways to heat the blade and apply the needed pressure. How this is done is up to your knowledge, comfort level, experience, and tooling that you have on hand.

As echoed in previous posts, reheat treating the blade is not needed and depending on the cross section of your sword can ruin a perfectly good blade.

Best of luck in your efforts!

Jean is correct, the ideal temp to heat the blade to should be no more then the temp that the blade has been tempered to. Tempering is all about time at temperature, if the blade was tempered for three hours, an extra 10 minutes at temp for straightening will not have a significant impact as far as our application is concerned. At this temperature the steel is stressed from deformation less, as well as the deformation actually having a effect on the steel. After all we are dealing with a steel that is heat treated to be a spring and to come back true.