Fixing a stubbornly warped blade ( I read previous posts on the topic)

[pullrich]

Looking for some tips on fixing a blade that warped during HT. I read prior posts that I could find and tried the strategies, but the warp wasnt fixed. Here's the short story:

9" blade, 1/8" thick, ground down from O1. Bevels were filed to leave the edge thick as a dime.
Heated to non-magnetic and then air-cooled, twice. Heated to non-magnetic a third time, then quenched in Canola. Placed in oven at 425f for one hour. Air-cooled, then repeated oven at 425f twice more.

Attempt 1: Sometime after all that I noticed a .5 - 1 cm warp with the main warp being 2-3" from the tip. So, I came here and read posts on the topic. I assembled a jig involving a C-clamp, an old file, and a punch for a shim. I put the blade back in the over at 425 for an hour, took it out and fixed it to the file with the shim under the tip, the C-clamp at the bend, and cranked the clamp down until the warp went in the opposing direction about .5-1cm. Let it cool and disassembled the jib to find the warp same as before.

Attempt 2: As above, except this time I assembled the blade cranked down in jig and left the entire jig in the oven at 425 for an hour. No improvement.

Attempt 3: Heated the warp to cherry red with little propane torch, then fixed blade in jig and let it cool. No apparent improvement.

So there you have it. Thanks for your attention and any tips.

 

[Carl_First_Timer]

Looking for some tips on fixing a blade that warped during HT. I read prior posts that I could find and tried the strategies, but the warp wasnt fixed. Here's the short story:

9" blade, 1/8" thick, ground down from O1. Bevels were filed to leave the edge thick as a dime.
Heated to non-magnetic and then air-cooled, twice. Heated to non-magnetic a third time, then quenched in Canola. Placed in oven at 425f for one hour. Air-cooled, then repeated oven at 425f twice more.

Attempt 1: Sometime after all that I noticed a .5 - 1 cm warp with the main warp being 2-3" from the tip. So, I came here and read posts on the topic. I assembled a jig involving a C-clamp, an old file, and a punch for a shim. I put the blade back in the over at 425 for an hour, took it out and fixed it to the file with the shim under the tip, the C-clamp at the bend, and cranked the clamp down until the warp went in the opposing direction about .5-1cm. Let it cool and disassembled the jib to find the warp same as before.

Attempt 2: As above, except this time I assembled the blade cranked down in jig and left the entire jig in the oven at 425 for an hour. No improvement.

Attempt 3: Heated the warp to cherry red with little propane torch, then fixed blade in jig and let it cool. No apparent improvement.

So there you have it. Thanks for your attention and any tips.

Attempt 2, was almost the way I do it except I put it in, jig and all, for 2 hours and leave it in to cool. It does not work every time. The last knife I did was a kitchen blade and it had a wicked warp in it. It took 4 tempers to get it straight. Mainly because I was working my way towards flat instead of just trying to get to flat in one foul swoop.

Any pictures of the jig?

 

[Salem Straub]

Sometimes the degree of warp requires some serious overbend in your tempering jig. I use washers, if the warp does not come out during the first temper cycle, I add a washer or two as necessary and do it again. Sometimes they can be very stubborn and take several temper cycles. Rick, who first brought this technique to the attention of many including myself, water cools after tempering. I think this may be the reason the method works well for him, I water cool the blade with it still in the jig and I suspect that sometimes this has more effect than the hour at temp did.

Sometimes (and you may as well, now that your tip has been partially annealed) you just have to bite the bullet and straighten hot and normalize again, then re-austenitize and quench again. It's still better than trying to straighten cold and snapping the blade in your 3-point bender.

I've been messing with things like spot tempering heat and cooling to pull the blade around. The Japanese do things like this very effectively in straightening swords. Try things to see if they work, it can be very frustrating working warp or twist out of a nice blade with a bunch of work already into it, but you will develop what works for you and over time your success rate will increase.

Another thought: you didn't mention what you are heating with, but it does not sound like an EZ bake. A gas forge? If you are getting chronic blade warp, try HT'ing with a pipe muffle in the forge. It really helps for even heat.

 

[pullrich]

Thanks for the ideas. I'm going to try a longer bake in the oven, in the jig, with more overbend, and maybe a water cool. I'm encouraged by your comments that it can take a few tries to get it right! I'll try to get a pic up later.

Straub, I use a big fire in my backyard so I should probably take your advice on a pipe muffle.

 

[pullrich]

Here are the pics of one of the earlier jigs. I've switched to sturdier c-clamps but the little one bent the blade just fine.