first knife slightly bent

C

chemistguy

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May 28, 2013
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the knife is bent slightly (but noticeably if you look at it closely) at the last inch of the blade, and also where the blade meets the tang. should I just finish the knife? It will still be functional.

I've heard you might be able to straighten a blade by whacking it in a vise right after heating it to temper temperature... should I try this or no?
 
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Best way is to clamp it to a piece of bar stock, a little past straight, then run another temper cycle. Second best way is to apply a little heat with a torch, then try and bend it. Least best way involves whacking or trying to bend it cold.
 
What Jason said. The three point clamp method during tempering has made any bow I have had in a blade dead straight, usually in one try. Best trick I know, and couldn't recommend it enough.
 
so I bend a piece of steel stock to be slightly more bent than my knife, and then put two c-clamps on (one on one side of the bend and one at the middle of the bend), then heat the whole thing in the oven to 400 ºF, then using welding gloves, put on a 3rd c clamp on the other side of the bend and crank down on it until it is just slightly past straight, and then run it at 400 ºF for an hour?

also after tempering am I supposed to quench in water or air cool? does it matter?
 
I take a angle iron piece, and using washers and clamps, clamp it just past where you want it. Through it in the oven and and check it an hour later, some times I'll have to redo it.

Water quench is a little better, but most wouldn't notice the difference, including me!
 
Cody does what I do, pretty much. I use a piece of thick steel (1/4") that is about the length of the knife. Using C clamps, clamp one end of the steel onto the end of the tang tight, clamp the other C clamp near the blade tip. The bar of steel should be on the right side, if the blade is bent to the left. Place a small nail right at the apex of your bow/bend, and then tighten the C clamp to where the bow is bent about the same amount, only in the opposite direction. Sight down the blade and make sure that you didn't ADD any bends by your C clamps, make sure the only bend is the bow being corrected in the opposite direction. You may need to scoot one or both C clamps up/down the blade to get things just right. It is nice to have a wife or buddy nearby to lend a third or fourth hand, as you're trying to fiddle with 5 things at once. Blade, C clamp, C clamp, steel bar, nail. Concerning the water quench, I think the idea behind that is to try and "set" the correction, but I'm apprehensive if it does anything. I just turn the oven off and let the whole thing cool to room temp before checking. Usually, just one time is all it takes, but you can do it as many times as you like. 400F is about the minimum temp for this process. One thing I have found out....if you get the blade nice and straight, but realize that it' still too hard and needs a higher temper, the bow will come back if you temper the knife at a higher temp than your last run, and you'll need to straighten it again.
 
So I tried what you guys suggested... (two c-clamps and a nail, and throw it in the oven)

But it cracked and broke right where the nail was as soon as I clamped it to where it needed to go. :mad:
This is NOT supposed to happen to a knife. A knife is supposed to flex like a spring (until a certain point of course), not shatter!
And, note that the bends I was trying to fix were relatively minor.

This is 1084 and I had already tempered twice at 400ºC. Why did it break? (and what is that brown/black crap at the spine in the crack? Did it already have a microscopic crack that let air and moisture in? The crack might have developed when I tried quenching it in water at one point, when I was having trouble making it harden properly... )

At this point, on my second failed attempt at a knife, I'm about ready to JB weld the MFer back together....

Photo_on_6_17_14_at_9_42_PM.jpg


Photo_on_6_17_14_at_9_46_PM.jpg
 
Id say that if it was already cracked at that dark spot ,then there was nothing you could do to prevent it from breaking there, , well almost nothing , you would have had to anneal it then weld it then heat treat it and temper it again. Even then you could never be sure it would not break there.
 
Yes, 1084 and water do not work well together. Use canola oil heated to 120 to 130 degrees for your quench.
Good luck.
Brion
 
chemistguy said:
This is 1084 and I had already tempered twice at 400ºC. Why did it break? (and what is that brown/black crap at the spine in the crack? Did it already have a microscopic crack that let air and moisture in? The crack might have developed when I tried quenching it in water at one point, when I was having trouble making it harden properly...
Click to expand...

I'm hoping you meant 400 degrees Fahrenheit...

Also, your blade was broken before you clamped it. The dark area is definitely evidence of a crack existing previously.

Why were you having trouble getting it to harden properly, do you think? How were you testing hardness, and what was your heat treating regimen?
 
On the plus side, the grain looks nice and fine. It is a bit hard to tell cause the pics are a little fuzzy, but if the grain growth was there, it would look like 180 grit sandpaper. You should shoot for 1000 grit sandpaper for grain. It is a learning experience. I have been making knives for about 10 years give or take, and I just broke one the other day. It cracked in the quench and I didn't notice it until I started hand sanding. It happens. Hang it on your wall, and make another.
 
Matthew Gregory said:
I'm hoping you meant 400 degrees Fahrenheit...

Also, your blade was broken before you clamped it. The dark area is definitely evidence of a crack existing previously.

Why were you having trouble getting it to harden properly, do you think? How were you testing hardness, and what was your heat treating regimen?
Click to expand...

yeah I meant 400 ºF

I was trying to judge 1474 °F by melting a bit of salt on the blade. 1st attempted quench (~100 ºF oil) and 2nd attempted quench (~70 ºF water) both failed to properly harden the blade. I think my salt was contaminated with water from sitting, so I melted some in a steel can bottom and then smashed up the cake of solidified salt. When I tested it again, it melted on metal that was at a bright red / starting to get orange instead of the previous result which was at a dull red.

I was judging hardness a) with a file, and b) by actually attempting to sharpen the edge of the blade

not sure how fine the grain really is. I can definitely see something that looks like grain, although it is pretty tiny.
 
Unless you removed the decarbed steel by grinding down a bit before testing, it's possible you didn't have any issues with hardness. I can't speak for your temperature gauge methods, as I've never done that, but I'd suggest doing some browsing here on the forums. Heat treating steels like this properly has been covered ad nauseum.

I agree with Matt - chalk it up to experience, and begin anew. I once asked Jim Siska how long it takes to become proficient at knifemaking, and he said by the time you fill a 55 gallon drum with scrap - twice - you should have it mastered. : )
 
Looks to me like your crack developed right at the point of the gut hook. Not sure how significant that is, but I don't believe in coincidences in things like this. How important was the gut hook to your intended usage for the knife?
 
.....The crack might have developed when I tried quenching it in water at one point, when I was having trouble making it harden properly........


DING! DING! DING! we have a winner.
Obviously ( well, now it is obvious :) ), if you try a water quench on a blade like that you will have a great chance of ruining it. If the HT wasn't going right, a harsher quench won't fix it.
To get the HT right, figure out why it wasn't hardening. Temperature/heating method is the number one reason, not quenchant.
 
tryppyr said:
Looks to me like your crack developed right at the point of the gut hook. Not sure how significant that is, but I don't believe in coincidences in things like this. How important was the gut hook to your intended usage for the knife?
Click to expand...

check the pics again... there was no gut hook. The overall shape is similar to an ESEE Izula
 
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