Problem with longer knives

Tony Manifold

Tony Manifold

Well-Known Member
I have started 2, 12 inch kitchen knives and I am having the same problem with both. I seem to be bending them some how. Is this common? Is there something I might be doing that is causing it? So far it is like 1/16 out of true but it bugs me and you will never get it back completely straight once it bends.
Tips, solutions, insults to my manhood?
 
Tony Manifold said:
I have started 2, 12 inch kitchen knives and I am having the same problem with both. I seem to be bending them some how. Is this common? Is there something I might be doing that is causing it? So far it is like 1/16 out of true but it bugs me and you will never get it back completely straight once it bends.
Tips, solutions, insults to my manhood?
Click to expand...

Tony when I was still grinding kitchen knives I would clamp a piece of angle aluminum to my blade blank (post heat treat) to help with the flexing to to give me better grip and control. Using a 1.5 piece of angle, I'd trim down one part to about 3/4" and leave the other part untouched... it helped me a bunch. Just make sure to clamp your blank so that you can see edge as you grind.
 
Possible tip. Annealed steel - especially on long thin knives - bends easily and yes, it's difficult to straighten. If you were to just profile and drill the blanks - maybe take just a bit off the edge to save belt shear - and then heat treat them and grind hard, the hard steel, when flexed should return to true. (within reason) It means attention to keeping cool and yes, it will use more belts, but is often the answer to bent blade problems. IIRC, Laurence often does this, so maybe he can elaborate.

Rob!
 
You've encountered two things that create nightmares for many makers.....long, combined with thin. Personally, on anything 1/8" of less thick, I only profile, then heat treat....and do all my grinding AFTER heat treating. This doesn't solve all the problems, but lessens them to a degree. If a blade is less then .100" thick, especially in anything more then 4-5", I place it on a "backer board" (something to support it when grinding).

There's no "magic formula" for overcoming the issues that "long" and "thin" bring to the table......honestly, it's one of those areas of knifemaking that require LOTS of time and experience.
 
I have found that sometimes I will get a slight bend in my blade due to the C-clamp I use to clamp it down while filing/sanding. I've since started using a piece of wood to help distribute the pressure of the clamps better. If you accidentally dropped an annealed blade...it will be bent. Also, uneven grinding will cause slight warpage. Depending on how you clamp your knives to your work station...that can cause unwanted and unnoticed warping. Sometimes even grinding post heat treat you might get a slight bend somehow or another, like Mr Caffrey said....lessens it to a degree. It's never been a problem tho, because any warps can be taken out very easily using 3 point clamping during tempering, or even by hand (gloved) after quench, before the steel has reached room temp.
 
I do a lot of long thin blades, and it is important to keep the steel cool with frequent dunking or misting, and secondly using an even number of passes on each side. I do most kitchen knives with asymmetrical grinds, and if I get a noticeable pull to one side, I stick it in the kiln flat on its side for an hour at 1200f rather than trying to bend it back by hand. It saves time in the long run.
 
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