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SpikeC
03-21-2011, 08:25 PM
I have an oven that will allow me to heat treat something up to about 10.5 inches long. I am wondering how long the tang needs to be to be secure. Or in other words, what is the minimum tag to blade ratio for a kitchen knife. I realize that sending out is an option, butt I am an inveterate DIYer!

StephanFowler
03-21-2011, 08:29 PM
I would want at least 2.5" of handle area,

you could braze a tang extension on after the fact.

would laying the piece diagonally get you any extra length

RRLOVER
03-21-2011, 08:53 PM
You could install a pin to help sturdy a short hidden tang.

SpikeC
03-21-2011, 08:54 PM
That is diagonally. I could get a bit more tipping it up as well, but I think things get a little dicey there. Still, a 2.5 inch tang would allow an 8 inch blade, or 210 mm.
If I do a wa handle brazing on extra length won't show so that is something to consider.

SpikeC
03-21-2011, 08:55 PM
I have considered a pin as well, and I like that for both security and esthetics.

David Broadwell
03-21-2011, 09:30 PM
It sounds like you're looking for a ratio from an engineering standpoint. A kitchen knife is not a bridge! :-) I believe that a hidden tang knife needs that tang to be as long as possible. If I'm making a 3" bladed hunter with a 4 1/2" handle, I like the tang to be close to 4" inside the handle. Same if the blade is a 9" fighter.

I believe that if you make the tang 2"-2.5" as Stephan suggested, then attach an extension you'd be fine. I usually hard solder an extension on with a dovetail joint, but it can be brazed, or before heat treatment welded.

A cross pin through the tang, whether through the original blade material tang or the extension, is used as a mechanical reinforcement to your adhesive. The pin won't take the place of the tang or make up for a short tang. If you use a good epoxy like System 3, West System, or Acra-glas you probably wouldn't really need a cross pin on a kitchen knife unless you just like the look.

Here's the problem with a short tang. If over time your wood handle moves around and cracks, or if it had a natural defect to begin with, you're handle is going to come apart probably at the end of the tang. There was a rather big name maker years ago who did just that. He was saving money by not using so much 440c. When some people actually used his knives to clean game the handle broke right at the end of the tang. So put on an extension and give your handle some reinforcement.

David

SpikeC
03-21-2011, 10:05 PM
Thanks David! I am constantly amazed at the willingness of knife makers to share information. I think that as I move to longer blades I will probably start to send out for heat treat, as much as I would rather do it myself. For now, the wood that I have has been seasoning here for years, and I am using system 3 T-88 epoxy.

SpikeC
03-23-2011, 04:17 PM
One more thought- how about doing a lap joint near the end of the blade and riveting the tang? My experience with making infill planes shows that done right the rivet virtually disappears. That would allow a considerably longer blade.

StephanFowler
03-23-2011, 04:19 PM
One more thought- how about doing a lap joint near the end of the blade and riveting the tang? My experience with making infill planes shows that done right the rivet virtually disappears. That would allow a considerably longer blade.

I guess you could. personally I wouldn't trust it.