Blackwood handles pulling away?

T

Technohedge

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Sep 9, 2018
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I have recently made some kitchen knives from nitro v with african blackwood handles glued on with epoxy and two brass pins through the handles.

Noticed on a couple of them the handle seem to be pulling away from the tang? They were ground flat and then left overnight to cool (didnt seem to be bent when i glued them) and clamped on lightly when glued.

Could water cause them to swell or contract? I try to dry them after use but sometimes they have been left in water for a short time. is this a big no no with these wooden handles?

Also noticed one has started to become rougher almost pitted in texture where some of the darker grain lines are.

they were originally rubbed with a coat of carnuba wax but i read that this wood dose'nt need much finishing other than sanding?
 
Two things that come to mind:
1 the blade may have a lot of flex and the scales may be pulled off by to much flexing.
2 I had wooden scales come loose because I cleaned the front of the scales with a lot of acetone during epoxy.
The wood absorbed the acetone and prefented a good bond.
 
Blackwood will swell and shrink like any other unstabilized wood. A knife that gets washed in water will have handle problems if all you are relying on is two brass pins and glue. Switch to Corby Bolts or a similar type fastener and you will eliminate this problem. I prefer three bolts in all but the shortest kitchen knife handles. Before I switched to Corby bolts, I regularly had fillet knives returned with scales lifting. BTW, it only takes one or two trips through the dishwasher to make a handle lift off the pins.

Another cause of handle warp is in the grinding after the handle is glued up. You can build up significant heat in the wood and it will warp. Take your time, use coarse belts for shaping, use fine belts at reduced speed.

Finally, a brass pin going through a hole in wood isn't really doing much beyond keeping the scales from moving sideways. Even if you buttered the pin and hole with epoxy, there isn't a significant amount of resin to make any strength to keep the scale from lifting off the pin. Add te that that in grinding you heat the pin a LOT and the epoxy bond gets destroyed. Peened pins are stronger but there isn't a lot of grip by a peened pin that has been ground flush on a kitchen knife.
 
Corby bolts are a must on tangs that are thin and can flex. If you use standard pins then it’s a good idea to peen them over a little. I have done straight pins and even hidden pins quite a bit with no problems but the tangs are always thicker in the 1/8”-1/4” range. On the other side of the spectrum Blackwood is very nice stuff and probably one of my favorite handle materials for kitchen knives. I will snap a pic of a kitchen knife my wife designed that I made for here years ago. She uses it on every meal every day. It’s a good testament on comparing natural vs man made materials as it’s got both. The Blackwood has not swelled, split, lifted or otherwise moved at all in all this time and use. She does not put it through the dishwasher. Brb getting picture
 
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