Corby bolts + epoxy ?

T

Travis_Wright

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Jan 27, 2019
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38
I'm having a terrible time with using epoxy and pins on my knife handles. I keep getting separation between the full tang and the wooden scales after a while. I'm curious to see if anyone has switched to using corby bolts vs. pins to help with this issue or will this even be helped with corbys.
 
All I use is corbys. Never had a problem and everything I've heard or read says that corbys are the solution to that issue.
 
It will help but there are other common issues. On issue I see with pins are that you ha e to clamp them. Too tight and you can press out too much epoxy and you have a glue starved joint that can fail. Good quality, slow cure epoxy is a must in my opinion. Unless you are using mosaic pins or some type of carbon fiber/g10 then I don’t know why anyone wouldn’t use Corby bolts. So, get everything flat, clean with a no residue cleaner, apply good epoxy, and just sung up the Corby bolts. This will last a long long time.
 
Be certain that both your tang and your handle material is absolutely flat. Even if it looks flat to you it may not be. That was my biggest problem when I first started.

I use a small granite surface table to check for flatness. I also will usually sand both the tang and the handle material on the surface plate as a final preparation before assembly. Do a dry fit and check. If everything looks good then use a good epoxy and don't over clamp. When I use Corby bolts I don't even use clamps. I simply tighten the Corby bolts up until I begin to just see epoxy around the edges. If you feel it's necessary you can tighten them up a bit more after the epoxy has set for a bit.
 
As the others have said, Corby bolts are the strongest and most secure handle construction. No gaps, no lift, no failures.

One trick to assure a strong handle construction is to grind out some metal from the center of the tang, leaving a flat perimeter that will seat flush with the handle scales. The epoxy pools in the recess and makes a strong bond. Altrenatively, drill lots of holes through the tang.
 
in my experience, if wood is pulling away, twisting or lifting it was too wet or too dry when the scales were applied and shaped. can you post a photo of the problem ? does it happen when you use micarta ?
 
i use pins but set up like stacy dishing the back of the scale and the tang to make sure good epoxy bond. why i use pins not corbies is if some one ends up with a dishwasher knife and scales pop often times i can save the wood by sanding the pins a hair driving them out then resurface the scale back . epoxy pin and refinish good as new jsut slightly smaller
 
I can try to add something here ... i have done a lot of adhesion work on difficult to bond materials in medical device design...

Agreed with what has been said before (dry stock to avoid warpage - critical; dont squeeze out epoxy - should not really be all that important; flat stock - important but critical for appearance; clean with alcohol or acetone - critical; clamp or keep secure until cured - critical).

I would add the following: flat does NOT mean “smooth”. A roughened surface(s) will absolutely help, and might well end up being THE critical factor in retaining adhesion over time. This, i believe, is especially true when using any plastic or resin containing materials (including stabilized wood), and my guess is also with any highly resinous woods (which of course are the most attractive ones ). So before bonding i would attack those mating surfaces with surprisingly rough sandpaper - like 100 or even 60 grit (a smooth surface is actually really bad for several reasons). Doing this will help retain adhesion over time, and should all but cure the “epoxy squeeze out” problem some have noted (a thinner glue layer should actually be stronger and last longer)

If you would like, i can give a somewhat longer explanation on the “why” of the above, but am not sure if you want that (and i am on my ipad right now ... and my fingers just do not work well with this keypad (or the other way around....)
 
For hidden tang I will use epoxy .For full tang and scale I will use epoxy but I will peen pins . Epoxy do not hold very much on steel and that is fact .Even with rough prepared surface.This tang was ground with angle grinder ...still no sign of epoxy there after separation . When you flex thin blade you will hear sound how scale peel in in front of the first pin....You can try this ...glue some wood /scale/ on steel without pins and try to separate ....you will be surprised how easy it will be to separate them .Pins are what hold all in the place . I found that polyurethane sealant is better for gluing scale on steel if pin was not secured .Wood is another story ...this handle on picture is from two part....glued part is stronger then wood

f2OsvC8.jpg
 
You can certainly make almost any joint fail. Flexure from side is the absolute worse (concentrates stresses on one very small edge .. then the rest of the thing just zips apart)
 
I already popped the scales off the handle so no pics. I think it was a combination of a few things with moisture being the biggest problem but I'm still not convinced that Corbys aren't the way to go in the future. Cleaning up epoxy around clamps is for the birds.
 
Travis_Wright said:
I'm still not convinced that Corbys aren't the way to go in the future.
Click to expand...

I think Corbys are cool (I have several sets and plan to use them) - however, my concern is that if you have a bad joint, the Corbys might keep the think from falling apart ... but they wont stop a fissure from developing between the tang and handle ... which then becomes a grime/dirt haven, ultimately having an impact on the appearance of the knife (also, many argue that getting the dimensions / depth of the holes correct for Corbys is harder than just drilling holes for pins. Plus, for small knives Corbys are just too big.... Better in the long run to understand how to operate without them (corbys)????
 
Crushing H, please do explain more in depth. I find this very interesting.

I usualy rough up a tang with cut off disks in a Foredom, have extra holes and hollow out scales.
 
john april said:
in my experience, if wood is pulling away, twisting or lifting it was too wet or too dry when the scales were applied and shaped. can you post a photo of the problem ? does it happen when you use micarta ?
Click to expand...

Wut John says above... If your wood isn't dry then even if you use mechanical fasteners/peening, it could still pull up and/or split. Even stabilized wood I'm paranoid and like to have it equilibrate a year or two in my shop before using, and I've heard one maker even say that he waits five years after receiving the wood back from the stabilizer! :eek:
 
weo said:
How small a knife are we talking about?
They've got 1/8" corbys.
Click to expand...
Huh, my mistake. Mine are 1/4 inch ... but i bought them so many years ago i guess i forgot (or never knew) they come in smaller sizes. Good to know - thank you
 
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