Strength of modern epoxy

Everyone knows epoxy is strong stuff.
Each joint is different, materials are different, expansion rates are different.
Again- epoxy probably will work.
Mechanical fasteners WILL work-and I'm not talking about pins that are just glued in. I mean real pins, that are peened-or bolts.
With proper mechanical fasteners, epoxy is not even needed.
 
So what did I learn? Well I'm not sure. One one hand I had an very I'm prepared surface that took one heck of a beating. Under normal or even some abuse I don't think this would come apart. The only reason I was able to get the first scale off is because I didn't finish the handle and there was a gap between the 2 pieces of wood. Had I sanded the scales flush there would be no way for this to happen. I do think however that a straight pin is only for decoration and doesn't serve a purpose to shearing forces like I thought it would so that's somewhat concerning. But these were unprepared surfaces that were also unfinished.
I didn't think about the expanding and contracting throughout the years. And what affect it would have. I think even for a "hard use" knife no pins and just epoxy would surfice for a bit. But I WOULD lose some sleep over it.
Would I have gotten the same results if I would have hollowed the tang, drilled extra holes, and drilled shallow holes in the scale and prepped it properly? I don't know. But the fact that the scale broke from the glue joint as cleanly as it did is what concerns me.
This was by no means scientific or be all end all test. But it told be what I wanted to know. Along with advice from everyone here.
Will just epoxy hold together a knife handle and last for years? Absolutely. Is it better to just spend the extra few bucks for corby bolts to ensure your tool will last long after your gone? You darn right. Like busto said. This could be a tool someone uses to save their life one day. It's worth the extra 4 bucks
 
The loctite hysol ea120hp epoxy is one of the structural aerospace grade ones, which is likely why (if I remember right) it came out either on top or tied for the lead in the glue wars of some years back.
I use it for everything, and that said even though I've tried beating it to death and it WILL NOT fail in anything even remotely in the realm of knife use, I still pin everything. Last stag handle I did had 12 sterling silver domed pins, and not a drop of glue. You'd never get that apart.
Both sides of this argument have merit, but remember nothing breaks from being too strong.
 
Geoff Flato said:
The loctite hysol ea120hp epoxy is one of the structural aerospace grade ones, which is likely why (if I remember right) it came out either on top or tied for the lead in the glue wars of some years back.
I use it for everything, and that said even though I've tried beating it to death and it WILL NOT fail in anything even remotely in the realm of knife use, I still pin everything. Last stag handle I did had 12 sterling silver domed pins, and not a drop of glue. You'd never get that apart.
Both sides of this argument have merit, but remember nothing breaks from being too strong.
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Oh yeah I forgot about the glue wars.
I agree, after reading more expierence makers advice and doing testing of my own that's the same conclusion I've come to. The pin just didn't give me that warm and fuzzy.
 
Gotta say if my knife was returned to me in the condition of yours after both scales have been beaten off it would not bother me to tell the client how much an new set was going to cost him. No way I would warranty that.
 
Horsewright said:
The company "off the record" admitted that they did it to sell more epoxy.
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I can see why that company didn't stay in business very long. Just wouldn't work at all. Can you imagine building a boat that's going to fall apart in 2 to 5 yrs?

On your test, if you notice the epoxy joint failed in the majority of the joint, only a very small portion where the wood is still stuck to the metal did the epoxy hold. Also, from the way the pin is bent, it looks like the pin did provide a lot of strength to the handle.
 
This is all very interesting.
Did you coat the pin in epoxy before installing it, or just pound it in?
 
Everybody should know that wood can move and certain ones can move a lot, even stabilized wood moves! Metal doesn't move quite so much, especially not in response to changes in humidity. So what happens when you ship an epoxy only knife from humid Florida to dry Arizona?

I agree with Geoff that nothing breaks from having extra insurance. Everybody has different amounts of tolerance for what they're willing to gamble...
 
Yes the pin was coated with epoxy when it was glued up. It was bent from me hammering it into the stump my anvil sits on then hitting it with a hammer.
G golfer1 there's no way I would warrant that unless it was used in Afghanistan to beat a terrorist. M milkbaby from my understanding gflex has chemicals in there to account for flexing. I also think that's why liners are a good idea.
I'm going to repeat this on a different knife. Except I will properly prep the surfaces and I'm debating if I should use a pin or not. And I won't use a prybar.
ETA I will say that for bolsters I don't really see a reason to use a peened pin. The epoxy is plenty strong to keep the bond.
 
golfer1 said:
Gotta say if my knife was returned to me in the condition of yours after both scales have been beaten off it would not bother me to tell the client how much an new set was going to cost him. No way I would warranty that.
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I understand your point, but I'm on the other side of the fence on this statement. I WANT that story of what took place with details of what it took to break the handle. I would offer a complete replacement knife. I want to continue testing whats left of the Knife STEEL to understand why it didn't snap or bend.
 
valknut said:
I'm going to repeat this on a different knife. Except I will properly prep the surfaces and I'm debating if I should use a pin or not. And I won't use a prybar.
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To really test the epoxy don't use a pin at all. Drill a few thru holes in the tang, then dimple the scales thru the tang holes so the epoxy can form epoxy pins thru the tang. Prep the wood and tang with 36 to 60 grit, clean really good with denatured alcohol. After the epoxy has cured fully, do a quick grind to pull the wood scales down to fit tang to form an actual handle. Doesn't have to be smooth at all, just rough grind.

Now, try to remove the scales from the metal tang at room temperature. I fully expect you'll totally destroy the wood removing from tang...... you did say you're using gflex? Doesn't matter, as long as it's a good epoxy, gflex, bladebond, etc.

That's how I put scales on knives, except I also use corby screws in addition.

Ken >
 
jdm61 said:
The comments about epoxy having issues with metal are interesting considering that epoxy has been used to bond metal in the aircraft and automotive industry for perhaps 50 years. ;)
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And that is true :) Here we are talk about joint wood and steel with epoxy .So , what is your opinion or experience with this ? Which hold better epoxy wood /will soak inside epoxy/ or steel with light film epoxy on surface ? ALWAYS when I separate wooden handle from tang ALMOST all epoxy is on wood , why ?
 
Natlek said:
ALWAYS when I separate wooden handle from tang ALMOST all epoxy is on wood , why ?
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Because the epoxy forms a MUCH better bond with the wood than with the metal. Epoxy isn't as strong an adhesive, but hold more due to the mechanical bond. that's why the metal needs to be "roughed" up so there are more places for the epoxy to form the mechanical bond to. With the wood there is a tiny bit soaking into the wood so gets a MUCH better bond.
 
John Blazy said:
I've never made a knife with wood scales, but I was an adhesives / coatings chemist, and my superhero power is gluing to dissimilar materials so here is my 2 cents (agreeing with nearly all the comments so far). Epoxy is awesome when used correctly, especially more elastic ones like G Flex, because the wood will move tangentially when the steel will not, and this is important for longevity of the joint (why you don't want to over clamp the joint). It will likely hold for a long time, but its the constant months of expansion / contraction due to thermal and moisture forces that will cause it to eventually fail, even with the ingenious ideas of multiple holes bonding though, etc because once loose, then the epoxy "pins" will break.
My favorite adhesive for wood to steel is not epoxy, though. By far superior is simple PL Premium polyurethane construction adhesive because it stays more elastic than epoxy, soaks into wood like epoxy, yet has insane bond to steel. I have never seen joint failure on high torque loads using PL for wood to steel. Its similar to Gorilla glue, as many know, but has higher cohesion due to less foaming, and is cheaper (7 bucks for 10oz tube - goes in a caulk gun). I made half my boat with it (other half epoxy).

The trick with any adhesive (particularly epoxies and urethanes) is to heat the wood prior to application - it off gasses air and moisture, then the heat lowers the viscosity allowing deeper soak in, then as the wood cools it literally sucks adhesive deeper into its pores as it returns to ambient pressure. Then the heat kicks off the epoxy faster. All around underutilized great tip if you have a heat gun.
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What is your opinion of CA. I pin each section of my two piece handles and set the pins with epoxy. But I use CA as the adhesive for liners spacers and scales. The Smith CA tech guys swear by their product for long term adhesion. Last point, I make largely kitchen knives.
 
If anyone goes to the trouble of putting pins in a knife handle, they should be peened, not glued in.
It's a very simple matter to surface peen them. That way, they will actually hold the scales on.
 
Howard1 said:
What is your opinion of CA. I pin each section of my two piece handles and set the pins with epoxy. But I use CA as the adhesive for liners spacers and scales. The Smith CA tech guys swear by their product for long term adhesion. Last point, I make largely kitchen knives.
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My opinion of CA isn't any better than anyone else's because technically it shouldn't perform as well as it does, being a high crosslink acrylate, which is the basis for the UV cured acrylates I worked with when I was a UV chemist (which often failed adhesion due to shrinkage). High-crosslink usually equates to shrinkage, which pulls away from the substrate, but thats where CA is magic. CA has such high ADhesion that it counters any loss of COhesion from crosslink shrinkage.

So, put simply, I love it, and am amazed how the fretboard inlay community loves it even for gap filling after inlay, even though I prefer epoxy. Forgot to mention also, that I also prefer clear adhesives, and that is downfall of PL Polyurethane - its not crystal clear. But for non-aesthetic joints its cheap and highly effective as a one part adhesive for making shop jigs, fixtures, and general construction for gluing dissimilar materials. I buy it by the case.
 
John Blazy said:
My opinion of CA isn't any better than anyone else's because technically it shouldn't perform as well as it does, being a high crosslink acrylate, which is the basis for the UV cured acrylates I worked with when I was a UV chemist (which often failed adhesion due to shrinkage). High-crosslink usually equates to shrinkage, which pulls away from the substrate, but thats where CA is magic. CA has such high ADhesion that it counters any loss of COhesion from crosslink shrinkage.

So, put simply, I love it, and am amazed how the fretboard inlay community loves it even for gap filling after inlay, even though I prefer epoxy. Forgot to mention also, that I also prefer clear adhesives, and that is downfall of PL Polyurethane - its not crystal clear. But for non-aesthetic joints its cheap and highly effective as a one part adhesive for making shop jigs, fixtures, and general construction for gluing dissimilar materials. I buy it by the case.
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Thank you for the informed and rapid response. It cuts my assembly time to 1/4. I love working with it.
 
Bill DeShivs said:
If anyone goes to the trouble of putting pins in a knife handle, they should be peened, not glued in.
It's a very simple matter to surface peen them. That way, they will actually hold the scales on.
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I use mosaic pins mostly. I have tried peening them with horrific result.
 
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