Eooxy Failure-Help Please

A

amoretti

Joined
Apr 26, 2009
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Finished epoxying the handle on a knife a few days ago. Dropped the knife by accident this evening and horrors of horrors the handle slab popped right off the tang!

The tang of the knife was roughened with a diamond grinder, and wiped with acetone just prior to gluing. The ironwood handle had a vulcanized liner glued to it. It was also cleaned with acetone prior to gluing. I used Devcon 30 min. two part epoxy that was perhaps 4 years old. Epoxy was mixed by weight.

The joint failed between the liner and the tang-perfect imprint of the tang in the glue with grinding marks on the tang perfectly replicated in the dried epoxy on the handle.

Could the epoxy be too old? Is there a better glue to use in this application

Any thoughts on what went wrong or how to prevent this in the future. The handle was not pinned yet and perhaps the pins would have prevented the problem but very disconcerting all the same. Makes me worry about other knifes I have done and how they might be holding up in use.

Thanks in advance for any guidance.

John
 
There have been some folks poo-pooing Devcon lately. There was a very extensive thread not too long ago discussing test results of a large number of epoxies and glues. I'll see if I can dig it up. I use a slow set 2 part epoxy that is similar to the devcon, but has better qualities and is sold by a number of different suppliers. The weakness of epoxy really is shearing. If your drop hit the handle material in such a manner to create a shearing force between the handle and tang, that would make sense. Kind of like how a magnet can hold 100 pounds in a straight lift, but if you shear it, it will move. Probably a bad simile, but that's how my head sees it.

There really should be pins in almost any handle of full tang construction to create maximum toughness. Better yet, how about corby bolts to give the look of pins while having the security of a bolted construction. Combine that with epoxy, and it will last.

--nathan
 
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Epoxy prevents very little shear force, that's what the pins are for. the main reason for epoxy is more about sealing the scales from moisture, etc. Epoxy's strength is rated pulling apart, not shearing as you experienced.
 
4-year-old epoxy raises some flags. It's not scotch, bud, use it up. ;)

Did you let the acetone dry completely? Did you wipe off the acetone residue with alcohol? I'm ok with using acetone on steel, the light residue is easily cleaned off; but I wonder if it's a good idea on wood. Just thinkin' out loud... :o
 
silver_pilate said:
There really should be pins in almost any handle of full tang construction to create maximum toughness.
Click to expand...

Absolutely. Same goes for hidden tangs, there's got to be a last one mechanical fastener (pin, rivet, peened tang, tang nut, etc.) in addition to any adhesive before the knife is done.

I'm still curious about the shelf life of typical epoxies. Even without pins, it doesn't seem like those should have popped off that easily.
 
There has been an ongoing discussion about epoxies over on my forum, but I will post a couple of what I consider VERY important points here....

Most commercially available two part epoxies (the types you will find in most dept. or hardware stores), namely Devcon, are designed/created with some notable drawbacks. First they are engineered with a shelf life on only 6 months from the date of manufacture. Secondly, they are chemically engineered to start breaking down is approx. 5 years. (this time can be shorter or longer depending on exposure to UV) I acquired this knowledge directly from chemical engineers who had worked for the company.

If you look at it from the companies perspective, it makes good business sense.....they want you to buy their product...and more than once...in the words of the individual I spoke with.... "We (the company) can't stay in business if we only sell our product to a person one time."

The problem that these limitationx CAN cause for knifemakers.. is that we strive to make a "durable" product, and most would not consider a knife to be durable if the handles either loosened up, or came off in 5 or so years.

If you used standard two part epoxy that had been around for 4 years, chances are very good that you were the victim of its shelf life. It may have mixed as if nothing was amiss, but chemically it simply did not work.

My answer to this situation is to always use some like Acraglass....which has a 10 year shelf life, and a 50 year hold life. Some folks use and like West Systems too, which has a slightly shorter term than Acraglass for both shelf and hold life. Neither product will last "forever", but either a far sight better than 6 months and 5 years. A lot of folks simply either don't know about the common two parts epoxy drawbacks, or never think about it until something goes wrong. If your a serious knifemaker, my opinion is that your reputation is far too important to take chances using a low quality epoxy.
 
Well stated Ed. I'll admint I'm still a novice, but I didn't really get in to knifemaking seriously until I found bladeforums and got advise from you and the myriad other brilliant minds on this site. I started right off the bat using Brownells "acra" products when it came to putting my name on it. "Acra-weld" is my favorite so far, although I have been experimenting with the gorilla super glue a bit... Before I found bladeforums and was still making kits, I knocked a handle that I fused with a devcon product with my ball-pein and it sheared in a few taps. After reading a number of opinions (everyone's got one, right?) I decided to try Acra-20... not long after, Brownell's introduced Acra-Weld. I'm very satisfied with the results... All too often one hears about something expensive failing due to a fifty cent washer or something. While I'm far from wealthy(and no desire to be so), it still seems to reason that if someone would put the time and effort into making a knife, then there is no good reason to skimp on ANYTHING that can make the knife better.
 
I need to check into the Acra products. I remember hearing nothing but good things about them from Ed as well as others including in the above links.

--nathan
 
I've had nothing but good experiences w/ the Devcon that I've used.

Not sure, but I dont use the quick setting time as you mentioned..30 Min? I think.

What I use is the 2 ton, two part epoxy and usually let that set up overnight or at least 6-8 hrs before I work on it. I havent had any problems yet, but then again..I havent been making knives that long so only time will tell.

I do like the sound of the Acra products though, may have to give them a try.
 
Ed Caffrey said:
There has been an ongoing discussion about epoxies over on my forum, but I will post a couple of what I consider VERY important points here....

Most commercially available two part epoxies (the types you will find in most dept. or hardware stores), namely Devcon, are designed/created with some notable drawbacks. First they are engineered with a shelf life on only 6 months from the date of manufacture. Secondly, they are chemically engineered to start breaking down is approx. 5 years. (this time can be shorter or longer depending on exposure to UV) I acquired this knowledge directly from chemical engineers who had worked for the company.

If you look at it from the companies perspective, it makes good business sense.....they want you to buy their product...and more than once...in the words of the individual I spoke with.... "We (the company) can't stay in business if we only sell our product to a person one time."

The problem that these limitationx CAN cause for knifemakers.. is that we strive to make a "durable" product, and most would not consider a knife to be durable if the handles either loosened up, or came off in 5 or so years.

If you used standard two part epoxy that had been around for 4 years, chances are very good that you were the victim of its shelf life. It may have mixed as if nothing was amiss, but chemically it simply did not work.

My answer to this situation is to always use some like Acraglass....which has a 10 year shelf life, and a 50 year hold life. Some folks use and like West Systems too, which has a slightly shorter term than Acraglass for both shelf and hold life. Neither product will last "forever", but either a far sight better than 6 months and 5 years. A lot of folks simply either don't know about the common two parts epoxy drawbacks, or never think about it until something goes wrong. If your a serious knifemaker, my opinion is that your reputation is far too important to take chances using a low quality epoxy.
Click to expand...
I have never used the Acraglass products, but I love West System. West is designed to hold up in an environment that most of our knives will ever see. Howe many times do you ask the wood on your knife handle to do 30+ knots through 6 foot seas year in and year out?. Thats what custom cold molded wood fishing boats do and those guys use West exclusively. :D Another good thing is that, if you feel the need, you can buy a West product that is specifically made for whatever you are doing.
 
Brownell's AcraGlass is the one that has been around for decades. You can read about it on the Brownell's site. It is the epoxy that won the "anything other than metal to metal" part of "The Glue Wars".

Mike
 
All this discussion has been on the difference between epoxies. One other major issue with gluing up slab handles is joint starvation.

Over clamping makes an invisible joint, but the word invisible also says there is no resin there. If the clamping is so tight that it squeezes out virtually all the epoxy, then the joint will pop apart with the least side pressure.

As said the need for pins is a must. Bolts, like Corby bolts, apply both the pressure for glue clamping and the strength for lateral shearing.

Grinding a slight hollow in the tang and scale will make a reservoir of epoxy that will prevent joint starvation.Drilling the handle like swiss cheese does a similar function, making "epoxy rivets".

Selection of a good resin is also important. Structural resins, like T-88 and Acra Glass, will have much more strength than some others. Stay away from the fast resins if possible. Use epoxies within a year . Old epoxy may not cure right. Mix them with a scale if you want to make sure the ratio is really exact.

Another trick is to make a mechanical spacer as part of the joint.Some makers have used a piece of 4 oz. polyester or fiberglass. Used with a West System epoxy it makes a super strong joint.

Stacy
 
Ed: That is very interesting about the "designed obsolescence" of certain brands.

This makes me wonder about the cost differential between using certain "things" over other "things"

For instance, I recently began using corby bolts in the assembly of my knife handles. I think they are a great idea. In the overall scheme, spending the few extra bucks will make the difference between making something that has the potential to turn to junk in a few years, or one that should work and continue to work through your lifetime and our childrens' lifetime. Using the corbys made me think that the epoxy in my mind (for this application) was downgraded from mechanical bonding agent to water sealant.

It would be interesting to do a cost study between what we might consider standard and convenient items and specially ordered items. (ie epoxy and brass pinstock from the hardware store and a better epoxy and fasteners)

I am guessing that for less than $10 we will see a significant difference in the expected lifespan of the tools we make.
 
fod said:
I am guessing that for less than $10 we will see a significant difference in the expected lifespan of the tools we make.
Click to expand...

I suspect you're right. I've certainly found that to be the case in almost every way. From tools to belts to steel. 90% or more of the time, quality really does pay for itself.

Being that we work on such a small scale, we can (hopefully) absorb a 20% increase in parts cost to upgrade to materials that may be 40% better, and command a higher price... (yanked those numbers out of the air, obviously, but you see the point.)

Hmm I'm reading a bit about AcraGlas gel... how do you guys feel about adding atomized metals to it for our applications?
 
I always pin my knife handle scales. The pins provide two purposes, one is to provide a strong mechanical joint to hold the handle together. Secondly pins just look good. The epoxy itself, while it does provide some strength, the real purpose it to be a gap filler and to prevent moisture from getting in between the scales.
 
AcraGlass is some pretty good stuff. As far as shelf life, I got this off of Brownell's site:

Storage - Store in a cool place (68°-72° F.). Shelf life of unmixed ACRAGLAS
components is Fifteen to Twenty years.
Vinegar - Great for cleaning up sticky ACRAGLAS

Brownells also recommends using Acraglass for gluing rifle barrel liners in place for barrels that have been shot out and lined as opposed to soldering. That says a lot about their confidence in their product.

Brian
 
Bufford said:
I always pin my knife handle scales. The pins provide two purposes, one is to provide a strong mechanical joint to hold the handle together. Secondly pins just look good. The epoxy itself, while it does provide some strength, the real purpose it to be a gap filler and to prevent moisture from getting in between the scales.
Click to expand...

Yeah, I agree wholeheartedly. But I still want the best epoxy I can get.

As a side note, anyone got a source for smaller diameter corby-style bolts? I like the principle a lot, but prefer the look of pins <.25".
 
Well it has all been said pretty much but can't help but throw in my 2 cents!
My opinion would be that the epoxy was too old.
Pins would have helped but I am not sure exactly how much in the scenario you had the failure happen under.
Not sure with out going back and re reading but like someone else mentioned I always drill thru holes in a blade handle and match those holes, to drilled pockets in the handle material. I figure that is like having an inertior pin in the knife. Often if I the situation allows for it, I will drill the pin hole through at the correct size, say (1/16") and before assembly I will drill the enteior of the handle slab where the pin goes through an 1/8' deep x 1/8" diameter. This creates a pocket for the epoxy to grab onto the pin itself. I often rough the part of the pin that will end up in this pocket allowing the epoxy the chance to grab the pin, especially if I don't intend to peen the pin.
Oh, and by the way I use Devcon 2Ton epoxy and if it has been opend long I dump it!
 
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