Epoxy Failure

[Bruno]

Not sure if this is the right section.

I've been working on a couple of machetes lately...  I had one just about finished and was testing.  Very pleased with it, rolled leaf spring, full quench, tempered at 400.   Got razor sharp and great flex in it.  Decapitates yucca's with single handed, single strikes

I've epoxied/pinned the handles on using Devcon 2 Ton (somewhat old, like 2 years).  Plenty of cure and set time. Was working out pretty well,  until my last round of testing with my offhand, must have not hit dead on...    I noticed as I was flexing the blade that the epoxy was separating at the top of the first pin, closest to the blade.   So I popped out the pins, which seemed easier than it should have been considering that I epoxied them in as well, and started to pry the scales away.    Needless to say, it seperated quite easily on both sides.  The epoxy appears to have adhered to the wood (white oak), very well, but not at all to the steel seemingly.   I did acetone/alcohol clean the steel before epoxy, and the surface is not really smooth, as I left the forged finish on the piece and soaked in vinegar.   I did thoroughly clean after the vinegar.   

Was my epoxy simply too old ?  Or is it the wrong epoxy for such a flexible blade without a real guard on it ?    I do have some much newer G-Flex which I am going to try next.    Should I bother scraping/sanding the old epoxy off the scales, or would it be beneficial to leave it on with the new epoxy ?   Just want to do it better next time.     This is a personal blade not meant for anyone, but I would like to do extensive testing on my process before I try and sell a few.   Can't have blades break, or handles flying off you know

What do ya'll think ?

[Geoff Keyes]

I'm thinking that it's an age issue.  I like to slightly hollow out the mating faces of the scales and put a couple of through holes in the tang to make epoxy "rivets" .  Epoxy doesn't like to be just in thin sheets, a little bit of space makes for a better hold.

 

g

[Bruno]

2 minutes ago, Geoff Keyes said:

epoxy "rivets"

That is great idea Geoff, Thanks, I will try that.   I'll try hollowing the scales as well....

[Geoff Keyes]

You don't need much, I use the top wheel of my grinder and make 1 or 2 passes.  Just don't break through the ends or the edges of the slabs

 

g

[Bruno]

Should I do the same on the tang also? I've seen that done on smaller blades, but I don't want to weaken this one too much, since  that's a lot of blade with forward weight on such a small tang.   The tang didn't really get hardened or spring tempered due to forge size limitations.   Just couldn't get the whole thing hot enough fast enough without the tip cooling off below critical.

Really need to build a HT forge.  I have two 33 gallon drums begging for it...

My pins are 1/8",  what size through hole do you use for the epoxy rivets?  Again, I don't wan't to weaken more that I have too,  would 1/16" be too small ?

Thanks Again Geoff.

Edited October 27, 2018 by Bruno

[C Craft]

Bruno, like Geoff said give it someplace to adhere to. I like to drill thru holes in the knife's metal to let the epoxy, travel from side to side, as well as small pockets in the handle material itself!!

 

1 hour ago, Bruno said:

(somewhat old, like 2 years)

Another thing the epoxy itself. I will use epoxy I have had for a while that has been opened and sitting for home projects but when it comes to gluing up handle components if it is old, (more than 30 days) I won't use it for handles!! I save that for things I don't care if it fails!!!! I used Devcon 2 Ton for a long time, so I don't it failed because of anything but its age!! I now use the G flex. and have been pleased with it!!

[Joshua States]

Epoxy does not like smooth surfaces. From what I see of the tang it's pretty smooth. Combine that with the flexing you describe and you have a perfect failure situation.

I used to do the top wheel thing that Geoff describes but here's what I do now for a full tang. I take a Dremel tool with a 60 grit sanding drum and rough up the mating surfaces of the tang pretty well. I leave about 1/16 to 3/32 around the perimeter of the handle untouched and smooth. You have to scribe the front edge of the handle with a pencil line and keep back from it. Then I do the same thing to the mating surface of each scale with a ball end engraving cutter. The epoxy rivet holes in the tang are also added as an extra bonding point.

[Bruno]

Thanks Guys,

I'll give it a try and do some more testing. All seems like common sense when you think about it.  Should have taken the time to do it the first time.  Lately, all my work has been limited to a few hours on the weekends, so I guess I just need to slow it down a bit and do it right.    I've decided to add a lanyard hole in the machetes,  while it's all apart, so I'll have to get some stainless tubing. I've used G-Flex once so far on my last damascus knife, and was very pleased with it. I like the extended setup time and curing time is not bad at all.   

 

[Gerhard Gerber]

Few things.....

I had something similar happen on a knife recently, the blade was from a torsion spring from the front suspension of a VW Beetle.  Spring steel....'nough said.

I made two similar knives, and the scales on the one went forward far enough past the pin that the bend in the blade undoubtedly made the epoxy let go.....can't fight the leverage.

Looking at your blade and handle that seems very likely.

I put notches in my pins, make sure that they're filled with glue, so even if the glue lets go of the pin material there's still a mechanical lock as the glue will hopefully adhere better to wood or micarta handles.

In my case I did some testing, and I'm happy to say that knife could've still lasted a lifetime without the handle coming loose to the point where the knife was unusable. 

[Bruno]

15 hours ago, Gerhard said:

I put notches in my pins

Thanks Gerhard, that is also a great idea as I first noticed the top pin coming loose during testing, which i really didn't expect. I did leave them smooth though. When I can get back to working on it, I will try all these methods.