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looking for advice on handle delamination issues

somber crow

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Hello. I've been looking into redoing the style of how I do my handle work for some of my tools I make, as well as maybe do a bit more bladesmithing than I used to, but I am coming across an issue, and looking back, it is one I used to have back when I was first starting out. And that issue is the handle scales essentially just falling off after the epoxy has cured. In this particular case I'm doing some hidden tang wa/japanese style handles with a few layers, and am having this same issue, and am looking for advice. Here is my example:

Handle is wood - 18g copper spacer - wood, with the grain all in the direction of the knife   ( -->cu-->blade  ). For prep I rough sand the ends of the wood that will be connecting. For any metal, I wash it with soap (while wearing gloves), and make sure it has a rough finish. Also experimenting with adding drilled holes in for the epoxy to fill through. Then clamp up, hard enough, but not too hard as to push out all the adhesive. I use 2 part epoxy (currently 5 min JB weld), making sure to mix well/evenly, and have over the years tried a few different brands with essentially the same results. Those results being maybe 2/5 handles failing, maybe even 3/5.

I guess I should note handles that do fall apart typically happen within the first 30 seconds of grinding the stack flush. If there is metal in the handle (especially thin metal), I try to only do very short bursts, then let it cool

Am I just missing something here ? I'd always been taught in regards to woodworking to not glue end grain, but clearly that is a thing that happens with these kinds of knife handles. Maybe I am making small mistakes, or one big one, or am just unlucky, but I'd love to hear some advice from some more experienced knife guys.



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Soap and water? What solvent are you using to remove the soap residue? What's with using cheap 5 minute epoxy, why not use good quality epoxy, like G-Flex by West Systems?

When you're using a 2 part polymerizing glue like epoxy or polyester resin glue, the faster it sets the weaker the bond though there is a point of diminishing returns for slow setting. You can adjust the amount of catalyst for set and cure times but only a little bit.

If you're really grinding the handles a short time after the epoxy sets it's really likely to separate and quickly. 

Next time use 1/2 hr minimum or 1 hr. setting Devcon or JBweld. Rough the metal and degrease with acetone or xylene and allow to dry thoroughly. Xylene is a solvent for epoxy so you do NOT want it contaminating the cement. 

Glue your scales up and leave them in the clamps over night in a warm dark place. Dark isn't really important but it's an easy hedge and if the knife is our of sight YOU won't be tempted to rush things. 

Lastly you have to pay big bucks for heat resistant epoxy cements so do NOT let the handle get hot when you're grinding. You won't be able to feel the tang overheat through the scales and depending on grade, 300f will cause most epoxy cements to lose bond. It's how we used to un-epoxy things, with an electric soldering iron.

One last pro tip. Do NOT hurry things, the ONLY thing rushing is sure to do is make your mistakes permanent more quickly.

Frosty The Lucky.

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Surface prep is essential for any glue ups. Frosty hit on most everything I'd say. I use acetone to degrease and follow up with 70% isopropyl alcohol. Check to ensure that no additives other than H2O are in alcohol .  Covid has people producing sugar alcohol  that has glycerin and other additives. That creates a film which leads to epoxy failures. Also  some acetone  can leave a  film on the metal. And  what you use use to apply the acetone and alcohol can leave films. White paper powers will sometimes have chemicals that can contaminate the surfaces. I use those little cotton facial squares that women use for removing facial cream and stuff. 

As for epoxies. You might check out a topic on the knifenetwork called Glue wars.  Two gentlemen spent a lot of time and  money checking out approximately 15 different common knife makers epoxies.  Interesting read on surface prep, and holding abilities. 

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The additive in paper that can contaminate whatever it touches is Kaolin clay, it allows ink to imprint without bleading out.

Alcohol swabs don't contain anything but alcohol and water. Do NOT buy the ones that won't dry your skin, they contain a lotion/skin cream.  

Gluewars eh? I'll have to check it out, thanks Velegski.

Frosty The Lucky.

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Okay, some follow ups.

-As for the epoxy brand, I'd been using combat abrasive's epoxy that they sell on any of my handles, but I ran out and was using JB until I do my next belt order, but I can try one of the other brands, I will look into that glue wars thread as well

-Every handle I make I glue up and let set overnight. Although I've usually only had the "quick set" epoxys ever lying around. I will look into the longer set ones. Like I said I let it set overnight, so there is never really any rush.

-I'd been cleaning with a de greasing soap I've seen other people use for stuff like this. I forget the brand off the top of my head. It's blue. Anyways, I will try acetone next time. I used to use it when I first started years back and had these same problems, but I was also an amateur overall, probably did something else wrong.

As for Frosty's comment on temperatures, I do wonder, thin(ish) sheets of metal heat up really fast. When I've done my glue up things aren't 100% matched and do need to be ground down. I usually go until it just feels hot (maybe 15-20 seconds of grinding tops), then let it cool. But maybe I should go even slower. Or use thicker spacers.

Anyways, thanks for the advice

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I've had problems with JB weld Kwik, but not so much the regular jb weld for similar projects.

Edited by Mod30
Remove excessive quote.
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Yes. To the slow down when grinding.  If you've got a variable speed grinder turn it way down. If not, take 3-5 second grinds.  Takes a little longer but doesn't kill the expoxies.  You mentioned you grind until it feels hot.  Thats probably too hot. A little online research will show that expoxies can start degrading at 140 F degrees with total failures  at around 300 f (that's unless you are using special high temp expoxies). To give you an idea. Holding 140 f can cause burns in about 3 seconds. So just guesstimating, your hot feel is probably 120 f or hotter. I typically  use a hair dryer to remove scales and for manufacturers safety reasons those  rarely go above 140f. 

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While searching out the link for the suggested adhesive test I found another on the bladesmith forum, I'm reading the knifenetwork test thread now. I'm seeing failure modes that suggest prep errors but I've only gotten to page 3. 

FYI: I'm not a knife maker, almost all my experience with adhesives comes from working in a plant in S. Cal, that made hot and cold ducting for aircraft. I mostly made flex ducting from neoprene impregnated fiberglass cloth or silicone impregnated fiberglass cloth. The high temp ducting was made with a (go ahead, laugh) secret rubber impregnated fiberglass cloth and phenolic resin impregnated fiberglass cloth. 

Lots of products required metal connectors: bayonet or flange being most common though there were a number of purpose specific connections. 

Where much of my experience comes from is using adhesives on some pretty oddball materials.

There are two basic types, "glues" and "cements."

Epoxies are cements, they form a layer between the joint surfaces and must bond to both materials. Mortar in a brick wall is "cement" literally.

Glues on the other hand react chemically with the joint surfaces causing them to fuse. Old time model glue is a perfect example, it dissolves the surface of both joint surfaces then the solvent evaporates and the surfaces have fused into one material. ABS glue is another example.

When using cements we learned that unless it is stronger than the materials being joined the thinner it is the stronger the join. 

Every couple few months a product representative held "class" at the plant, on a couple occasions one of us traveled to another plant or manufacturer's seminar. We  used IIRC no glues, everything was a cement.

I'm a long LONG way from knowing everything about adhesives. What I said above is based on my experience and long ago classes.

Adhesive choice is #1. The slower the set and longer the cure the stronger the joint.

Joint prep is actually more important IF you chose a good adhesive. A poor adhesive isn't going to be good no matter what.

One of the fellows testing epoxy used brake cleaner to degrease. Be aware brake and carb cleaners have changed since those tests and do NOT cut grease like they used to. Carbon tetrachloride has been eliminated from the formulas for REALLY GOOD reasons. 

We used MEK (Methyl Ethyl Ketone) to degrease metal components before cementing and Toluol to "glue" neoprene. Acetone was the general tool and hand cleaner. Yeah, we had our hands in low yield hydrocarbon solvents 8 hrs a day. It's a wonder any of us have functioning nerves and internal organs. 

If I were to start making knives I'd probably use MEK to degrease the tangs with acetone a close second. Both evaporate clean, leaving zero residue. Cleaner than fresh water unless it's distilled.

I know that's a long ramble for a little back story but I don't want anybody thinking I have any experience cementing scales to knife handles. 

Frosty The Lucky.

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Did I miss the part about oily woods needing to be treated to get the adhesive to stick to them?  Common in woods often used for knifemaking like cocobolo, teak, rosewood, etc---things that take a high shine on their own and resist moisture.


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