A lot of issues with scales peeling off

M

molten_river

Joined
Feb 11, 2025
Messages
3
Hey everyone,

I’m having some extremely frustrating issues with scales peeling off my full tang knives around a month or so after friends start using them.

In the beginning, this happened twice with tapered tang knives, so I assumed it was that and then I stopped tapering the tang.

Then, it happened with completely flush scales. I used a plasma cnc to cut a few out and added some cutouts in the handles to increase contact area for the epoxy. Seems to have limited how deeply they peel, but they are all splitting at the shoulder.

I use G10 liners for the most part, but none of the knives I’ve made without the liners have, to my knowledge, split.

I clean both blade and scales with acetone or isopropyl alcohol before epoxying.

I weigh the epoxy - it’s West Systems 2part

I’ve experimented with pre tapering the pinch grip before gluing - and doing it all post gluing - it still peels.

I’ve tried using clamps as well as yarn because I thought the metal clamps weren’t dispersing pressure evenly.

the wood is almost always stabilised, so I expected warping wouldn’t be an issue but I suspect the liners are somehow causing this issue. The liners and scales are glued together prior to the final gluing.

Now I have three knives to fix and I’m worried it will happen again. Any help would be massively appreciated

https://imgur.com/a/ZNFPkxf
 
The tang likely isn't flat right to the front of the handle slabs. You are flexing the handle slab to contact the tang even as it starts to taper thinner. It holds for a while, but is under tension and springs open eventually.
Test the tang and handle slabs for perfect flatness and roughen both to 120 grit before gluing.
 
I also roughen up the tang area, the deeper the scratches, the better, assuming you are not overtightening and that your are degreasing and gluing up at adequate temp I agree with the above, you do no have true flat. Disc grinder for scales and tang should help. i also like 60-80 grit scratches better then 100 or 120 for glue up.
 
I use 36 grit abrasives to scratch up everything.

Clean everything with acetone

Careful about weighting the epoxy 1:1 by volume isn’t the same as 1:1 by weight. Gflex isn’t designed to be mixed 1:1 by weight.
 
Welcome to BladeForums!!

Don't overclamp. Check your epoxy for it's "operational thickness."

Avoid using acetone that says "For cleaning". It is recovered acetone from industrial processes and filthy with contaminants that can get in the way of a good glue-job. For those who scoff, put some on a clean piece of glass and let it evaporate. That doesn't mean you can't use it up until the final rinse, though. That should be something clean like 70% or 90% rubbing alcohol from the pharmacy. Allow to dry thoroughly.

Do you have a blasting set-up? Glass bead blasting provides about the very best surface you could imagine for glue holding.

Your very design with that very long taper on a narrow front may even be contributing some to the failures. Even stabilized wood absorbs a little water, and glued onto something else like ultra-stable G-10, may create some tension. I find it a bit disconcerting that it looks like the front of the scales have actually curled ever-so-slightly from the tang. I would make sure no one is putting your work in the dishwasher, either.

Peened pins or other mechanical fasteners like Corbys go a long way towards eliminating that issue...

Good luck. PITA problem until you figure it out.
 
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molten_river said:
the wood is almost always stabilised
Click to expand...
Stabilized wood will still absorb/loose some moisture and can change shape, although not nearly as much as un-stabilized. This is one reason why I switched to hidden tangs on my kitchen knives years ago.

(Looks like Fitzo covered this pretty well, even included the long taper I was about to comment on. I'm not a betting guy, but now that i see that Fitzo confirmed my thoughts, I'd put some money on that being the main reason.)
 
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The others have covered most of it. Make sure you have a pin toward the front of the scales as well. Check with the owners to ensure they’re not leaving the knives in standing water in the sink or putting them through the dishwasher. If prep is done right (everything flat, clean, surface roughed), modern epoxy should not be letting go like that.
 
G10 needs to be scuffed with sandpaper until there is NO gloss anywhere. After sanding I wipe it with acetone and check under a good light, usually I find a couple small areas that still need sanding to remove the glossy finish.
 
wow, that's wild. Never seen anything quite like that.
in the picture, it looks like a kitchen knife. These knives haven't gone into the dishwasher, have they?
 
Thanks for your help everyone, I really appreciate you all stopping by to help me out.

No point in being dishonest - I have not been roughing the scales and I’ve probably also been over clamping. I think the clamps themselves might not be ideal as the feet as pretty small so the pressure might not be even.

There is zero chance they’ve gone through the dishwasher, the guys that are using them are very aware of what that would do.

i use hidden pins for alignment, the new knife
im working on will have 6 full pins. ill rough up tang and scales, be more gentle with clamping pressure and go from there.

thanks again
 
One other thing, the scales are permanently bent. I pulled off a set from the green knife in the photo, warped to hell. So I think clamping is really messing with them, maybe they’re absorbing moisture too
 
I've had some stabilized wood scales, that were not on a knife, warp over time. I've had others that haven't. It might be the material.
 
If you are using hidden pins, why not just use real peened pins or Corby bolts? I would think it would be easier than hidden pins and the handles won't come off.
I would never trust just glue on a full tang knife.
 
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All glued handle material should be flattened and roughened just before bonding. You would be surprised how not-quite-flat things like 3/8" Micarta can be. Roughening removes the glossy surface, but it also exposes underlying material and often improves wet-ability. Speaking of which, apply glue to both surfaces, really smear it on so that you have deliberately wetted both surfaces. Not 100% necessary, but if you are having problems, might as well do all you can to improve your odds of success.

Do you bond the G10 liner to the handle material, wait for the adhesive to cure, then bond the composite scale to the tang, or do you form all four glue lines at the same time?

The long taper could well be contributing, and it looks as if the handle material extends into the area that has started to be tapered for the blade. That permanent warp bothers me. It looks like the handle material has shrunk, pulling the liner away from the tang. It looks like it has pulled past the point where the liner would be merely straight.

How new is the stabilised wood and where did you get it? I have had wood stabilised by K&G and it takes weeks for the chemical smell to dissipate. There is no question that the resin is continuing to cure over that time ( it stops feeling slightly sticky, and stops smelling, it seems to get harder than when it is brand new). I haven't used it in this condition, so don't know if it might still be moving, but I can imagine it isn't as stable as it will become.

Where are you located, where is the wood stored, and where are the customers? Some years ago, Spyderco had 800 knives made in Taiwan (humid) with what was sold as stabilised spalted maple. A large number of the handles cracked after they were shipped to Colorado (dry), and other dryish places.

What epoxy are you using? West Systems make several, some are better for knives than others. Many here use the G/flex toughened, but there is a 5 minute version (as a general rule, the longer cure, the better...many good epoxies take 24 hours or more to cure), there is also 105/205/206 etc system, which tends to be brittle.

If you need to spread clamp load, use cauls. They don't need to be shaped, just thick enough that a 90degree cone of pressure from the point of your clamp has room to expand to cover the area you want to clamp over. I usually don't bother for handles because I am usually clamping thick enough material, but I use this sort of thing for gluing thin-ish wood together for wood projects.
 
Aside how I'd do it differently....
Others have covered it well with Actual fasteners (not pins), not using g10 liners. I prefer micarta. Properly flattened, drilled holes for glue wells, quality stabilized wood, not some cactus juice or another.. etc. etc.

What I don't understand is

-Could somebody please explain the taper issue?
In My head, a taper is just an angled scale.
Why would That matter with the adhesion?
Thanks.
 
It doesn't bother me that the shape of the handle slab tapers. What bothers me is that the tang clearly tapers and likely isn't flat.
 
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