epoxy

[Cushing H.]

The issue for us in our workshops is that we do not enforce a standoff distance to set the layer thickness as they do in the study. We simply adjust how tightly we clamp and hope that we don't squeeze out all the glue.

agreed. these days I treat the epoxy as a moisture barrier, and to temporarily hold the scales in place until I get pins placed. btw .... these days I have moved to peened pins, with no epoxy in the pin hole. seems to hold just fine, is much faster and less fussy than corbys, and gives a clean look.

 

[navman]

I use the cheap plastic "medium" spring clamps from harbor freight and have not had an issue with epoxy being squeezed out of the joint.

 

[Natlek]

In my opinion from what I've seen, epoxy is Only a seal between the scales and the steel. A barrier to help keep moisture out. Nothing more.

Why would you risk selling a knife that Will fail eventually. If it's a decorative knife only, that's fine, I guess..... But a real knife that is going to be Used NEEDS mechanical fasteners too. Straight pins/tubing is Not good enough. (My opinion)

This is not my knife, but another well known maker.....


We could probably have an entire post of just failed handle materials....

What should I be looking at in this picture ?

 

[Natlek]

This thing is older then some members here , half of the blade is missing, it has been reshaped many times. Used in auto service for everything , even for opening empty 50 liter engine oil barrel .Wood is walnut glue is Araldite and pins are brass and steel is only 1.5mm thick ................contact with oil, antifreeze, fuel...what not ...... Look at it , not even sign of failure between steel and wood .

 

[Seedy Lot]

Note that the minimum I am talking about is half that test data's thinnest test. I agree that there is a sweet spot between .005-.010" where the bond is strongest. My point was you don't want to go below that point in thickness.

I'll recap my statements on installing scales in case there is a translation difficulty:
The rougher the surface the better the bond.
The "reservoir" is only a minor additional thickness to get a sufficient bond. We aren't talking about a lake, just a shallow puddle.
The glue line should not be less than .005" thick.
With proper sanding at low grits and minimal clamping pressure the reservoir is probably unnecessary, but won't hurt on a properly installed knife handle.
Mechanical fasteners should always be used on knife scales.
Corby bolts are the strongest mechanical fastener for knife scales. Once you learn how to install them properly and drill the counterbore seats they are also very easy to install.
The best epoxy for scales is slow cure type resin. 24-hour cure is what I recommend.
Clean everything well and wipe off with alcohol.
Alcohol is the solvent for un-cured epoxies. Acetone is the solvent for cured epoxies.
All glued surfaces should be reasonably flat and sanded to no higher than 120 grit. A lower grit is even better.
DO NOT clamp hard. This can squeeze out most or all the resin from the joint, creating a "glue Starved" joint.
Kant-twist clamps are one of the best for clamping scales. Other choices are the weakest spring clamps you can find. Screw clamps are not a good choice.
With Corby bolts you don't use clamps at all. Just tighten to snug, wipe off the squeeze out, snug again a tad, clean up, let cure. Again, don't torque them down hard, just comfortably snug. Another plus with Corby bolts is the scales can be put on and taken off while fitting the scales to the tang. Clamping the scales together with the bolts will also guarantee that the scales will be identical at the ricasso when finishing that area prior to final assembly.

That should provide the basic info I was trying to convey.

I'm going to start dropping out of these discussions when Natlek starts in. I have better use of my time than replying to a troll. Natlek can post whatever he wants, I'm not going to respond. You folks deal with him.
However, as a moderator, if any thread takes a downward turn or becomes argumentative, I or one of the other mods will step in.

Great writeup Stacy.

 

[A.McPherson]

On the topic of corby bolts, is anyone out there making g-10 corbys?

 

[Crag the Brewer]

What should I be looking at in this picture ?

It's a long beater/chopper. Thin blade.

all that chopping applies alot of torque and twist, and vibration.
With only it's straight tube fittings the epoxy let go.

I was flexing the blade some to show the gap and forces that can get applied. Especially with such a long lever arm.
(pin/tube popping out & gap between the scales and the tang)

 

[Natlek]

It's a long beater/chopper. Thin blade.

all that chopping applies alot of torque and twist, and vibration.
With only it's straight tube fittings the epoxy let go.

I was flexing the blade some to show the gap and forces that can get applied. Especially with such a long lever arm.
(pin/tube popping out & gap between the scales and the tang)

What was that black behind pin , is it one piece scale or ..... ? Handle is not glued ?

 

[Crag the Brewer]

What was that black behind pin , is it one piece scale or ..... ? Handle is not glued ?

Handle was glued..... I will have to rehandle it someday. I haven't yet. I'll put actual fasteners on it then.

I think the black behind the pin you are asking about is the silicone tape that I like to use for a hand wrap. It makes the handle grippy. With enough wraps, it can fill the handle out more, for comfort. i use it on knives that i want the handle to feel different/bigger.

Currently the tape is what is keeping the scales on

 

[Natlek]

Handle was glued..... I will have to rehandle it someday. I haven't yet. I'll put actual fasteners on it then.

I think the black behind the pin you are asking about is the silicone tape that I like to use for a hand wrap. It makes the handle grippy. With enough wraps, it can fill the handle out more, for comfort. i use it on knives that i want the handle to feel different/bigger.

Currently the tape is what is keeping the scales on

Are you sure about that ? I don t see any sign of epoxy on scale ? not on front on scale , not around that pin ?

 

[weo]

The main reason for a glue reservoir is it prevents a glue starved joint.

I always thought the main reason for grinding a hollow was to make fit-up easier and the scale fit better....

 

[rodriguezryan14]

My mom has a kitchen knife I made her probaly 4 years ago. I wanted to see how well Gflex epoxy held on scales with no pins or fasteners. The scales are some exotic oily hardwood from a cutting board. The epoxy is still holding but I don't know for how much longer as the scales are looking like they are starting to want to separate from the tang.

I personally am a firm believer in mechanical fastners and quality epoxy.

My mom’s separated. I did the same thing. It lasted quite a while. But one scale finally came off! I’d use pins from now on. I like corbys. And I use flared tubes and gflex on my outdoor blades!!

 

[Crag the Brewer]

Are you sure about that ? I don t see any sign of epoxy on scale ? not on front on scale , not around that pin ?

I haven't completely broke it open yet.
I have pushed that pin in and out a bunch, but I know what you mean, I'd Like to see more evidence of adhesive Showing. ....

Again, I didn't make this, but I generally know how he makes them. Once I pop off the scales during the rehandle job I'll see better.

Maybe what I'm seeing is "confirmation bias"
Seeing what I Want to believe.....?

Let me change the direction on this post by asking a question....

What advantage are no pins (just glue), or just straight pins/tubing with adhesive vs mechanical means?

Why not make the handle as strong as possible???

 

[Lorien]

I haven't completely broke it open yet.
I have pushed that pin in and out a bunch, but I know what you mean, I'd Like to see more evidence of adhesive Showing. ....

Again, I didn't make this, but I generally know how he makes them. Once I pop off the scales during the rehandle job I'll see better.

Maybe what I'm seeing is "confirmation bias"
Seeing what I Want to believe.....?

Let me change the direction on this post by asking a question....

What advantage are no pins (just glue), or just straight pins/tubing with adhesive vs mechanical means?

Why not make the handle as strong as possible???

relatively less weight

 

[ScarFoot]

For what it’s worth I taper the pin holes and peen the pins on all my knives now. I flatten the scales and the tang on the flat disk then rough the surface with either 40 or 60 grit sandpaper and clean thoroughly. I’ve also started trying to get my front pin as far forward on the scales as possible without blowing out the scale material when I peen it per the picture below. I figure that is where the epoxy is most likely to start failing due to the blade bending/flexing. Most of the squeeze out takes place while peening. I really only clamp the scales to make sure I don’t have any visible air gaps. I also put two 1/4” holes in the tangs for fixture mounting so I guess that would create the epoxy bridges but I’ve never really put that much thought into that aspect of it. I’ve never really understood the epoxy reservoir concept but certainly don’t discount the experience/advice of the makers on here who use them.

I changed the scales on one of my knives last year because I didn‘t like them. It wasn’t easy, I had to grind the pins out then knock the scales off with a chisel. After that I had to heat the g10 liners with a torch to get the epoxy to fail.

 

[Lorien]

agreed. these days I treat the epoxy as a moisture barrier, and to temporarily hold the scales in place until I get pins placed. btw .... these days I have moved to peened pins, with no epoxy in the pin hole. seems to hold just fine, is much faster and less fussy than corbys, and gives a clean look.

I'm curious about the lack of epoxy on the pins- what's the rationale?

 

[ea42]

I'm curious about the lack of epoxy on the pins- what's the rationale?

Not answering for Cushing but from my experiences if you're countersinking the hole you want it clean so the pin can fill it when peened. If you put the pin in with epoxy and let it dry first before you peen the glue will invariably get into the countersink making it useless. Try to avoid that by peening the pins with wet glue and you'll have a god-awful mess on your hands. You don't need any glue on the pins as the peened pin is plenty capable on its own.

Eric

 

[Cushing H.]

Not answering for Cushing but from my experiences if you're countersinking the hole you want it clean so the pin can fill it when peened. If you put the pin in with epoxy and let it dry first before you peen the glue will invariably get into the countersink making it useless. Try to avoid that by peening the pins with wet glue and you'll have a god-awful mess on your hands. You don't need any glue on the pins as the peened pin is plenty capable on its own.

Eric

Exactly. Plus if you use epoxy and let it cure before peening you then have visible epoxy between the pin and the handle material (looks bad).

if you countersink the outside of the holes slightly, you can then peen (carefully) until the pin fills the countersunk area. The result is a really strong reinfircement of the handles, and a really clean look where the pins meet the handle material (plus it is *much* faster)

 

[Lorien]

I assume the handle's been bonded and mostly shaped before the pins are added?

 

[ScarFoot]

I peen mine with the epoxy still wet. I really don’t worry about the mess since I generally contour the handles after they’re secured in place. I don’t like the idea of peening after the epoxy is cured. I feel like the shock you‘re putting through the pin/tang while peening could ultimately be detrimental to the bond. But, to be honest, I feel like there‘s a chance we might all be overthinking things…