How durable just to epoxy on handle?

L

louied

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Mar 17, 2011
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Was wondering what can I expect if I was just to epoxy on slabs without pins or bolts,as I like the look of just the wood.I know that I need to prep both surfaces but would i get long lasting bond on say carbon steel with moisture or blood and what would be the best expoxy to use for this application.Thanks for any input
 
Might work, probably wouldn't. I'd at least use some hidden pins for shear strength. Surface prep would be important.
 
Not a great idea. In 40 years of knifemaking i've never seen anyone install slabs without either pins or cutlers rivets.
 
If you took the time to make a nice knife, I wouldn't skimp at the end and skip some way of anchoring the handles. If you are going for a sleek look maybe some short pins with plugs that match the rest of the handle blended. Or if you can be precise, some hidden pins that don't go all the way through the handle. Something is better than nothing.
 
Imagine you have a rod, and you epoxy a really heavy metal weight to the end of that rod. The epoxy is strong stuff, and it will very likely pick up that weight when the rod is lifted straight up into the air. Now, with the rod vertically in the air and the weight hanging below it, give a sharp, crisp rap to the side of the weight with a hammer. It is very likely that the weight will break free in this hypothetical scenario.

Epoxy is strong and needed in handle attachment not only for strength, but also to seal out moisture. However, in certain shear force events, it needs help from pins to make the handle stronger.

--nathan
 
I actually did some testing around this just the other day:

[video=youtube;PGmydrLT2Fo]https://www.youtube.com/watch?v=PGmydrLT2Fo[/video]

However my testing only addressed the initial strength of the bond, and says nothing about gradual weakening of the bond through corrosion of the tang, or degradation of the epoxy itself.

Personally I use epoxy mainly as a 'sealer' in between the handle scales and the tang, and I count on my rivets/pins to hold the handle in place. When I say pins I don't mean straight pins either, my testing says straight pins will simply pull away with the epoxy, they have to to be peened. I think Corby bolts or a similar fastener are probably the best way to go.
 
jonekatt said:
How much stronger do you think the bond would be if you roughed up the tang with 36 grit? in the video it looks kinda shiny underneath the handle
Click to expand...

From what I've seen it would make little difference, and possibly even make the strength worse. The epoxy was sanded into the tang with 150 grit sandpaper while it was still wet, as advised by West Systems.

Glue bond strength is mainly related to surface area (all other things being equal), and if you think about it the surface area created by 36 grit scratches is probably not much different to 150 grit. Fewer scratches but deeper, or more scratches and less deep, kind of evens out.

The best way to prepare a glue surface from what I've seen is to sand-blast it. My tests a while ago showed that sand-blasting both glue surfaces increased the strength of the bond a lot. I didn't show that in the video because I only had 2 test blades, and also because most people don't have sand-blasting equipment.

When it comes down to it I don't think I'll ever trust epoxy just by itself. The combination of epoxy and mechanical fasteners is great though!
 
+1 on hidden pins or using a pin of the same material as the scales

I did a bunch in black Micarta and black micarta pins recently, and you had to look really close to see them. Had a couple people ask how durable it was gonna be with no pins and another guy got mad and essentially called me a liar for telling him pins were there. So, yeah, they hide pretty good! :)
 
Some very reputable custom makers are using the 3m double sided tape for adhering inset handle elements, but I'm not aware of any that are using just epoxy for full handle scales without some kind of hidden aids or fasteners.
The whole topic of epoxy is one I'm following with great curiosity- if it's just a sealer, there are better sealers out there. If the main issue is brittleness, there are epoxies that don't get particularly brittle.
Looking forward to doing some controlled experiments with this that include the wet sanding technique that West recommends.
I've just got a FEW LITTLE THINGS TO DO FIRST, ha ha.... :)
 
I've seen knives pop up from time to time with wood handles and natural micarta pins that are very hard to see.
I'm just wondering, but can natural micarta pins be stained with wood stain to match different types of wood?
 
aarongough said:
Glue bond strength is mainly related to surface area (all other things being equal), and if you think about it the surface area created by 36 grit scratches is probably not much different to 150 grit. Fewer scratches but deeper, or more scratches and less deep, kind of evens out.

The best way to prepare a glue surface from what I've seen is to sand-blast it. My tests a while ago showed that sand-blasting both glue surfaces increased the strength of the bond a lot. I didn't show that in the video because I only had 2 test blades, and also because most people don't have sand-blasting equipment.
Click to expand...

I like the idea of sand blasting, I cant think of a better way to get a clean debris grease free surface

I think the surface area created by using coarse grit abrasive is much higher then fine grit though, a simple illustration, print this out and measure the legs of each, you will see the coarse area has 40% more surface area

Too bad you don't have unlimited funds to do more tests, I would like to see the results of wet sanding with 36 grit
 

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elementfe said:
Some very reputable custom makers are using the 3m double sided tape for adhering inset handle elements, but I'm not aware of any that are using just epoxy for full handle scales without some kind of hidden aids or fasteners.
The whole topic of epoxy is one I'm following with great curiosity- if it's just a sealer, there are better sealers out there. If the main issue is brittleness, there are epoxies that don't get particularly brittle.
Looking forward to doing some controlled experiments with this that include the wet sanding technique that West recommends.
I've just got a FEW LITTLE THINGS TO DO FIRST, ha ha.... :)
Click to expand...

I have made some paring knives and small bait/fillet knives with 3M VHB sheets. It is very strong. I have not had any fail yet, but it still makes me nervous that I have knives out there that have no rivets. From what 3M says, the bond gets stronger with time and the bond life is of unknown length, but suspected to be very long.

That said, I put rivets or bolts.

To get the strongest epoxy only bond, it requires the right resin and the right methods. Use a strong and somewhat flexible slow set resin. G-flex is the perfect one. T-88 is also good.
The method is called wet-sanding. Mix the resin by weight with a gram scale, and mix well for 60 seconds. Prepare the surfaces well with 80-100 grit paper. Clean off with alcohol, and apply a thin film of resin to both surfaces. Sand the resin into the surface with some 80-100 grit paper and ( apply a bit more resin if needed) and place the scales in place. Check the alignment and LIGHTLY clamp in place. DO NOT USE HEAVY SPRING CLAMPS! If you clamp hard, you will squeeze out all the resin. A strong joint needs just enough distance between the two surfaces for the resin polymers to extend from one side to the other just right.
Allow the handle to set well ( about 2 hours) before cleaning up any squeeze out at the ricasso, and allow to fully cure for 24 hours before doing any grinding/sanding.

I haven't tried it, but have read where some people making epoxy joints where they don't want a glue starved joint will place a sheet of toilet paper in the joint. It soaks full of resin, and spaces the two pieces just a few thousandths apart....just enough for a strong bond. In the furniture industry, they use a thin mesh type fabric the same way.
 
Wondering if anyone has tried and tested what I call "epoxy pins"? I drill a few extra holes in the tang and into the scales about a 1/16 to an 1/8". That way the epoxy goes into both scales and thru the tang. I still use regular pins ,but seams like the epoxy going thru all 3 pieces at the same place would make a stronger bond than just on the surface of the scales and tang. Or am I waisting my time with an extra step?
 
I have done some harsh testing with this for my own curiosity. What I did was bring out handle shapes with no blades, and rough them to 36 grit. Scales were roughed the same, and no pins were used. I used standard lepage slow cure 2 part epoxy that is available in most hardware stores. I glued them up, let the cure for a week. And finished them out as I would a normal handle. One set of scales was Inlace and one set was walnut. They were left in my truck door cubby and not touched for over a year. Where I live, in cab temps when the windows are sealed can vary from over 50C to below -40c. I understand this 90c variance is extreme, but that was the point. After about 18 months both handles had seperation between the tang and scales. I believe the drastic climate changes caused the scales to warp a bit and the epoxy alone was not enough to keep them on.
 
Grayzer86 said:
I believe the drastic climate changes caused the scales to warp a bit and the epoxy alone was not enough to keep them on.
Click to expand...

Thats a great real world test

Where did The bond fail? between the wood and epoxy, or between the steel and epoxy?
 
I tried using no pins on a full tang knife I made for leather work. After about a year, one side came off. I would never sell a full tang knife that didn't have pins or bolts along with epoxy.
 
jonekatt said:
I like the idea of sand blasting, I cant think of a better way to get a clean debris grease free surface

I think the surface area created by using coarse grit abrasive is much higher then fine grit though, a simple illustration, print this out and measure the legs of each, you will see the coarse area has 40% more surface area

Too bad you don't have unlimited funds to do more tests, I would like to see the results of wet sanding with 36 grit
Click to expand...

I hadn't thought of doing up a drawing like that, point well taken!

Another user on here, Ian (HallHandmade), said that he'd had to do glue strength tests for his previous job and that be strongest bond was created with epoxy applied to surfaces sand-blasted with fine grit as that surface had the highest surface area...

You've got me trying to think of ways to directly measure surface area now!
 
Last year I experimented with this , I was using Acraglass. The one that I cleaned good with a sanding belt had an amazing glue bond, I hit the knife several dozen times with a hammer and it looks good. I did one without cleaning and it didnt take much of a tap to break it off. I would never give or sell somebody a knife without pins though. These knives were made to see first hand how good this new to me glue was and then they were tossed in the junk drawer.
 
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