Full tangs, pins, scales, and does epoxy really hold anything on steel?

tkroenlein

Well-Known Member
I'm wondering what everyone's experience is with the real holding power of epoxy is where only straight pins and are used on full tangs.

For what I've "disassembled" myself, I don't feel as though there is any real bonding strength against the steel, regardless of the preparation of the tang. Big hollows/fullers, and any manner of scratch pattern at various grits don't really provide any significant peel or shear strength. Ultimately, I feel like the only real holding power is the connection between the pin and the scale.

I'm inquiring because I see a LOT of glue/pin knives all over and I wonder if I'm missing something.
 
I use corby bolts plus epoxy ( West ) and so far have not had any failures.
I think the epoxy does provide some bonding strength, and helps keep moisture from getting beneath the scales.
Here's an interesting video:
 
I'm wondering what everyone's experience is with the real holding power of epoxy is where only straight pins and are used on full tangs.

For what I've "disassembled" myself, I don't feel as though there is any real bonding strength against the steel, regardless of the preparation of the tang. Big hollows/fullers, and any manner of scratch pattern at various grits don't really provide any significant peel or shear strength. Ultimately, I feel like the only real holding power is the connection between the pin and the scale.

I'm inquiring because I see a LOT of glue/pin knives all over and I wonder if I'm missing something.

I had this very same question some years ago. The answer came when I had to remove a handle because I had stacked liners and gotten the order wrong on one side. I thought it would be a fairly simple matter to drive the pins out, pop the scales off, and redo it. I was shocked by what actually happened.

Not only could I not drive the pins out, I could not pop the scales off by any means. Once I realized that I was going to have to destroy the handle I decided to see just how good the epoxy had bonded. I put the blade in a vise and tried to break off the scales with a big set of channel locks. All that did was chew up the wood. I then tried to beat the scales with a hammer to shear them. Nothing budged. And so I started grinding the scales off.

There were three vulcanized fiber liners on each side between the tang and the scale. The epoxy had completely bonded the liners such that as I was grinding, the liners appeared to be a single bonded mass. They did not peel from each other as I grinded, nor did they let go of the tang. I expected to be able to peel them but no such luck. I had to grind all the way to bare metal to remove the last traces of liner material and epoxy.

I don't worry anymore.

My prep: I scuff the tang and the 1/4" pins with a sanding block. I clean the tang, the liners, pins, and the scales with denatured alcohol. Then I put it all together with GFlex650 epoxy. I use a lot of epoxy. I treat it just like I'm fiberglassing a boat, meaning I lay the epoxy on thick and I go slowly to give everything a chance to 'wet out', meaning if any material is going to absorb any epoxy I want it to do that so that the epoxy can impregnate anything that it possibly can and fill all voids. Granted, it's not going to wet out much at all, but at least there won't be any air pockets or dry spots because I went too light on epoxy. About 20% of it squeezes out as I clamp up the knife. I don't care. In the big scheme of things epoxy is cheap- much cheaper than having to redo a handle because I wanted to save fifty cents on epoxy.

I have never had a knife come back to me with handle failure, and a large percentage of my knives are kitchen knives that are constantly wet and used hard. However, my knives don't see a lot of shock forces. If I was making camp choppers I might use corby bolts, or I'd at least test some knives to the point of destruction.
 
That’s a good question and has come up from time to time.
In my opinion the more you can connect the two sides the better. By this I am referring to epoxy bridges (my term).
Most all the makers WIP I see multiple holes drilled through the tang in addition to the pin holes. This serves to lighten the blade but it also serves as a bridge allowing the epoxy to bond with itself on each side of the tang. By drilling small divots on the inside of each scale and also multiple holes in the liners (if using liners) you are coming pretty close to having full epoxy contact on both sides of the tang. The pins through both sides become part of this bond providing shear protection.
This is my observation only. Others may differ.
I think Smallshop designs his scales so they mate completely in the tang. I may be wrong on that but I think I remember reading something about that.
 
Note in the video that there are only three pin holes through the tang. Would multiple holes make a difference? I believe it would but that’s just my opinion.
Who is going to abuse their knife like that in real life?
 
My experience is the same as John Wilson's. If you've ever had to remove a set of scales you'll see how well a good epoxy bonds. opaul is correct also about using multiple holes in the tang. They seem to act as internal pins. I don't worry about a scale popping off even if the knife is abused.
 
All good input! Especially what John said.....

Don't underestimate the rampancy of idiocy in the human race.
Common sense is so rare, its practically a super-power.

Many know of my experience with knives being returned for "loose" handles.....and that was the experience that put me on the road of researching "epoxy".....and finding out about "hold life"...... of course proper prep has as much to do with it as anything, but after I started using Acraglas, no returns/issues in 20+ years. I want so bad to say that if you're using XXXXX epoxy, you should change......but that would likely hurt somebody's feelers. ;)
 
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I am way out of my league here but I am going to interject here as well. I have only made a hand full of knives, that said I like the combination of a mechanical hold as well as good epoxy, I don't have acraglas yey but you can bet I will be ordering some before I start making many knives. I have really enjoyed using corby's to hold my full tang knife scales on. (I've not built a hidden tang knife yet) on one knife I did I counter sunk the pin hole and peened the ends of the pin to fill the gap then sanded smooth to provide a mechanical bond as well. just my opinion here
 
All good input! Especially what John said.....



Many know of my experience with knives being returned for "loose" handles.....and that was the experience that put me on the road of researching "epoxy".....and finding out about "hold life"...... of course proper prep has as much to do with it as anything, but after I started using Acraglas, no returns/issues in 20+ years. I want so bad to say that if you're using XXXXX epoxy, you should change......but that would likely hurt somebody's feelers. ;)
Ed.
where do you get the Acraglas and what do you use. I think there are several different applications.
 
Sand blasting is how manufactures make coupons to test for their performance numbers. If you want excellent adhesion, sand blast your parts.
80% of epoxies job, IMHO, is to seal the seams on scales or fill the cavity on a hidden tang. 20% for holding. The rest is pins or corby's.
 
I had not ever thought of the "hold life" on an epoxy until Ed mentioned it in another post. I guess it boils down to am I making a knife good for 5 years, 10 years, 15 years or for generations. to come. I want my knives to be here for generations. After I am dead I want the poor maker who has to re-handle one of my worn out knife handles to stop and say "Holy Crap, did he weld the scales on". Ed did the research already, so to me the choice is clear as far as epoxy goes.
 
Ed.
where do you get the Acraglas and what do you use. I think there are several different applications.

There is only one real source..... Brownells. Anyone else offering it is likely reselling it, and hiking up the price on you. I use the plain old original Acraglas..... I tried the gel....but it's FAR TOO THICK for most knife applications .....here's a link...
https://www.brownells.com/gunsmith-...ock-bedding-adhesives/acraglas--prod1033.aspx
THE FIFTH ITEM DOWN IS WHAT I BUY...."shop kit". It's 28oz or resin, and 7oz of hardener. Before I got sick, and was at it full time, that was about enough to last me for a year or so.... at $76 it seems pricey....until you start adding up the cost of what you've been using......and frankly, there's nothing out there to match it.
 
Best thing I have done recently is go over to G Flex, I love the stuff. I thought Two Tonne was good but the G Flex is thicker and doesn't catalyse when I have added pigments, Two Tonne has and gone off like a rocket and so hot the glue pot was extremely hot too the touch. The G Flex seems to take an age to cure but that's a bonus as a strong bond.

One thing I have done in the past to break the epoxy bond is freeze the knife in the freezer at its lowest setting then immediately hit the pins with a hammer and punch, they ping straight through and the handle and liner come off a breeze when hit with the hammer. This is on knives that the handle has been laser cut with a central handle void in order a huge amount of epoxy can be used in the handle.
 
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