Glue Wars

[Sando]

(Disclaimer: this thread isn't to promote or slam any particular adhesive. Also I'm gonna use the word glue a lot. Epoxy is too specific and adhesive is too much typing.)

OK I'm worried about the glues we use on knives. The more I learn about what's out there the more a "this is the one to use" solution is getting silly.

I'm gearing up to run some tests, but I'd like to present some thoughts for feedback. How should I test, what kind of testing have you done, etc.

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Purpose

I think there are 2 basic purposes for glue in knife making.

1. To keep the parts together
2. To seal and protect parts.

For example, if you are using hidden or straight pins, then the glue has to hold the parts together forever and ever. However, if you are peening or screwing them, then you only need something to seal the parts.

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Filling vs. bonding
The next issue is adhesion vs. filling. These are two different roles and require very different characteristics!

1. For adhesion you want the parts as close together as possible so no glue line shows. (like between scales and tang.)

2. For filling you want gaps to get filled with something that won't shrink or expand while it sets and becomes it's own material. (like filling the hole in a hidden tang knife.) Adhesion is still important, but gap filling is more so.

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Like and unlike materials

The next issue is materials

1. Glueing likeminded materials together. At least ones that stick to the same stuff and expand and contract together. For example steel on steel. Or steel on brass. Or wood and wood

2. Glueing unlike materials together. Things that expand and contract at different rates.

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Environment
The final subject is environmental and applies to everything. Does it breakdown, loose it's bond, or become brittle with the following?

1. Heat
2. Solvents (water, hand oils, deer blood, ....)
3. Time

Another interesting issus here is, if you heat it it might lose it's stick. But when it cools down will it be sticky again? Some glues do, some don't.
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That's enough to set the stage.

Steve

 

[Sando]

Bonding vs. filling.

For these tests I'm interested in bonding. For filling the solution is acraglas. It is dimesionally stable (it's designed for that) and is way sticky enough. There just isn't anything else I'll use.

However, for bonding is it the best choice? There are some super glues that have the same shear strength as epoxies. Plus there is expansion/contraction rates. So for bonding I don't think there is a one-size fits all solution. That leads to the other topics.

Steve

 

[Sando]

Purpose.


OK here's the rub. I was thinking I wanted something with incredible shear and peel strength. But maybe no. What if it's ivory on steel? If it's like welded on there with a super stiff, unyelding adhesive it's gonna crack.

Besides the more I look into this subject the less I think you should rely on an adhesive to hold your knife together.

So now I'm thinking the purpose (for me) should be to seal and protect. Then rely on mechanical stuff to hold it together.


Steve

 

[Sando]

So if I'm not going to hold the parts together with glue, then I'm looking for something that lasts forever, resistant to heat, offers some flexibilty, bonds to both surfaces.

Now sealing bolsters you have metal on metal. If they are peened, they'll stay together, but still need sealing. Soldering is a choice, but is there something easier?

I've found that Loctite has a product just for that: 609 retaining compound. Hmmm........

Steve

 

[Sando]

Now if I'm doing wood slabs and loveless bolts, I want something that bonds to wood and steel, but remains flexible so the wood can change overtime without cracking or breaking the seal. Shear and peel strength are of minor concern.

That looks like a 2 part flexible epoxy is in order. Like Scotch-weld or Loctite Hysol 90FL.

Hmmm......

Steve

 

[peter nap]

Steve, you chose a man size job and it will still not tell the real story. For instance, your bonding test may show one thing but the way I learned joints (of any kind) was that you started with a good mechanical bond. This means dovetails, mortise and tenon, pins etc. In that case, a lesser glue will hold just as well or better than the most advanced polymer.

Filling, the same holds true. I rarely use glue as a filler in large cavities like bone for stick tangs. I make the tang as wide as possible and fill with 50/50 bar solder or lead or some strange concoction. The glue is used to make sure it doesn't flow through the thing while it cools.

Yep you picked a big job

Oh...while your testing, did you know Knox Gelatan (unflavored) is a very refined hide glue ?

 

[jhiggins]

Steve, I just want to say that there are a lot of decaffeinated brands that taste almost as good as the real thing. :footinmou

 

[Sando]

For instance, your bonding test may show one thing but the way I learned joints (of any kind) was that you started with a good mechanical bond.

Peter,

That is EXACTLY what I was talking about. I don't think we should rely on glues for holding a knife together. I'm coming to the conclusion (while developing the test plan) that we're looking for more sealant properties than adhesion. You're assuming I wanted to test bonding for it's own sake.

Nope I want to test bonding in the context of how we really put our knives together. So the criteria is based on very different goals than just holding things together.

AND - there won't be one sealant for all parts.

For example, I was using Acraglas to hold some metal wafers together while I shaped them. What could be better right? Well one gave way. So in frustration I put it back together with a superglue gel. Guess what? It's holding better. Seems steel on steel and pressed together superglue is better than acraglas epoxy.

That's what started my research desire.


Steve

 

[indian george]

Steve, I just want to say that there are a lot of decaffeinated brands that taste almost as good as the real thing. :footinmou

Damn!!! You and Higgy MUST drink the same coffee. The Rambling. HEHEHE!!!


Good point Steve.

 

[peter nap]

I still say it's a big job Steve....but worth posting and discussing for the newer makers. I have epoxied scales on knives just like everyone else. I also was a little ashamed of it.

Just to pick one maker out....I'll use Mike Hull. Look at his knives. They are put together so each part seems to support another. This is what Custom Knife making is about. What's inside as well as out.

 

[Sando]

I still say it's a big job Steve....but worth posting and discussing for the newer makers. I have epoxied scales on knives just like everyone else. I also was a little ashamed of it.

Just to pick one maker out....I'll use Mike Hull. Look at his knives. They are put together so each part seems to support another. This is what Custom Knife making is about. What's inside as well as out.

Yup, big job. But I still think your missing my point there buddy. I don't want to pick a glue that can hold a knife together. I want to make knives like Mike Hull. For sealing the parts together I want the best possible 'stuff'.

Again, I'm not trying to find a substitute for a good mechanical bond. I'm looking for stuff that works BEST with a mechanical bond.

Am I making sense?

Steve

 

[Sando]

Maybe an example will help.

Lotite Hysol e-90FL is an industrial grade epoxy adhesive. It's shear strength is 'only' about 1000 PSI on steel and 1100 on wood. However! It remains flexible forever and ever. So steel and wood bonds won't crack. (flexible in the adhesive sense - not that the wood moves)

Also, when subjected to temperatures 300 degrees for 750 hours, it cures more and becomes stronger. In otherwords, it won't break down in the dishwasher. I don't think you can say the same thing about good ol' devcon. So even though Devcon is rated at 2000 PSI, for a kitchen knife 90FL would be better.


SO the issue for my testing is to START with the assumption that we're using mechanical bonds. Now what's best.

Steve

 

[jhiggins]

I don't think we should rely on glues for holding a knife together. I'm coming to the conclusion (while developing the test plan) that we're looking for more sealant properties than adhesion.
Steve

I have had a lot of experience with adhesives in my day. They can make or break what I do. You would not believe the temp-fixes I have made on some machines with the right glues. All levity aside - this is a good thread, Steve. I agree with you that we should never allow a glue to hold a knife together. It goes without saying that they should be mechanically fastened, but I would also like to comment that glues can add to the ridigity and strength of said knife assembly, agreed? Don pours pewter into his stick-tang holes. Some folks use jb weld and some use 2-ton. I use acra-glass myself, but I could see where a metal would work better in some cases.

A good primer on adhesives can be found in the McMaster-Carr catalog, but the Machinery's Handbook really has a wealth of info on the matter.

 

[Dan Gray]

Steve
go mechanical all the way, as in a take down and if you want or need sealing
use a latex or silicon depending on the materials your using?
this way you can take it a part when you want there are more complicated ways to do it if you want to also..
but that would be the way if I'm reading you right?
a lot if Folders are done mechanical and I think are largely prefered that way...

 

[Sando]

IIt goes without saying that they should be mechanically fastened, but I would also like to comment that glues can add to the ridigity and strength of said knife assembly, agreed?

Jeff, thanks that's the stuff I'm looking for. (BTW I've been living on the McMaster, Loctite, and 3M websites for days now )

Also, on filling applications, if your filler is stronger than the material you're filling (acraglas is stronger than antler) and it bonds well under all conditions - what more can you ask? For me you've hit the limit.

as in a take down and if you want or need sealing use a latex or silicon depending on the materials your using

Cool beans Dan! Yes I'll add take down criteria for some applications and testing. And put latex and silicon on the list.

Steve

 

[peter nap]

Steve, while your making a list you might want to look at UV stability and chemical resistance.
I'd also look at West Systems Epoxies.

 

[Alpha Knife Supply]

We are also testing adhesives. An interesting test was using black superglue. Black superglue is superglue combined with rubber to make it tougher and more heat resistant. We tested 1"x.250" steel hex glued to 6AL4V titanium. The glue was applied to the hex lengthwise and then put on the titanium. When the hex was pushed onto the titanium and allowed to dry, the hex could be twisted off by hand. Almost all of the glue was squeezed out. When the hex was set on the titanium and allowed to dry, a hammer had to be used to remove the hex. The glue underneath the hex was .003-.005 with uniform coverage. If the pieces being bonded together do not have the minimum spacing required for the adhesive to work, the bond will fail.

For example, I was using Acraglas to hold some metal wafers together while I shaped them. What could be better right? Well one gave way. So in frustration I put it back together with a superglue gel. Guess what? It's holding better. Seems steel on steel and pressed together superglue is better than acraglas epoxy.

Steve,

Did all the adhesive get pushed out when the wafer were stuck together?

Was there a tiny piece of the epoxy left over that provided space for the superglue bond to occur?

 

[Sando]

Thanks Peter! Will do on those tests too.

The West Systems stuff looks good but pricey. May not get to that.

Test Chamber

I was thinking that one of the best torture tests I can do is the good ol' dishwasher! think of it. Water, detergent, heat, steam....

Anything we use should retain it's properties even after a dozen cycles! I mean even most people don't run knives thru there, somebody might. It doesn't matter if we're sealing bolsters or attaching scales, all the glues should be subjected to this test. It's kinda like chopping thru a 2x4 before the cutting contest - if you can't do that there's no reason to proceed.

Steve

 

[Sando]

Chuck thanks for the 'fortified' superglue. Wow! That's on my list now!

RE: my wafer problem.

Minimum/maxium thickness is a real big issue! I mean if the stuff is black and has to be .005" thick to work it might be awful on wood handles, but no problem on G10.

RE: the wafer thing. For both I had squeezed out everything. The surfaces were resanded before the superglue, so it was tight too. But it still held up quite well.

Both Peter's right. This is a big job. developing different criteria for different parts is gonna be a challange in itself.

Steve

 

[Mark Williams]

May as well throw in some old fashioned cutlers resin in with the test subjects.

I believe it was more for sealing. I took apart (broke) a small rat-tail tanged Sheffield knife. The hole was filled with lead or pewter and has cutlers resin throughout.