Don't use old epoxy, and my evaluation of AcraGlas

Nathan the Machinist

Nathan the Machinist

KnifeMaker / Machinist / Evil Genius
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Knifemaker / Craftsman / Service Provider
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Feb 13, 2007
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I used to use a high end areo marine epoxy that was a 4:1 system. It comes in bulk, and it is spendy. I failed to use even half of it before it died.

I tried the Locktite 1 hr epoxy at Lowes and it failed my testing, so I never made a knife with it. We all know about the consumer grade devcon stuff and the 5 min epoxies.

So I tried some the 30 min epoxy that Pop's was selling. The other knife supply shops have the same stuff, differently labeled. It worked fine. I went to use some the other day, but before using it I tested it (I'm anal) and it had died.

It sets up fine, but the adhesion was poor. I'm not knocking Pop's epoxy, it had gotten past it's shelf date.

So, time for more epoxy. We have all heard about Brownells Acraglas. Supposed to be some good stuff. Advertized as having a 5 year shelf life, which is what I want.

I'm primarily concerned about adhesion, because the longevity, weatherability and shock resistance of acraglas are already well known. Many consumer grade epoxy tend to let go after a few years, which is not suitable for a knife, but acraglas has a reputation for holding for decades. But I wasn't sure how "sticky" it would be.

So I tested out the adhesion and it was just fine, the vulcanized fiber liner tore and pulled away in chunks leaving paper behind. The older epoxy failed this test. So it is good to remember that just because an epoxy hardens doesn't mean it is still fresh enough to use.

They recommend against using a scale to measure the epoxy because you'll get the ratios wrong and this epoxy is very sensitive to getting that ratio exactly right. Well, I have a powder scale that reads a thousandth of a gram, and I want to be able to use it to make my measurements. So I measured the density of the two parts so I could calculate the ratio correctly. At room temperature, the epoxy has a density of 1.20 and the hardener has a density of 1.14. And they're mixed at a 4:1 ratio by volume. These densities may not be accurate, because the volume I was measuring was not precisely calibrated. But I did get the two volumes the same with accuracy, so the ratio I will calculate is still valid.

For what is is worth, this means the epoxy will weigh .042 pounds per cubic inch (excluding wetting and shrinkage, probably .005 in/in, so actually a bit more). Steel is about .283 and aluminum is usually in the neighborhood of .098. I think titanium is about .160.

So, to make up a batch of epoxy I set a container on the scale and zero it out. I then pour however much epoxy I want and take note of the weight and then zero it out again. I multiply the weight by .263 to find the correct amount of hardener to add. The scale allows me to add this accurately down to a tiny drop. Mix for 4 min and it is good to go. Example: pour in 15.000 grams of epoxy, then add 3.945 grams of hardener.

It has a working pot life of about 15-20 min at 75F, so an entire lot of scales can be glued in no particular hurry. This is like the old aero marine epoxy I used to use that I liked so much.

This epoxy suits me so I'll be using it going forward. It is probably too thin for most people's preference.

In order to maximize adhesion, both surfaces should be chemically clean, and it helps if they have a bit of tooth and a fresh (not oxidized) surface exposed. Wax and oil are a real problem, even hand oils. I use acetone to clean the surfaces. If gluing an oily wood, this will temporarily remove some surface oils so the epoxy can get hold of the wood fibers before more oil migrates to the surface from the rest of the wood. Also, I like to use a screwdriver to rub the epoxy into the surface of the wood.

In conclusion, I think that acraglas is a viable adhesive for our use and it can be metered using a scale by applying a factor of .263 to the hardener.
 
Good stuff Nathan :thumbup:

You always contribute threads of substance. This one is no different.

I'll soon be trying acraglas on a special project myself. Your finding will come in very handy........... and they're right on time ;)

If a guy doesn't have a good scale for measuring small amounts, what in your opinion, would be the best alternative method for getting acraglas ratio correct ?
Would small disposable measuring cups be accurate enough ?


And btw, Thanks :)



:thumbup:
 
Unless you're mixing up a fairly large batch, I don't think mixing cups (medicine cups) are good enough because the small amount of hardener used makes it very sensitive to small variations causing large variations in ratio. I looked into that and experimented with the one ounce cups I use for 1:1 epoxy and didn't feel the accuracy was there unless I was mixing up a very large batch. You'd need small graduated cylinders, and they don't make disposable cylinders for a reasonable price.

Brownels has these little measuring scoops you can use. To me, that is a messy pain in the butt.

I forgot to mention, folks need to be sure not to squeeze all your glue out. I think the best thickness to aim for is .005-.010. even a 1/16" will work fine, though it may not look very good. Folks need to remember not to squeeze all the glue out of the joints.
 
That's awesome that you have taken the time to figure out the conversion factor so you can weigh the epoxy. That I need to add to my knifemaking info vault for sure.

I have taken the first step towards purchasing premium glue a month or so ago. I got the Speedbonder 324, now I need to upgrade my epoxy. Acraglas has been mentioned in the glue wars threads several times and the ratings were fairly high compared to the other epoxies used. The only other ones that were good was the Golfsmith shafting epoxy and Loctite HP120. I have not had the need to use epoxy yet, my bonds have been manmade to metal (speedbonder) and wood to metal (gorilla glue). But the Acraglas having a 5 year advertised shelf life could be a selling point.

Ditto on squeezing too much. I try to leave a real rough surface on both surfaces (60 grit scuffing) so even if I do clamp too hard I still have glue left in the scratches.
 
Great info. Master Smith Greg Neely told us he uses (and recommends) Acraglas in his "Handles and Guards" class at the ABS Hammer-In this weekend. He did not, however, say anything about how to mix it.
 
I also use Pop's epoxy and it appears to be good stuff.

I have heard one thing about epoxy glue from those in the industry (I suppose they would know!): If you let the epoxy freeze in your shop while waiting to use, it will never be as good as advertised. My shop gets well below freezing in the winter and ever since keeping my epoxy in the house until I need to mix, I have had zero problems.

I never ever thought of that until this friend told me that little secret. Since then I have seen on a few mixing labels to never let it freeze, etc...might be something there!
 
Have you had any experience with West Systems epoxy, Nathan? I have some that is about 2 years old... your testing intrigues me....... can you tell us a bit about the testing process?

Rick
 
Thanks for the review Nathan, I've been meaning to get some Acraglas however having to be THAT precise seems like it might be a bit of a pain for a relative noob.

I mean if I had the measuring device already then it would be that much better. But is there an easier way to mix this stuff a bit easier to make sure the ratios are precise that aren't messy?
 
I've loved acraglas since I've been using it. It has a great shelf life but can thicken up over time, especially when not much is left in a larger container. I believe you can thin it again, but I haven't looked into that.

For accuracy, I just use two different syringes and measure out the volumes. I mark the syringes and clean them afterward. Great thing about acraglas is that it's designed to fill voids and thus works great in hidden tangs and to fill any hollows/holes used to lighten the tang.

--Nathan
 
When you are talking about acraglas is this what you are talking about? how pourable is it, and does it expand while curing? I am looking for something to glue up the replacement handle that broke on me and am thinking about this and can get it locally.
 
Original Acraglas is stronger than the Acraglas gel in the glue wars tests that I've seen. I'd go for the original if you can get it. It's VERY pourable, much more so than typical two part epoxies. Its intended purpose is as a bedding compound for increasing rifle accuracy, so it's made specifically not to expand much and to be very tough. As for the gel, aside from what I've read about it not being as strong, I don't have any experience with it.

--nathan
 
So if I got the Acaglas gun stock bedding kit I would be all set, and it is cheaper then the Arcglas gel kit too.
 
Magnussen said:
Have you had any experience with West Systems epoxy, Nathan? I have some that is about 2 years old... your testing intrigues me....... can you tell us a bit about the testing process?

Rick
Click to expand...

Hey Rick,

I didn't mean to imply I was doing any kind of high tech special testing or testing like in the glue wars. When I get a new epoxy or when an epoxy has been sitting on the shelf for a while I test it. Meaning: I glue a liner to a scale and a day later I take note is the epoxy hard almost like glass (fingernail won't leave a mark) or is it a bit sticky to the touch and when I pull the liner off the scale does it come off in pieces, leaving a layer of liner stuck on the scale. If it does pull off, did it come cleanly off one side indicating I may have botched the prep and I need to repeat the process, or does it pull free from both surfaces fairly equally etc. Nothing fancy, just looking to see if it sticks. The bond should be stronger than the substrates, so it shouldn't come apart at the epoxy joint unless something is dirty or the epoxy is too old. or just bad epoxy. I have had so many epoxies fail this test that I'll bet folks here would be surprised if they would do it themselves with epoxy off their own shelf.

I haven't used West Systems (I don't think) but a similar "system" where you can choose different epoxy and hardners that, 8 years ago, was being sold here: http://www.jgreer.com/
 
Acraglas is good stuff. I use it exclusively. Shelf life is one of the main reasons. I buy in bulk bottles (much cheaper than the bedding kits), also buy the brown and black dyes which allows you to leave glue in the joints without the unsightly glue gap, and the thinner for cleanup and sometimes on hidden tangs. As for mixing I use syringes and measure 1cc of hardener to every 4cc of resin and I've never had a problem. I always let what is left in the mixing cup set up and it always gets hard as woodpecker lips. In my opinion the shelf life, adhesive quality, ease of use and the ability to dye and thin make it the all around best adhesive for knifemakers. Oh and if you buy in bulk the cost is less than $1 per knife.
 
Since I saw it here, I have used Acraglas exclusive. I also read (here) to avoid using the gel because it doesn't hold as well. Nathan is correct, it is very thin when mixed, and takes a LONG time to set up (especially in the colder temps in my area). It wants to set up at 70 degrees or higher... good luck getting there in my house until summer time. But even at, say 60 degree, it will set up... overnight, or so. It says let it set for 3 days or more to be really done, but if you're doing a multi-part assembly, you won't have a problem going to the next stage once the overnight setting up is done. Just don't go to the sanding and finishing stage until it's fully set.

One problem with the stuff... it's hard to find. I went to every gun store in the area, and nobody carried it. Finally had to order it online, so I bought two kits. Bit of overkill, but at least I won't run out soon.

- Greg
 
darrin sanders said:
Acraglas is good stuff. I use it exclusively. Shelf life is one of the main reasons. I buy in bulk bottles (much cheaper than the bedding kits), also buy the brown and black dyes which allows you to leave glue in the joints without the unsightly glue gap, and the thinner for cleanup and sometimes on hidden tangs. As for mixing I use syringes and measure 1cc of hardener to every 4cc of resin and I've never had a problem. I always let what is left in the mixing cup set up and it always gets hard as woodpecker lips. In my opinion the shelf life, adhesive quality, ease of use and the ability to dye and thin make it the all around best adhesive for knifemakers. Oh and if you buy in bulk the cost is less than $1 per knife.
Click to expand...

There are only two problems with me buying it in bulk
  1. I am too slow at making knives:o
  2. I haven't found it in bulk locally yet, even though I am sure its available around here some where
Once I get those two things fixed I most likely will start buying in bulk:thumbup:
 
unky_gumbi said:
There are only two problems with me buying it in bulk
  1. I am too slow at making knives:o
  2. I haven't found it in bulk locally yet, even though I am sure its available around here some where
Once I get those two things fixed I most likely will start buying in bulk:thumbup:
Click to expand...

I could be wrong, the I think it is a Brownell's exclusive product, so finding it locally may be tough. Wish I still had my Brownell's FFL account and discount!
 
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