G/Flex Expoxy Bond

MTBob

MTBob

Well-Known Member
I'm new to this forum, and I've tried to find the answer to these questions in previous postings related to bonding epoxy, specifically G/Flex 655.
Two Questions:
1: I know that epoxy needs a roughened surface to bond adequately. I've used a dremel tool to roughen the surface on a few knives, but it's a rather random effect and, without care, can mark the edge of the tang or G10 that might be visible on the final finish. Recently I tried lightly blasting the tang and G10 with 70 grit aluminum oxide media. That process results in a uniform abrasion to the surfaces of the metal and scale and eliminating any shiny / slick surfaces.
So, do you think that media blasting the surfaces is better, or worse, than using a hand grinder to roughen the surfaces? Or, is there some other process that I should use?

2. Also, I understand that too much clamping pressure can result in a weakened glue bond. I see some of you use spring hand clamps, while others use c-clamps, or some variation of those clamps. How do you know how much pressure to apply to the scales? I've been using c-clamps with a lot of pressure, thinking that a lot of pressure will assure that the glue is pushed in the microscopic holes and bond better. But... I've also read that too much pressure will reduce the epoxy thickness to a point where it can result in delamination.
Any thoughts would be appreciated.

MTBob
 
This is my opinion based more on my time making laminated longbows than knives but the same things should apply. First opinion, rough is rough do how it works best for you. Second opinion, moderate at the most clamping pressure. The trouble with applying too much clamping pressure is that you WILL cause too much "squeeze out" which means your joint will be glue starved and weaker than if you use moderate pressure. Third opinion, (you did not mention this but many people make this mistake). Both items being glued get glue. Put glue on your handle material and on your steel. I never asked "why" for this one but every bowyer and wood worker I have ever learned from applied glue to all surfaces.
 
Although I'm not a fan of the GFlex, proper preparation cannot be overstated, no matter what "glue" you are using.
"roughen" can mean different things, to different people. In my case, I tend to go with a 220 grit or heavier..... and in most cases prefer 120 grit finish. But that's only the beginning. Nitrile or latex gloves.....not to protect you....but to keep hand/body oils from contaminating things. Clean with acetone or other cleaner of your choice.....the cleaner, the better the bond. Media blasting is a perfectly viable choice, but again....CLEAN afterward/before gluing.

If all parts are flat/uniform, minimal clamping pressure is all that's needed.....again, it's about the prep. In reality, if parts fit as they should, and are CLEAN, a 1/16" is about all that the higher quality epoxies require. That being said, whenever I build full tang blades, I always cut a "hollow" down the tang with a 1 1/2" contact wheel at 50 grit.... that is a "channel" for epoxy to reside. That's mostly a peace of mind thing for me. :)
 
I believe that applying glue to both pieces allows for better "wetting" of each surface. That is to say you reduce the chance of capturing a major air bubble between the pieces.

I think it was Boss that suggested sandblasting was how epoxy was tested for strength by the manufacturers in a thread I started awhile back. Because epoxy forms a mechanical bond, it stands to reason that the random directionality of the divots created by blasting would be very good.

I don't have a sandblaster. I use a hard backer and 80 grit to sand in a cross hatch pattern and maintain flatness. Seems to be working out for me.
 
Normally I taper my full tangs with a used 50 grit belt unless the knife is really small. Then, I just leave them rough for glue up...kinda kills two birds with one stone.
 
You can hit the handle area with a lower grit belt to create some texture or many will drill extra holes to give the epoxy a better bonding area.

As for clamping pressure, I use c clamps but I don't crank it down super tight. Just enough so I can't see any space between scales and the blade
 
I use Gflex and have done both sand blasted tangs and big grit scratch marks. My personal belief is the sandblasted texture is probably best. I've never had a glue failure on a customer knife so guess I have no real world results really. I have repaired a couple of other makers knives, I think one of them I did on youtube, and the scales popped off really easy. Both cases the tang was mostly slick, no texture.
 
60 grit cross hatch and swirls, clean truly well, Gflex and spring clamps.
Hardest part is waiting on them to cure. ;-)
 
Ed's comment may be based on the fact of his system has never failed him and if it ain't broke, don't fix it. Maybe I shouldn't speak for Ed but I believe he favors Acraglass.

Doug
 
Doug is correct. My preference for "glue" is Brownells AcraGlas. The reason I made mention of not favoring GFlex is because I was asked to be a "tester" for the product before it was released for sale. I could go through all the details, but suffice to say that between the answers (or the lack there of) from the folks asking me to test it, and not liking a number of things about it during testing, I can't with any honesty recommend it.

Everybody has their favorite epoxy/glue......for various reasons. The main reason I choose AcraGlas is that it's shelf life, and more importantly, it's hold life are longer then any other product currently on the market.
 
EdCaffreyMS said:
Doug is correct. My preference for "glue" is Brownells Acraglad. The reason I made mention of not favoring GFlex is because I was asked to be a "tester" for the product before it was released for sale. I could go through all the details, but suffice to say that between the answers (or the lack there of) from the folks asking me to test it, and not liking a number of things about it during testing, I can't with any honesty recommend it.

Everybody has their favorite epoxy/glue......for various reasons. The main reason I choose AcraGlas is that it's shelf life, and more importantly, it's hold life are longer then any other product currently on the market.
Click to expand...

I'd be very much interested in the details and the "number of things" you didn't like about it in testing.

You are the ONLY person I've ever heard say negative things about g/flex or west systems.....but they've always been vague.

For the record, I've used acraglas and had no issues with it, nor have I heard of anyone else having any issues with it.

I found acraglas to be a bit messier than g-flex and I like the 1:1 mix ratio of g-flex a lot better.

I have twice had to remove handles that were held on with g-flex, one full tang with scales and one hidden tang. Both required hammer/bandsaw/grinder and left me extremely impressed with the adhesion and durability of g-flex.
 
J. Doyle said:
I have twice had to remove handles that were held on with g-flex, one full tang with scales and one hidden tang. Both required hammer/bandsaw/grinder and left me extremely impressed with the adhesion and durability of g-flex.
Click to expand...
That’s good to know. I do not currently use G-flex but I will add it to my possibles list.
 
I researched acraglas and west systems epoxy a bit today. Here's what I found:

Acraglas does seem to have a BIT longer shelf life than west systems with a couple notes:

1. Acraglas does not have the "guaranteed 10 yr shelf life" as sometimes claimed. The product description on regular acraglas on brownells website lists a shelf life of "over 5 years". The tech I spoke with gave a range of "7 up to 10 years".

2. West systems puts a shelf life of 3 years on resins and 2 years on hardeners to be safe but "in actuality is much longer than that, with several reports up to 15 years".

Neither company was aware of any claims of specific time limits on bond life, such as the "guaranteed 50 year hold" that is sometimes claimed. Both companies maintained that their products are engineered to last for life and that it would be difficult to put an exact timetable on the life of an epoxy bond due to several variable factors such as uv exposure, materials being bonded, use/stress and proper use/prep/user error.

Here's an older thread on the subject with some great info, especially post #6 which pretty much mirrors my findings:

Which epoxy do you use, and why?

I've been using 30 minute slow cure from Midwest Knifemakers Supply. It's what was recommended to me a while back, and for the most part, it's worked pretty good. I do a lot of segmented scales, and the 30 min stuff gives me plenty of time to get things where they should be before it's too...
knifedogs.com
 
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I use nothing but West System nowadays. since I've been using it I haven't seen a need to look elsewhere for anything that may or may not out perform it. it works and it works good, one thing I noticed and like about it is I mix it on construction paper and keep that next to the knife while it's curing to give me an idea of when it's cured, unlike some epoxies after it's cured you can flex the construction paper and the epoxy flexes with it while some other epoxies will crack and break at the flex.
 
I'd be very much interested in the details and the "number of things" you didn't like about it in testing.
Click to expand...

As a preface.... I really don't give a hoot what anyone uses for their adhesives, but when asked, I will give my input/opinion of what I consider the best "knife" adhesive(s) based on my experiences.....if folks don't like my advice, then simply ignore it.

During all of this, I had been using AcraGlas for over a decade, and using it as my standard/comparison. I conducted many other tests besides what I listed here.....and for my purposes, found it lacking when compared to AcraGlas.

Reason #1 I prefer AcraGlas: When I asked the question of G-Flex's shelf life, they were unable to give me an answer....at all.

Reason #2 I prefer AcraGlas: When I asked the question of G-Flex's hold life, they were unable to give me an answer. And what I was told was "Uh, I'll have to check on that, and get back to you". They never did, and dodged the same question a number of times afterward.

Reason #3 I prefer AcraGlas: The mixed consistency of G-Flex is too thick for my uses/likes. I build a lot of hidden tangs, and far prefer adhesive with with a thinner mixed consistency.

Reason #4 I prefer AcraGlas: One test I conducted was to glue up a full tang with G-Flex/wood scales with no mechanical fasteners.....roughly finish out the scales, then set it on the dashboard of my truck, in the summer heat. By the end of the day one of the scales had popped off. That didn't happen with AcraGla. (Same test, same time)

Reason #5 I dislike Gflex: Another test I conducted... "glued" G10 to full tangs, let it cure for a week, and then into a can of water overnight...... next morning the G-Flex did not "let go" but there was a noticeable swelling in the glue joint, and none in the AcraGlas test piece.

Reason #6 I dislike Gflex: Whenever I reported what I considered issues with the adhesive, or ask questions, it was always met with a very defensive attitude, and more times then not, my questions went unanswered, and any issues I'd report were shrugged off. In the end, I really don't think they wanted real testing/results from me, but rather wanted my endorsement of the product. I ended up giving the G-Flex to someone visiting the shop....and kept on using AcraGlas.

Bottom line is this: AcraGlas is the best adhesive that I have found to date for knifemaking....period. Sooner or later, I suspect something better will come along.....but it hasn't happened yet. If you use/like G-Flex, or any other adhesive, that's fine..... use it......but it's not going to change my view/experiences/opinions, on what I use/recommend.
 
The subject of epoxy life comes up from time to time. Rather than rehash info I'll link to a couple of threads where the life of cured epoxy was discussed by 3 different epoxy manufacture companies, all of which couldn't understand the question of "cured epoxy life" because they all felt it was more or less forever. Raka, West Systems, and Bladebond (company that manuf epoxy special for knifemakers.
Here is the Raka and West Systems in my post #6: https://knifedogs.com/threads/which-epoxy-do-you-use-and-why.40604/

Here is the thread by Andy Dear, owner of Axis Outdoors...were a new sponsor on this board specializing in high performance epoxies:
https://knifedogs.com/threads/bladebond-epoxy-in-stock-and-ready-to-ship.41296/ That thread you'll have to read 2 or 3 pages of posts to get the full info. I used AcraGlas many years ago for bedding rifle actions and it's good stuff. Not sure if the bedding epoxy is the same as the gluing up epoxy or not, but if it's made by AcraGlas I have full confidence it's good stuff. West Systems stands very high in the marine world. Raka is a smaller less well known epoxy company but have been around for a long time.

As others have said, surface prep is the really BIG most important thing.
 
You cannot go wrong with either one.

Acraglas has been used to bed more large bore rifles than any compound on Earth. It stands up to absurd levels of recoil and I've never heard of a good bedding job coming loose inside of a stock. That speaks volumes.

GFlex was designed to secure crossbeams and struts in boat hulls. The "Flex" part of that name means that it is designed to take enormous stress loads and shock loads and will flex rather than shear. There are sailboats crossing oceans and rounding capes at the extreme ends of the Earth which have hulls made from GFlex. If GFlex was letting go, people would be dying and GFlex would be no more.

I have to echo what John Doyle said. The times that I've had to remove scales that were put on with GFlex required me to utterly destroy the handle I literally had to resort to grinding the handle off until I got to bare metal on the tang.

I buy the 32oz Gflex kit (16 ounces of resin and 16oz of hardener) and the kit lasts me about a year. I cannot speak to shelf life other than to say it looks and cures the same at the end of the year as it does when I first open it.

The only handle failure I ever had was when I first started out and I was using 5 minute epoxy from the hardware store. Chances are it was my fault because I probably didn't know anything about surface prep. Most likely I cleaned the tang with Windex and went for it.
 
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