Epoxy Problem

just took some extra time..... mixed it up as best as i coud. made sure there were equal ammounts of epoxy and hardener, and stirred like a bastid. scuffed up the handles and tangs really well, cleaned everything down with acetone. glues it all up. now its sitting in the warm house. its been about 2 hours.... i don't plan on touching it untill tonight at about 11 after work, if not then tomorrow morning. i'll keep you guys updated and post some pics when i finally get it right. thanks again

Mike
 
With a 5 minute epoxy like you are using I would look to heat and unstable handle material as the possible culprits. The quick set epoxies that I have used have generally held up well.
From my experience they do not handle heat well. Always remember that epoxy is a thermo-plastic. They are 2 part glues for a reason. The largest part is always the resin (glue) that holds the parts together. The 2nd part is the catalyst. The function of the catalyst in epoxy is to cause a chemical reaction that heats up the resin and causes it to harden. Generally speaking, The more resin the stronger the joint the more catalyst the quicker it will set up. The resin has to reach a certain temprature in order to harden properly. If atmospheric temperature is too low the resin will not harden. This problem is easily resolved by putting your work in a warm environment (70 degrees?) or artificially heating it with a portable space heater or even a hair dryer. It all depends on the epoxy you are using.
The second variable is the handle material. Organic materials, basically, contain fiber, water and oils. If you have ever viewed wood or any other organic materials under a microscope you will realize that after they dry out they have aiir pockets in them. These pockets shrink or enalarge depending on the moisture in the environment and the denseness of the material. If your handle material is not dried properly, or stabilized, and you pin/bolt/rivet it together in the middle of the piece and it is not fully dried/stabilized it is going to lift up in the areas that are not held down.
An excellent treatise on epoxy can be found at the http://www.wessex-resins.com/westsystem/wspotlife.html . As much as we knifemakers use epoxy these days it pays us well to understand what is going on with it.
BTW I am not recommending these products for knifemakers, they will work if you do your research and buy the right ones but they are made for boatbuilders. I discovered them while building a Kayak. The information on the site and in the literature they provided greatly increased my understanding of epoxy and help me to decipher cure problems I was having.
Just can't leave without telling a true "Epoxy" story. The production shop I worked at had a two resevoir epoxy "mixer". both resevoirs had their own pumps that were connected by a chain to regulate the amount of epoxy and catalyst that were mixed together. Everything went fine for years. Twist the handle and the perfect proportion of epoxy would pour out into your cup. Well' one winter we had a problem with the epoxy coming out of the pump.It would hardly pour out at all and when it did the handles wouldn't stick. I couldn't figure out what was wrong. Then I did a careful inspection of the mixing machine and discovered that both pumps had zerk fittings on them. As anyone who has worked on any type of machinery would know Zerk (Zirk?) fittings are for greasing bearings and other fittings. Well' Dad taught me that if it's got a zerk fitting it needs to be greased on a regular basis. So I did. I got the grease gun and greased every fitting I could find on that epoxy machine. LSS I ruined 4 gallons of epoxy. Epoxy does not react well to petroleum based products. I had to completely tear apart the machine and clean every part with acetone.
Moral of the story is that epoxy is a finnicky critter. You find a good system that works stick with it and try to repeat your conditions closely. If something ain't working investigate and find out why.

my 0.02cents worth

Dwight Hazelett
 
Like good ol' Gib, I like Brownells products. Quit messing around with the crappy stuff, go ahead and order yourself some Brownells Acra glas gel. I have used enough of it over the years to say it is the best epoxy on the market. Grouchy old bastid, ain't I?
 
Lots of good advice here! One thing I'd add is curing in the oven. Most of the epoxy data sheets I've read talk about warm curing and it's always a benefit.

I heat my oven to about 120 degrees, put the knife in, turn it off, and leave it over night.

Problems (already mentioned) that I've had are:

Wood shrinking
Not perfectly level tang (don't compensate by using multiple c-clamps to torque the wood.)
Not warm enough cure temp
too much clamping.

Steve

PS I also add lots of divits in the wood now. Some call them epoxy pockets.
 
Very good ideas, Steve. I like to add hidden threaded pins to my handles. I haven't had any 'glas let go, but the pins are for my own piece of mind, probably. I used to use some horizontal hidden pins when I used a lot of different materials in a stacked handle. You know those pleshett (sp?) darts from the artillery rounds? they make great linear hidden pins, hard and tougher than you can believe.
 
Is there any optimum thickness for the epoxy ? In brazing the optimum is .003" .
 
I'd like to pass one more epoxy tip before this thread goes to the archives.
In boat building when we want to put in internal nailers for the inside of cabin walls that must conform to the shape of the hull we have a good trick that can also be used for knife scales.
We coat the strip with our 24 hour epoxy but spaced along the strip we leave a few small blank areas. In those areas we use 5 minute epoxy.
That way we can put up a quick brace and take it down in a few minutes to get access to the next rib while the slow set gives the strength we want.
I see no reason for knife scales that you should have to sacrifice the strength of slow set for the speed of quick set if you want to do it this way.
 
adammichael said:
I have been using the K&G brand 24 hour epoxy. It is great. i have never had any trouble with it. it is pricey at $8.95 for an 8 oz kit but i think it is worth it. It is alot thicker when mixed than the other 24 hour epoxies that i have used but i like that.
It comes in 2 seperate tubs and lasts forever. If I could figure out how to mix up the correct amount so i dont toss half of it every time i glue up a handle it would last alot longer.
Click to expand...
K&G was my favorite before Acuraglass. I found the 24 hours to be a bit optimistic sometimes though. Thats ok, the slower the stronger. As far as mixing it, buy a cheap set of stainless kitchen measuring spoons (the deeper the better). If you use the same spoon for both, make sure you clean it with solvent or brake cleaner between bottles. I also use the table spoon for mixing because it makes a handy container. You can bend the handle so you can use the vise to hold it stable for you.
 
If you use spoons make sure you scrape the epoxy out well. Small amounts of epoxy are the most difficult to mix. You lose some on the spoon and lose some on the mixing stick. Use 2 sticks and scrape each stick on the other. The small amount on the stick is often not scraped down and mixed. You don't have a lot of play with the mixture. Less than 10% off on either part and you lost that batch. You can consider epoxy properly mixed if it's even in color with no streaks.
If you want to mix small amounts you can buy large syringes from woodworking suppliers, marine chandelrys or fiberglass dealers.
They're good because you can fill them and you're good for numerous batches. If you are off a bit on mixing make sure it's not the hardener. Commonly called part 2. You have slightly more play with the epoxy base.
But not much in small batches.
Some expoxies give you more play than others. As stated here numerous times. If it isn't curing heat it's usually the accuracy of the mix that causes failure.
 
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