Epoxy Question

A

axeldoomeyer

Joined
Dec 31, 2005
Messages
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I read somewhere that if you "bake" epoxy once it is on the knife it will be much harder than if it were air dried. I thought heat would cause the epoxy to become brittle. Can anyone confirm or shoot this down? Also, if the knife epoxy and handles are heated what temperature are they heated to and for how long? By heating the epoxy does it harden quicker?
 
Hardening in epoxy is a chemical reaction.It is sped up by heat.150-200 degrees for a couple of hours will set most epoxies hard.All epoxy is not created equally.Test any you want to use on scrap wood first.Some will turn soft when over-heated and others turn hard and brittle.A hot box can be made from an old cooler and a heat lamp.A rheostat (dimmer) will control the temperature.Use a cheap indoor/outdoor thermometer with the thermometer on the outside and the thermocouple on the inside
(one of those through-the-wall type).
 
Heat, like the oven is used to break down epoxy to remove handles from knives because of some screwup or another.

Most epoxies will break down at about 200 degrees F. You can put the handle of the knife in boiling water also to break it down. That's 212.

I usually go 250 if I have to remove a handle. It takes less time in the oven and is not enough heat to hurt the blade.

Never heard of baking the epoxy to make it stronger.

Epoxy is usually meant to be used in temperatures above 70 degrees so maybe someone is using a lamp on the handle out in the cold shop to help it set up. I bring mine in the house for that in winter.

Good idea to store your epoxy in the house too. They don't like extremes of temperature and can go bad on you if left in the cold, or high heat too long.:eek:
 
Do not depend on epoxy to dependably bond to your blade steels or your guard metals or your man fabricated scales or handles. It will not in my experience bond. Ensure that you have designed locking cuts or groves into your handle and otherwise and securing bolts or penned pins is a good idea too if the design permits. Even at that it may not bond but the epoxy will provide a lock. Just remember not to depend entirely upon the epoxy to bond to your blade tang or materials such as micarta, NS, and etc.. It will not. Beside using it as a bonding or locking material it is also usefull in filling otherwise small voids, making it a good source of penetration protection.

RL
 
I have not been doing this for too long; however, every tutorial and book that I have seen says to use epoxy the handle material to the tang of the blade. With that said, I also use Corby rivets, blind bolts, or pins to attatch the scales to the knife in addition to epoxy. I just want the strongest bond possible when I affix the scales to the knife.
 
when I used to make tumblestone jewellery, I used to grill (broil) the epoxied gemstone and the fitting. I think the heat not only helped the cure but made the epoxy clear and smooth. We broiled as soon as the epoxy set.
 
Epoxy does repond to heat by forming a generally stronger bond. The epoxy becomes harder if heated to high temp, and the subsequent temperature at which it will debond is significantly raised. As mentioned the speed of cure is also accelerated. Harder epoxy is usually "stronger", less prone to creep or deformations that result in failures. I have never seen it get so brittle that it might shatter like glass. I have heated epoxies in bows and golf clubs, and despite the rough and tumble they work great.

The classic example is a bow limb which if left strung in the trunk of a car might debond, violently, in warm weather. To help stop this, makers cure the bow in a hot box. This raises the "glass transition temperature", or the temperature at which the epoxy will release. It isn't necesarry to cure the epoxy in the hot box. One can let it cure at room temperature, and then put it in the box. Some tests show the benefits can occur up to a month after the initial bonding. Heating can be for 6-8 hours.

This is not something to count on with cheap 5 minute epoxies. Quality glues are recomeneded.

Heating epoxies can cause the epoxy to catch fire, as can also occur if a large amount of the stuff goes off and can't shake off the heat. The epoxy can foam causing expantion or get too runny and leak out. The use of heat up to about 180 degrees is not a big deal, just proceed carefully so as not to get any undesired side effects. Heat with epoxy can increase the fume load. Consult the manufacturer for information on correct proceedures.
 
A couple of things I've noticed about epoxies...
Some will blush and leave a waxy film on the surface...these are to be avoided. The wax doen't make for a good bond.
Check epoxies for curing shrinkage...Take a flat piece of foil, pour some epoxy across it, and see if it has remained flat after the cure. If not, throw the epoxy away.
 
Andrew Taylor said:
when I used to make tumblestone jewellery, I used to grill (broil) the epoxied gemstone and the fitting. I think the heat not only helped the cure but made the epoxy clear and smooth. We broiled as soon as the epoxy set.
Click to expand...


Exactly what type of epoxy(s) were you "grilling". Need names here. Most knifemakers are using stuff like Devcon, Duro, etc. Two part epoxies.

If you subject those types to heat in the 200 degree range you will harm the bond. It might reset after it cools if held together, but will not be as strong as before.

It's a simple matter to make most any material to bond to a steel tang.

If it's a full tang and you taper it, you should have a 60 grit aprox.hollow grind in the middle of the tang left over from the tapering operation. That will help hold epoxy. If it's not tapered, hollow grind the center of the tang anyway, don't run outside the borders of the tang. It doesn't have to be real deep.

I also put 1/16" deep(aprox.) dimples on the inside of all my handle slabs with a small drill bit(I use a B&D 1/8" bullet tip power point for this), lots of them. Just keep them slightly away from the edge area. Make sure the tang has a 60 grit, or rougher finish on it, the same for the inside of the handle material and guard where the handle material butts up against it.

Before you batter them up with epoxy, wipe all mating surfaces down with acetone or lacquer thinner and don't touch them with bare hands again.

I use "C" clamps to hold my material together while curing and make sure not to really torque them down and force all the epoxy out. Just snug will do the trick.

I used pins only with epoxy on micarta and woods for many years and never to my knowledge had a handle failure.

On many stick tang knives, I used epoxy only and never had a failure. Just notch the tang before assembly.

I'm simple, I just use Devcon two ton and have found it to work great. I've used it for 20+ years, and the only failures I've had was the epoxy going bad(it won't set up when this occurs, stays rubbery) from storing it in the shop where the temperature extremes here vary greatly, so now keep it in the house and no more trouble.
I let it set up for 24 hours before working the handle again and try not to overheat the tang, or pins while working so as not to break the epoxy down. It's very easy to do that(you can exceed 200 degrees F quickly grinding, especially with dull belts) and you can have separations occur if you do, or rings around your pins.

The handle material must lay flat to the tang before assembly. Don't count on epoxy and "C" clamps to pull them together. Make sure it's right and everything fits well first.
 
Protactical said:
Epoxy does repond to heat by forming a generally stronger bond. The epoxy becomes harder if heated to high temp, and the subsequent temperature at which it will debond is significantly raised. As mentioned the speed of cure is also accelerated. Harder epoxy is usually "stronger", less prone to creep or deformations that result in failures. I have never seen it get so brittle that it might shatter like glass. I have heated epoxies in bows and golf clubs, and despite the rough and tumble they work great.

...................................
Click to expand...


We need the names of the epoxies here. You are comparing apples to oranges. Most knifemakers use two part epoxies, some what you call "cheap 5 minute epoxy". I use the 24 hour stuff myself but I have a feeling it's nothing like you use at all.

In fact most knifemakers use two part epoxies that are available at home depot, the local hardware store and God forbid, "Wal Mart" with great success and have been doing this for many, many years without any measurable degree of failure. I'd say that's pretty good when you consider the abuse some knives take, the places they're used, etc.
 
Epoxy can be heated but it must be done in 10 degree steps. Each brand will have different formula. I have a friend who makes aircraft body sections and they use a vacuum seal and very precise incremental temperature steps with thermocouple to control it.

I want my epoxy to take a full 24 hrs to set so that it soaks into every pore and crack. This means I do my epoxy work in my shop where it is cooler then inside the house.
 
"In fact most knifemakers use two part epoxies that are available at home depot, the local hardware store and God forbid, "Wal Mart" with great success and have been doing this for many, many years without any measurable degree of failure. I'd say that's pretty good when you consider the abuse some knives take, the places they're used, etc."

The question wasn't a referendum on Knifemaking techniques, the question was do epoxies respond this way. The answer is yes, and you can find massive evidence by Googling epoxy glass transition, or something similar.

I don't heat all the epoxy I use, in fact hardly any of it. Any time one does something structural one has to ask the question what the objective is, as I mentioned with archery equipment there is a well known failure mode for epoxy relative to heat, so it is wise to take precautions. I can think of some knife making situations that are similar, for instance blacked out knives for Iraq could easily get into the same kind of heat envelope. And earlier in the thread there was some reference to epoxy failures in holding on handles, that would certainly be a wake up call for me. I would also be concerned about sending a knife from my 50 degree shop to some guy in Texas who might leave it in his car truck in the middle of summer. My low heat vs. his high heat could be a problem. But whether there is a problem is up to you to decide when you make the knife.

Keep in mind that if you heat the epoxy during the setup, or post cure it with heat (another google search there). It's glass trans will rise. This means you can't disassemble the product later with a lower heat. I once ran into this problem with a golf club and had a great deal of difficulty removing the head from a broken shaft. I had post cured it by placing the head on a coffee cup warmer/hot plate. So the higher structural characteristics and heat resistance aren't always advantageous.

I use WEST System G5, in preference to Devcon these days, I don't heat this one so I don't know what happens. Devcon is neat for certain things because it is said to expand a little during the cure. Generally 5 minutes are low performance glues. And there are brands much worse than Devcon and G5. Like anything they have their place, like flytying.

I use Golfsmith shafting epoxy for a more durable bond when doing stuff where there is a socketed fit, and I might conceivably want to separate them later. This epoxy does respond well to heat.

The bow guys use Smooth On, which is designed for heat.

I use West System or System III boatbuilding epoxies with and without heat for critical applications. They are very thin compared to 5 minutes so they will instantly wet out materials which can be good or bad. Generally any 1-1 mix epoxies are pretty low performers. 1-5 part mixes are usually good in this range. I use this stuff for bows, boats, whatever.

"I want my epoxy to take a full 24 hrs to set so that it soaks into every pore and crack. This means I do my epoxy work in my shop where it is cooler then inside the house."

That is the opposite of the way I work, but if you wanted to post cure your work, you could do just what you are doing, and then heat the stuff for greater heat resistance, assuming the glue allows it. Not suggesting you need to do this, it's just an option since the cure and heat phases can be done separately. Sounds like you are already getting the results you want.
 
A trick I learned a few years back from R.W.Wilson is to use fiberglass resin thickend with a little talc (baby powder) on a hidden tang knife to fill the void around the tang. It works great and its a lot cheeper than epoxy,I buy it by the quart. I've never tried it on a full tang but it might work as well as epoxy....John
 
ive been using Gorilla glue on most of my scales, but i also do pein them or use corby style bolts. ive considered using it on a stick tang with a somewhat tight fit already as it does expand some.
 
Fiberglass resin isn't a glue but a casting medium for molds and such. One can use it for stuff like bedding rifles where the bolts do the work. Sounds like you have a similar balance in what you are doing.
 
Mike Hull said:
Exactly what type of epoxy(s) were you "grilling". Need names here. Most knifemakers are using stuff like Devcon, Duro, etc. Two part epoxies.

If you subject those types to heat in the 200 degree range you will harm the bond. It might reset after it cools if held together, but will not be as strong as before.
Click to expand...

It was a standard two part standard hardening (as opposed to Rapid) called Araldite. This was in England. Is it sold in the US?

The gemstone books said to heat it just after it set. You heated it until it went completely smooth, but the point in doing it was to make it clear and thereby invisible as well as smooth.
 
I said it earlier and I'll again here now: do not depend on your epoxy to bond with your tang and certain handle materials. It will not. You must provide cuts within for it to harden into. There are many materals exopies will bond to. Your steel and many of your man fabricated materials it WILL NOT bond to. I use it, for one of several reason, to provide a closer for moister penetration. Even that is ifie.

RL
 
Andrew Taylor said:
It was a standard two part standard hardening (as opposed to Rapid) called Araldite. This was in England. Is it sold in the US?

The gemstone books said to heat it just after it set. You heated it until it went completely smooth, but the point in doing it was to make it clear and thereby invisible as well as smooth.
Click to expand...


Ah, thanks. I'm not sure if it's available here as I've not seen it, but then I haven't looked for it either.:confused:

The 24 hour Devcon(2 ton) I use dries with a glass like appearance. Very smooth hard and glossy where exposed.
 
I too, have found that DevCon works very well if not the best. From what I can tell that is what others use as well.
 
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