Does Epoxy shrink when it cures?

Mundele

Mundele

Joined
Aug 5, 2000
Messages
403
Hey guys...

I've used epoxy to secure the blades of some stick-tang knives. On every one I've done, I am careful to fill the hole with epoxy, and yet when it dries or cures, I have a little sunken in place. Am I inadvertently squeezing some out, or is it shrinking or what???

I was using the slow-set 12 hour epoxy (or was it 24?? anyway)

(I suppose I could start putting ferrules or soldering metal guards at the front and it wouldnt be an issue...)

--Matt
 
I dont think it is shrinking so much as it is air bubbles rising to the top before it hardens, thereby lowering the overall level. Your Idea of putting something in front is a good idea. One other thing before pouring the epoxy in, drill a small hole, about 1/16th-5/64th"on the underside of the handle material near the base of the hole angling downward(the tang hole being in the upright for descriptive purposes), about 45deg.,angle,when you pour in the epoxy it will fill the hole faster by forcing the trapped air out the small hole. When epoxy starts to flow out the small hole, just put a piece of tape over it. When dry and finished it is virtually unnoticible. Hope this helps a little.
 
On the average epoxies shrink 3.5% by volume, some special ones practically nothing. I agree with MJHKNIVES that the most propable reason is air bubles, depending on your handle material that might also take in some.

TLM
 
Thanks for the info. I figured if it shrank as much as i suspected, that it would end up pulling itself loose and coming "unstuck". On one of my knives, the tang goes through the handle so there was a sizeable hole. (the tang plugged it though, I guess)

I need a big disposable syringe to inject this stuff with. oh well...

--Matt
 
Matt, TLM pretty much summed it up. Most do shrink some and it settles and air bubbles take up room. I just finished a stick tang last night and filled it in two pours.(three counting the initial stick together)

It has a pinned guard so I used 5 minute JB weld to stick the guard and bolster and the handle together. Not much just enough to keep them exactly where I wanted them.

I used candle wax under the guard to make sure I got no leakage on the blade and just to make extra sure ran a bead of wax around the bolster/handle junction. I clamped the tip of the blade in a padded vice so the knife was upright and used thinned epoxy, heated with a heat gun (to make it flow better. I filled the hole about half full.

This was after the nut was tightened and ready to be finished. After an hour I did another pour to bring it flush with the butt of the handle.

This has worked pretty well for me and gives a complete seal to both the inside of the handle and the guard/bolster/blade junctions. No moisture or dirt will ever get in there. Of course the knife will never be taken apart either.

If you intend to use a butt cap and screw it to the handle you can insert a steel, threaded bushing in the second pour.
 
Peter,
I guess you filled it from the butt end? Will a coating of candle wax on my blade keep the epoxy from getting on it also? I might hve to try that. My handle was all wood and the end of the tang went through a brass end nut and was peened down onto it. I filled mine in one pour (which might be my problem). I filled the hole as best I could by using the knife tang to spread it down into the hole and once I thought it was full I flipped it over and put hte blade in the vice and peened the tang. I flipped it back over again (pointing up) and filled around the blade. I will probably mix a little more and fill the little crevice left. It makes me wonder if I have a lot of bubbles down in there.

Do you make a lot of stick tang knives? I sure would like to see some pics....
 
Candle wax will work but would be a Bit@h to clean over the entire blade. A better approach would be to use epoxy bedding release agent (Brownells) or just boil a bar of Ivory soap until you have a thick syrup.:)
 
So what do you do with this syrup? Do you apply it to the areas you dont want epoxy to stick to? Will it mess up unfinished wood handles? (i.e. make them not take stain)
 
Yep, just paint it on and let it dry. It's the same release agent I make to take latex molds of things I want to copy.

It won't hurt finished wood but it will stain unfinished or porus wood.
 
I was having trouble measuring epoxy ( I buy the quart size) so I use a syringe to measure. One for each part!
Just because I'm so cheap, I guess.
Lynn
 
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