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Dumb epoxy question...

Mundele

Mundele

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

I'm just curious. Someone mentioned that epoxy broke down at relatively low temperatures. What happens to it? Does it melt and become soft, or does it break down chemically, or does it burn? I suppose I could mix up a little and try it (but then again, I'm lazy and you guys are so smart!!)

--Matt
 
Matt, I didn't see the post you were talking about but it depends on the epoxy. For instance, JB Weld (regular) will withstand tempatures in excess of 400F.

What happens when it beraks down is it loses it's bond and releases. I've never melted any but have burned it a time or two.
 
Thanks for the info. The post was one I read a few weeks ago. This was more curiosity than anything...

--Matt
 
Because of regular epoxy loosening with high heat, I'm thinking about epoxying my handles, but setting the pins with JB Weld because the JB Weld can take much higher temperatures. Does anyone notice any gap between the pin and the scale when using a #30 hole on 1/8" pins? I've been wanting to use a #30 bit and JB Welding my 1/8" pins in, but was afraid of a little gray ring around the pin. Currently I'm cutting three little tiny indentations/notches near the centers of the pins, so the JB-Weld will have something to grab, but thats a bit troublesome.
 
In fact it's a good idea to use a #30 drill for 1/8" pins. When the hole is too tight, you squeegee the epoxy off the pin when you push it into the hole. I use a size F drill for 1/4" pins also. You can't see the 0.0015" gap.
 
i use a #30 for 1/8" mosaic pins. it's enought to give a little room for the epoxy but it's not visable. keep dunking the handle to keep it cool while shaping so you dont over heat the epoxy.
 
Mundele~

i remember reading somewhere that the epoxy can melt down and will regain its strength once it has had time to return to its normally hard state ... so long as it has not been burned beyond recognition ..

hmm .. i will have to find the source of that info before i am truly quoted on it.

i knew there was a reason i was supposed to tidy up my workshop..
oh well .. time to sift & search..

D.
 
A #30 bit and a 1/8 pin will work fine. One thing that I try to do is use soft metal and after setting the pin tap it with a hammer. This peens it enough to completely fill the top of the hole while leaving the bulk of the pin the same size. Grind it down flush and it looks like it grew there. It's also (IMHO) a stronger joint.
 
Another thing I do to make epoxied pins secure is to cut little notches into the sides of each pin (I use a Dremel cutoff wheel for this). This provides a place on each pin for the epoxy to "hide", even if the pin is a fairly snug fit in the hole.
 
Depending on type epoxies can either soften or soften and melt and finally they all disintegrate with heat, softening temps vary from 40 C to 180 C. Most epoxies turn kind of rubbery with heat and they harden back when temperature is lowered usually without loss of strength.

The word "epoxy" covers several thousands concoctions so saying anything definite is somewhat difficult.

What ever you want to fasten with any adhesive it should be clean.

TLM
 
Jerry, Don: I've been sandpapering horizontally on the pinstock to give it some texture, as well as putting three little notches (large enough to add traction, but not big enough to weaken the pin) with a hacksaw (just push a 32 tpi saw gently across it once). Tried pushing at the pins after the epoxy set, and it doesn't seem to want to come out. However, I'm having trouble with the thong hole tube liners. I drill a 1/4" hole, and the thing is extremely tight, I have to sand down the tube and beat the crap out of it with a rubber mallet and squeeze it in slowly with a vise to get it to go in. Because the fit is so tight, I've split a nice set of stabilized maple before, and am not looking forward to ruining another set of scales. What is a good drill bit size to fit in 1/4" thong hole tube lining so I don't have to beat it with a mallet and risk messing up my scales. #F drill bit or is that still not loose enough?
 
Chang, before you go to a larger bit try sticking the thing in the freezer for 1/2 hour try to put it in right away. If you are only a couple of 1000 off it should shrink enough to go in without a lot of force.
 
The problem with the freezer trick is that it's hard to keep it dry when it comes out. I use a size F drill for all my 1/4" pins and thong hole liners. Works great.
 
OK, sounds good, letter F drill bit it is then. Thanks. I started oversizing my 1/8" pin holes in the steel by 1/64", making a 9/64" hole, but thats a little too loose and requires the gaps to be filled with JB-Weld to prevent wobble (too much trouble), so I'm going to get some #30's as well.
 
In general the harder it is to cure a type of epoxy the higher the heat that it will tolerate. I've used heat cure epoxies that would tolerate hundreds of degrees when cured. On the other hand I've found 5-minute epoxies that noticeably soften in water below the boiling point.

Epoxy can be heated to the point of slight softening and it recovers most of its strength on cooling. A big problem is if there is an expansion coefficient mismatch between the materials that you are bonding. If you bond steel to a highly expansive material the epoxy will be stressed by differences in expansion of the two materials when you heat them to a different temperature than when they were first bonded. The bond may break down when the epoxy weakens and is stressed by expansion mismatch.
 
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