Hand Tools Archive

Subject:
Re: epoxy
Response To:
Re: epoxy ()

William Duffield
I'm not sure how to answer your question, since I haven't done any in vitro testing of these joints. Also, I can't remember any instance I actually epoxied brass to brass. I've epoxied brass to M2 stainless steel and C4 carbide, wood to brass and, it goes without saying, wood to wood. None of my tool joints have been particularly high stress, because I try to use the largest brass ferrule that will work with the size of the handle, to retain as much wood inside the ferrule as possible. In one of these awl threads, I provided a link to Doc Green's website on how to choose a ferrule and tool mortise depth to minimize splitting the wood handle. It is a good reference source for anyone using a ferrule for strengthening the attachment of a handle to the shaft of a hand held tool, be it chisel, awl, screwdriver, turning tool or carving gouge.

Also, I make sure my fit is not so tight that the epoxy is completely scraped off one surface or the other. I am also careful to not apply so much clamping pressure that the epoxy is squeezed from the joint. To the contrary, if I know that both surfaces are wetted by the epoxy and all the air pockets are eliminated, I avoid using clamps whenever possible. Sometimes, the joinery or gravity or a small weight or even the weight of the tool in the handle will be enough to hold the joint in place until the epoxy kicks. Unlike the water-borne glues that we use for joining wood to wood, epoxy doesn't shrink appreciably as it cure, so very high clamping pressures are not needed.

There are other techniques to increase the odds of a sufficiently strong epoxy joint. The most important is to thoroughly clean all surfaces. For metals and oily tropical hardwoods, I use acetone to remove the oils and other contaminants. Compressed air or a vacuum and brush remove sawdust. For additional joint strength (belt and suspenders :D ) I will sometimes add some "tooth" to the metal surfaces with coarse sand paper or diamond file.

When building a prototype tool, i have sometimes left the tenon a little too large or chosen an inappropriately brittle wood. That has resulted (double crud! :( ) in stripping its threads when installing the brass nut. For expediency, I have resorted to a quick application of cyanoacrylate instead of epoxy, and even this has not failed when i tested the tool. That is only for testing "proof of concept"--I don't trust superglue for long term applications.

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