What will epoxy NOT stick to?

Feb 08, 2009 37 Replies

I have a small project which involves expoxying some brass threaded inserts into some (high value) wood. Specifically, these are cylindrical inserts with wood screw threads on the outside and 10-20 machine threads on the inside. The wood threads have loosened and I'm going to try to fill the voids with epoxy. However, the inside (machine screw) threads must remain epoxy free so that screws may be installed/removed repeatedly.



If I just coat the outside of these inserts and install them, the central machine threads will (undoubtedly) fill with the excess squeezed out. Even if I insert a machine screw (dry), the epoxy could be squeezed into the inside threads. So, I figure the way to go is to coat that screw with some sort of grease that the epoxy will not adhere to. Once the epoxy is cured, I can clean the grease off the inside threads with solvent.



What's the best grease (or other coating) to use? It should be viscous enough that it doesn't migrate to the outside of the insert and interfere with the desired bond.


Paul Hovnanian mailto:Paul@Hovnanian.com ------------------------------------------------------------------ In theory, practice and theory are the same, but in practice they are different -- Larry McVoy

"Paul Hovnanian P.E."

** Assuming the wood is a " hardwood" you may be better off using fast setting "super glue" than epoxy - particularly the quick setting type that tends to go soft over time.

If there is even the smallest gap around the threaded insert - super glue will wick down it and be absorbed into the wood locking the insert tight.

Otherwise, unwind the insert a couple of turns, apply a film of super glue to the outside and quickly screw it back.

One precaution, make sure the insert is quite clean on the outside before you do any gluing, a wire brush is the go.

..... Phil

"Paul Hovnanian P.E." wrote in news:498E46B6.1F907D62 @hovnanian.com:

Paraffin (candle wax) ought to work, be easily removed, and it'll lubricate the threads. There's a coating material used for gold-plated edge connectors to prevent a solder bath from adhereing that's probably a silicone rubber that'll probably release (but not guaranteed to so).

--Damon

I've used a product called "Mr. Grip Stripped Screw Repair Kit" to repair screw holes in wood. It's primarily used with tapered wood screws, but I don't see why it wouldn't work with an insert. Here's a listing for it.

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An alternative to normal epoxy might be the kneadable epoxy putty. It shouldn't run into the threads, and should hold just as well as regular epoxy.

Should be able to get either or both at Home Depot or Lowes.

Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer it gets to the end, the faster it goes.

Damon Hill wrote in news:Xns9BABBF620F0F2damon161attbicom@127.0.0.1:

also,if the wood is a tropical exotic,you may want to clean it with acetone to remove oils.I've seen it recommended in Wood Magazine for some exotics.

Jim Yanik jyanik at kua.net

shouldn't

I'd second the epoxy putty, or even Bondo, for normal repairs but the "high value" makes me skeptical whether any epoxy is a good idea. Had not seen the Mr Grip gizmos before and they're probably the best idea to at least *try* before gunking up a valuable piece.

Rich Webb Norfolk, VA

Epoxy should be fine. It will wick into the grain of the wood and provide a stong bond. Look for the thicker Epoxies, they have a filler in them that will fill the larger voids. As for the machine threads wax would be good, or mold release.

Cheers

Silicone grease? Teflon-loaded silicon grease? Liquid graphite?

wrap teflon pipe tape on the machine screw threads first. (if you haven't got any use wax or grease)

adhesive tape over the bottom end of the threaded barrel?

epoxy paper or cloth over bottom end of each and allow to set before mounting the inserts?

smaller hole drilled in center to form a well? (so excess doesn't back up into threads)

How about threading a lubed up nylon bolt into the hole. Nylon is naturally slippery and smooth so even it a bit of epoxy does touch it, you will be able to get it out.

I've used those threaded inserts for many years. The 1/4"-20 are favorites. Every insert, no mattr its size, was a bugger to install but not even one of them has come loose. Maybe your pilot hole was too large? Or your wood is soft/crumbly? (I work with hard maple mostly, some walnut and cherry.) Well, anyway....

If I were doing the repair job you describe, I would stuff the insert with beeswax and heat until melted, topping off as needed. I'd use beeswax instead of candle wax because it is soft. (I happen to have blocks of beeswax, left over from my misspent youth when I used it to wax heavy thread for stitching leather.)

By the way, coating whatever-fastener with varnish before inserting into wood is an old woodworker's trick.

Dry lube. Either mold release spray (food grade or not).

That way there is no build up.

You should consider, however, drilling out the threads that are loose, and installing an insert. You get the right sizing, and do not have to jump through these hoops. Heli-coil?

Yes, there are nice, tiny wire brushes out there specifically meant for fine thread cleaning. NOT!

Sheesh, dude. Think about the application!

Nix epoxy in a cup, and let it sit there until just before it loses its "pot life". At that point, you can apply it without so much worry about it flowing into every little crevice.

The pot life is usually declared on the web site for a product on the spec sheet for that product, which is not always included with it in the packaging.

I have some very wet stuff at work that after a couple hours from mix time, it is useable (hard enough)as a staking compound for connectors so they do not vibrate apart in the field. When wet, capillary attraction forces and surface tension come in to play. When it has nearly polymerized already, it does not move quick enough for such processes to take place before full polymerization (hardening)takes play.

Simple mold release spray. A dry silicone lube.

Almost as bad as Phil with the wire brush suggestion.

If you get epoxy on the machine threads, chase the threads with a bottom-tap to clear out the epoxy.

The teflon tape used in plumbing can also be used to prevent epoxy from sticking to a screw.

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