Can you tap epoxy?

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ridgy

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Have to replace an engine mount and having removed the old one, it was screwed rather weakly in to a wooden base but the screw hole is a bit of a mess.

One option is to use a bigger screw but I can't find and stainless hex head self tappers of a good size.

Was thinking to drill it out and fill the hole with epoxy then tap it so I can use a proper bolt. I was wondering if epoxy sets hard enough to make this work?
 
ridgy said:
Have to replace an engine mount and having removed the old one, it was screwed rather weakly in to a wooden base but the screw hole is a bit of a mess.

One option is to use a bigger screw but I can't find and stainless hex head self tappers of a good size.

Was thinking to drill it out and fill the hole with epoxy then tap it so I can use a proper bolt. I was wondering if epoxy sets hard enough to make this work?
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are the existing fixings "Coach Screws", your description doesnt make total sense to me
 
I believe you can tap a thread into epoxy, yes. Never tried it myself, but seen it described and I can well believe it works. Best to give the epoxy plenty of time to cure fully (overnight or more) before drilling and tapping, I'd have thought.

Pete
 
I would be inclined to drill the hole out to quite a large size (maybe 1/2 in) then epoxy on a wooden dowel /peg -quite tight fitting. then drill a pilot hole in the peg for you mounting screw.
 
If you are talking about a hole in wood where the screw has stripped the hole out, best bet is to drill out well oversize and glue a wood plug in. Effectively you are then starting with a new piece of wood. Always drill a pilot hole when using large diameter wood screws.
 
It is a tapered screw with a hex head. It is maybe 4cm long but only the last 2cm are threaded and with a very coarse thread.
I've never seen anything like it before and would prefer to use a normal bolt to replace it. The hole has also had some water ingression hence my thought to drill it out.
 
How you deal with it depends on how bad the current thread is. The correct fastenings for this job are stainless coachscrews with a hex head. M8 probably - they are not self tapping but require a correct size pilot hole. If the hole is more or less the right size and the wood is good, then you can pour some thickened epoxy in and rebore the pilot hole. If the hole is too big and rough then bore it oversize, epoxy in a dowel and redrill to the correct size.
 
As said before the best way would be to epoxy a block of wood and then screw into that.As an alternative you could enlarge the hole,fill it with microfibers thickened epoxy and place a coachbolt coated in vaseline in the correct position.Once cured the bolt can be unscrewed and you're left with a tapped hole.
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What you are talking about is a coach screw designed to go in wood.

A bolt is normally designed to go into metal and the thread is much finer - absolutely no use for going into wood even if epoxy is used.

Peg the hole with wood and replace original coach screw.
 
30boat said:
As said before the best way would be to epoxy a block of wood and then screw into that.As an alternative you could enlarge the hole,fill it with microfibers thickened epoxy and place a coachbolt coated in vaseline in the correct position.Once cured the bolt can be unscrewed and you're left with a tapped hole.
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And use an additive with the epoxy that makes the whole lot very hard.
E.g. graphite powder can be added to epoxy (bought from chandlers) - some of the additives make the epoxy easy to sand (you don't want that) and some make it rock hard.
 
Yes you can drill and tap filled epoxy with metal taps for normal bolts.
Ideally fill the epoxy with aluminium powder.
Alternatively, epoxy in a stud.
Exactly how strong that is depends on how well it's done. but it can be very strong.

If you use those coach screws in a hole that is mostly epoxy, you may find they bind or split the wood apart if you don't drill the hole big enough. Epoxy is not as crushable as wood.
Epoxying the hole and inserting a plastic plug (e.g. rawl plug) can work very well.
 
ridgy said:
Very helpful everyone, dowel and coach screws it is.
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If you have a pillar drill it might be worth getting a plug cutter and making your own dowels from a piece of scrap hardwood. That way they you will be screwing into cross grain instead of end grain.
 
davidej said:
I would be inclined to drill the hole out to quite a large size (maybe 1/2 in) then epoxy on a wooden dowel /peg -quite tight fitting. then drill a pilot hole in the peg for you mounting screw.
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+1 on this method.........

You need new wood in there and if it has had water ingress I would treat with thinned epoxy first to kill off all spores if you havent removed all the damage with drilling a new hole.

Tom
 
lw395 said:
Good link, thanks.
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I saw a convincing demonstration of the technique when I attended a course at Wessex Resins Ltd.

The instructor bonded an eye bolt into a piece of timber and then put the whole thing in a test rig and pulled on the eye bolt. The timber broke but the eye bolt did not pull out of the epoxy plug.
 
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