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Old 03-03-2015, 03:39   #31
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Re: Best Practice for Repairing Worn Threads in Wood?

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Originally Posted by minaret View Post
No toothpicks or match sticks, they are very very soft wood. The pro method is known as a "sweetnail", as opposed to a treenail (trunnel). Just take a block of timber which matches the finish, ie teak or what have you, about 3" x 3" x 4" is good, and kerf it on a band saw in a closely spaced grid pattern with a taper to it. Then chop the blunt end off in a chop saw. This gives you a few dozen sweetnails, which are about 3" long and taper from about match thickness to about triple that. They are also square, not round, which is key. Dip them in 5 min epoxy (I like G5), and then gently hammer them in to the screw holes which need retapping. You are hammering a square peg into a round hole-the hole will conform, locking the sweetnail in place. This is the same reason treenails are not made round, but octagonal. For larger diameter holes, you just trim some of the front off of the sweetnail, matching the diameter of the taper to the diameter of the hole. This leaves less nail proud to trim off after the glue cures. This is done same as you would trim a bung, but is trickier as you are trimming end grain. A japanese flush trim saw is excellent here. Sweetnails done properly will dissapear much better in a finish too, as they leave a very small diamond shaped joint, as opposed to a circle, which draws the eye. Super fast and easy to do once you've got the method down.
Extremely useful, and I suspect not just for me! Thanks!
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Old 03-03-2015, 03:42   #32
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Re: Best Practice for Repairing Worn Threads in Wood?

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Originally Posted by carstenb View Post
I've had good sucess with saving the sawdust from some teak (or similar) wood I have cut. I keep a little bag of this around in my box of assorted fix-it things. Then I mix the sawdust with wood glue and fill the screw hole with it and let it dry.

Now you just drill a pilot hole and reinsert the screw - this is better than a dowel and will hold virtually forever.
That's an interesting idea -- and I need teak sawdust anyway for my rail. I'll try to get some and try it. Cheers.
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Old 03-03-2015, 03:49   #33
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Re: Best Practice for Repairing Worn Threads in Wood?

Thank you, Minaret, for what sounds like the most professional solution. I'm not so wood-crafty, so I keep some golf tees around for the repair. Maybe I need to find a place for a small band saw...

Fair winds,

Leo
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Old 03-03-2015, 05:56   #34
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Re: Best Practice for Repairing Worn Threads in Wood?

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Originally Posted by rwidman View Post
That's correct.

There's another, more complicated way that hasn't been mentioned - metal screw inserts.



Drill the hole out to fit one of these, screw it in and use a machine screw instead of a wood screw. This is a good way to attach something you will be removing from time to time.
An intermediate method to thread inserts I use.
Fill the hole with liquid epoxy precoating.
Fill the whole with thick epoxy glue.
Insert Bolt coated with spray on vaseline without the hinge.
Wait for the epoxy to cure.
Remove bolt. (The vaseline will keep the epoxy from tacking to hard and you should be able to remove it with a spanner)
Now you have strong epoxy thread and you can use small bolts instead off screws.

I use this method on handrails and other stuff mounted on my wooden cabin for easy removal before the 6 monthly sanding and varnishing.
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Old 03-03-2015, 22:44   #35
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Re: Best Practice for Repairing Worn Threads in Wood?

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Originally Posted by ccgarnaal View Post
An intermediate method to thread inserts I use.
Fill the hole with liquid epoxy precoating.
Fill the whole with thick epoxy glue.
Insert Bolt coated with spray on vaseline without the hinge.
Wait for the epoxy to cure.
Remove bolt. (The vaseline will keep the epoxy from tacking to hard and you should be able to remove it with a spanner)
Now you have strong epoxy thread and you can use small bolts instead off screws.

I use this method on handrails and other stuff mounted on my wooden cabin for easy removal before the 6 monthly sanding and varnishing.

Complicated for less than accurate installations, because they use machine screws to hold the finish panel.


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Old 04-03-2015, 02:45   #36
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Re: Best Practice for Repairing Worn Threads in Wood?

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Complicated for less than accurate installations, because they use machine screws to hold the finish panel.


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Maybe,

But for something you expect to remove and reinstall 2 times or more a year well worth the trouble.
If you use normal wood screws for this it wont last more than a few years.

Also I use a cut to size rubber gasket for everything mounted this way. Still waterproof and again easy to remove an replace.
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Old 04-03-2015, 11:09   #37
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Re: Best Practice for Repairing Worn Threads in Wood?

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Originally Posted by Stumble View Post
As always I find it hard to argue with Minaret, but I would suggest using wood glue instead of epoxy for this. G5 helps solve the problem because it has a little flex to it, but epoxy is brittle and cracks, while wood glue is much softer and takes screws better. Certainly stay away from WestSystems ect.
I've argued enough with him to be on his ignore list but this time I agree with him and I also use G5. I use the triangle shaped toothpicks, tap them in and cut (not break) them flush, then mix up some G5, add some microfiber filler to syrup consistency, which makes it tough instead of brittle and fill the voids up with that.

Epoxy changes properties with the additives you use. Just the resin and hardener is very different from adding colloidal silica which again is different from micro-balloons, sawdust (sawdust works very well) or microfibers. You can even take a little piece of T-shirt, stir that through the mixed epoxy, then take it out roll it up tightly and plug the hole with that.

Always pre-drill the hole for the screw in the right size. When screwing into fiberglass you can go one size drill-bit larger and when screwing into gelcoat, countersink the hole before starting the screw in to prevent the gelcoat cracking and flaking off
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Old 04-03-2015, 11:16   #38
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Re: Best Practice for Repairing Worn Threads in Wood?

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Originally Posted by ccgarnaal View Post
Maybe,

But for something you expect to remove and reinstall 2 times or more a year well worth the trouble.
If you use normal wood screws for this it wont last more than a few years.

Also I use a cut to size rubber gasket for everything mounted this way. Still waterproof and again easy to remove an replace.
You can also tap it. I know boats who attach the genoa tracks like that and never a problem.

The high density filler is the best choice as it makes the strongest threads. I believe that when the thread is 3 times as long as the diameter of the screw, the strength is already over that of the screw.
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Old 04-03-2015, 13:04   #39
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Re: Best Practice for Repairing Worn Threads in Wood?

This forum should have a smiley for "making a mountain out of a molehill".
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Old 04-03-2015, 13:07   #40
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Re: Best Practice for Repairing Worn Threads in Wood?

I like to fill the hole with epoxy, put a very light coat of silicon grease on the screw and then screw it in before the epoxy hardens. With the silicon grease on the screw it is still removable and yet the epoxy fills in all the gaps that caused the screw to become loose.
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