Is there a reason not to glue a wooden bolt into its threads?

Question

I am eagerly awaiting the arrival of my new tapping set from Beall and one of the uses I was thinking about was creating a mallet--turn a head and then tap a hole and screw in a wooden handle (I have a couple other similar projects on the docket as well).

Now other than not being able to easily remove the handle (should I break it or want a different one), is there any other reason not to do it? Even on the flip side, are there very good reasons to do it? (I'm thinking it won't come loose when in use!)

Answer 1

is there any other reason not to do it?

If you really want it glued, there's no problem with gluing it. But the whole point of using threads instead of glue or a wedged through tenon is that you can disassemble a threaded connection.

are there very good reasons to do it?

Two, that I can think of:

1. Although threads cut in wood are plenty strong for many uses, they are cut across the grain and can break. If the threads are at all loose, the force of a mallet blow might be applied to just a part of the threads and cause them to break. Glue could help support the threads and spread the force of the blow more evenly.

2. If your mallet handle isn't round, then you'll want it to maintain a particular orientation relative to the head. It'd be hard to thread the handle so that it bottoms out with the handle in exactly the right position, so you'd need glue or some other means of keeping the handle oriented correctly.

Answer 2

If I were to glue it, I would just make a standard taper joint with a wedge in the end - much simpler.

Gluing it would give you the strength of a mechanical connection with the permanence of glue, but you could get very nearly the same strength by just threading it, and basically draw boring the head in. Once the handle is threaded on, drill a hole through the head, into and through the screws, and put in a screw or dowel to hold it in place.

Answer 3

As Caleb mentioned, the entire point of using a threaded joint is to make it easy to disassemble--typically to replace a part or to break something down for storage. If you want a permanent connection, you're wasting time, effort, and possibly money (if you had to buy the tap specifically for this project) by threading and then permanently gluing the connection.

If you want to be able to disassemble the joint later but want to lock the threads in place in the meantime you can use hide glue. When you need to disassemble the joint in the future, you can simply heat up the joint and unscrew it. But then again, you could do the same with a plain old mortise and tenon.

...on the flip side, are there very good reasons to [glue a wooden bolt into its threads]?

Sure...

1. if making a threaded wooden rod (e.g., for a vise) that will only ever need to be detached at one end, or perhaps will never need to be detached.
2. if you want to get practice tapping threads but you want to knock out a few projects at the same time.
3. if you have a design that uses threads as visual elements but which is never supposed to be dismantled (e.g., maybe some wooden threaded rods used as through cross-bracing between legs on a stool.
4. if it comes unscrewed when you don't want it to, and you've decided you never want it to come unscrewed again.

Answer 4

I concur with LeeG's answer. Put the whole thing through and use another piece of wood through the thread as a stop.

Reusable Handle

If you don't seal the handle in the head then you could use it with multiple heads if you so desired. If you wanted to make the handle something more that just stick with threads then not glue would be preferential. Say if you were to turn one and put a grip on it? Then you wouldn't need to make a bunch. Or if your head broke you can reuse the handle.

Glue could weaken

While this would take time, actually using the mallet, could weaken the glue joint. I have seen this happen with shop brooms. Since you are threading it I would see this process taking a while but I suspect it will happen. Using a stop like a piece of dowel wouldn't be a bad idea.

Perhaps you could do both. Might be overkill for just a mallet though. I guess I'm suggesting it is wasted effort to glue it. If the glue did break the seal the mallet could move while you are using it.

Another useful point would be if you get tapping happy then you could use the same handle for multiple tools.

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Mine is just an old croquet mallet that I adjust periodically with wedges as it moves.

Answer 5

Now other than not being able to easily remove the handle (should I break it or want a different one), is there any other reason not to do it?

I think that losing the ability to easily re-handle is the main reason not to do it. I don't imagine you'll have any problems with a threaded handle staying tight in use without any glue.

Even on the flip side, are there very good reasons to do it? (I'm thinking it won't come loose when in use!)

To be honest I can't think of one!

If you want one extra bit of security, before threading you can dry out the end of the handle stock by placing near a heat source for a couple of hours, then thread and screw home. As the handle's moisture content comes into equilibrium it will swell, locking it even more firmly in place. At a guess for most woods this is likely to result in the fixture becoming permanent; a thorough waxing of the threads might prevent this but no way to be sure.