Process question for mounting with threaded inserts

[Cagey]

You guys. Why do you want to experiment with $500 necks? DO IT RIGHT!

Don't rethread a threaded hole with a different threaded insert. If it's an insert that wants a 5/16-16 thread, then that's the tap you need. They're not easy to find, but they're certainly out there and I've given links to suppliers. If you forcefully rethread it, you're just going to chew up the wood and wreck whatever thread you have, which defeats the purpose of the whole exercise. You're trying to get a tight bond between the neck and the body.

Don't epoxy the things in. You may need to get them out some day, and you'll have a bitch-kitty of a time doing that if they're cemented in. The likelihood of your needing to do that is small, unless you cross-thread the insert going in, or cross-thread the bolt when you install the neck. But, both of those things are easily possible if things don't end up square.

If your insert, hole and tap are matched, the thing will be in there plenty tight, it's likely to go in square, and all will be right with the world.

 

[stubhead]

unless you cross-thread the insert going in, or cross-thread the bolt when you install the neck

This is the one reason I can't quite see using brass parts. Yes it's strong enough, technically, but jeez if you're going to all this trouble in the first place, what's the extra couple of pennies it costs, or minutes it takes, to find steel? Steel don't crossthread. You're already 98% there... and, you would certainly be insane to epoxy parts in that you didn't know fit. But once you find that out, there's no downside. Why could you ever possibly need to remove that neck, to... somehow, want to put it on a guitar that  you couldn't figure out, how to make it fit? A genuine 1953 Telecaster that can't be be drilled for 10-32's? It doesn't belong on any guitar like that.

 

[Jumble Jumble]

You guys all make this sound so hard too. I'm not the world's biggest expert with tools or anything, but I'm not useless or stupid either. I had a nice Fender neck where the holes got stripped, and it seemed to me the best idea would be to put in inserts, rather than try to repair those holes with toothpicks or dowels with the grain pointing the wrong way.

I got a threaded insert kit from eBay for about $10. Then I knelt on my living room floor, with the neck face down on the carpet, and used my electric hand drill to drill the mounting holes out to the new diameter. The inserts went in straight, with no tap required (although plenty of care was required). Then I put the neck on the guitar, ran the screws in nice and tight, and forgot all about it. Yes, it wasn't really the best way to do it, and I'm not recommending that method to anyone. I just want to point out that it's not quite as easy to completely frig up as you might be worried it is.

 

[swarfrat]

Thats what I did too, and it started ripping up a huge chunk of wenge. Made me absolutely sick

 

[swarfrat]

Bought some oak for shop project, since it's a relatively hard wood also prone to splintering, I figured it'd make a good test block. Here it is:

First two holes on the left are drilled 17/64 (barrel diameter). I grabbed the 3/8-16 tap I had on hand, and cut just enough thread to start the insert, then ran the insert in by itself. It's going to need a better driver to go any deeper, alignment needs help (ie a jig).  Hole on the top right, is 3/8-16 tapped all the way down, insert fits a lot more snugly than I expected, but turns freely with a screwdriver. It doesn't feel like it has any play, and doing the math from Machinery's handbook, a 5/16-16 insert in a 3/8-16 hole still has 50% engagement on the thread (which is why it has no slop - it's riding the thread, not just jostling around in a thread shaped hole).  Hole on the lower right was drilled 5/16 and the insert run in with no tap. This is what I got in Wenge too, but worse.  (The other holes were used for tapping tests. Plug, Self-aligning, etc... Self aligning taps are like taper taps but have a very long cylindrical lead in, designed to align better when hand tapping)

(And oh yeah, in the interest of science, the push-in Finserts are MUCH much smaller diameter than the knife thread inserts for the same size screw. I'll use them on jigs and fixtures in the future. I did find some literature and they're substantially weaker than the threaded inserts, but it remains to be seen whether it would matter. String tension puts only a few inch-pounds of torque on the neck screws, so what your neck screws are really doing is holding up to handling stress - but that's a fairly long lever arm you got there.)

Since the 5/16-16 external thread in a 3/8-16 hole is pretty much workable, but can be easily backed out after checking fit, and THEN epoxied into place.  I'm going to do another test if I can figure out how to do a reasonable strength test. I think I can say with emphasis:

Don't just try to let the inserts cut their own threads in really reallly hard splitty woods. Don't do it.
Don't try to use the slot to drive it unless you already have perfectly clean threads already cut.

 

[Jumble Jumble]

Cool, that's all really helpful.

 

[stubhead]

Since the 5/16-16 external thread in a 3/8-16 hole is pretty much workable, but can be easily backed out after checking fit, and THEN epoxied into place.

What I would suggest here is, be really careful about spreading just enough epoxy around, SO - you can use some correctly-sized "neck bolts" to hold the inserts straight up and down while the epoxy cures. And they don't need to be the real neck bolts, in fact it works much better if you buy four much longer bolts of the right threads just for this part. At that point, you can tape two necks plates together with a little 3/4", 1" something (wood block, stack o' washers taped together etc) in between them. All you're looking for is something that will hold the upper end of the four screws in the right alignment while the bottom of them are holding the inserts straight during epoxy cure time (you can see why 62c of extra long bolts is better). The body of the actual guitar will do this spiffy - though I'm likely off dicking with that while the epoxy sets. Solution - more bodies! :laughing3: :laughing7: :laughing3:

And I know this is OCD and overkill and I've done the Jumble quickie too, but I find it interesting to devise processes that "fool-proof" whatever steps I can. There will always be another guitar... I can't convince myself otherwise anymore. :icon_thumright: