Official Luthiers Forum!

Knowing how to fix one's luthierie mistakes is an incredibly important part of building. This is probably one of the most valuable things I've learned over the past eighteen months. And, realizing that each day brings a new lesson, this evening's was a tough one.

The neck I'm currently working on is the sweetest thing I've built to date. Bling city. The inlay turned out great, having never bound a fingerboard or headstock, I LOVE the look of this thing!

So this evening I was doing some fine tuning of the neck angle and finally drilled through the block and installed the bolts to make sure everything was going to line up perfectly.

To my dismay, after tightening up the bolts, the neck popped right off and left the inserts in the mortise!

I didn't swear, I just turned off the lights, went upstairs and booted up the laptop.

Hopefully someone can chime in and offer a suggestion or two.

Somewhere I read where some people install a dowell in the tennon to avoid the endgrain issue (which is what I'm probably dealing with here) but I don't know if that is a possible fix or not. If so, what species of dowell stock should I buy?

In another post I thought someone mentioned epoxy on the inserts, but I didn't think that was advised for various reasons.

In any case, I'm going to sleep on this one and look forward to seeing some replies.

Hopefully someone has some good news. I could use some after this AND getting called up for jury duty starting monday!

thanks in advance,

Dave

But it CAN be fixed. I'm interested in some pix to see the damage, tupe of conection, etc. The archives will appreciate it for future reference

Dave,

You mention that the neck has a tenon. That makes me think that you could still switch to using cross dowels, if the tenon is long enough. The cross dowels you'll see most frequently are like the photo below, 10mm diameter. Is your tenon 3/4" long or longer? Should work.

-Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

here we go.

1) Drill out insert holes, glue in dowels.
2) Drill down through heel cap and glue in dowel. (Somone will post a pic if needed)
3) after all glue dries, redrill insert holes
4) Insert inserts
5) Smile, it's a brighter day!

Post some pix!

1/2" Dowel. Any hardwood will do, but try to find a maple one.

It might be simpler to epoxy a couple of bolts into the holes left by the torn-out inserts.
Then you could use nuts and washers on the inside of the guitar.


BTW, the inserts may have been driven out of the neck if the bolts were a bit too long- just a possibility. I've had to grind a bit off the end of bolts because of this.

Cheers
John

I've been using a 3/8" maple center laminate on my 5-lam necks, and I epoxy my inserts. I have yet to pull an insert out (knock on wood!), I attribute that to the maple center coupled with the epoxy. If I were to switch to anything else, I'd dowel vertically through the heel as others mention.

Is there a reason not to use cross dowels? I'd guess they're not too traditional, but to my mind, they seem like they'd be stronger. No concerns about them pulling out. I'd also guess they buy you a little bit of slop when locating your holes too. Of course, maybe I'm the only one who really needs and values his slop. You all probably just get everything right on the first try.

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Mike Lindstrom

I am surprised that you striped out the threads inside the inserts rather than pulling the inserts out of the wood. I suspect some cross threading going on. The wood is usually the weak link, but seeing that you have a good hold on the wood, you could use a Helicoil. If the Helicoil fails you are putting way to much torque on it.
Just a heads up, Helicoil sets are not cheep, but it’s worth saving the time and effort you have already put in.
You can get the Helicoils from McMaster-Carr

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Rich S

"The inconvenience of poor quality will linger long after the thrill of a bargain has been forgotten"

If you go with epoxy, be sure to coat the inner threads with a thin layer of vaseline, and do the same with the bolts, and have them screwed into the inserts when you epoxy them in. This will keep the epoxy from wicking up into your threads and making them unuseable.

All you need is a little, coat the bolt and run it into the insert by hand (outside the neck) so you can wipe off any squeeze-out. Then they're ready to go in. Use a couple of nuts on each bolt to lock the bolt down on the insert, then you can use the bolt head to screw it into the hole in the mortise.

Or you can just dowel the holes and use hangar bolts like Grumpy.

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The member formerly known as erikbojerik....

Hey everyone,
Thanks for the suggestions!

Dennis; I've never seen the cross dowell thing. Cool idea. Have/do you use them instead of the straight inserts?
If I did try this, would you suggest plugging the existing holes, then drilling all new and essentially starting from scratch?

Terry; I'm leaning toward drilling down through the tenon and insterting a dowell. Would you suggest titebond or epoxy for maximum strength? The big concern with that is the 1/2 dowell with a 1/2 diameter on the insert. Wouldn't that make the dowell holding 1/2 of the insert and the end grain of the tenon holding half?
Still something to ponder and maybe someone can let me know if that is a regular practice.

John; would epoxy bond to the tenon wood well enough to hold the massive pressures exerted on that joint? I don't know, I've never worked with epoxy on an instrument.

Rich S; it wasn't the metal threads that stripped, but the wood threads inside the tenon that the insert cut when it was installed.

Erik; great tip on the vasoline. And does Grumpy seriously use hanger bolts? Why don't more people talk about that? It doesn't seem much different than the inserts used in a traditional bolt-on.
Hmmmmmm....

All; Maybe not needless to say, but this is probably the LAST one piece neck I do. The artistic variations as well as the strength of the laminates are just too tempting to overlook.

Thanks again for everyones suggestions and reminders that this is small potatoes and VERY remediable.


Dave
(aka livermo1, but didn't have my resently reset livermo1 password handy.)

Would Birch be a suitable dowel?

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Time is a great teacher, but unfortunately it kills all its pupils - Louis Hector Berlioz

Chansen / C hansen / C. Hansen / Christian Hansen - not a handle.

Christian

Hi Dave,
Just glue it up with something. I think you should go with what you know re: inserts. Cross dowels are fine, but then drilling the holes squarely after the neck is shaped may pose a problem for you. Don't know. Your self education opportunity is great here. The worst (& unusal) has already happened. Almost anything you do now is going to be better, yes?

Good advise above, make a choice and git er done. Don' sweat maple vs birch.

Think it through with the supplies, tools, and tecniques you have, or can access.

And were still waiting for pix of your pride and joy!

Thanks Terry,
I wrote the request last night after I had shut the shop up.
The reply from today was from a lull in the work day.
And I just got home this evening.

After I tuck the kids in I'll set up the ShopSmith for drill press. I stopped off at Menards and got a dowel (oak... its the hardest thing available) and at a local hardware store for some inserts with coarser threads. In short order I should be back on track. And of course I'll take some before and after pictures.


Dave

Dave,

Sounds like you're going with the wood dowel (90° to the insertion angle), and I know a bunch of guys are doing it successfully, so it is certainly a viable option. More than viable for those that use a butt joint, either glued or adjustable (a la Harry Fleishman.) But, when you have a tenon, then the metal cross dowels make more sense to me. (Disclaimer: I'm a beginning luthier, but experienced woodworker.) Regardless of how you put in inserts - with epoxy, or into a 90° crossgrain wood dowel - if you crank hard enough on the adjustment screw, I think the inserts could pull out. Or, maybe a better way to say it is that if you have a neck with a tenon where you can drill holes for metal cross dowels (back at least 1/4" from the end of the tenon), then it would take a lot more force to break the cross dowels through the end grain that it would take to pull inserts out.

I think that Terry is correct, that it would be more difficult to drill the holes for the cross dowels at this point, especially compared to drilling a squared neck blank. Even though you're going with inserts this time, you may want to investigate the metal cross dowels. Plenty of luthiers are using them successfully. And, they work whether you are creating a glued neck joint, or an adjustable neck joint.

Good luck on the repair. I'm sure it will be fine.

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Thanks for muddying the waters for me.

I didn't mention that when I got the coarser threaded inserts, I also picked up a pair of cross dowels as well.

It is good to keep the options open.

Thanks for the suggestion.

eschew obfuscation!

Dennis

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Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Resolution at last.

I decided to go with the dowel and new inserts route.

It was tough to wrap my mind around the cross dowels as even after the tenon was reinforced with the oak dowel providing contrasting grain direction, there would be so little of it to support the cross dowel that I thought there would have been too little support. It does seem like a good idea and lucrative alternative to the traditional inserts.


Here's a bad picture of the before; notice the smooth inside of the holes where the threads just chewed up the hole that should have been a good tap



Here's the reason. The inserts I bought had threads that were much too tight. Sorry, again, bad picture.



I purchased some 1/2" dowel stock and new inserts.
Here are the new inserts with steeper threads



Then I drilled out the tenon and plugged it with an oak dowels.




Then re tapped the pilot holes (just a little bigger than the 5/16" insert diameter) and installed the new inserts.



Finally, the reason I didn't just trash the whole thing and start new




Now we're ready to go on to the next step.


Thanks again to everyone who offered input.

Dave

I've also had some similar problems with the bolt inserts. I've epoxied the inserts in before after stripping them out and it seemed to work.

I've also found that it's very important to watch the depth of the hole. I've run into problems with having the bolt just a hair too long like someone mentioned above. I've started to drill the hole for the insert a little deeper than the insert to give a little extra space if the bolt is too long.

Question: The other problem I still grapple with periodically is cracking the tennon along the grain when inserting the tennon into the hole. I guess this is because I am not drilling the hole large enough, but I don't want to make it too big because I'm scared that the outer threads will not grip the wood.

Has anyone else had this problem of splitting the grain on the tennon? Do you have any suggestions?
I think I'm going to start using a tap to thread the hole before putting the insert in.

In Harry Fleishman's class, we did a butt joint with threaded inserts. We purposely drilled the hole just big enough so the whole insert could slid in, not engaging the threads into the wood at all. It was epoxied into place. If you wax the bolt and thread it into the insert while the epoxy's setting, you can pull it out without worrying about epoxying your bolt into place or gumming up the threads on the insert.

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Jonathan Kendall, Siloam Springs AR

Bingo! Every hardware store these days is selling dowels of Chinese mystery wood. Go to a good hardwood lumber yard where the dowel species are identified. You can get walnut dowels which will also do well.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Dave, which of those dowels did you glue in first? It should have been the pair that plugged the insert holes. If it was the other way around, you still have only end grain holding the inserts; also, when doweling a hole that is to be redrilled and hold a screw, you should if at all possible dowel off-center to the old hole. This helps avoid the tendency for the dowel to strip. I probably would have gone with a smaller diameter for the long dowel (so as not to weaken the tenon), but you should be OK. You have more alternatives if this fix should fail--you actually don't need the tenon.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

That's great to know. Thanks for the tip!

Dave, Did you really tap the pilot holes? If you did, then that is the problem your having. The inserts need to be threaded right in to an untaped pilot hole... I think the ones you were using need a 3/8 hole.

long

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"No man ever steps in the same river twice, for it's not the same river and he's not the same man.” -Heraclitus of Ephesus

Howard, thanks for the reminder that there's always another chance should this not work out. I was already thinking about that.

long: The holes were re-tapped when I screwed the the new coarse threads into them.

Sorry for the confusion.

d