Official Luthiers Forum!

I made my first neck that will be a bolt on using threaded inserts that also have an external thread & screw into the heel. These inserts are brass because they are the only ones I could find with a 1/4-28 internal thread. I thought a fine thread would be better for this application than coarse.

I bored the holes in the heel perfectly square but when I drove in the inserts, they went in crooked.

I was able to get them out but I can't drive them in straight because I've cut crooked threads in the heel.

I can bore out the holes, plug with Mahogany dowels, re-drill & install new inserts or I can bore out & epoxy in new inserts.

The epoxy route would be easier but I'm concerned about if the brass stripped in the future then it would be a nightmare to get them out.

Opinions, ideas, experiences?

Thanks,
Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Hi Kevin,

First, what type of joint do you have? Butt joint or mortice/tenon? That will drive the potential solutions to your problem.

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Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

IMO either of those options will work. I always epoxy mine in. The chances of stripping the threads is minimal. You only strip threads by excessive force or by cross threading. Since there is not that much force and you are not going to be constantly screwing in and out the bolts you don't have to worry about that.

Here's a question for the group - why not just use good quality wood screws? I've done this before on screwed and glued neck joints and it works fine.

Trev

_________________
http://www.PeakeGuitars.com

It's a Mortise & Tenon.

I used a Martin neck billet so the tenon is not long enough to use the barrel bolts method.

Thanks,
Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Go to
www.mcfeelys.com & order their steel deep thread
inserts.
You may not have to dowel or use epoxy with these babies!
Mike

_________________
Mike Collins

Been there, done that. Life goes on.

I had the same issue a few years ago on a build. Fixed it good by plugging the holes with dowels and boring and plugging another dowel down the length of the tenon. My thinking was that it would add some strength to the tenon by biting into grain that isn't end grain.

The solutions you suggested should work.

Since that issue, I've made sure to NEVER use the fine threaded inserts and epoxy them in. Haven't had an issue since.


For a quick and dirty fix (which can be cleaned up with a counter sunk nut and a cover over the hole in the heel block) you might just use hanger bolts.

Dave

you should use 1/4 20 . but what you have will work. I have seen wood screws fail as the thread is pretty small compared to the inserts and what you are looking for is the mechanical advantage of the inserts.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

John,
Is there an advantage over 1/4-28 other than there are a lot more 1/4-20 fastener options than 1/4-28?

I may be wrong, but it seems like a finer thread would have less of a tendency to loosen over time & you can more precisely tighten a joint with fine thread fastener. Please correct me if I'm wrong.

Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

Hi Kevin,
Like David L. say, "Been there and done that" too. I did the down and dirty fix by daubing some epoxy in the hole and positioning the insert where it should be with the bolt screwed in. As the epoxy hardened I would unscrew and screw the bolt in and out until it set up to keep it off the threads of the insert.

Btw.....the mahogany tenon did crack the first time I tried to thread in the insert. Lance K. suggests you should bore the holes and install the insert before you cut the tenon. That's what I've been doing and haven't had any problems since.

Hope this helps,
Hutch

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"After forty-nine years of violin building, I have decided that the search for a varnish is similar to the fox hunt. The fun is in the hunt."
Jack Batts Maker and Repairer of Fine Violins

Martin has been using 1/4 20 for many years with success. The key to getting these inserts in square is to not oversize the hole too much. That way the barrel of the insert lines up the insert pretty well. I don't think there is any true advantage of the 28 thread to the 20 so use what you think will do the best job for you.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Yep...Threaded inserts are great but getting them in straight is the hardest part. Your dowel idea should work ok. I got a T-handle driver tool to install them. Much easier than using a screw driver.

The fine thread is a solution in search of a problem.

Doweling leaves you screwing your inserts into end grain. It works--that's what most of us do from the other side--but it's less than ideal. You could cut plugs instead and get a better grain presentation. Go way oversize on the dowel if you do it, and offcenter the dowel (or plug) on where the insert will go. That helps prevent stripping out the dowel.

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Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

IIRC, the vertical dowel and the hanger bolt is exactly how Mario attaches his necks, not as a quick and dirty fix, but as a regular production method. And I have to say that like everything Mario does, it makes sense to me.


And who would dare argue with Mario ?

I think Collings also uses hanger bolts ...

FYIW .. I use the drill press to drive the inserts in by hand .. the press gives you ample downward pressure, plus holds everything square as you drive them with with a bolt/nut chucked in the press, and a wrench to turn the nut. They go in as straight and square as you have neck lined up.

We just took a couple out as a friend did them at home and they didnt go in square .. so we took the inserts out, drilled the 3/8 hole a touch deeper and epoxied in dowel .. then set up on the drill press, redrilled, and reset new inserts .. worked perfectly.

_________________
Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

I make a quick and dirty reamer out of one of the inserts and drill the smallest hole I can, which on the inserts I use is 5/16. That keeps the insert from going in crooked.

+1 for the vertical dowel fix.

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Ken Franklin
clumsy yet persistent
https://www.kenfranklinukulele.com

Thanks for all the replies.

It's relieving to hear how many others have had the same problem.

It makes sense that having the hole the "perfect" size should be the key so I got out my calipers & took some measurements.

The base of the thread on the inserts is 0.370".

I used a 3/8" bit but when I measured the holes, they were about 0.389". They may have enlarged a little from the threads on the inserts but I think the problem is my sloppy drilling. I drilled them on a Shopsmith in the horizontal boring machine mode. I didn't rigidly clamp the neck billet when drilling - I just held it against a fence with one hand while operating the drill press with the other.

I'm sure this 0.019" of slop was the culprit.

Lesson learned.

Kevin Looker

_________________
I'm not a luthier.
I'm just a guy who builds guitars in his basement.
It's better than playing golf.

I do essentially the same thing Tony Karol does. Take the time square up the neck on the drill press and use it to keep the insert straight while you turn it in. I put the insert on a headless 1/4-20 bolt with a nut and chuck the end of the bolt into the drill press. I drill the holes and put in the inserts in the same operation so I don't have to re-locate the neck. I also put a bit of epoxy on the side of the hole to lock it all in.

_________________
Steve Smith
"Music is what feelings sound like"

I've had inserts fail (by stripping wood), but have never seen any evidence of a screw failure (I'm gluing and screwing btw).

_________________
http://www.PeakeGuitars.com

Kevin,
My experience won't help you solve your current problem, but maybe it'll help you on your next instrument. I used a hex drive threaded insert with wide, self-tapping threads like these:
http://www.grainger.com/Grainger/bulk-h ... alog/N-8ns
I was able to find what I needed at my local hardware store. First, I experimented by drilling and driving a couple of times into scrap wood. I had already cut my neck tenon, so I clamped hardwood blocks to either side of the tenon to reinforce it while driving the insert in. After drilling out for the main shaft of the insert, I eased the insert in, a bit at a time, to get the threads started. Then I backed it out and lubricated the threads with a little bit of epoxy. This helped "grease" it into position, and presumably locked it securely there about an hour later.
Now...I'm not saying this method is foolproof. I might have a similar problem to yours the next time I try it. But so far, this method sure works for me.

Good luck!
Patrick