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Argh! Bolt on Neck Failure.
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=17840		 Page 1 of 1
Author:  Flori F. [ Wed Jul 02, 2008 7:33 pm ]
Post subject:  Argh! Bolt on Neck Failure.
So, some of you may've seen my thread about my first. I had trouble getting the heel joint flush. Steve Kinnaird recommended I take another look at the joint. Unfortunately, he was right.

The bolt had pulled the upper threaded insert out, stripping the slot I'd drilled for it.

I used a McMaster-Carr 1/4-20 zinc plated steel taplok insert. Since the hole is stripped to 3/8ths of an inch, I can't just use another insert. Does anyone have any advice on what to do?

Should I just go with the 5/16-18? It has an external thread of 15/32", which I think should work with the current hole of 3/8ths (12/32).

Thanks.

Flori
Author:  Dave Fifield [ Wed Jul 02, 2008 7:47 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
Hi Flori, if I were you, I'd drill the hole out to 1/2" and glue in a piece of hardwood dowel, then when it's dry, flush the dowel with the surface of the heel and then re-drill it 3/8" and put in a new 1/4" x 20 insert. Did you use any superglue on the insert? Somewhere I read a tip that said you can run some superglue (medium or thin - I used thin) carefully into the thread/wood join. The thinking is that it a) glues the insert in solidly and b) makes the wood much less likely to tear out. I did this on my first guitar and haven't had any problems with the inserts moving at all (yet!).

Good luck!

Dave F.
Author:  Michael Dale Payne [ Wed Jul 02, 2008 8:03 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
move away from in line inserts. Go to barrel nuts. this puts the loading on the tenon and nut perpendicular to the grain and the tenon. With inserts running in line with the bolt loading even with hardwood dowels either perpendicular or in line there is always the chance of overtightening the bolts and pulling the inserts out. This never happes with barrel nuts
Author:  Jim Watts [ Wed Jul 02, 2008 8:05 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
I second Michael, barrel nuts, they work great.
Author:  Howard Klepper [ Wed Jul 02, 2008 8:12 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
Not sure what a "taplok" insert is, and I can't find it on McMaster Carr. I don't use their inserts, but the knife thread hex drive looks like the right one. You need a deep thread.

Using a threaded insert in end grain is problematic, but it can work fine. You need to drive it straight; I use my drill press and a simple bolt and long hex nut system (that Tony Karol showed me here at OLF; he can describe it better than I can). I lube the threads with wax. Since you have already pulled one out, I'd suggest that you do not just drill and put a dowel in. A new hole centered in a dowel is more likely to strip than the original hole was. One way is to drill off center for the dowel with a Forstner bit (which is rim guided) and go up to about a 3/4" dowel (a good hardwood dowel of a known species, not the hardware store dowels of Chinese mystery wood). Even better is to dowel at right angles to the insert so you won't be driving your insert into end grain again. For this a 1/2" dowel would be fine. To do this you may need to remove the end cap on the heel in order to bore for the dowel.

If you don't have a tenon, it's too late for barrel nuts. Besides, I worry that there's not a lot of wood between the barrel nut and the end of the tenon, which looks like a failure waiting to happen (apparently it works, though).

With either system, don't over tighten. You get it firm, not as tight as you can.

[edit] Dave F.: see Cumpiano's site. You use a tenon, and the barrel nuts go across the tenon; horizontally, not vertically.
Author:  Dave Fifield [ Wed Jul 02, 2008 8:14 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
I thought about using barrel nuts, but I couldn't decide exactly how to do it.

Do you drill a vertical hole from the top surface (where the fingerboard is going to glue down) down into the heel to drop the round barrel nuts into or do you drill up from the bottom of the heel and then cover with the heel plate later? I think I'd go for the first - drill from the top surface of the neck - that way, the nuts could be placed further back in the heel = more solid. What about spacing them? If you drop 2 barrel nuts down the hole so they touch, what is the spacing? Or, do you use dowel to separate them? Got a tute on this anywhere?

Thanks,
Dave F.
Author:  Michael Dale Payne [ Wed Jul 02, 2008 8:22 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
actually easier to install. mark and drill two holes per bolt, one in line with the tenon 1.25 the dia. of the bolt this is the line of action of the bolt, one the size of the barrel nut dia. centered in the tenons depth on line with the other hole but perpendicular to the path of the bold. This is where the barrel nut goes. I use 1/4-20 x 1/2 dia x 3/4 long barrel nuts.
Author:  Dave Fifield [ Wed Jul 02, 2008 8:59 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
Do you mean like in the drawing I just below did Michael?

Attachment:
BarrelNutMethod..jpg


Regards,
Dave F.
Author:  Michael Dale Payne [ Wed Jul 02, 2008 9:24 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
Dave Fifield wrote:
Do you mean like in the drawing I just below did Michael?

Attachment:
BarrelNutMethod..jpg


Regards,
Dave F.


you got it. you want the hole for the bolt to pass the hole for the barrel nut by a tad because you want the bolt to fully engage the thread of the nut the full depth of the nut for the strongest possible bolting strength.
Author:  Dave Livermore [ Wed Jul 02, 2008 10:11 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
I hear your pain.

Did the same thing.

Here's a link to how I came out of it.

http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=16035

I now install a vertical dowel down the tenon AND make sure the inserts have REALLY coarse threads.

Good luck with your fix. The good news is that when you get it all done, only you will know there was a problem.

Dave
Author:  Steve Kinnaird [ Wed Jul 02, 2008 10:30 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
I want to second Howard's advice.
In fact, before drilling for the inserts, I always run a 1/2 mahogany dowel the length of the heel. It comes up through the truss rod slot (gets trimmed with that channel), runs down and ends at the heel cap. I like the security of drilling into that long grain. I also wax my threads, and then run superglue around the outside where the threads bite the heel.

Steve
Author:  Frei [ Wed Jul 02, 2008 11:00 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
I thought someone asked if you should glue them in? Maybe you should have glued em. eek
Author:  Dave Fifield [ Thu Jul 03, 2008 4:31 am ]
Post subject:  Re: Argh! Bolt on Neck Failure.
McMaster-Carr call those things "Dowel Nuts". "Barrel Nuts" are something completely different.

For a butt-joint bolt-on neck, why couldn't you use a couple of dowel nuts vertically, like this:

Attachment:
VerticalDowelNutMethod1.jpg


It wouldn't be quite as strong as having the dowel nuts horizontal (in a tenon, per my previous drawing above), but it'd still be much stronger than an insert pulling out the end grain, wouldn't it?

You could space the two dowel nuts with some hardwood dowel if needed. Another issue would be keeping the dowel nuts turned the right way round. Perhaps place them in the drilled shaft, then run some super glue in to hold them in place?

Cheers,
Dave F.
Author:  Terence Kennedy [ Thu Jul 03, 2008 7:11 am ]
Post subject:  Re: Argh! Bolt on Neck Failure.
For the Dowel Nuts I've used a jig that Mark Swanson showed on the mimf 5 or 6 years ago. It's worked fine for me. The drill guides are 3/8" and 5/16". The nuts are 10mm so you have to ream the hole slightly or run a 10mm drill bit in reverse to get a snug fit. I flood the whole area with thin CA as well to toughen it up. The attachment bolts are 1/4" so there is a little play for proper fit. No failures so far on around 23 instruments over a span of about 4 years.
I usually get the body all done and fit the neck with the fretboard clamped on and use a 5/16 transfer punch through the neck block holes to mark where to drill the tenon. You can use the same transfer punch to align the jig for drilling the holes. You can put tape on the sides of the tenon to make sure the jig fits snugly and centers. That also helps with any chip out from the drill.
After I drill the first hole I stick a drill bit or transfer punch in the hole to better stabilize the jig. These are pictures from several years ago. I use a little longer tenon now so the lower hole isn't so close to the end. It seems quite reliable and I have had no disasters to date.
Terry

Image

Image
Author:  Flori F. [ Thu Jul 03, 2008 9:42 am ]
Post subject:  Re: Argh! Bolt on Neck Failure.
Thanks for all your replies. I'm wishing I'd discovered this forum earlier in my build.

For anyone curious, here's the part number of the insert I used: 90240A001

And here's the tutorial I followed: http://liutaiomottola.com/construction/ ... ocId379139

Next time I'll certainly use a dowel and most likely go with the barrel nuts. I'd seen that Cumpiano was now using them. I just didn't realize why. Where does one get good hardwood dowels?

Unfortunately, with the flat butt joint I've got on there, barrel nuts aren't an option. Any opinions on whether I'd be better of with part # 99362A200 or part # 90240A002?

Next time I won't over tighten.

Sigh...I wish I weren't learning so much.
Author:  Howard Klepper [ Thu Jul 03, 2008 11:11 am ]
Post subject:  Re: Argh! Bolt on Neck Failure.
You used an insert intended for metal or plastic, not for wood. That's probably why it didn't hold--wood requires deeper threads with wider spacing. The McMaster-Carr part that most resembles the inserts I use (that I get from McFeely's) is 90192A121. The 99362 looks like it may work, but the threads appear to be shallower and closer spaced, and besides, they don't come long enough in 1/4-20.

Good hardwood dowels are found at good lumber yards, especially those that specialize in hardwoods. Use the telephone--it's quaint, but effective. I'd probably use maple, but oak is fine, and walnut OK, too. Do not use the Chinese mystery wood! I think you should be OK just boring into the end grain and running a dowel the same way if you don't want to bore from bottom of the heel, since the original problem was likely the insert. But it is better to bore off the center of your old hole and go larger on the dowel. A screw or other thread placed iinto end grain n the center of a dowel tends to strip the wood fibers when the dowel is just a little bigger than the screw going into it.

I also flood with CA glue around the perimeter of the insert after it is installed.
Author:  Michael Dale Payne [ Thu Jul 03, 2008 11:35 am ]
Post subject:  Re: Argh! Bolt on Neck Failure.
idunno [headinwall] [uncle] I learned them as barrel nuts, MMC calls the dowel nut, my hardware store calls them blind furnishing nuts and there is one other name I forget right now . What ever you call them they work, are simple to use and solve the issue of inserts pulling out, possibility cracking the tenon when threading inserts in (if you did not use dowelsand under drilled the hole on a one piece neck don't ask how I know this :oops: ) and eliminate any gluing if the fit is right.
Author:  Howard Klepper [ Thu Jul 03, 2008 11:59 am ]
Post subject:  Re: Argh! Bolt on Neck Failure.
MichaelP wrote:
idunno [headinwall] [uncle] I learned them as barrel nuts, MMC calls the dowel nut, my hardware store calls them blind furnishing nuts and there is one other name I forget right now .

KD nuts? [short for knock down]
Author:  Jimmy Caldwell [ Thu Jul 03, 2008 12:09 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
One of the many reasons I use a dovetail joint. Once you learn it, it's really the simplest joint, and contrary to popular belief, it's not difficult to disassemble.
Author:  Michael Dale Payne [ Thu Jul 03, 2008 12:14 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
Howard Klepper wrote:
MichaelP wrote:
idunno [headinwall] [uncle] I learned them as barrel nuts, MMC calls the dowel nut, my hardware store calls them blind furnishing nuts and there is one other name I forget right now .

KD nuts? [short for knock down]


Yep that the one I was thinking of
:D
Author:  Michael Dale Payne [ Thu Jul 03, 2008 12:22 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
Jimmy Caldwell wrote:
One of the many reasons I use a dovetail joint. Once you learn it, it's really the simplest joint, and contrary to popular belief, it's not difficult to disassemble.


To an experienced wood worker there is nothing really difficult about dovetail fitting. True but no easier either. It is more work and riskier work to do a neck reset on a dovetail joint.

But both are great neck joints, just two sides of a river both hold the water back
Author:  WaddyThomson [ Thu Jul 03, 2008 12:31 pm ]
Post subject:  Re: Argh! Bolt on Neck Failure.
MichaelP wrote:
Yep that the one I was thinking of
:D


No, No Michael, that's the one you couldn't think of! :D
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