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  #16  
Old 05-30-2016, 01:58 PM
Alan Carruth Alan Carruth is offline
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One of my students had a problem with those round furniture nuts installed crosswise, and I know one other maker who's had the same issue. The heel broke through the upper nut hole, and the instrument dropped to the ground when it was picked up by the neck.

The issue was that the nuts didn't bear properly in the holes. The FAA mandates that in wooden aircraft structures that are bolted on, such as propellers, the bolts (or, in this case, nuts) should be tight enough in the holes that they need to be driven in. This insures that the load is spread all the way across the hole. Otherwise the load is on a line at the bottom of the hole where the nut touches the wood. This puts a splitting force on the hole, particularly if you over tighten the bolt, which is easy to do. The split goes across the neck, parallel to the fingerboard surface, and if it's the upper hole that splits out there's nothing to hold the neck except the fingerboard extension. In my student's case the break happened when he accidentally tapped the head on a ceiling beam when he picked it up and the shock, although small, did the rest. The head was not marked: the body, on the other hand....

Putting the nuts in a hole that's drilled perpendicular to the fingerboard surface works better. Even if the nuts are not tight in the holes the neck won't fall off, since the the split runs up the heel, and the two sides are captured in the mortise. If I were you, I'd pull those nuts out, plug the holes with dowels, and re-drill them. This also allows for the use of a longer nut in the lower position, which spreads the force out and reduces the chances of problems.

In an ideal world we'd all reason these things out before hand, and never have this sort of problem. That doesn't always happen in the world I live in. As Bismark is reputed to have said: "Any fool can learn from his own mistakes; a wise man learns from the mistakes of others".
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  #17  
Old 05-30-2016, 02:07 PM
arie arie is offline
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ok now i see them. not the best of pictures though. did you drill the holes unsupported?
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  #18  
Old 05-30-2016, 03:18 PM
murrmac123 murrmac123 is offline
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Always nice to give credit and acknowledgement where such is due ... so I will just mention the redoubtable William Cumpiano, who first pioneered this neck joint using barrel nuts.

Even though using barrel nuts is a million times better than his previous neck joint (as detailed in his book) I still look forward to the day when he realizes that the hanger bolts as used by Collings (and by Mario Proulx) is the ultimate method as far as bolt-on neck joints are concerned.
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  #19  
Old 05-31-2016, 09:32 AM
jonnyschanny jonnyschanny is offline
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Lots of great advice here. Looking back, I'm pretty sure that the tenon cracked when I tightened down the neck for the first time. I had no problem drilling the holes. I probably over tightened causing the cracks. They weren't there until after the trial tightening.

And as someone mentioned, I did use Cumpiano's book partly as a guide. Also lots of web sites and several other books. I guess that's the danger of picking and choosing from different sources. I may have made the tenon to narrow as result.

So I guess there are two solutions. One is to stick with the dowel nuts, glue the cracks, and chisel off the sides of the tenon, then laminate cross grain sections on the outside to strengthen it. The other way would be to fill in the holes with glue and dowels, then redrill, but this time smaller holes for hanger bolts. Looking back, I wish I had used the hanger bolts. It seems that they would give you a better sense of how tight the neck was since you could feel them on the inside. I'm afraid I might over tighten again.

Halcyon/tinker, Yes, I think you are right. Even if I decide to use hanger bolts, I think it would be best to widen the tenon and mortise. That was probably the initial problem. I think it was too small.
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  #20  
Old 05-31-2016, 10:14 AM
dekutree64 dekutree64 is offline
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Quote:
Originally Posted by murrmac123 View Post
Always nice to give credit and acknowledgement where such is due ... so I will just mention the redoubtable William Cumpiano, who first pioneered this neck joint using barrel nuts.

Even though using barrel nuts is a million times better than his previous neck joint (as detailed in his book) I still look forward to the day when he realizes that the hanger bolts as used by Collings (and by Mario Proulx) is the ultimate method as far as bolt-on neck joints are concerned.
Yep, that's where I learned the tenon reinforcement trick as well And apparently he learned it from Michael Millard. I should have just linked the original page instead of going to the trouble to edit the photo, now that I think about it... http://www.cumpiano.com/#!an-improve...dy-joint/c1umc
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  #21  
Old 05-31-2016, 10:42 AM
Halcyon/Tinker Halcyon/Tinker is offline
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When I was still doing the m&t joint, I would add a cap to the end grain of the neck before cutting the tenon. Glueing to the end grain is of course not the strongest joint, but it proved more than adequate to prevent those splits. As well, you can make the tenon a little bit deeper so there is more wood in front of the barrel nuts. There's lots of ways to make that system work fine.

In practice, I found that time wise, the m&t joint required much more futzing about than a plain old dovetail, which is very fast to accomplish once your jigs are dialled in.

For myself, I went from the m&t joint to the butt joint with threaded inserts in the heel, and it was like an epiphany of efficiency. Maybe do a mock up of one of those and see how it works for you.
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  #22  
Old 05-31-2016, 11:18 PM
Goshen Goshen is offline
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There is a thread on this forum titled, R.M. Mottola neck joint, that would be a good read for anyone considering bolt-on neck construction. I am sorry I am not able to attach a link. Maybe someone will.

Pay special attention to the posts by Frank Ford and John Arnold. Both of these highly respected gentlemen recommend a hardwood dowel running from the heel cap area toward the fret board. Without the dowel the hanger bolts would be threaded into end grain. I can not tell from the Op's photo if the heel cap has been added, but it would be a small job to remove and reattach/make another in order to add the dowel. Less chance of doing major damage to add the dowel to the heel, rather than risk enlarging the mortise in a completed body.

Last edited by Goshen; 06-01-2016 at 10:24 AM.
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  #23  
Old 06-01-2016, 03:28 PM
jonnyschanny jonnyschanny is offline
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First of all, thanks to everyone for posting and giving me advice. I've decided to switch to hanger bolts instead of the cross dowels. So far I've started filling in the holes with lengths of dowels. I will probably widen the tenon and mortise as well. And I'll probably run a length of dowel from the heel perpendicularly up through the neck. I'll have to remove the heel cap but I wasn't very happy with it anyways.
I'll give updates when I have some pictures to show. Thanks everyone for the Wonderful advice. I was getting ready to make a completely new neck before you all swooped in and saved it!!

Jonathan
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  #24  
Old 06-05-2016, 02:30 PM
jonnyschanny jonnyschanny is offline
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So I've filled the holes with dowels and also put a vertical dowel down through the heel. Then I put in hanger bolts.


However, when I attached it I realized there is now a gap between the sound board and the fret extension.





It looks to be about a millimeter between the two pieces. It may change slightly when I actually bolt the neck down for good, but I'd guess is going to remain. I trial matched the bridge using a straight edge down the fret board and it ends with the straight edge just above the bridge top. Do you guys think it would be ok to leave the gap there and when I bolt it down, glue and shim the gap? I'll need to double check the fret board because I might have a fret or two that are higher then others right now.
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  #25  
Old 06-05-2016, 04:43 PM
Alan Carruth Alan Carruth is offline
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You could shim the fingerboard end, or simply enlarge the holes in the neck block to allow for pushing the neck down. Glue the fingerboard down the top with a dab of hot hide glue, clamp the neck and tighten the nuts, then warm up the fingerboard with a hair dryer to melt the glue and get it to stick.
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  #26  
Old 01-17-2017, 05:14 PM
jonnyschanny jonnyschanny is offline
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Thanks for the advice again. I enlarged the holes slightly and was able to make it fit much closer to the surface!
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