Great minds thinking alike Sprokett. At least that is what I keep telling myself.
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| Reason to use a mortice and tenon http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=3190 |
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| Author: | Mike Mahar [ Sun Sep 11, 2005 11:43 pm ] |
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I have just discovered a good reason to use a mortice and tenon on the bolt-on neck. I mean the kind where you use the screw in inserts. On all of my guitars to date, I've just made the join between the heel and the body a butt joint. When I set the neck, I shave a litte from one side or another, or both to get the neck angle correct. This, however, leaves me with a source of error. If I shave one side too much, the neck will go on crooked and the center line of the neck will not be in line with the center line of the body. Fixing this problem makes it more likely that I'll get the set wrong and have to shave some more to fix that and perhaps making the neck crooked again. Before too long you're working on a 13-3/4 fret guitar. It's very hard to tell that you've gone wrong since there are no good right angles on your heel to key off of. If you make a mortice and tenon, however, the side angle issue goes away since the tenon won't let you tilt the neck that way. You've reduced your degrees of freedom and then you only need to concentrate on the neck set angle and making the cheeks of the heel flush with the side of the body. The tenon has to be a snug fit in the mortice but not insanely so. The mortice and tenon are easy to make co-planer because you cut them while the heel block and neck blank are still in their square from. |
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| Author: | Rick Davis [ Mon Sep 12, 2005 12:33 am ] |
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Yes, right, but you introduce the need to locate the headblock very accurately. If it is skewed, you now have the problem of a tilted neck (bass side higher or lower than the treble) and/or misalignment from the center line. And the fix is more difficult than with a butt joint, involving careful shaving and/or shimming of the tenon. You can avoid most of these problems by routing the mortise (using an accurate jig) after the body is assembled, as Tom Ribbecke does. Or you can create a reliable way of holding the headblock in position when gluing the rim. Of course, now you have to make the tenon equally precisely ... I use the mortise-and-tenon because to my tradition-bound thinking, it's more secure, not because it's easier in any way. I've never trusted the screw-in inserts though there's no evidence of them failing in a production guitar. And the wood-to-wood contact of the butt joint is limited which may create tonal or structural problems, or both (or neither). Ultimately, I think it's a personal decision. The butt joint is more tolerant of minor cutting and drilling inaccuracies; the mortise-and-tenon can be a little more self-aligning (And stable? strong? Maybe.) if made well. |
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| Author: | John Kinnaird [ Mon Sep 12, 2005 1:24 am ] |
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If you cut a mortis in your mold to match the mortise in the end block and then assemble the entire thing with a spline that locates the end block in the mold over a spline which is inserted in both mortises assembly goes pretty well. John |
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| Author: | Dale M [ Mon Sep 12, 2005 4:25 am ] |
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John! Great idea! I have scribed lines on my mold for aligning the mortice but the block in the mold is even more precise. Now if I can just get the block in the correct place---- |
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| Author: | Sprockett [ Mon Sep 12, 2005 4:40 am ] |
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Hey John... You stole my idea!!, I just had John Hall make me a new mold and was showing him how I do this, since I do a bolt on I use a piece of UHMW the same size as a tenon the barrel bolts in it (soon to be inserts), it gets clamped into the mold (each side has a 3/8" slot for the tenon to clamp it in tight). Then I trim my sides down to just touch that in the mold, then I glue in my mortise block using the bolts to pull the block even. Now as I'm doing this I do check with a ruler that the block points to the center of the tail block, that way I can adjust a little if needed... So far it's worked pretty good for me... -Paul- |
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| Author: | John Kinnaird [ Mon Sep 12, 2005 5:27 am ] |
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Great minds thinking alike Sprokett. At least that is what I keep telling myself.
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| Author: | Alan Carruth [ Mon Sep 12, 2005 6:08 am ] |
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I have seen a couple of butt-joined bolt-ons that have broken through the barrel nuts. The hardware is a stress riser, and there's not much wood around that lower one. |
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| Author: | Sprockett [ Mon Sep 12, 2005 6:43 am ] |
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Al.... Did they tear out the wood at insert point or did the tenon split? My intention was to use the insert but apply some good epoxy on the outer threads and make sure the insert did not stress the tenon at all when it was inserted... That should have alot more holding power than just fitting it in dry... Thanks -Paul- |
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| Author: | RussellR [ Mon Sep 12, 2005 9:38 am ] |
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Paul I've used both inserts and the Campiano System, The Cross Dowels are now my standard. I use a 20mm x 20mm mortice and drill the centers of the cross dowels at 8mm instead of 6mm, I've not had a problem with them. On the inserts I found they were fine in mahogany but had a tendancy to split the tennon in other woods. The reason for this I belive is they excert pressure allong the grain lines, just where the good wants to split. Of course by setting in expoxy maybe this will provide a cushion and prevent this. |
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| Author: | Rod True [ Mon Sep 12, 2005 9:46 am ] |
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Do most or any of you install a hardwood dowel vertically in the tennon? This will greatly eliminate the posibility of the insert pulling out. Also epoxying the inserts in also reduces potential. So I do both, the dowel and the epoxy. That should do it. |
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| Author: | Alan Carruth [ Tue Sep 13, 2005 6:58 am ] |
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The heel split at the barrel nut. |
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| Author: | Sprockett [ Tue Sep 13, 2005 7:25 am ] |
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Thanks Al... Going to have to think about that one for a while before I proceed... -Paul- |
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| Author: | Mattia Valente [ Tue Sep 13, 2005 9:03 am ] |
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Paul, I thought you were using inserts. Isn't Al talking about nuts, a la cumpiano system? |
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| Author: | Sprockett [ Tue Sep 13, 2005 9:27 am ] |
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Your right.... brain fade on my part 
I had that happen at the start but modified my design with a deeper tenon to give the bolt more wood to pull on. I still think inserts are the way to go, I'll post some pics of first prototype... -Paul- |
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| Author: | Alan Carruth [ Wed Sep 14, 2005 1:03 pm ] |
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I'm talking about the barrel nuts that Taylor used. Threaded inserts is another name. |
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| Author: | Mattia Valente [ Wed Sep 14, 2005 6:50 pm ] |
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Ah, OK, my bad. I was just getting a tad confused by all the terminology floating around. When I hear 'barrel nuts', I think Cumpiano, because, well, they're cylindrical tapped things. |
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| Author: | Rick Davis [ Thu Sep 15, 2005 12:00 am ] |
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I learned about barrel nuts, AKA cross-drilled dowel nuts -- NOT the screw-in inserts, from Michael Millard of Froggy Bottom. Don't know if he was the original user or not, but he uses the same system Cumpiano now recommends. At the time he showed me the system, he also showed me a neck with a neat chunk of the tenon pulled out by overtightening the bolt. Michael said it was the first one he'd seen (in over a hundred guitars). I began using the system with a 1/2" wide tenon (the length of the smallest dowel nuts I could find) and a hardwood spline epoxied into the tenon. I drill the tenon as close to the cheeks as possible. On a test rig, it withstood 90 ft-lbs of torque -- more would probably have sheared the bolt. I now laminate most of my necks with a maple or ebony center section, replacing the spline I used to use. I've also gone to dowel nuts drilled and tapped for 10-28 bolts which are lighter and less intrusive than the 1/4-20 ones, and leave more wood in the tenon. I don't have the tensile strengths handy, but even these are many times stronger than they need to be. The smaller diameter bolts are also less likely to vibrate loose, though wood movement can cause any bolt-on to loosen. Use a drop of low-strength Loctite (#222) if you're worried. The reason for a 1/2" wide tenon is to allow it to be nearly full-length but still have a narrow, tapered heel. The 3/4" wide tenon either has to be short or the heel has to be wide (a la Froggy Bottom). While the narrow tenon is definitely less strong than the wider, I feel that on the basis of my one test and subsequent 100+ guitars, it's more than strong enough for this use. Works for me. |
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| Author: | Dave Rector [ Thu Sep 15, 2005 12:44 am ] |
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Rick, can you recommend a source for the barrel nuts? |
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| Author: | Mattia Valente [ Thu Sep 15, 2005 2:27 am ] |
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Lee Valley carries both inserts and barrel/dowel nuts. |
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| Author: | Dave Rector [ Thu Sep 15, 2005 7:13 am ] |
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Thanks Mattia! |
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