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Improved neck heel mount
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=52397		 Page 1 of 3
Author:  Tai Fu [ Mon Sep 23, 2019 6:02 am ]
Post subject:  Improved neck heel mount
Image

Image

I made the aluminum insert for neck heel mounts. There is no way this will fail. The aluminum is machined with a dovetail that goes into the neck heel, and the aluminum is then drilled and tapped for a bolt. The dovetail mounts into a matching dovetail in the neck heel so it can't fall off, and the aluminum is scored to provide a place for the epoxy to grip onto.

It's a lot of work (actually, not really) but it should be extremely durable. However due to some miscalculation with the template, I messed up the dovetail slot. The epoxy will fill all the voids.
Author:  Woodie G [ Mon Sep 23, 2019 6:16 am ]
Post subject:  Re: Improved neck heel mount
Interesting idea - a loose tenon dovetail. What is the problem you feel this design addresses?
Author:  Tai Fu [ Mon Sep 23, 2019 6:35 am ]
Post subject:  Re: Improved neck heel mount
It solves tenon failing or inserts coming loose I guess.

I see guitar players are very much stuck on tradition. It's just another way of doing things.
Author:  Colin North [ Mon Sep 23, 2019 8:45 am ]
Post subject:  Re: Improved neck heel mount
So it's actually using 2 joints to fit a neck instead of one?
So do you glue the aluminium in the neck first and then floss the neck joint to set the neck angle?
Author:  Tai Fu [ Mon Sep 23, 2019 9:08 am ]
Post subject:  Re: Improved neck heel mount
pretty much...

Not "tried and true" but will see how it works.
Author:  Chris Pile [ Mon Sep 23, 2019 9:20 am ]
Post subject:  Re: Improved neck heel mount
Drive on with your bad self, Tai - the learning experience will be worth it.
Author:  Tai Fu [ Mon Sep 23, 2019 9:30 am ]
Post subject:  Re: Improved neck heel mount
So you don't think this will work? I'm not understanding what you guys are trying to tell me.
Author:  SteveSmith [ Mon Sep 23, 2019 9:56 am ]
Post subject:  Re: Improved neck heel mount
If the geometry is right then it should work just fine. My only thought is it looks like extra work but if you want to try it out then you should go for it.
Author:  Michaeldc [ Mon Sep 23, 2019 9:57 am ]
Post subject:  Re: Improved neck heel mount
Have you stress tested it yet?

My brain says that dovetail would tend to split the neck right down the middle.
Author:  meddlingfool [ Mon Sep 23, 2019 10:03 am ]
Post subject:  Re: Improved neck heel mount
Seems like it should work, esp cialky once you get the dovetail to fit properly.

Michael raises a good point though, might be worth checking.

What do you plan to use for bolts? Don't you usually want your inserts to be of a harder material than your bolts, so that if anything strips, it's the bolts and not the inserts?
Author:  Tai Fu [ Mon Sep 23, 2019 10:09 am ]
Post subject:  Re: Improved neck heel mount
Well, necks will fail at some point depending on what force you put into it.

Would your brain tell you that it would split the neck down the middle if you were to use it as a baseball bat, or it will do it all on its own without provocation?

Seems every mounting method has its drawbacks. Except dovetail neck attachment I guess.
Author:  Michaeldc [ Mon Sep 23, 2019 10:17 am ]
Post subject:  Re: Improved neck heel mount
Would your brain tell you that it would split the neck down the middle if you were to use it as a baseball bat, or it will do it all on its own without provocation?

Wow...

Don’t do meaningful testing then...

Best, M
Author:  Colin North [ Mon Sep 23, 2019 10:25 am ]
Post subject:  Re: Improved neck heel mount
Tai Fu wrote:
Well, necks will fail at some point depending on what force you put into it.

Would your brain tell you that it would split the neck down the middle if you were to use it as a baseball bat, or it will do it all on its own without provocation?

Seems every mounting method has its drawbacks. Except dovetail neck attachment I guess.


I think what Michaeldc was saying is that the dovetail part of the aluminium is being pulled towards the body by the neck mounting bolts and as such one is relying on the lap shear strength of the adhesive (epoxy) to resist the wedging effect of the dovetail tending to split the neck.
Author:  SnowManSnow [ Mon Sep 23, 2019 11:49 am ]
Post subject:  Re: Improved neck heel mount
Honestly I’m happy to see someone implement a new idea


Sent from my iPhone using Tapatalk
Author:  Colin North [ Mon Sep 23, 2019 12:14 pm ]
Post subject:  Re: Improved neck heel mount
SnowManSnow wrote:
Honestly I’m happy to see someone implement a new idea


Sent from my iPhone using Tapatalk

Me too.
Here's another neck joining system someone's tried -
Attachment:
lockingjointopen.jpg

Quote from the maker -
Quote:
pushing the neck tenon into the body mortice will make the contact between neck and body snug. In the case of the self locking joint the backward sloping dowels on the neck tenon fit into backward sloping slots in the body mortice so the further in the neck goes the tighter the joint becomes. This joint requires no glue to hold it although I always smear a little glue on the tenon to be sure, to be sure!

Not unlike a dovetail in principle, retains the weight advantage, but without the tricky woodwork/geometry some may feel is involved.
Author:  Tai Fu [ Mon Sep 23, 2019 12:24 pm ]
Post subject:  Re: Improved neck heel mount
So on that doweled construction, how would you reset the neck, and the dowel doesn't provide enough back pressure to keep the heel pressed to the body?
Author:  Clay S. [ Mon Sep 23, 2019 12:36 pm ]
Post subject:  Re: Improved neck heel mount
Interesting idea Tai,
I would be inclined to lose the tenon and just make it a butt joined heel with the aluminium insert, if I was going to add the epoxied in insert. If you then held it back in the heel some it might make flossing the neck angle a bit easier. I think you would still have enough threads in the metal as the average insert has and would be plenty strong.
On my travel guitars I add a metal plate (and dowel)in the heel for the bolt to bear against. It helps spread the force over a larger area. Since it is in the middle of the heel it doesn't interfere with fitting the neck.
Author:  Colin North [ Mon Sep 23, 2019 12:43 pm ]
Post subject:  Re: Improved neck heel mount
Tai Fu wrote:
So on that doweled construction, how would you reset the neck, and the dowel doesn't provide enough back pressure to keep the heel pressed to the body?

Personally (I don't know about the person who used it) but I would be thinking of a similar way to a dovetail reset.
Shim and re-cut the dowel recesses in the neck block to pull the tenon further in because the neck angle will change, necessitating realignment.
Author:  Tai Fu [ Mon Sep 23, 2019 12:45 pm ]
Post subject:  Re: Improved neck heel mount
I just figure that it will take a lot more force to split the neck apart, far more than it would require compared to barrel nuts or threaded inserts. I mean the dovetail is bearing against good 2 inches of wood compared to maybe 1/4" in a barrel nut setup. You'd have to slam the neck against concrete very hard to split it apart, and even then other part of the guitar will break before the heel does. I think it should be plenty strong for the application.

Some people just flat out don't like bolt on necks... because "Stradivarius never used them, why should we?" except I'm pretty sure bolts didn't even exist in the time of stradivarius. Steel in those days were too expensive to be used for anything other than knives or armor. So he most likely took what was available and did the best he could with it. Heck in those days aluminum cost more than gold!
Author:  Fasterthanlight [ Mon Sep 23, 2019 12:47 pm ]
Post subject:  Re: Improved neck heel mount
I'm loving this... i have my doubts about having two joints on the neck > body area, but i appreciate the attempt at innovation.

G.
Author:  DennisK [ Mon Sep 23, 2019 1:04 pm ]
Post subject:  Re: Improved neck heel mount
That dowel joint looks like a pretty terrible idea to me... similar to the Somogyi permanent joint, but even harder to get it just right, when Somogyi's is already a lot more work than just doing an integral neck in the first place.

As for the aluminum tenon, I agree with Michael that splitting is a concern due to the short grain of the heel. Assuming the epoxy has a good bond with the aluminum then it should be fine since it won't be wedging the dovetail open anyway. But in that case you might as well not go to the trouble of crafting the dovetail and just use a straight block of aluminum.
Author:  Woodie G [ Mon Sep 23, 2019 1:17 pm ]
Post subject:  Re: Improved neck heel mount
Problem definition is usually the first step in innovation; I was simply asking what problem you were attempting to solve so as to better understand your approach.
Author:  Tai Fu [ Mon Sep 23, 2019 1:28 pm ]
Post subject:  Re: Improved neck heel mount
The problem may be specific to my situation.

Barrel nuts, threaded inserts are difficult to obtain. Not to say you can't obtain them, but I simply don't know enough places to obtain the good brass ones (they only have the thin steel ones that aren't that good), and making barrel nuts seems to entail machining steel and all that, not to mention it would have problems with the very short grain splitting. So I thought, what if I made a tenon where it can't split like aluminum. But then if I used aluminum why bother using barrel nuts when I can just directly thread them.

So since my neighbor makes motorcycle parts out of his CNC machine he has a mountain of scrap materials. I just get a few scrap aluminum from him and use it to make small parts.

I know aluminum doesn't really bond well with epoxy so what I ended up doing is scoring the dovetail with a dremel tool so that it has an aggressive texture. The idea is that the epoxy would bite on it and not slip off. I could ask to anodize the part and hopefully make it more bondable, but the neighbor said that anodized surfaces don't hold paint that well, and he had better luck painting bare aluminum when the surface is very rough.

I heard you can treat aluminum with Alodine to make it take to glue aggressively but I seriously doubt you can ship hexavalent chromium by air. Also Alodine is very expensive.
Author:  ThomLuth [ Mon Sep 23, 2019 2:56 pm ]
Post subject:  Re: Improved neck heel mount
"So on that doweled construction, how would you reset the neck, and the dowel doesn't provide enough back pressure to keep the heel pressed to the body?"

The example in the picture appears to be a very poorly executed version of the neck joint Irving Sloane used in his steel string book. His version had one long dowel on each side, angled so the bottom of the dowel was closer to the soundhole then the upper part of the dowel. As the neck was tapped into the the neck block, the neck was locked tightly against the guitar. I built my first guitar in the mid-70s using this method and it worked very well. But you are right, in the picture, it would not do a good job of keeping the neck tight against the guitar body.

At that time Sloane wrote his book, the only book I can think of that showed how to do a dovetail joint was Joseph Wallo's How to Make a Classical Guitar. The pictures showed him with a carpenter's saw, cutting into a completely finished guitar . . . I opted for Sloane's method.
Author:  phavriluk [ Mon Sep 23, 2019 3:52 pm ]
Post subject:  Re: Improved neck heel mount
If that aluminum floating tenon wasn't glued in it sure would be dead easy to fine-tune the neck angles. Just remove the tenon and sand on the disk sander. Nice and square. That feature alone makes that tenon's argument.
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