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Adjusting the tenon after coming off the jig...
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Author:  bcombs510 [ Sat Nov 05, 2016 6:27 pm ]
Post subject:  Adjusting the tenon after coming off the jig...
Hello,

First, I have to say that I just received one of the Luthiertool Neck Angle Jigs to replace my homemade one. So far it's pretty great. The process is straightforward and the results from my first attempt were good. It was easy to dial it in and everything felt stable during the operation. I have a question, not specifically about the jig but just in general.

The guitars I've built so far are 00 and parlor in size. That means the top of the body is very rounded at the shoulders. I've been taking this into account when cutting in the jig and what I do is cut it a little short, 3/4 instead of 7/8. Then after coming off the jig I have been setting the table saw at 5 degree angle and cutting the cheeks on an angle so that they sit down on the shoulders correctly. Here is a pic that might help:

Attachment:
Tenon.jpg


I did the same thing today with the Luthiertool jig and it worked out fine for the parlor that I'm working on.

Question: My next few builds will be the Antes Dreadnought plan from LMI: https://www.lmii.com/products/media-gif ... t-6-string

I'm thinking that I'll have to do less or no adjustment to the tenon coming off the jig. At least in terms of the angle of the cheeks like the pic above. Will that be the case? I'm thinking that the top of the body should be dead flat in both directions and that the cheeks will be able to be flat as well. I'm thinking the only adjustment will be a bit of flossing. Will that be the case?

Any input is appreciated.

Thanks!
Brad
Author:  George L [ Sat Nov 05, 2016 7:53 pm ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
Actually, I think you'll find that the flatter area of the larger guitar is even more finicky, as even the slightest variance along any mated surfaces can cause headaches. I always remove material to create narrow contact points (as you've illustrated) no matter what type of guitar I'm building. I find this makes the flossing process much faster/easier and results in a superior fit.
Author:  bcombs510 [ Sat Nov 05, 2016 7:57 pm ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
Thanks, George!

Sorry, I might have confused the situation. Indeed, I also relieve the cheeks so that only a knife edge is contacting the body which does make the flossing faster. What I'm illustrating here is trying to match the rounded top of the smaller body guitars. I do that by cutting the angle you see above on the table saw. Then I use a template to make the sides of the base of the neck then I carve relief into the cheeks and floss.

But you've answered the question, that the setup can be finicky but at least I won't have to do this step on the table saw.




Sent from my iPhone using Tapatalk
Author:  Terence Kennedy [ Sun Nov 06, 2016 12:09 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
If you put a 6" ruler on a curved surface like a pop can it will fit flush if lined up with the long axis of the can. If you angle it like the heel of a guitar neck it winds up high in the middle. Even angling or undercutting the cheeks won't fix that if you have a curved upper bout.

You need to be aware of that when flossing. I don't think I appreciated that concept until Todd S mentioned it in a post years ago. Made final fit go faster as you know a little more wood has to come off the middle of an angled heel initially.

My archtops have a flat upper bout and no taper in the heel. They are a lot easier to fit.
Author:  murrmac [ Sun Nov 06, 2016 5:52 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
It does occur to me that it might be advantageous to flatten the contact area on a round shouldered guitar with a V shaped heel, so that you have two plane surfaces making contact, instead of fitting to a curved surface.

How feasible it would be to disguise the flattening afterwards I can only guess, but I would think that if you used a V-shaped flat sanding block in the first instance, in order to mimimize the flattening , and then sanded the adjacent area on the upper bouts after the neck is fitted , it should be possible to make it more or less undetectable.
Author:  Colin North [ Sun Nov 06, 2016 1:01 pm ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
For me anyway, a bit trickier than just flossing one in, and maybe flossing it's also easier to adjust for yaw.
Aso, I wonder, how would you sand a flat area on a curved upper bout?
If the area being sanded is anything other than parallel to a plane tangential to the upper bout . when the sanded area will be rectangular) that "angled" sanded area would have outward curving sides.
And I would not like to try to sand that in, especially on the likes of an SJ, which is a comparatively small radius curve.
CNC anyone? ;)
Author:  Mike OMelia [ Sun Nov 06, 2016 7:57 pm ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
Wait till you try that jig on a cut away. Ugh. If you go to their website, you will see a post about a "upcoming" edge vise to deal with this. its been there for a year. After an unfortunate stink i raised. But its nowhere to be found. Still, I like the tool. Just wish they would address this one issue.
Author:  murrmac [ Mon Nov 07, 2016 6:36 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
Colin North wrote:
For me anyway, a bit trickier than just flossing one in, and maybe flossing it's also easier to adjust for yaw.
Aso, I wonder, how would you sand a flat area on a curved upper bout?
If the area being sanded is anything other than parallel to a plane tangential to the upper bout . when the sanded area will be rectangular) that "angled" sanded area would have outward curving sides.
And I would not like to try to sand that in, especially on the likes of an SJ, which is a comparatively small radius curve.
CNC anyone? ;)


According to my rough calculations, on a 3.5" wide upper bout joint with 12" radius, if you sanded a trapezoidal flat 2.25" wide at the soundboard and 7/8" wide at the back (which is pretty much the size of the average tapered heel) , you would create a plane which is 0.7 degrees out of line with the line of the unsanded joint. I don't think this would be a problem as far as cutting the tenon is concerned ... you would cut at 2.2 degrees instead of 1.5 degrees.

Sanding the contact area to be perfectly perpendicular (laterally speaking) with the center line of the body would admittedly be tricky... it would almost certainly require a shop made guide, both for the lateral and longitudinal parameters, and might well be more trouble than it is worth.

My gut feeling is that sanding out the witness line between the edge of the flat and the radiused surface wouldn't be all that much of a problem, and the line could be rendered pretty much invisible.
Author:  Colin North [ Mon Nov 07, 2016 9:29 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
Hey, sure you're correct, don't mind me, go ahead.
Jist it a' sounds sic a guddle fur nae benaefit.
Author:  SteveSmith [ Mon Nov 07, 2016 11:02 am ]
Post subject:  Adjusting the tenon after coming off the jig...
Colin North wrote:
Hey, sure you're correct, don't mind me, go ahead.
Jist it a' sounds sic a guddle fur nae benaefit.


I have to agree with Colin. Once you learn how to do it, it's not that hard to floss it in - curved or flat makes no difference to me.
Author:  Terence Kennedy [ Mon Nov 07, 2016 12:12 pm ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
SteveSmith wrote:
Colin North wrote:
Hey, sure you're correct, don't mind me, go ahead.
Jist it a' sounds sic a guddle fur nae benaefit.


I have to agree with Colin. Once you learn how to do it, it's not that hard to floss it in - curved or flat makes no difference to me.


I agree, get the neck angle right off the jig, undercut the cheeks to leave 1/8"-3/16" contact surface and floss for perfect fit understanding it'll be a little high in the middle on a tapered heel. It's not that big a deal.

One big deal is not having the mating surface of the body flat in the vertical plane. If there is some rounding or drop away of the binding area getting a good fit is very difficult. I usually put the body in the guitar vise, draw pencil lines in the contact area of the heel and use a 6x3" flat sanding block to true up the mating surface.
Author:  George L [ Mon Nov 07, 2016 4:08 pm ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
Just for the sake of clarity, what you guys are saying is that after cutting #1 and #2, executing some variation of #3 will result in a high point in the middle of the arced (or tapered) edge ... am I right?

Image
Author:  Colin North [ Tue Nov 08, 2016 4:33 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
idunno
Too early...
Brain not in gear...
Coffee...
Author:  SteveSmith [ Tue Nov 08, 2016 6:08 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
George, I don't make the angle cut you show in #1. I think it would make it hard to fit the neck. That's a right angle cut on mine. Actually #1 and #2 are done on a jig then I mark and taper the heel. Finally I use a chisel to undercut the heel next to the tenon leaving about 1/8" untouched for flossing and final fitting.
Author:  Terence Kennedy [ Tue Nov 08, 2016 7:51 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
I don't make the angle cut either, just rout the tenon in the jig, do the cheek profiles, undercut with a chisel like Steve said, install the attachment hardware and fit it to the body by flossing.

I have a curved upper bout on all my flat tops so the angled heel rocks slightly in the middle. I have a surrogate fretboard with slots cut for the sandpaper strips that makes the fitting easier. Being aware that the middle is a little high initially and altering pressure accordingly is a big help. Sometimes it can still take me a while.

Typically the heel cap is not on at this point so that's a help too.

Some pictures.

Image


Image

Here is what it looks like after undercutting.

Image
Author:  bcombs510 [ Tue Nov 08, 2016 9:23 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
This is really helpful.

I make the cut in the #1 picture that George posted because if I cut all the way to the 12th (or 14th, wherever it meets the body) flat on the jig then by the time the cheeks are resting on the top of the body, the center has moved up to above the 12th. I hope that makes sense. Could the difference be that I've only made 00 and parlor sized guitars where the upper bout curve is different than say a dread?

See the pic below. I've always tried to keep the "Higher than 12th" line at the actual 12th by cutting the tenon a little short in the jig and then cutting the angled cut in #1 above up right to the 12th fret line where it meets the tenon. Otherwise you end up with what is in the pic below. Did I not need to do that?

Attachment:
Tenon.jpg
Author:  Terence Kennedy [ Tue Nov 08, 2016 9:59 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
If you undercut you should not have to angle your initial cut. The undercut gets rid of the wood that hits the body keeping the heel proud.
The flossing will put a little angle on the remaining rim especially near the top where the heel is wide.
Author:  SteveSmith [ Tue Nov 08, 2016 10:48 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
The part of the body joint you care about is where the outside edge of the heel meets the sides (i.e. right where your 12th fret line arrow is). Where the center of the neck joint matches up with the body is is of no importance for the 12th fret join. The heel area right next to the tenon usually has a 1/16" or so gap in the method I have been discussing.
Author:  bcombs510 [ Tue Nov 08, 2016 10:59 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
Terence Kennedy wrote:
If you undercut you should not have to angle your initial cut. The undercut gets rid of the wood that hits the body keeping the heel proud.
The flossing will put a little angle on the remaining rim especially near the top where the heel is wide.


And it all becomes clear now... [clap]

Thanks, Terence!
Author:  George L [ Tue Nov 08, 2016 11:07 am ]
Post subject:  Re: Adjusting the tenon after coming off the jig...
Steve is exactly right. [clap]
Saw, chisel, sand, scrape--however one gets there makes no difference. Personally, I do it the way Steve and Terence describe. I do leave the cheeks just slightly proud of the body join fret line and then work them down as I finesse the neck angle and fit.
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