LP Junior Geometry - mortise/ tenon question

Slowtwitch

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I'm doing a body for a guy, someone else will do the neck. It's his own design based on/ inspired by an early Les Paul Junior, so flat slab body, angled glued-in neck, full width tenon. It'll have a wraparound bridge like they came out originally (so neck angle will be something like 2.5 -3 deg).
Juniors have full width tenons which arguably contributes to the tone but def simplifies the build (compared to the smaller joint of a LP).
My question is around the mortise/ tenon detail which I can spec.

Here's the body, but don't mind the tenon/ mortise detail, that'll change.

I'm keen to do a mortise detail based on the Double Cut Junior with the tenon extending well into the body for good gluing surface. So there's no body wood on the treble side till the neck hits the body - like a Tele/ strat.

We've decided to do the mortise (body pocket) level, and sort the angle of the neck out on the tenon, but the basic principle as I see it in terms of height, (and here I'd like confirmation from you guys), is the edge of the fretboard should be level at the point where the neck hits the body on the bass side, which, as shown on the 2nd pic, is the 16th fret. The neck will then start sticking out above the body at the 2.5-3 deg up to the end of the fretboard. the rest of the tenon will be cut flush with the top of the body once glued in - like on a DC Junior.

Okay if that's in order, how deep do I make the neck pocket (mortise)? I can decided that, because the neck design will just follow whatever I decide?.Total body thickness is standard 1 3/4 inch. Obviously the pocket is normally much deeper than a Fender 0.65", but what would you recommend? Also I assume the mortise sides beyond the fretboard are just a straight line extension of whatever wedge the neck does i.e. nut width to 12th fret wdth to 22 fret wdth extended, correct?

Anything I've missed?



IMG-20220603-WA0008.jpg IMG-20220603-WA0005.jpg
I'm
 

Freeman Keller

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Slow, I don't have time right now to try to work thru all the details of your post. As you know, LP Jr's used several different neck configurations, some of which were notoriously weak. Melvyn Hiscock has pictures and sketches of several of them and it would be a good idea to look at them.

I would also suggest doing a full scale rendering with your cad software of the side view of the guitar with accurate measurements of the bridge you are using. You should be able to determine the exact geometry from that and build both the body and neck to that geometry. Whoever does the actual fitting of the neck to body should be ready to tweak the angle or overstand upon assembly.

Here is how I go thru the thinking process of neck geometry


More tonight, I'm going for a hike right now.
 

guitarbuilder

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You really need to draw a side view of your parts to determine the angle. Gibson single cut LP Jr's are elevated above the body by about 1/8". You could do the tenon flush to the neck but that would change the angle. Gibson in the 70's elevated some of the SG's so much that there really wasn't any neck angle.

The mortise and tenon depth would be determined by you, as well as any other details.

On my cnc melody makers ( and a LP junior) I put the angle on the tenon like you intend to do. Since I used a narrower tenon, I put wedges on each side to fill in the gap.

glue in wedges.jpg





Not sure this will help but it's a thin version of a LP Junior :). I opt for a Standard kind of tenon because I wanted to....



This could be helpful to see how things look and shapes of the neck at the tenon end.




See the German site for more LP info.

junior.png





guitars.jpg




You can see zero neck angle on an SG here:


And lastly if you get bored.


 
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Moldy Oldy

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Yes, do the side drawing including accurate height of the bridge you will be using. My doublecut Jr. has the fretboard about 1/8” or a little less above the body at the joint. Otherwise the 2-3 degree neck angle will be to low. If I understand your question about the tenon sides, I think they should be parallel to the center line.
 

Freeman Keller

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Okay if that's in order, how deep do I make the neck pocket (mortise)? I can decided that, because the neck design will just follow whatever I decide?.Total body thickness is standard 1 3/4 inch. Obviously the pocket is normally much deeper than a Fender 0.65", but what would you recommend? Also I assume the mortise sides beyond the fretboard are just a straight line extension of whatever wedge the neck does i.e. nut width to 12th fret wdth to 22 fret wdth extended, correct?

I'll just comment on this part. I have never made a flat topped set neck guitar nor a full width tenon - all of mine have been arched or carved tops and LP style tenon. I have repaired a couple of full width tenons, I think this was an ES125 or something

IMG_4982.JPG


This guitar had everything possible wrong with the neck joint. When it failed the owner just pored some quick set epoxy in. When it failed again he brought it to me.

IMG_2728.JPG


I think the thing these guitars have in common is not enough gluing area and too short of tenons.

The tenon on an LP is 4 inches long, 1.5 wide and 1.450 deep. That gives 17 square inches of gluing surface - that seems to be plenty. I've seen neck heels broken on Lesters but neveer the glue joint.

If you do a LP style tenon the sides are parallel and it makes setting it much easier. I think setting a wedge shaped tenon (other than a dovetail, of course) would be a nightmare. If I was doing a full width tenon I think I would make the sides parallel and put a wedge shaped piese under the f/b extension. That is commonly done on archtops (I just did it on mine).

As far as how far down the neck sits in the pocket, there is nothing that says it has to be flush at the front but that is the way I do it. At least some of the Juniors, Melody Makers, etc have some overstand, the red 125 in the picture above does. Remember that overstand and angle work together to establish geometry.

One thing some Gibsons have is the body is slightly wider than the neck heel which gives a little ledge all around the heel. Here is a MM that shows what I'm talking about, most SG's have it too. Personally I don't like it, I think it looks unfinished.

IMG_5096.JPG


Some other things to think about around the neck area is that if either or both body and neck are to be bound you want the width at the joint exactly the same. I usually build the neck and establish that width, then bind the neck. Fit the neck to the body and bring the insides of the cutaways flush with the heel. Then bind the body.

Here is an LP body and neck under construction. The tenon is a nice snug fit - it will easily hold the weight of the body. The neck is still oversize, it will be carved next. I like to fit the neck with the fretboard off - I often wait until the neck is glued to the body before gluing the f/b on - that lets me deal with the transition at the body joint

IMG_1970.JPG

IMG_1969.JPG


IMG_1971.JPG


And here the pickup cavities have been routed - that clips the end off of the tenon but the bottom gluing surface is still there

IMG_1975.JPG


Edit to add another picture. This is a 335 style double cutaway. The body joint is at the 18th fret which somewhat weakens it, I made up by pushing the same 4 inch long tenon all the way to the end of the pickup cavity. Its got almost the same gluing surface as the LP

IMG_3230.JPG


Frankly it would scare me to have two people independently building a set neck and body, but I suppose with accurate CAD drawings and good mills it would be possible. I do it the old fashioned way - building one against the other in steps. I also check and double check and check the geometry over and over and over as I'm building - once you put the glue on you are pretty much committed.

Hope this helps, I still recommend looking at the pictures in the Hiscock book.
 
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Moodivarius

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On the LP Special, I’m helping my friend build, we did the same as Marty, Post #3.
Basically an LP mortise & tenon, with small wedges under the fingerboard to match up with the body.

94D722E6-A479-4BDE-81E2-2AB2BB3F0816.jpeg



EA3C3215-867A-4F2B-BCBE-47E3C38D205B.jpeg



Scott
 

Slowtwitch

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Thx for this Freeman. I've studied your build threads and how you do the necks and joints (3,5deg/ multi piece scarf necks etc) on all your builds, it's helped me a great deal in understanding set necks and what to pay attention to.

ITO 2 guys doing the work, I don't really see it as an issue. The guy doing the neck will have the body in hand when he makes the neck and can match the tenon to the mortise, but I agree, BAD idea to do them independently and then try marry them afterwards.

I think you have reinforced my proposal to do a long tenon like the DC Junior has.
 

Slowtwitch

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I'll just comment on this part. I have never made a flat topped set neck guitar nor a full width tenon - all of mine have been arched or carved tops and LP style tenon. I have repaired a couple of full width tenons, I think this was an ES125 or something

View attachment 992044

This guitar had everything possible wrong with the neck joint. When it failed the owner just pored some quick set epoxy in. When it failed again he brought it to me.

View attachment 992045

I think the thing these guitars have in common is not enough gluing area and too short of tenons.

The tenon on an LP is 4 inches long, 1.5 wide and 1.450 deep. That gives 17 square inches of gluing surface - that seems to be plenty. I've seen neck heels broken on Lesters but neveer the glue joint.

If you do a LP style tenon the sides are parallel and it makes setting it much easier. I think setting a wedge shaped tenon (other than a dovetail, of course) would be a nightmare. If I was doing a full width tenon I think I would make the sides parallel and put a wedge shaped piese under the f/b extension. That is commonly done on archtops (I just did it on mine).

As far as how far down the neck sits in the pocket, there is nothing that says it has to be flush at the front but that is the way I do it. At least some of the Juniors, Melody Makers, etc have some overstand, the red 125 in the picture above does. Remember that overstand and angle work together to establish geometry.

One thing some Gibsons have is the body is slightly wider than the neck heel which gives a little ledge all around the heel. Here is a MM that shows what I'm talking about, most SG's have it too. Personally I don't like it, I think it looks unfinished.

View attachment 992053

Some other things to think about around the neck area is that if either or both body and neck are to be bound you want the width at the joint exactly the same. I usually build the neck and establish that width, then bind the neck. Fit the neck to the body and bring the insides of the cutaways flush with the heel. Then bind the body.

Here is an LP body and neck under construction. The tenon is a nice snug fit - it will easily hold the weight of the body. The neck is still oversize, it will be carved next. I like to fit the neck with the fretboard off - I often wait until the neck is glued to the body before gluing the f/b on - that lets me deal with the transition at the body joint

View attachment 992058
View attachment 992057

View attachment 992054

And here the pickup cavities have been routed - that clips the end off of the tenon but the bottom gluing surface is still there

View attachment 992059

Edit to add another picture. This is a 335 style double cutaway. The body joint is at the 18th fret which somewhat weakens it, I made up by pushing the same 4 inch long tenon all the way to the end of the pickup cavity. Its got almost the same gluing surface as the LP

View attachment 992066

Frankly it would scare me to have two people independently building a set neck and body, but I suppose with accurate CAD drawings and good mills it would be possible. I do it the old fashioned way - building one against the other in steps. I also check and double check and check the geometry over and over and over as I'm building - once you put the glue on you are pretty much committed.

Hope this helps, I still recommend looking at the pictures in the Hiscock book.

On the LP Special, I’m helping my friend build, we did the same as Marty, Post #3.
Basically an LP mortise & tenon, with small wedges under the fingerboard to match up with the body.

View attachment 992113


View attachment 992115


Scott
Scott I've studied your recent thread on the LP done with the cnc, you're doing your neck and joint different to FK, but was good to see how you do it.

In my case though I want to stay with the ethos of the Junior which uses a simplified neck joint i.e. full width on a flat slab body. So I get the wedges under the fretboard solution for slab body (didn't know of this solution before and wondered how one will deal with the problem if you do make a narrower tenon on a flat body)
 

Slowtwitch

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You really need to draw a side view of your parts to determine the angle. Gibson single cut LP Jr's are elevated above the body by about 1/8". You could do the tenon flush to the neck but that would change the angle. Gibson in the 70's elevated some of the SG's so much that there really wasn't any neck angle.

The mortise and tenon depth would be determined by you, as well as any other details.

On my cnc melody makers ( and a LP junior) I put the angle on the tenon like you intend to do. Since I used a narrower tenon, I put wedges on each side to fill in the gap.
Marty what do you mean by this?
BTW I've seen a pic of a early Junior prototype with 0 deg neck angle - the fretboard is sitting so far off the body surface, it really looks silly.

Back to how deep to make the mortise.....this is on a Junior neck which as I understand it has no steps, but just a level bottom face (at an angle in my case). The way I understand the matter, the depth of the pocket is really only a function of how much of a step there will be between the bottom face of the body and the bottom face of the tenon, and I'm trying to decide how much to make that step. In the case of a Fender it's 1.75"-0.65" which is a big step, but needed for the bolt-on neck design. In a set neck I can make the step smaller i.e. the pocket deeper, but what's the norm?
 

guitarbuilder

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Marty what do you mean by this?
BTW I've seen a pic of a early Junior prototype with 0 deg neck angle - the fretboard is sitting so far off the body surface, it really looks silly.

Back to how deep to make the mortise.....this is on a Junior neck which as I understand it has no steps, but just a level bottom face (at an angle in my case). The way I understand the matter, the depth of the pocket is really only a function of how much of a step there will be between the bottom face of the body and the bottom face of the tenon, and I'm trying to decide how much to make that step. In the case of a Fender it's 1.75"-0.65" which is a big step, but needed for the bolt-on neck design. In a set neck I can make the step smaller i.e. the pocket deeper, but what's the norm?

What I mean you ask?


As I said, you can stick the tenon flush with the top, or elevate it. It just will change the neck angle and the esthetics. My heel steps down .375 from the backs of the bodies.

My Gibson Sg is .125 from the back. My Gibson LP Special is .25 from the back as is the Gibson Melody Maker Reissue.


I'd draw that side view in CAD if you can and then you can change things around easily and see if you like it. IN the LP thread you linked, I see people already have two different angles..... draw your own drawing to determine the correct angle.


Here is the trig calculator I use.



You could scale up this drawing to 100% and see what this person did:
step.png
 
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Freeman Keller

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One minor thing to remember is that if you do the wedge shaped tenon without any heel cheeks it will want to loosen as you set the neck. A dovetail is an elegant mechanical joint that tightens as the neck drops down into the mortise but yours won't do that unless it has something to work against.
 

Slowtwitch

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So I did the 3d model of a SC and DC version joint. he doesn't like either. I feel like I've wasted all of your time a bit here, sorry.
No treble side lip, and no extension past the fretboard under the pickguard

As it turns out, he's not all set on a traditional Junior neck.
This is what he wants (but the tenon will be angled at the neck angle, the mortise remains level).
So it is still a wide tenon but will need wedges under the fretboard, and it's not full depth - there's a step from the heel bottom to the bottom of the tenon. So does tht mean I can make the pocket shallower, maybe 1 inch?
What's your thoughts
IMG-20220610-WA0013.jpg
 
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Slowtwitch

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You really need to draw a side view of your parts to determine the angle. Gibson single cut LP Jr's are elevated above the body by about 1/8". You could do the tenon flush to the neck but that would change the angle. Gibson in the 70's elevated some of the SG's so much that there really wasn't any neck angle.

The mortise and tenon depth would be determined by you, as well as any other details.

On my cnc melody makers ( and a LP junior) I put the angle on the tenon like you intend to do. Since I used a narrower tenon, I put wedges on each side to fill in the gap.

View attachment 991945




Not sure this will help but it's a thin version of a LP Junior :). I opt for a Standard kind of tenon because I wanted to....



This could be helpful to see how things look and shapes of the neck at the tenon end.




See the German site for more LP info.

View attachment 991943




View attachment 991947



You can see zero neck angle on an SG here:


And lastly if you get bored.


Marty it seems we're now looking at a joint similar to your MelodyMaker.
What's the dim's on it?
I assume the mortise sides are parallel and not wedged (so not following the FB edge line)
 

guitarbuilder

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That tenon is like a LP standard. 1.50" wide. 3" long by 1" deep on a 1-.375 thick body. I always rout the body first and then trim the tenon to fit the width. You can make it wider or narrower too if you like. It's a straight tenon with the angle on the bottom.

clean up tenon with chisel and see chips.jpg
 
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Slowtwitch

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That tenon is like a LP standard. 1.50" wide. 3" long by 1" deep on a 1-.375 thick body. I always rout the body first and then trim the tenon to fit the width. You can make it wider or narrower too if you like. It's a straight tenon with the angle on the bottom.

View attachment 992535
Great! Do you have more pics of this, or a build thread?
 

Slowtwitch

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The neck is very rough I know but you get the idea
this is at 1.5 deg, that top of FB, still need to add fret wire, and confirm lowest saddle hight

I'm placing the fretboard glue line (underside of FB) at the body intersection
The tenon is 83mm long and 42mm wide, parallel sides, 1 inch deep
IMG_20220610_154226.jpg IMG_20220610_135231.jpg IMG_20220610_135213.jpg
 




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