Neck joint - LP body, flat (not carved) top, neck angle and FB support

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Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Steve Sawyer » Thu Mar 29, 2018 12:22 pm

I posted awhile back asking about a bolt-on neck on an LP-style guitar. After doing the calculations (see below) that show I need a 1 1/2 degree neck angle, I'm re-thinking this, and figuring I might as well learn to do a set-neck.

A pencil-and-paper drawing and the drawing shown below both yield the same value - 1 1/2 degrees - for the neck angle. The only thing that I'm unsure of is dealing with the lack of support for the body-end of the FB. On carved-top guitars, the FB actually rests against the sloping guitar top on either side of the tenon. In my case, the top is flat. As you can see, my original drawing was considering doing a fender-style joint, to keep the neck shaft full-width below the FB. However, again as you can see from the drawings, I only have a gap of 0.084" between the FB and the flat guitar top. Is there any reason I couldn't glue on wedge-shaped "wings" beneath the sides of the FB, and a similar shim on the end of the FB to provide that support?

Thanks!

LP Neck Angle Calc.png


LP Neck Joint.png
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Bill Raymond » Thu Mar 29, 2018 12:39 pm

I assisted my son in constructing a flat solid body guitar and that is exactly the solution that we came to: 2 wedge shaped pieces, one along each end of the FB and a small filler at the end of the board.
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Chris Richards » Thu Mar 29, 2018 12:47 pm

There's no problem at all with adding wedge shims under the unsupported sides of the fretboard. You mention adding a shim at the end as well but I think you'd be far better off making the male part of the tenon at least as long as the fretboard otherwise you're not going to end up with a very strong joint, on a Les Paul the tenon extends along the bottom of the neck pickup cavity.
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Steve Sawyer » Thu Mar 29, 2018 2:19 pm

Bill/Chris - thanks!

Chris - good point - I don't have the drawings in front of me at the moment, but I believe you're right about the length of that tenon!!
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Dan Smith » Thu Mar 29, 2018 10:22 pm

I prefer to simply sand the body at the neck area to match the angle of the neck.
This allows the fretboard to sit flush on the body. I like to leave a very small gap under the fretboard and do not glue the fretboard to the body. If the neck moves near the joint, I want the fretboard to be able to move with it. I always let the end of the board overhang the end of the neck tenon to hide the joint. Just my opinion.
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Chris Richards » Fri Mar 30, 2018 6:33 am

I hope these two pictures come out ok...I don't think it's vital that the tenon extends into the pickup cavity I can't see that adding a great deal more strength especially as some LP neck tenons had a rounded bottom so the neck angle could be easily adjusted. Personally though I would keep the tenon at least the full length of the fretboard, I've also seen on some cheaper LP copies that they only step the tenon on the cutaway side and leave the neck full width for the upper bout, this saves quite a bit of work as you only have to make an accurate shoulder on the cutaway side of the tenon, it looks a bit odd not being symmetrical but I can't see any problem with doing it that way?

Cheers Chris
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Brian Evans » Fri Mar 30, 2018 7:50 am

So I went and looked at the neck joint on my 1962 Gibson Melodymaker, which is about as close to a flat top Les Paul as you might find. It has around a 1.5 degree neck angle, and the neck/fingerboard seems to simply be set into a neck-width tenon all the way to the end of the neck. It might be a narrower tenon, in which case there is a wedge, but it doesn't look like it to me. I've seen pictures of really early Melodymakers where the neck joint is a full width tenon (they called it a "box joint") and there is a router gap at the end of the neck of about 1/8" (the body rout kind of over-shoots the end of the neck to accommodate the rounded router bit. So that is how Gibson did flat top solid body necks away back in time.
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Steve Sawyer » Fri Mar 30, 2018 10:55 am

Brian - thanks for the research!!

I played with the idea of a full-width tenon, but it requires a Fender-style neck rout that is open on the cutaway side. (See my second pic above). However, I was looking at a new Gibson LP at a local guitar emporium and was shocked to see this ugly boss on the cutaway side, which suggested to me it might be using a full-width tenon on the neck. It was REALLY ugly!

I think I'm going to go with a narrow tenon and wedges.

IMG_2481.JPG
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Brian Evans » Fri Mar 30, 2018 11:43 am

The melody maker has the same cutaway feature, slightly wider than the neck, on both sides (it's a double cutaway). Looks fine because the MM is and was intended to be a very fast build (I bet they went from raw wood to finish in one day) high volume (higher volume than any other Gibson electric I read one time) cheap student guitar. But mine has 55 years of mojo...

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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Freeman Keller » Fri Mar 30, 2018 12:04 pm

Steve, if 1-1/2 degree angle and the little wedge work for your geometry, then thats what you should use. I have been successful with 3-1/2 degrees and no overstand, but my tops are pretty arched. I have used wedges on a couple of true archtops - that is pretty common with their geometry.

I question your 0.48 bridge height - did you take that from an actual bridge or an engineering drawing? Most of the ToM's that I've worked with are closer to 0.625 at their lowest adjustment. My rule of thumb has been that the fret plane should just hit the top of the saddle at its bottom point - that seems to give adequate adjustment for almost any action you want and to provide for future changes in the guitar. (I can go thru the reasoning but maybe not this thread, I've posted the question here and at OLF on how other builders calculate their geometry but never had a good reply).

Anyway, if that bridge works then there are a range of angles and standovers that will work - the more you make the angle the more you can drop the front of the wedge.

If you decide to go with 1-1/2 degree angle I would suggest making the bottom of the neck pocket at that angle, make the tenon rectangular (parallel to the top of the neck). The neck will stand proud of the body, just fill the sides with the wedges. Most of the time the tenons extend into the front pickup cavity - there are "short tenon" versions but they seem to be problematic - I have repaired one and heard of other issues. It seems link the longest gluing surface is desirable.

Here is a picture of a guitar with no overstand and 3 degree angle but if you imagine the neck standing proud then the wedges will be obvious.

Image

A couple of things to think about if you do make the neck stand proud - first you will need to notch the end back down to the top of the guitar so you can fit a pickup ring (assuming you are going to use a humbucker). You can see that line across my neck next to the end of the truss rod slot - the fretboard ends there and that little gap is filled by the ring. You will probably need a tall ring at the neck (normally they are the short ones) - take a look at LMII's elegant wood rings.

Another slight problem is if you are going to bind the neck and body - you will have a gap between them that needs to be finished. Here is an archtop with a little wedge - it had to be finished in red instead of bound

Image

Here is the guitar from the above picture with no overstand

Image

There were lots of versions of Les Paul Juniors - single and double cuts, one or two pickups, P90's or HB's, but I think they all had flat tops and mostly were unbound. There are a couple of sets of plans out there, I honestly don't know how true to the guitar they are - here are a couple

https://www.ebay.es/itm/Luthiers-Projec ... 1801233715

https://www.ebay.com/itm/Gibson-Les-Pau ... 2429435489
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Steve Sawyer » Fri Mar 30, 2018 10:23 pm

Freeman Keller wrote:I question your 0.48 bridge height - did you take that from an actual bridge or an engineering drawing?

From the actual bridge. It's a Mighty-Mite ABR ToM style, and I measured from the bottom of the adjustment wheels to the bottom of the saddle slots - the lowest possible position for the strings. And yeah, I'm using the same logic you do to determine the proper neck angle, though I'm taking into account the nut height.

Freeman Keller wrote:If you decide to go with 1-1/2 degree angle I would suggest making the bottom of the neck pocket at that angle, make the tenon rectangular (parallel to the top of the neck). The neck will stand proud of the body, just fill the sides with the wedges. Most of the time the tenons extend into the front pickup cavity - there are "short tenon" versions but they seem to be problematic - I have repaired one and heard of other issues. It seems link the longest gluing surface is desirable.

That's the way I seem to be going, Freeman.

Freeman Keller wrote:the fretboard ends there and that little gap is filled by the ring....Another slight problem is if you are going to bind the neck and body - you will have a gap between them that needs to be finished.

As you can see in the pic below, I was planning on notching the tenon to go under the pup right at the end of the FB, but while this will leave clearance for the ring between the pup and the FB, this will leave no support for the ring, so I'll need to mod this as you describe. Also note that I do plan on binding both the neck and the body. I'm doing a natural finish, so as long as I use some carefully selected scrap sapele for those wedges, they should look ok.

I'm working from some plans that I got a couple of years ago, and don't remember where they came from, but one of those plans you linked to might help with the issues of doing a flat-top.

LP Neck Joint Detail 1.png
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Freeman Keller » Sat Mar 31, 2018 8:09 pm

Interesting about the measurements on that bridge, my notes show that the three different ones that I have used are 0.544, 0.565 and 0.599. Guess thats why its good to measure them. Many Fender style bridges seem to be right at a 0.500 but I did run into one that was substantially higher - a small angled shim in the pocket took care of that.

Looking forward to your build
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Steve Sawyer » Sun Apr 01, 2018 8:57 pm

Freeman Keller wrote:Interesting about the measurements on that bridge, my notes show that the three different ones that I have used are 0.544, 0.565 and 0.599.


Your question made me go back and use a different (hopefully better) technique to double-check, and I was a little off - it's actually 0.510". Not sure how much difference that will make to the neck angle, but I'll re-calculate that.
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Steve Sawyer » Mon Apr 02, 2018 11:38 am

Heh, heh...

A little trig shows that my .012" bridge height error translates to an angle correction of .027 degree. I'm having enough trouble measuring a 1.5 degree angle!! I think I'm still good... :)

ARCSIN(.012/24.75)=.027
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Freeman Keller » Mon Apr 02, 2018 12:01 pm

Ultimately I get it close and then use the actual bridge sitting on top of the guitar to finesse it into place. It is a multi dimensional geometry problem that is best solved with a chisel and sandpaper

And remember that the goal is to have enough adjustment in the bridge to come up with playable action (how ever you define that) all the way up the fret board, and to have enough adjustment to correct for any movement in the future.

Kind of makes Leo's screw on necks look good, eh?
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Freeman Keller » Mon Apr 02, 2018 12:14 pm

By the way, Steve, I happen to be working on an old Les Paul that had its neck popped out of the pocket. The owner glued it back in with a type of glue that expands as it cures (you can guess what) and it pushed the neck up so it stands proud of the body by about 1/8 inch (it's parallel to the body so the angle didn't change much). I can't get it apart to fix it but it looks like the bridge will go high enough to get playable action so I'm doing the rest of the repair work - its not going to be pretty but its going to be playable.

I'll add another comment - I have always thought it would be interesting for someone with solid modeling software to model the neck geometry of the average guitar. Since I retired I no longer have a CADD or solid model software (I spent too much of my life doing that, it was time to walk away). The little rules of thumb that I use are based on high school geometry and a bit of experience building a few, but it would be interesting to confirm it with a model (is that working backwards?).

That also means to take what I suggest with the grain of salt - it works for me but I have not seen any other builder talk about how he or she defines the starting geometry of a guitar. In the acoustic world we shoot for the fret plane to just hit the top of the bridge, I'm kind of doing something similar here.
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Paul Rhoney » Mon Apr 02, 2018 1:38 pm

Regarding the idea of using wedges, I don't see any reason why you would have to do it on both sides of the neck on an LP shape body. You could just do it on the treble side, and keep the bass side full-width. Less wedges to make, and the grain will look better on the side that the player sees the most.
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Freeman Keller » Mon Apr 02, 2018 2:49 pm

Paul Rhoney wrote:Regarding the idea of using wedges, I don't see any reason why you would have to do it on both sides of the neck on an LP shape body. You could just do it on the treble side, and keep the bass side full-width. Less wedges to make, and the grain will look better on the side that the player sees the most.


According to the pictures in Hiscock's book, LP Juniors didn't have wedges on either side - the tenon is the full width and the necks stands proud just like a Fender. An accurate set of plans should show this.
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Freeman Keller » Mon Apr 02, 2018 2:56 pm

Steve, I got curious and measured that broken LP that I'm working on. There is an 1/8 inch gap between the f/b and the top that I'm not going to try to fill. The fret plane is 0.750 above the top at the bridge location. It has a Nashville style ToM (small pressed in bushing). The action will be marginal but I think OK.

All of the LP style guitars that I have made use the so called modern bridges with the large pressed in bushings. My notes show that I set those at 0.625 above the bridge. Your original style bridge seems to be less tall.

And to clarify, all of my measurements of fretboard plane are taken in the center of the board, so those heights are basically the 3rd and 4th strings. Obviously the E strings will be closer to the top. Unfortunately those thickness of bridges that I gave you before were to the E strings so they probably aren't valid in this context.
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Re: Neck joint - LP body, flat (not carved) top, neck angle and FB support

Postby Steve Sawyer » Mon Apr 02, 2018 10:12 pm

My Sketchup model used the D or G string (don't remember which without going back and looking at it), but I seem to be hewing to your logic.

Obviously I think solid modelling would be fantastic for builders!! :)
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