Chasing the neck angle on an MT joint plus some issues?

[nkwak]

I had the neck angle set on my laminated MT neck but there were visible gaps in the cheeks so I wanted to fix that but I think I screwed it up. Here were my mistakes and initial impressions on how to fix it (though I am lost on a few things):

1: I've already installed the fretboard and frets, making if difficult to floss the cheeks. What's done is done but the reason I did that was because I could not envision how to set the proper angle without having the fretboard, frets and bridge placed. I know that I need to crunch the numbers better but I was never good at math and it all seems very arbitrary anyway; there always seems to be something that can be thinned to compensate - at the cost of structural integrity of course.

2: I shaved excess material off the side of the tenon to get the neck straight. It no longer fits flush and the neck rocks side to side so I've temporarily shimmed it with painter's tape. I know that I need to use something firmer, but more on that.

3: I used barrel bolt inserts laterally through the tenon itself which removed a significant amount of material and weakened the tenon. Being that it's a laminated neck, the tenon is made from the middle 3 plies of a central layer of walnut flanked by maple. The real mistake was that I overtightened the barrel bolts and created several hairline cracks in the tenon and even the heel itself. Being that this is my first build and I worked a LONG time to get my neck this far I'd like to save it if at all possible. My quick fix was to spit coat shellac on the exposed areas and wick CA glue into the cracks and put a coating of CA on the surface of the tenon to reinforce it. Next time I do and MT neck I'm going to use the threaded inserts. Now I know why since I learned the hard way.

I've been thinking long and hard about this - and sorry but I don't have pics - and I think I've got at least a partial solution, though I'd appreciate either verification or warning to walk away and think of something else. For now the neck seems straight again but the angle is now too shallow; the straight edge appears to touch the bridge about 1-2mm low. I need to get my eyes checked!

Option 1: shim the sides of the tenon. I have some rosewood veneer or 1/4" scrap maple left over to use. I estimate that the gap on either side is around 1/16" or less all told so the rosewood seems more attractive. This will complicate things since I will have to basically chase the angle to make sure the neck is straight along the centerline. Still, I need to both reinforce the tenon and tighten its fit slightly in the mortise.

and/or:

Option 2: just shave the bridge down. It was at the optimal height and angle and I'd already sanded the radius into the underside previously though so I'm not quite comfortable doing this. I'm thinking walking away from that idea might be better.

I don't know though. Am I missing something here? Please help me uncross my eyes and fix my mistake/neck.

[tippie53]

yes on shimming
no on shaving the bridge.

Here is a way to visualize what you need to do. Since this is a bolt on neck you can attach it a number of times to get it correct.

Add a few spacer shims between the sides and the heel. With the frets on the board you would like to see about 3/8 in off the top at the point of the saddle . So using a straight edge adjust the heel against the sides to get the neck to this point.
Be aware of the center line of the neck to the center line of the body, within 1/8 in should be fine.
Now you can see the area that needs to be adjusts. Before removing the neck you can now scribe a line on the heel to get the proper angle.

Once you take the neck out you can use a VERY SHARP chisel and just shave it nice and easy to get to the lines.
Also feel free to call me if you can we are here to help

[nkwak]

Thanks, John. I fashioned the shim out of Rosewood and things are much tighter now so I'm breathing a little sigh of relief. I've marked my line and will sharpen my chisel in anticipation of the next step.

[nkwak]

One more question, John: you said that with the frets on the fretboard when I lay the straightedge along the length of the guitar (with the nut removed) I should have a gap of 3/8" above the bridge itself (without the saddle of course) or is did you mean above the top of the guitar without the bridge? Right now it looks like I have a gap of about 1/8" above the bridge.

Also, I had to drill holes in the side of my shim for those pesky barrel bolts because - believe it or not -the neck seems to fit better without the bolts in. I'm tempted to just glue the neck on without the bolts in because then for some reason the neck wants to sit off center.

[tippie53]

I shoot for a 3/8 line off the top at the point of the saddle. Most bridges are 3/8 . When the bridge is placed a 1/16 gap to 1/8 is about where I want to be. How thick is the bridge?
You can glue in the neck but you still will be needing the bolts, that is what really will be holding the neck on.
Also if the neck is a bit off center . How much? it is noticable ? Post some pics and we can see what you have

[Darryl Young]

The cheeks of the neck are what should be holding your neck stable.....not the tenon. How is the fit of the cheeks to the sides of the guitar?

[Kevin Sjostrand]

I was going to say, but not to go against what John is telling you, that if your bridge thickness is more than 3/8" you could take some off the top surface to bring it down to that, if this helps with your set. Is it possible that your top has raised up since you first started the process, as in it has been in a higher humidity environment? This could cause some of the change in the straight edge height over the bridge location.

Kevin

[nkwak]

I shoot for a 3/8 line off the top at the point of the saddle. Most bridges are 3/8 . When the bridge is placed a 1/16 gap to 1/8 is about where I want to be. How thick is the bridge?
You can glue in the neck but you still will be needing the bolts, that is what really will be holding the neck on.
Also if the neck is a bit off center . How much? it is noticable ? Post some pics and we can see what you have

The bridge is .332" thick at the apex. With the bridge off the height of the straight edge above the top is a little more than 13/32" (or about 3/64" more than 3/8") so it's close.






Finding the true centerline has been difficult. I messed up somewhere with my fretboard and the edges are not a straight line (they're actually concave) so the trick of trace the lines all the way to the end of the guitar and finding the median probably doesn't apply. Fortunately the neck is straight; I just got sloppy planing away at the side of the fretboard. Instead I've been trying to use a square - or rather the squared end of my draftsman's cork-backed ruler - to see if the frets are perpendicular to the centerline of the body. But even then, that's not going to determine where the centerline is so I'm still scratching my head on that conundrum as well.

The measurements are arbitrary though because the cheeks do not appear to be making total contact with the body of the guitar. The neck appears to be leaning toward the bass side so it looks like I'm going to have to sand away more from the treble side of the heel.

[johnnparchem]

If you were happy with the neck to body joint the measurements look good to me.

[tippie53]

I agree , it looks good from here