Neck Fit: The Tenon is Too Long

[Darryl Young]

Well I have another learning opportunity <smile>. Seems I've had my share lately, ha.

I trimmed the sides where they cover the neck mortise and test fitted my neck. Wouldn't you know it, the tenon bottoms out in the mortise before the surface of the neck (where the fretboard mounts) is level with the top of the guitar. It stidks up about 0.080" above the surface of the soundboard. The depth of the body at the neck block is 3.334" (measured with my dial calipers)......not sure if that is narrower than normal or not. This is a 000 with a bolt-on neck from Hanneli-Moon that is built fairly close to Martin specs (a custom kit from John).

Anyhow, appreciate you input on the best way to correct this. My guess is I need to trim the bottom of the tenon where the neck can slide down further. In the pics below you can see that portion of the tenon is rounded over corresponding to a rounded area in the mortise.

So if this is the proper fix (please tell me if there is a better way), then a few questions.

1) After trimming the tenon, do I need to round it over to match the mortise in the neck block. If so, what is the best way to do that? (doesn't look simple)

2) I assume I will need to redrill the holes in the neck block to align with the threads in the neck dropped down 80 thou. Any suggestions on how to locate and drill these new holes accurately? I doubt I will be outside the original holes so the bit may want to walk over in alignment with the old holes. This may be the most difficult part of correcting the problem.......align the new holes on the centerline, spaced the correct distance apart to match the neck holes, and moved down about 0.085" - 0.090" (assuming the holes are a little oversized).

Appreciate your thoughts. Here are the pictures. You can see the binding I put on the top (with the extra B/W strip inside and outside the herringbone) on some of the pictures. I can only add 3 pictures per post so I'll include a pic of the tenon in the following post.

The first shot of my guitar with the neck in place:

Guitar.JPG

Side View:

SideView.JPG

Top View:

TopView.JPG

[Darryl Young]

And here you can see the shape of the tenon. Do I need to replicate the rounded over section after trimming?

If it makes a difference, I sanded a 1 1/2 deg angle in the rim from the top of the soundhole forward before gluing the soundboard on. Possibly this created a drop in the top leaving the neck 0.080" proud.

NeckTenon.JPG

[kencierp]

Where did the neck and neck block come from? There was no allowance for the top thickness figured in the block mortise. Anyway you'll need to trim the end of the tenon, make sure to maintain the radius pretty close so the tenon does not get stuck on the sides of mortise in the curve/radius.

You'll also need to elongate the boltholes in the neck block to allow the neck to drop down. This is not a big deal I see it all the time. The KMG neck blocks have elongated hole and oval counter bores to allow for some adjusment and plate dimension variance.

[Darryl Young]

The neck and neck block are from Hannali-Moon. I can't assume he got it wrong........I likely should have paid more attention to this before glueing the block to the rim.

Anyhow, does anyone know an easy way to elongate the holes in the neck block? If not, I follow another suggestion and fill the neck block holes and grind points on a pair of bolts that screw into the neck to mark the center where the new bolt holes need to drilled. Will probably shorten the tenon about 0.085" so the neck is in the correct position.

Any suggestions for cutting the tenon? I'll probably just use a pull saw I have that is made for cutting dovetails. Essentially no set in the teeth as it is made to ride along a jig so should ride along the shoulder of the neck ok I'm hoping.

[naccoachbob]

If you do this that I'm about to put out, I would suggest you really, really take care and also wait to see if someone with more experience says not to do it. But I was thinking you could take a drill bit the same size of your bolts and put it into the neck block, then rock it up and down to elongate the holes.
There is probably a safer, better way to do it, so please don't do it with just my post here. I'd hate to have you come back and say you ruined a guitar trying to do what I said.
I'm just throwing it out in case an experienced luthier just hasn't seen the posts yet and may think it would work.
Please do be careful however you do it.
Bob

[Darryl Young]

I have it fixed! <yeah, claps-hands, smiles>

I'm stoked, I trimmed 0.085" off the tenon using my Veritas dovetail saw. I used a washer of the correct size to draw the correct rounded shape. I undercut the tenon slightly on the corners with the dovetail saw then used a chisel to remove most of the material followed by sandpaper to round everything off. The repair looks like this (not perfect but not too shabby):

TenonRepair.JPG

I realized that 0.085" isn't a lot, so I used a rattail file to elongate the holes in the neck block. I monted the neck and had to remove just a tad more material from the elongated holes and everything fit great.

Now here is why I'm stoked. I clamped the fretboard in place and positioned the bridge. The fretboard extension is perfectly flat on the soundboard! Sanding a 1.5 deg angle in the rim works like a charm. And if that isn't enough, it appears the neck angle is about perfect! Pics:

FlatFBExtension.JPG

NeckAngle.JPG

[Darryl Young]

So now I need to trim the heel of the neck which was made to fit either a dreadnaught or a 000. This is a Martin style guitar. With the heel cover in place, how far should the heel block cover be below the back line of the guitar? Seems the heel is slightly recessed from the edge of the back......I just don't know how far and I need to know this to determine where to trim the heel. Also, should the cut be parallel to the fretboard surface of the neck or perpendicular to the face of the shoulder? I would guess perpendicular to the face of the shoulder would look better as it would keep the point of the "almond" shaped heel from protruding and possibly getting dinged when the guitar lays on it's back. Here is a pic of the heel with the neck mounted:

HeelTrim.JPG

And finally, should I use the ebony pyramid that came with the kit or should I make my own out of Brazillian Rosewood????

BrazBridgeMat.JPG

[naccoachbob]

I'm glad you got it finally set and didn't put a drill to it. Your solution was perfect.
Shame you have so many good choices for that bridge. If you don't go with the original, I like the one next to it. Also, I was wondering how the far right piece might look, but I see that dark streak going across it. If you flipped it over, would it match the saddle trough? Would that look good or bad?
Not sure about where to cut the bottom of the heel, but when completed shouldn't it be flush with the back of the guitar body? I see some that don't come completely down to the back, but I like it when they do.
Good job.
Bob

[tippie53]

Hi
call me and we can get this fixed. Not an but that neck will have to swapped out .

[enalnitram]

great job Darryl.

we seem to be going parallel in so many ways with our builds. it's freaking me out. i'm actually working on the tenon on my #3 right now which is my first bolt-on neck. i say i'm "working on" it...what that means, is i'm actually building up the courage to maybe do it on a bandsaw...or maybe i'll break down and buy a jig template and do it with a router.

how should you cut the neck heel? try looking at pictures of them online, and copy one that you like. on my first guitar i made it so that it was cut off, right where the binding ended. so the heel cap matched the binding and was in a line with it.



i like it also when the heel cap is flush with the back. it's an aesthetic decision, ultimately up to you. follow your gut.

would you make another pyramid bridge out of BRW? this is just me, but i prefer the longer saddle, and it might be purely imagined, but i have to believe they sound better, too. a slender bridge like you have there, but in a martin style with a long saddle would be easier to make. and BRW would be sweet.