Bolt on neck, elongate hole to vertically align neck with body?

I really don't have much more than about .004" of difference between the neck surface and the body at the heel. I think the simplest fix is to elongate the quarter inch hole that holds the body and neck together. This is my second build so I am asking if anybody does that and is there any downside to it? Last neck I did not have the headstock veneer glued on and could simply stand the neck surface to get a better match. This time sanding is not an option.

Thanks folks!

You could do that. Gluing the joint, yes?

I usually shape the heel and make sure that joint is where its supposed to be before I finish the neck (headstock and inlay is last). If the mortise & tenon joint (for me) is not good, then get it good.

Building is not really building, at first. It's a series of fixes. And once you nail down all your jigs, then it becomes. . . A series of fixes.

Is there a tenon on that neck, or is it just a butt joint that's bolted on? If there's no tenon, dowel, or other locating feature, I'd try to keep the bolt hole "tight" to the bolt as that becomes part of your method to lock in location for the joint. Then again .004" isn't very much elongating to do in that hole and gluing the fretboard extension helps lock in location anyways.

Another option would be to plane .004" off the top of the neck blank (or just a couple swipes on a flat and true sanding board).

And Kekani is really on to something. The magic isn't in knowing how to do a step. The magic is in knowing how to adjust/true-up/compensate for the step you're doing (or just did) because it's a tiny bit wrong.

1 tenth of a millimetre? I tiny bit of sanding will be fine, an maybe a small amount on the underside of the fretboard where it overhangs the top. As long as you get the fretboard surface flat and you can get an acceptable glueline on the fretboard I wouldn't sweat it.

Kekani said:

Building is not really building, at first. It's a series of fixes. And once you nail down all your jigs, then it becomes. . . A series of fixes.

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Well put, Aaron.

Great pictures! Shows the situation exactly...

While the bit of proud neck showing might be very small, it is significant to how the fretboard will lie and on later set up considerations. Couple of things to think about:

1: You could ignore it and do a "floating" fretboard. Probably not a good idea as it will look terrible and like there was a goof.
2: Sanding the neck bed down flush to the body is tempting but could lead to problems getting it perfectly flat without "waves". The presence of the peghead veneer over hang complicates things too.
3: Enlarging the bolt holes and bringing it down flush would work, but who wants an unsecure bolt in a critical place?

It is up to you how you want to approach this problem, but if it was me (and it ain't), I would do option number three and shim the enlarged bolt holes with a little stock (or whatever) and snug down those bolts. If you are using inserts, same deal. Just embed the inserts in something to secure them.

Anybody else?

Enlarge the bolt hole. When the neck is bolted on tight, with the fingerboard flat on the top, nothing is going to move, even with a non-glued butt joint (no tenon). The heel of the neck will also, with a little time, 'stick' to the finish. I have taken a couple of bolt-on necks apart, with no tenon or glue, and one has to give the neck a pretty good whack to break the neck free, even with the bolt loose. A tight bolt, and the tension of the strings, makes things very tight, and, if worst comes to worst, just loosen the bolt, realign, and tighten the bolt.

If you glue the neck to the body there is NO problem with elongating the hole in the body. I do this all the time to get a better alignment. I have had to take off some of my necks for repairs. It was NOT easy and I have never worried about that joint again ....even if you take the bolt out I doubt you would ever know. I do have bare wood on the neck end and on the body at the joint. I glue the fretboard to the body also..... This is a 90 degree glued joint and it is VERY secure. The bolt for me is to suck it all up into place while the glue dries. I always make the body bolt whole larger than the bolt so I can get the alignment perfect.

My feeling is that it is the clamping of the the end of the neck to the body that holds it in place, the clamping force being applied by the bolt(s). In the majority of threaded fastening applications, there is some clearance between the threaded fastener and the hole. If the location of the neck depends on the OD of the fastener bearing on the hole in the neck block, then the bolt is too loose. I think it's fine to elongate the hole that small amount.

I have always wondered why one would build a bolt-on neck, and then glue things. Isn't the idea/usefulness of a bolt-on that the neck can easily be removed? I've had to do it a couple of time to effect repairs, like a parlor guitar that got its top crushed (a week-and-a-half after I sold it, don't ask). Take neck off (easy), put on new top.

But this thread got me to thinking about how much force is really on that bolt. How much force from the string tension does it really need to counteract?

A diagram of the forces is shown below.

We have long beam, the neck, with a shorter beam, the neck heel, at right angles.
N - the length of the long beam
H - the length of the short beam

The long and short beams are attached, and pivot around point P where the top of the neck hits the instrument body.

A force F (the string force) is applied to the outer end of the long beam, offset to the neck at angle A.
This induces in the long beam (neck) a rotational force S.

A corresponding opposite force on the short beam B is such that it balances the rotational force S.

With help from my son at MIT, this is a simple torque problem. The force on the bolt, B is:
B= F*sin(A)*N/H.

Using a total string tension of 39 pounds for a tenor ukulele, with a neck/body join at the 14'th fret. a string height at the 14'th fret of .14" and a bolt location 1.75" below the fingerboard, the force on the bolt necessary to counteract the string tension is about 4 lbs.

Looking up bolt clamping force, a 1/4" bolt (which is what I use) torqued to 4 ft/lbs, which is about hand-tight plus a quarter to half a turn, yields 500 lbs. of clamping force.

So, just hand-tightening the bolt good and snug way over compensates for any string tension. I currently use a threaded brass insert in the neck to receive the bolt and now feel that this is plenty secure. I also insert a cross-dowel in the neck to give the threaded insert cross-grain to grab but even that is probably unnecessary from a string tension standpoint.

I drill an initial 1/4" hole so i can place and align the neck bolt.

After that, I always either use a file to elongate the hole (to correct for a slight misalignment) or just drill it again with a bigger drill bit.

I do this on EVERY build.

Kekani said:

Building is not really building, at first. It's a series of fixes. And once you nail down all your jigs, then it becomes. . . A series of fixes.

Click to expand...

I love this forum!

This is a butt joint bolt-on neck. Maybe someday I'll graduate to something different but for now it gives me enough challenge.

On my first build, I glued the fretboard down to the top but I did not glue the neck heel to the body.

I think of all of the tasks that need to be addressed in building, the one that challenges me the most is the building of the neck start to finish. The order in which things are done has kept me scratching my head. Somehow I thought that establishing the location of the nut by setting the headstock veneer in place was a good idea. Not so sure at this point.

I opted for the simplest fix: 80 grit sandpaper on an LMI leveling bar. I carefully lined it up onto the top of the neck and gave it four pulls the full length from nut to end. That was perfect, and there is a little slop between the existing quarter inch hole and the bolt so that I could actually modify that height ever so slightly.

I will have to decide in this case if I want to glue the fretboard down or if I want to glue the neck heel to the body. The fretting job I did in the Ebony fretboard left it with a slight back bow. I'm not sure on my radius top if that fit will require glue or not.

I thank you, all! I never cease to be amazed at how much information one can gather by asking a simple question.

Now on to shaping the neck and binding the instrument. Somewhat scary stuff for Chuck!

This is great stuff! Thank you, so much for taking the time.

Beau Hannam Ukuleles said:

I drill an initial 1/4" hole so i can place and align the neck bolt.

After that, I always either use a file to elongate the hole (to correct for a slight misalignment) or just drill it again with a bigger drill bit.

I do this on EVERY build.

Click to expand...

Thanks, Beau! I appreciate the wisdom of you guys that have been in this for a long time.

Thanks, Tom. Yes I spotted some of that clearance. Didn't seem like the natural position the neck wanted to hit the body at. So I went ahead and did the sanding and then did ever so slight a modification of the height using the slop in the hole.

I appreciate the encouragement. I think you and Beau Hamill are in agreement.

I always appreciate your logical way of looking at life, I chose to send the neck. That worked well.

Thanks, Red Cliff. Yes, it didn't seem to be much. But when you're a rookie, everything looks big!

On one of my banjo builds I stuffed up the bolt and neck angle so completely I had to flatten, or rather crookeden the bearing surface of the head of the bolt so it sat firmly and evenly flat against the inside of the pot. Because I had the bolt too close to the fretboard I really couldn't get it to pull the heel flat otherwise.

Titchtheclown said:

On one of my banjo builds I stuffed up the bolt and neck angle so completely I had to flatten, or rather crookeden the bearing surface of the head of the bolt so it sat firmly and evenly flat against the inside of the pot. Because I had the bolt too close to the fretboard I really couldn't get it to pull the heel flat otherwise.

Click to expand...

One said to me early on that one of the best things about building is developing the ability to do wirk-arounds!