Neck Tenon vs No Neck Tenon (for Bolt-On Necks)

[Darryl Young]

For bolt-on necks, what is the benefit of using a mortise and tenon vs a butt joint? I'm curious about this. A tenon can't fit tight in the mortise else you wouldn't be able to adjust the neck angle side-to-side to center the neck.....or even difficult to adjust the neck angle up/down to set string height. We do this by sanding the heel near the perimeter but the neck wouldn't move if the tenon fit tight so it relies on a loose tenon fit.

So if the tenon is loosely fit, then what is it doing for you? Why have it at all? Would a butt joint serve the purpose just as well? If so, the neck would be a little easier to make and you wouldn't need to worry about cutting the mortise in the neck block (before or after assembly). It would also be easier to set the neck.

What are your thoughts. There could easily be some issue I'm not thinking about so please post your thoughts.

[tippie53]

you will find that the tenon and mortise work to help line things up.

[Darryl Young]

Would the bolts and bolt holes not align everything? I would guess there is as much or more slop in the tenon to mortise fit as there is in the bolt to bolt hole fit. Both systems rely on the bolt remaining tight and not loosening. Seems with or without a tenon, bolt hole location is important,

[B. Howard]

You can shim a loose tenon easier than you can shim a bolt hole. Of course I am 100% dovetail so...

[darren]

I've wondered the same thing. seems like 2 things would dictate butt vs tenon:

1. your tooling (as in I have an *insert name of jig* and it cuts a tenon at the correct angle)
2. your preferred hardware (insert vs. kd nuts)

So far I like a Cumpiano style joint with the kd hardware, but see myself going to an adjustable butt joint in the future.

[Darryl Young]

Brian, on a bolt-on, why would you need to shim a loose tenon? Don't you need the tenon slightly loose so the neck set can be adjusted?

You can shim a loose tenon easier than you can shim a bolt hole. Of course I am 100% dovetail so...

[tippie53]

Unless you cut the joint at the time of the neck set , the process will most likely force you into an adjustment. Then setting the neck is made a bit more difficult in that when you place the neck you should have a secure location. Often butt bolted necks will also have a dowel pin to locate the neck.
No matter what system you use , Bolt on with Tenon dovetail or butt you still will have to set the neck. On fail of the butt bolt is now you requite total reliance to a mechanical fastener. Yes the mortise and tenon also will require a bolt but there is , in the Martin neck a glue joint, This has been discontinued for a sliding dovetail and no longer are used.
For Butt bolt necks I have seen a few and the ones I have seen were actually cut into the sides. It would takes some accurate layout and you can make that work though why not learn to do a dovetail. It is the only joint that is self supporting. If you say it is easier to do a reset , I would say that as reset should be about 15 to 20 yrs down the road. My oldest guitar is 14 and is still a long way from a neck set.
Just my opinion as there are many ways to do the same task. What are you thinking in terms of the process ? It may make for an interesting discussion.

[B. Howard]

Brian, on a bolt-on, why would you need to shim a loose tenon? Don't you need the tenon slightly loose so the neck set can be adjusted?

You can shim a loose tenon easier than you can shim a bolt hole. Of course I am 100% dovetail so...

If I were doing bolt on necks I would want the tenon snug to provide positive placement for not only bolt up but in the long term as well. Even if sized very snug, the threads on the bolt will quickly cut into the sides of the hole allowing the neck to move and shift as the wood cycles seasonally and string tensions are brought up and dropped for replacement. The bolt will only hold the neck on the guitar, there must be something else providing the indexing or it will shift. Take a look at Taylors system, it's the only bolt on worth anything IMHO. They don't make all those different shims out of whimsy, they do it because the bolts alone will not keep the neck positively in place on there own. I suspect most bolt on makers create their own need for premature neck resets by fitting things sloppy and thinking the bolt will do what only good clean joinery will do.

[Darryl Young]

You bring up a good point John. I would of course plan on setting the neck with a mortise/tenon or when using bolts. So how would you position the neck for fitting?

Seems fitting needs to work for the rough fitting early on and the final fitting after finish. One way to do this is to use a stud bolt sunk into the neck and use a nut inside the guitar (as opposed to a bolt inside the guitar threaded into a recessed nut in the neck). Using this method the neck is always located by inserting the neck studs into the 2 holes going through the neck block/sides. That would locate the neck in 2 dimensions and fitting the neck would locate it in the 3rd dimension.

I don't like the way Martin does their bolt-on necks so I wouldn't want to copy that system (and from John's comments, it sound like Martin doesn't like it either). I would want 2 studs (or bolts) and no use of glue except to glue down the fretboard extension.

It really makes no sense to do this unless it's easier or faster. I've only done 2 guitars but so far, I've not located the neck block correctly so the bolt holes/tenon are in the right position so I've had to elongate the bolt holes on both builds. My thought is that it would be more accurate to cut the mortise and bolt holes after the box is closed when you know where the neck needs to be located. Well, it seems it would be much simpler to locate 2 bolt holes than to build jigs to cut a mortise plus 2 bolt holes after closing the box. Also, I would guess it would be a little simpler to build a neck without a tenon.

I think I would want to strengthen the heel area of the neck to use neck studs. I've seen some folke drill a hole from the heel cap area down almost to the fretboard surface and glue in a wooden dowel. the direction of the grain in the dowel would strengthen this area considerably.

You could build a jig to locate the two holes in the neck that will be used to insert the studs. Then use the same jig to drill the holes in the body/neck block. The jig would index off the fretboard surface of the neck and then index off the soundboard of the closed box. That should align the fretboard surface of the neck with top on the closed box.

Same as a mortise /tenon neck, you would want the perimeter of the heel carrying the load so you would chisel out the interior portion.

I think it is workable. Many folks have done it so I know it can work. The only question is how much work could it save.

[Ben-Had]

When I've done bolt-ons (except my first one), I fit my neck first, then drill two holes into the neck block, use dowel points to locate the holes on the tenon, drill those holes and add threaded brass inserts. I have a spade bit that I machined to cut counter sunk holes in the neck block. I insert the bit shaft from the inside the body to the outside, attach my drill and run it in reverse to drill the counter sunk holes, then put a label over the holes to hide them (of course after the neck is on:)).