Neck joints - Separating the myths from the facts

[sylvan]

Rick is absolutely right. Don't sweat the loose bolts. I have done something over 150 instruments with bolt on necks and have yet to see one with bolts that have loosened. I am sure it does occur but it is very rare. I think John touched on the reason why, namely the large surface area of the type of bolt I use. I use a furniture knock down 1/4-20 bolt available from any big box store. I do not use loctite or anything like that. If you think of the forces on the guitar neck the bolts are never relaxed as the neck is constantly putting pressure on the bolts to hold it together. Nothing is needed. As a matter of fact, I use the bolt pictured below and then use a 1/4" cover double sticked to the block so they are invisible. The bolt heads are so wide and thin that doing this makes the block look like it is one piece rather than a "cover". Below is a photo of the bolt and insert I have been using for the past fifteen years.

[Ben-Had]

Sylvan, 3 questions -

1. Do you find that threaded insert superior to the knife thread brass insert, why or why not?

2. What size hole do you drill for that threaded insert?

3. Are the threads on those bolts 10-20 or 10-24?

Thanks.

[tippie53]

I use the 1/4 20 threaded insert.

http://www.reidsupply.com/sku/STI-225/

I like this unit and the bolt in the above post is the one I like

I use these in my kits and building.

thanks for all the info sharing.

[tippie53]

The beauty of the inserts is they self align in a 5/16 hole and the thin knife thread cuts into the wood without fracturing. I use them on some in shop jigs also as they are quite strong.

Using a shoulder bolt, the slotted end goes in first. That's the way it was designed. Some think the slot is for a screw driver, but the slot at the bottom of the hole makes the threads seat tighter as you tighten the bolt.
This is the same insert Martin uses and I haven't had one fail yet.

[sylvan]

I like the steel threaded inserts over the brass ones that Martin uses and John recommended to me. I have used the brass ones on many guitars but I always come back to the steel ones. Really, one big reason, they are alot easier to thread into the cut tenon. I believe the inserts use a 5mm hex wrench and you do not have to fight the brass inserts into place with a bolt with two lock nuts or wrench. My inserts (as is everything in my shop) are 1/4-20 threads. They take a 3/8" drill bit. Rick, I do not use the cross threaded inserts as I find it more work to install them. They work fine and are maybe actually stronger but the ones I use don't come out or cause me problems. I insert them into the tenon after the guitar is together and the tenon cut and fit. The only caveat in inserting the inserts in this sequence is to be sure and wax them with beeswax to avoid cracking the tenon. BUT, I have had some crack in the past and superglue fixes it just fine.

[Ben-Had]

I use the brass inserts. I cut off a 1/4 -20 bolt thread a couple nuts on the shank, thread the insert and chuck it up in one of these:

http://www.harborfreight.com/angle-dril ... 95622.html

Then I lock the neck in my neck jig and screw the inserts in. The go in perfectly straight. For shorter items I use my drill press to screw them in.

[B. Howard]

John and Slvan cover this very well and both have far more experience with these joints as applied to lutherie than I. That said, I am a Dovetail guy, partly because of tradition but I also like the simplicity of the joint and the fact that the wood itself does all the work and not the glue. There is no hardware to loosen, and in my experience with furniture and such, seasonal expansion and contraction of the wood when in use will cause any type of mechanical fastener to eventually loosen. I have seen wood literally spit nails back out after 150 years while not necessarily being under that much stress. I am very familiar with tapered dovetails like we use for necks and have used them as knock down joints on large pieces of cabinetry so they could be assembled, taken down , moved and set back up. Sometimes those joints were not even glued so the next time moving is required it can be accomplished easily. And honestly if one is in total control of their manufacturing they are really simple to fit. If the templates are accurate to each other and the bit is sharp most of the work is done for you and you merely need to work the cheeks a bit to get a proper fit. No more work on my part than a regular mortise and tenon, whether it would be glued or bolted. Of course I do not cut the joint in my head-block until after the box is constructed and I am ready to fit the neck. Those buying their parts already cut are at the mercy of whoever made them and the templates and tooling used for each piece. I can see how that would be frustrating and difficult to fit well.
I also agree with Sylvan on the head-block. Bigger is better, more glue surface equals more stability and resistance to rotation. Mine are 2" thick and actually but up against the upper face graft on the top. I think a bit of centralized mass here also helps the instrument feel balanced when played and that is a large part of my reason as well. But I doubt that head-block rotation is really a key factor in a guitar needing a re-set as it goes through life. If that were the case the block would need to shear loose from the top, the back or both in order to rotate. Most of the deformation I see that leads to the change in neck angle is actually collapse of the top at the soundhole. The fact that the spruce does not run continuous under the string path actually promotes this condition. As the top caves in at the soundhole the neck and bridge start to fold together like a book closing. I mention this to illustrate that the type of neck joint has no effect on how soon a guitar will need a neck re-set. Only in how easy it will be to do. Finish, more specifically, when it is applied will figure into this also.
While I prefer dovetails, the only joint mentioned I do not care for is a butt joint. I do not like it as there is no real positive indexing of the two parts together unless one uses dowels. The bolts will hold it on but not really keep it located properly. Some manufacturers of lower end guitars have done this with dowels and glue and if you think re-setting a dovetail is a pain... Without the dowels or some other indexing it will move. Not much, but this is a game of thousandths of an inch so it doesn't take much movement to mess things up. Any way you do it getting the neck set correct is a critical part of guitar making and you will need to master what ever method you choose.

[sylvan]

I agree that I don't particularly like the butt joint but only because it is more difficult to clamp and glue properly. The first eight guitars I built in the mid seventies were all done via David Russell Young's guitar making book. All were epoxied butt joints. I have two of them. They are still strung to pitch and neither shows any sign of the neck destructing. The joint works, there are just so many other better (and easier) alternatives. So, as I said in the first post, find what works for you and then execute it well. If the guitar stays together and sound great, what else matters?

[tippie53]

That last statement is the crux of the thread.
Any joint that is secure and can withstand the stress will be a good joint.

[Darryl Young]

What is everyone's thought on using studs in the neck with nuts inside the body? While it's not my favorite look (viewing through the soundhole), I like everything else about it.

I think Mario Proulx uses a butt joint with studs. Here is my understanding how he does it. Before capping the heel of the neck, he drills a hole from the heel of the neck down toward the fretboard surface and glues in a dowel. This vertical grain added in this area reinforces the neck well. Then he drills and inserts studs into the neck and drills holes in the neck block for the studs. The location of the holes in the neck block locate the neck. Ther is no mortice or tenon......except the bolt studs act as a tenon and the bolt holes act as the mortise. Can't see why the bolts would be any weaker than a wood tenon. So when he goes to floss the neck to fit to the body, the studs locate the neck.

So what is the downside of a butt joint using neck studs with a nut inside the body with a glued down fingerboard extension? I believe my Art & Lutherie guitar has nuts on studs inside the body.