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Hello, Friends,

I'm contemplating an arch top guitar with a bolt on neck. This has been done successfully by others. For example, our friend, Dave Stewart, posted an excellent tutorial about this a few years ago. I've pondered this for several years. My question is not about the advisability of this method. Rather, it's about the two-bolt method that seems to be the standard approach.

It seems to me that a single, well-anchored bolt below what I will call the "pivot point" should be enough to anchor the neck. I would think that this single bolt, somewhat below vertical center in the heel block, would be sufficient. The string tension alone should be sufficient to ensure that the upper part of the heel would remain snugged up against the guitar body. A well-fitted mortise and tenon joint should be sufficient to keep the fingerboard playing surface from slanting however slightly to one side or the other.

I felt secure enough in this belief to build a mandolin this way a few years ago and it's still going strong. I've got another of those in process, so I admit the second one has not been tested yet. Some of the most desirable and collectible banjos have a single dowel stick anchoring the neck to the rim.

I realize that guitars, banjos and mandolins are different animals. Guitars are bigger and longer than mandolins and the strings have more leverage. My guitars are longer than my tenor banjo, too. But are the principles any different? Even in the case of flat top guitars, I wonder why most bolt-on builders use two bolts. Is it just convention? Or am I missing something that is not obvious to me, but which might be very obvious to the rest of the bolt-on community?

Please give me your thoughts.

Many thanks in advance and my best wishes for a blessed Christmas and holiday season to each of you.

Patrick

Patrick,
Your plan sounds fine.

Do you use inserts or barrel nuts? Solid necks or laminates?

These details could help give better advice.

Dave

Thanks, Dave. All of my necks have been laminated. Four were made with integral heels. Two used stack-laminated heel blocks added to laminated necks, but I probably wouldn't do that again. Two arch top necks were made with conventional dovetail neck joints. Two mandolins are mortise and tenon with single anchoring bolts, as described in the original post. These both have threaded anchor inserts. However, I can see that a free-turning barrel bolt might provide a slight advantage in the case of an eventual neck reset. My tenor banjo used dual coordinating rods, so, obviously, two lag bolts. Ironically, I was working on that when I began to wonder about a single neck bolt in a guitar.

While it does seem viable to use one bolt since, as you say, the string tension will serve as the other anchor. But, two bolts do make for a safer joint. Consider what a jolt to the neck might do with only one bolt, maybe even while the strings have been loosened. Also, the weakest aspect of the joint appears to me to be the part that is in the neck, whether it is a barrel nut or a threaded anchor. Under two much tension the wood can fracture weakening the anchor. Two anchors are better at holding the neck on with less tension per bolt and therefore less worries.

Just my two cents....

_________________
Joe Beaver
Maker of Sawdust

For my butt joined bolt-on flat top necks I use one 1/4 inch bolt (below center) in the heel. The fingerboard extension is glued and holds the alignment of the neck when the strings are off. In the future I may go with a 3/16th inch cap head bolt. This is what I use for the "travel guitars" with removable necks. A small bolt is much stronger than the typical amount of wood in the heel. By reducing the amount of metal in the heel we can leave a little more wood.

Hi Patrick and Happy Holidays to ya my friend!

I hate to be a naysayer and especially today but my answer to your question would be a bit different...

One of the reasons why I decided to divert my own building and get some repair experience was that so I would learn how in some instances guitars fail.

If you ask this question on FRETs where the core competency is repair someone including me is sure as shootin going to bring up the Martin 15 series. The 15s are lower end, lower priced Martins with a single bolt bokt-on neck and a glued mortice and tenon neck joint.

Nice guitars like most from Martin and they can play and sound pretty OK IMO.

Problem is the neck joint has been a source of failures and we have seen lots of them that have failed and had to fix them as a result. The single bolt is not enough to do the job as a bolt-on only joint but since the 15s have the tenon glued as well you would think that everything was going to be just fine...

Not the case, the glue joint is in constant shear until, of course, it lets go and they often do as well. This leaves the entire strength of the neck joint to that single bolt and the glued fret board extension.

Now the necks don't go flying off in some dramatic fashion that we might enjoy seeing under the right, no one gets hurt circumstances...

But the heel starts pulling away from the box, the action rises, the player gets upset, and then someone brings it to us for repair.

Thinking more specifically about your OP an arch top is going to have less than stellar access inside the box without unnatural acts being required. As such I think that it's even more important to have not only a very serviceable neck joint on this one but also a neck joint that has a very high likelihood of not ever needing servicing.

As such consider going with two bolts?

Thanks.

Merry Christmas, Guys and thanks for the replies! Now, in all honesty I'm going to admit that I hadn't thought about what might happen if my guitar got dropped or if the neck got smacked--especially with the string tension off. Of course, no one ever thinks such a thing is going to happen to his own guitar, but we know it happens to other guitars. My thoughts were obviously roaming around in a perfect world where accidents don't happen.

I appreciate all of this advice very much. Dave and Clay, thanks for the initial support of my "theory". Joe and Hesh, thanks for helping me re-think this. Hesh, I've thought about the access difficulty, too. I made a long allen key bolt driver for the mandolins and had no trouble inserting that through the tail pin hole and moving it from side to side. I know I'd need to be sure this will work equally well with my guitar tail block. Before I commit to doing it, I'll test it out on some sort of mock up. I've been using a tail pin output jack with a larger diameter hole than a normal tail pin. If I don't make the tail block too massive--or if I taper the hole a bit from the inside while the box is open, that ought to facilitate some maneuverability with the driver. I'll be sure I can do it before committing myself.

At my rate of production, it might be a LONG while before I post a finished guitar here, but I'll let you see it when it's finished. Thanks again to all. Best wishes for the holidays and a productive and prosperous New Year!

Patrick

I have done four arch tops with bolt-ons accessed through the end jack hole. I think a barrel nut approach is better because of the high angle of an arch top neck and I would not trust one bolt with that setup.

The first is 4 years out. It gets played daily and gigged out 3 or 4 times a month and I am in contact with the owner because it is me. It has held up very well so far. I have checked the tightness of the bolts on a regular basis but they have stayed snug. I think it is a dependable joint.

It only adds another 30 seconds to loosen or tighten the second bolt and I think you will have a more stable joint.

Good Luck!!

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

Hi, Terrence. That looks like a very nice guitar! I appreciate your input on this. When you have time for one more picture, I'd really like to see how the "business end" of your bolt driver works. I can't quite make it out, but it looks like a nifty tool.

Let me ask all of you guys another question:

After posting my earlier response this morning, I started thinking again about a dovetail joint. We know that they provide a strong mechanical joint, but are pretty fussy (at least for me) when it comes to aligning everything properly. I've always figured that the glue in a dovetail joint was primarily to keep it seated and locked at full depth. Has anyone ever considered a dovetail joint with one or two bolts to keep it seated? Overkill or underkill? Seems like it would make removal easier than the conventional steaming method--and safer for the surrounding glue joints than steam injection, too. Anyone have any thoughts on that?

Terrence, one more question, please. How did you do that beautiful, warm honey colored finish? That looks elegant and I think it has a great vintage vibe going for it.

Easy, I sent it to Addam Stark. Only took him eight months. It was worth it. Absolutely spectacular.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

Patrick the traditional dovetail is a thing of real beauty when done well. You are correct the glue is only there to hold the dovetail in place where the mechanical nature of the joint does the heavy lifting.

When done well, and I know I keep saying this...., a dovetail is not all that difficult to get to release either. Sadly many manufacturers don't do dovetails all that well and may either use way too much glue, glue the cheeks to the sides, or have so much in the way of filler and crap shims in there that come release time difficulties happen.

Using a bolt (or two) with a dovetail is most certainly possible but over kill in my view and you also have the added mass of the bolt-on hardware.

My first choice would be either a two-bolt design like Terry's or a traditional dovetail using an appropriate amount of HHG so that the joint can be easily released in 50 years or so when it's reset time. Hat's off to you too for thinking in terms of future serviceability.

Beautiful and classy Archie Terry!

I just epoxied a cut off ball end 4mm Allen wrench onto the end of some 1/4-20 threaded rod covered with rubber tubing and glued a handle on the end. The ball end makes it much easier to engage.

It fits fine through a 1/2" jack hole. Be sure to measure your end block and add the thickness of the tailpiece if you use one with a body plate. You'll probably want to countersink the tail block so the output jack will fit. I have done all that after the body is completely finished as you really don't know where you want the hole until the tailpiece is fitted. A reverse spot facer is a good way to countersink after the box is closed.

I soldered a bicycle brake cable to a 1/4 jack pin so to adjust the bolts you can just loosen the jack with the pin in place and push it inside and the wrench will go in fine. Pull the jack back with the cable to reinstall.

_________________
It's not what you don't know that hurts you, it's what you do know that's wrong.

What a great idea!

_________________
Doug

Don't let fear or common sense stop you from trying to build something

Terrence, you "sent away" for that finish. How simple is that? It made me chuckle. Man, that's a yummy axe! I think it's fabulous. Thanks, too, for explaining your bolt driver. Mine also uses a 4mm key (welded to a long rod with a t-handle on the other end. However, I didn't think to use a ball-end key. That's a great idea. I might need to make another one. My tailpiece jacks are Stew Mac threaded end pin kind. They provide a good anchor for the tailpiece and for a strap.

Hesh, thanks for the response about the proper way to glue a dovetail joint. You don't know it yet, but you just reinforced me. That's the way I intuitively glued the two that I have done. I didn't know for certain that I was doing it correctly, but it seemed correct to me at the time--and I did leave clearance behind the tenons for excess glue squeeze and steam insertion. Thanks! I'll admit I had to use a thin veneer on either side of both joints, once I quite shaving and filing the tapers. (I eventually manage to get them well-fitted, but it sure doesn't come easily for me yet.)

Great job Patrick! Sounds like you did an excellent job with your dovetail. You also gained some important repair experience as well and more specifically the use of shims is not uncommon on the repair side (and believe it of not not all that uncommon on the new instrument side either).

In the repair world releasing the dovetail may mean that the joint has to be rebuilt before reassembly. Shims of an appropriate wood (hog for hog etc) are used to build the dovetail back up and then material is removed from the shims for the perfect fit.

Good going Patrick!

An example of how bolts can fail.

One of my students elected to use a bolt on on his first guitar. We used two bolts, with cross dowels crosswise in a tenon. After getting the finish leveled he bolted the neck on. When he picked it up from the bench he tapped the head on a low beam in the ceiling. The heel split through the upper dowel, and the box dropped to the floor. The top was marked up pretty badly, but otherwise nothing broke, and we were able to repair it.

In hindsight I think we made several mistakes. One was to use the wrong drill bit for the cross dowels. The ones I can get locally are 10 mm in diameter (.3937"); my closest drill bit is a letter X (.397"). Three thousandths isn't much bigger, but it's bigger, and it's not uncommon for drills to cut a little over size. I remember reading years ago in an Experimental Aircraft Association magazine that the standard in aircraft calls for a tight fit when a bolt is used in a wooden structure: you should need to use a hammer to get the bolt in. The idea is to have such good contact between the bolt and the hole that the load is spread over the entire width. If it's in a larger hole all of the load is on a single line along the edge. You could flood the hole with CA after you put in the dowel, and hope that it penetrates, but getting the right drill bit is probably better.

The second mistake was to over tighten the bolts. Again, this just increases the force that's trying to break the wood, without making the joint more secure. All you need is enough tension to pull the neck in snug when the strings are on.

Finally, it might have been better to have the barrel vertical in the tenon, rather than across it. That way, if the wood did spit it would have no place to go, since we still fit the tenons snug.

In general, hardware in wood is a stress riser. It's probably better to use over size hardware and spread the stress out. I don't know if threaded inserts are any better: I have the remains of an old-style Taylor 12-string neck where the heel split through the upper threaded insert. In using the cross dowels I was trying to learn from their mistake. Maybe you can learn from mine...

Thanks, Alan. I sure appreciate all this feedback.

One last thing regarding one way to anchor the bolts in the neck.

I started with the inserts. They worked OK but you had to be very careful not to tighten the bolts to much or the wood holding the insert would rupture. I did have to repair one or two of these. Then I read the write-up by William Campiano of securing the tenon in the mortise. He is using a barrel nut and has lined the sides of the tenon with hardwood to improve service.

I now do that plus I use a a 5 piece neck so in the neck I have a rosewood center, then 2 strips of maple, preferably hard maple, then some of the mahogany. Then I put a 1/16" strip of African blackwood on each side of the tenon. I use African blackwood because of it high modulas of rupture and stability. I drill through all of those layers and insert the barrel. It makes for a decent anchor.

_________________
Joe Beaver
Maker of Sawdust