Cumpiano's Hardware Based Neck Joint VS Tapered Dovetail Joint

[Christopher Perkins]

Hello all!

I was wondering if i could reach someone on here that has direct experience with both said neck joints and could share with me their feelings on each. I would like to know the benefits and downfalls of each style. I am finishing up my first guitar (which was constructed with a tapered dovetail) and am starting my second. I am thinking of giving Cumpiano's hardware based neck joint a try. As Cumpiano says, "If there was ever a joint designed in hell, that one is it! The tapered dovetail is unnecessarily complex, requires endless fussing to get it to fit properly and as well, to disassemble it for resetting". Based only on my first building experience, I would have to agree...so far.

I look forward to any feedback anyone can provide.

[Barry Daniels]

It is good that you built a dovetail joint just so you can appreciate the difficulty involved and understand how it works. Cumpiano's barrel bolt joint is definitely easier to build and really has no downsides as long as you strengthen the mortise to prevent splits.

Other hardware based options include threaded inserts (with mortise and tenon joint or butt joint), and hangar bolts in a butt joint neck. All of the various hardware based joints are easier to build and MUCH easier to adjust later on if needed.

[Darrel Friesen]

I think you meant strengthen the Tenon and not the Mortise Barry.

[Barry Daniels]

Of course.

[Rodger Knox]

The tapered dovetail is IMHO an elegant joint, and has been used for decades as the normal method for attaching necks.
That said, I've done one dovetail and 6 or 8 of the Cumpiano joint. It's not as elegant, but it's much easier to get right.

[Michael Lewis]

Use whatever works best for you. For me it is the dovetail, at least so far. It is a very solid and strong joint, and fairly easily removed if done right.

I have been talking with some folks regarding the adjustable neck joint, and think it can be a good alternative. If you look up the Martin/Stauffer "clock key" neck joint you can get the idea, but make the adjustment from the inside.

[Bob Hammond]

I've used only the hardware joint with barrel nuts on steel strings, and conventional slots for classicals. Every so often, I think about making an adjustable neck using barrel nuts with slotted holes in the tenon for the bolts. The slotted holes would not need to be very long for only a few degrees of adjustment. The bolts' heads would probably need to have locknuts and curved 'washers' that fit into matching seats in the headblock.

[Dave Stewart]

I have been talking with some folks regarding the adjustable neck joint, and think it can be a good alternative. ....

FWIW, Martin Keith does an adjustable neck joint that really intrigues me
http://www.martinkeithguitars.com/const ... ails.shtml#

[Mike Sandor]

Dave,
The attachment is very interesting as I to have been working on a clean system that is similar in design. My design uses a sliding member as well, but I am trying to keep all the adjustments located inside the guitar.
I also use two small allen head bolts to lock it down, in effort to maintain good coupling.
The struggle I have is the seam between the heel and the body. I do not like any gap, so I cut a shallow relief in the body, to match the heel profile.
Regards..........
Mike

[Craig Bumgarner]

I have used both and personally think Cumpiano's joint is better is every regard except weight, it adds about 50-70 grams. Part of this is because I also use a bolted fingerboard tongue ala Taylor and Trevor Gore which complements the Cumpiano joint nicely but adds to the size of the neck block and again more hardware, though for the tongue I use two 1" 10x24 socket screws, only a gram or two each. In my guitars, I tie the tongue block to the top brace making this area very resistant to caving. All up, this is a better way of doing things. I'll admit to contemplating titanium bolts and dowel nuts.

In search of a lighter alternative, I tried wood inserts ala Liutaio Mottola. I was pretty careful about it, used the inserts he spec'd and was very careful with the drilling and installation but both inserts pulled out of a mahogany neck the first time I snugged them up good and I don't believe I over did it. I reset the inserts with epoxy and they held fine and continue to do so, I get to see the guitar often, but the experience unnerved me to the point I don't want to go there again. I mean no disrespect to Mr. Mottola as his method clearly works for him, but for me, not so good. If I were to do it again, no doubt I would install the inserts with epoxy right from the start. Cumpiano's method seems much more positive though it is heavier, I sleep better.

[Martin Keith]

Hi Dave,

Thanks for the shout-out!
My sliding system is, at least functionally, inspired by Ken Parker's, which I've had the good fortune to examine in depth.
The adjustment must be outside the guitar, since the drive screw has to be coaxial with the direction of travel.
However, my design goals included being able to adjust the guitar at pitch, and even during a set if needed.
This is where the sliding design has a clear advantage over the tilting approaches - it barely detunes the guitar at all during operation, whereas most of the tilt adjusters require significant retuning after each change.
Visually, I think the tiny grommet for the adjuster access is about as low-profile as I could ever want.

Mike - I'd be curious to see some more description of the system you're working on.
Specifically, how do you inset the heel into the sides and not end up with a gap below the heel when it's adjusted "up"?
I considered insetting the neck into the sides to close the gap, but the gap can actually be made nearly non-existent, and I preferred to keep the system as simple as possible.

Craig - I'm embarrassed to admit I haven't weighed one of my adjusters yet! It's not much though, since it's mostly aluminum with just one steel drive screw and a few small steel roll pins. I'll weigh the next one, I promise!
Titanium screws and dowel nuts, huh...? If you find any, let me know where so I can buy some too!

Cheers,
Martin Keith

[Louie Atienza]

I did a tilting adjustable neck that worked with cams, so that getting the string height lower decreased the scale length slightly, and increasing the string height pushed the neck sightly away, to compensate for the increased action. While it did require a little retuning, the intonation was very good. The hinge was near the top, and the adjustment bolt was inside, and spring loaded, so that the neck would not flop around when a string change was done.

Alas the guitar (which was one of my acoustic challenge entries) dropped off a stand during a gig, and I did some damage to the tailblock. I have pics somewhere. The only downside was that the hinge was partially visible. One day I may revisit it.

[Jim Ashby]

Hi Martin,
Took a look at your sliding neck joint - kinda reminds me of the joint on my Babicz Spider - but your adjustment is less obtrusive and the 'revealed' part of the guitar body is much neater!
Do you machine the parts yourself or do you buy in standard parts?
Jim

[Dave Stewart]

Hi Martin..... thanks for jumping in!
Don't know if I'd ever try it but like Jim I'm also curious about the parts (...maybe a marketing opportunity for a kit???)

[Martin Keith]

Hi Martin,
Took a look at your sliding neck joint - kinda reminds me of the joint on my Babicz Spider - but your adjustment is less obtrusive and the 'revealed' part of the guitar body is much neater!
Do you machine the parts yourself or do you buy in standard parts?
Jim

Jim,

I have the male part custom machined (which attaches to the neck), and the female part is a commercially available extrusion.
I also do some of the machining myself - cutting, remilling, and pinning the block on the bottom of the track, drilling and tapping the holes, etc.

There is a "T" shape to both sides of the system, and the mortises are undercut to receive that profile, so the system doesn't rely on fasteners to hold the parts in place - it's not exactly a dovetail, but it's similar in function.

What I like about this sliding approach is that the string tension essentially draws the two parts together against each other. In contrast, with most of the hinged systems, the string tension is essentially trying to pull the pieces away from each other - this feels safer, somehow.

Dave - I'm not sure it would ever pay to sell this as a kit. There's a learning curve to getting the parts to fit right and work smoothly - I'm still dialing in some of the details. It would be a fussy thing to try to design a kit flexible enough to work with a variety of different designs and guitars - some of the machining has to be done mid-process.

There are many, many different ways to accomplish this - you might enjoy Googling James Ham, the brilliant upright bass builder in Vancouver, BC. He has a sliding neck system on his basses which uses an entirely different approach, but works beautifully and might inspire a different take than mine.

Cheers,
Martin

[Dave Stewart]

Thanks Martin!

[Martin Keith]

Dave,

No sweat. By the way - gorgeous work!
Really beautiful instruments - reminds me of how much I still have to learn!

Best wishes,
Martin