Making Acoustic Guitar Necks and Bolting Them to Bodies!




This is a version of a talk that I gave to the 2017 Cordefactum event in Belgium on May15th 2017. It contains all the images and brief expanations of them.


If you were at the talk and are only interested in the diagrams with dimensions and other notes please go straight to the end of this document.

 

I learned that quarter sawn wood was most stable but there isn’t much of it about because of the way commercial lumber is sawn so I realised that laminating flat sawn (most common wood in timber yard) would make it quartersawn.




Flatsawn maple and walnut for laminating. Laminations are probably more stable than single pieces of wood as distortions can counteract each other if grain direction is used.




You all know how to plane and thickness boards so why am I showing you this? Because it is essential for this method to work that the wood is square.




Laminations glued. A luthier can’t have too many clamps. I use Titebond as my main glue because it is convenient, strong and can be separated by heat if required. The block is about 90mm wide, 100mm tall and 730mm long as I’m making acoustic bass necks here. For regular acoustic guitar necks you can work out the sizes to suit the shorter scale. After gluing the block needs to be trimmed and squared.




The trimmed and squared block marked out. So what are these markings all about?  You can probably make out two vaguely neck shaped bits with a large slab between. I have marked the block so I can always know the orientation of the pieces.




The drill press, one of my favourite tools, and a 13mm bit makes access holes where the bandsaw blade can turn. You can see how it works in the next pics.






So there are a couple of neck shapes with the central block. I’ve marked them A&B
 
Almost all my necks are made with scarf joints, that is, the headstock is glued to the neck shaft. To me this, and the Fender style of neck where the headstock is in the same plane as the neck shaft, makes the strongest neck design. Any body who has done much repair work will have come across Gibsons, and other guitars that have fallen and the headstock breaks from the shaft at the point where the headstock angles away from the shaft.
 
A &B will become the headstocks for the two necks.




Normally headstocks are wider than neck shafts so, to save wood, I glue ‘ears’ onto the headstock blank to make up the difference




I never make a single neck so, even if I only need one I will make two. The ‘spare’ will get to be used on another project and no wood is wasted. I always have a stock of neck blanks for future projects.




At this stage I add the headstock veneer to the ‘soon to be’ headstock and glue the laminates together.






The neck shaft is marked for where the scarf joint will need to be cut. I prefer a 15 degree angle so this is marked (right arrow) on the neck shaft which is where the scarf joint will be made. How do I know where to put it? I have done some calculations using the position of where the fingerboard will start (left arrow) and then moving the start of the cut back by an amount that my calculations suggest. The note with these details on is one of the documents at the end of this page.





This the jig I made for cutting the scarf angle. I made this up using the angle gauge that came with the bandsaw. The wooden part is clamped to the metal fence at the correct position using a key that fits into a hole on the fence. The angle can be adjusted as you can see.




The shaft is positioned so that the blade lines up with my mark and clamped in place.




By slowly pushing the jig through the blade the scarf cut is made.




The headstock face at the joint end is also cut at the same angle. Why do this? It will make glueing the headstock to the shaft easier later.




This little bit will be useful later so I don’t throw it away.




Don't do this at home! The scarf face on the neck shaft needs to be perfectly flat to make a good joint. I used to plane this by hand. Then I tried this method – dragging the scarf face across the surface planer with a very small cutting depth. It works but you need to be very careful. I don’t recommend that you try this. But it works. I had two great students in the workshop last year from Puurs. When they saw this being done they were appalled and terrified!
 
 


So now we have jointing srfaces. The squared line at the angle of the joint is to help
with alignment of the laminations.




The two parts are aligned so that the laminations on the headstock and the shaft are together front and back. The squared line gives a good initial position. Three pins are used to maintain the position for gluing.







Using a liberal spread of Titebond, two cauls, the little triangle of wood from the top of the headstock to ensure the pressure is equal and the pins for
alignment. One neck blank made and another in parts for when needed.




I realize that most of you will know how to do this but I’m showing the next few slides anyway!
I use two way trussrods that are made in Korea. For thirty years I made my own trussrods from 5mm mild steel which I cut, threaded and fitted an anchor, washer and adjusting nut which was fitted in a  curved channel routed in the necks. This was fun to do but very time consuming and only worked in a backward direction. Here is the jig I use to do this.




The jig is screwed to the neck (screws in places that will be covered by the fingerboard) and the channel cut by multiple small passes.
 



I also use two carbon fibre bars for neck reinforcement, which run parallel to the trussrod.
 
I fit them using the same jig with a different cutter and do not glue them in place as wood can move but carbon fibre doesn’t.
I have these made for me and, after shipping, they cost around €15 each. Source for these will be in the table at the end and also on the website.





The trussrod and carbon fibre rods are covered by slipd of hardwood. When the slips are planed level with the top we are ready to go with making the joint.




Now to make the joint.

I started out making solid bodied guitars and for these I used fixed necks with mortice and tenon glued together. When I made semi acoustic guitars I used the same system. Following on from the archtop semis I made my first acoustic guitar which was an archtop jazz guitar – not the usual route! I realized I would have to attempt a dovetail for this but didn’t know if my joinery was good enough and so I made a self locking mortice and tenon which  was glued in place. When I came to regular acoustic guitars I carried this over and, eventually developed it so that it did not need to use glue and could be separated easily. I still use this for archtop jazzers as I can’t get my hands inside an F hole to fit bolts!
 
When Bob Taylor re-discovered bolt on necks for acoustics and made them acceptable I started thinking about this as an alternative. The advantages were obvious. The joint could be made and dissembled in minutes as required without any damage to the instrument. This made neck re-sets a piece of cake. Without having specialist machinery I needed to come up with a system that was simple to make without any special tools or fixings. And this is how I do it today for all my acoustics from Parlours to 35” scale 6 string acoustic bass guitars. I have never had one move or fail and I was able to do a re-set on a 7 string baritone guitar (I misjudged the baritone neck angle versus string tension) in 40 minutes start to finish.
 
It could be considered a disadvantage that the headblock has to be 50mm deep for this system which is added weight and also stiffens the top at the joint area. But, as it seems to me, very little acoustically happens in this area I don’t find these to be any real disadvantage.

This is the Perspex router jig I made for cutting the
mortice in the body. The jig is aligned with the centre line of the body then screwed to the top with two screws that fit into the neck block and the holes will be hidden by the fingerboard when fitted. To adjust the depth of cut I have made different spacers that fit into the bottom of the slot in the jig – where the blue tape is.




I use a Black and Decker workman with two clamps and spacers to protect the top to firmly hold the body in the working position. I use a router with suitable cutter and a guide to follow the jig cutting with many small passes. The height of the tenon is adjusted to suit the instrument and the depth I chose is 26mm.




So here is a cut mortice. You can see several extra screw positions in the jig. These allow for adjustment if, when the jig is screwed to the top, the alignment needs to be altered. Not in this case!




Now to the tenon. I cut the tenon on the big bandsaw. This is one reason that I mentioned keeping the components square in the earlier picture - it makes cuttingthe tenon vertically to the top surface much easier!. I’m aiming at 20mm wide.





The mortice width usingmy jig and cutter.




And here is the width of the tenon.




So why do I cut the tenon width so small? A couple of reasons. The first is to allow me to strengthen the tenon. By the nature of the way the grain runs through the neck it is short in the tenon that is it runs parallel to the fingerboard and so presents endgrain to the jointing surface. This is not the strongest. To spread the load of the fixing across the whole tenon I add two ‘ears’ of quartersawn hardwood (Irish oak in this case) to the sides of the tenon the the grain running vertically.


 

And the tenon width with the 'ears'.




This tenon width is still less that the mortice width which allows for a small amount of alignment adjustment side to side if required. The tenon length is trimmed to 25mm at this stage The mortice is 26mm deep so there is a clearance of 1mm.


At this stage I cut a slot in the top of the body to allow the overhanging trussrod adjuster to fit.




The neck body joint at the correct angle is made in the usual way. This is how I clamp the two components together which I check the fit and alignment.




Time to see what we are trying to achieve on the neck end. This is what the tenon looks like with the fittings in place. We have 2 x 20mm long metal dowels with M6 threaded holes and 2 x 50 mm long bolts with M6 threads and M4 hex key sockets. Here you can clearly see the oak ‘ears’ that spread the load of the fixings across the whole of the tenon.
 
I will have the contact for the supplier of these parts that I use at the end of the presentation but you can probably pick these bits up from a good hardware store locally. They are standard fittings in KD furniture.




How to drill the holes that are needed with precision? The table on my drill press does not extend low enough to fit a body in place so I adapted one of my trolley tables (great idea trolley tables!) instead. The drill is fitted into an old drill stand that is turned through 180 degrees so that it overhangs the table. The body is supported by an adjustable bracket so I can fit all my body sizes and clamped vertically. 




And here is the centre line of the mortice. The centerline I marked (at the second attempt) is lined up with the centering mark on the jig that ensures a vertical hole.




Pointy drill. All the holes are drilled with spur bits that are easy to centre on a mark and cut cleanly.





Mortice holes. The distances that the holes are apart depend on the type of guitar and depth of the body. These distances are on the diagrams that are at the end of this document.
 




The bolts are 6mm diameter but these holes are 7.5mm. Why? It gives a little room for adjustments to ensure good alignment. We need to transfer the position of these holes to the tenon.
Here is how I do it. With the neck clamped in place and aligned correctly to the body the 7.5mm drill is placed in the headblock holes and tapped to that the point of the drill marks the tenon.
 


 
 
 



You can just see the point marks and, from these, I have drawn squared lines across and down the tenon faces.




Next job is to drill the holes for the cross dowels. Turning the drill around I can drill the 10mm holes for the dowels. These need to be as close as possible to the jointing surface but real care needs to be taken that the drill doesn’t hit the jointing surface! The tenon is supported underneath to prevent any drill breakthrough.




Using the same jig as for the body the holes for the bolts to pass through can be drilled. You can see the sliding adjustable bracket that supports the neck and body as required. Note the neck is clamped at the correct body/neck joint angle.



The drill is 7mm diameter this time. Again, this is to allow for small adjustments as required.
 




So now we have come to this. The undercutting inside of the joint area is to make sure the maximum pressure is on the joint surfaces.




Now the neck can be bolted in place. The extra allowances I have made in drillingthe oversized holes and the difference in widths of the tenon and mortice ensures that everything can be aligned perfectly. A bolt inside the body. You can’t see the other one! Bolts are tightened to finger tight and should be checked from time to time. I supply a short hex key with each guitar that would be difficult to overtighten.





It all works!




This is how the trussrod adjustment works. A long hex key passes through a hole in the top cross brace.




Here are some I made earlier! All I have to do now is carve the necks, fit the fingerboard and frets, tuners, nut, bridge strings and tune up. About ten minutes work!




One last thought.
In a normal neck joint the underside of the fingerboard that sits on the body top is glued in place. I tried this for a couple of the first bolt-on neck guitars and wasn’t happy as, in order to remove the neck the top/fingerboard joint had to be broken with heat and a knife which could cause damage that would need repairing. This is what I do now.



I use two small screws (13mm long - the ones that hold humbucking pickup rings down on solid body guitars) to fix the fingerboard overhand through the top and into the cross brace. At first I hid the screws under wooden plugs but then thought it would be more practical to just countersink them and allow them to be seen – less change of somebody clumsy doing damage when they tried to remove the neck.

And that's it. If you have questions then please email me and I will try to help.

The next few pictures are diagrams with dimensions and a list of suppliers. The beautiful CAD drawings are by my son Kieran who made my clumsy sketches look like works of art!