Peter Coombe Mandolins and Guitars
Neck and Dovetail
The top of the side assembly is sanded flat on the linisher.
It is important to mark a centerline since everything hangs off the centerline.
Here is my dovetail cutting template. It is lined up along the centerline.
Marking out the dovetail on the headblock, making sure it is centered.
The dovetail is cut out on the bandsaw.
A slight taper is then cut into the dovetail joint in the headblock. At this stage it is a good idea to make sure the sides are at 90deg to the headblock. The best was to do this is to trim the sides with an oscillating sander which guarantees a 90deg angle, but I don't have one so do this by hand with a chisel and sandpaper.
The way I line up and cut the dovetail joint is similar to how Lynn Dudenbostle showed how he does it, so thanks Lynn. Firstly double sided tape is glued on to the headblock and tailblock.
A strip of about 60mm wide cardboard is cut, and a centerline marked on the cardboard.
The cardboard is glued to the headblock and tailblock with the double sided tape.
The dovetail shape is carefully cut into the cardboard.
A smaller blade is required to reach into the joint.
The whole thing is then flipped over and the cardboard removed so we now have a cardboard template of the dovetail.
A centerline is then drawn on the cardboard, using the centerline on the other side as a guide.
The 12th fret position on the top is marked by using a spare fingerboard.
The end of the top is then cut at the 12th fret position on the bandsaw.
The cut edge is then sanded smooth
Making sure it is straight and square.
The top is then placed onto the side assembly and the cardboard template is fitted into the dovetail.
Using the spare fingerboard the position of the nut is marked onto the cardboard.
At this stage the position of the top is also marked across the headblock so we will know where to place it later.
A small hole is cut into the cardboard at the nut position so we can see the end of the headstock veneer when the cardboard template is placed on the neck to mark the dovetail.
The cardboard template is used to mark the dovetail on the neck.
This is my dovetail cutting jig, the idea thanks once again to Lynn Dudenbostle. It is cut exactly to an angle of 4.5deg.
The dovetail is cut on the bandsaw, and with the jig will be cut exactly to 4.5deg.
Here is the neck with the dovetail cut straight off the bandsaw. Now we can fit the carbon fiber rod.
I use 1/2" x 1/4" carbon fibre reinforcement in my necks. The carbon fibre rods come in 18" lengths which is enough for 2 mandolin necks so they need to be cut to length. Do not attempt to cut carbon fibre in a bandsaw, it is guaranteed to ruin a bandsaw blade in less than a second. Cut carbon fibre with a hacksaw, at least hacksaw blades are easily and cheaply replaced. Also be careful about carbon fibre dust, it is toxic so wear a dust mask when cutting or sanding carbon fibre.
The carbon fibre rod is glued in with epoxy.
Here the carbon fibre rod has been glued in. The epoxy will take at least 24hrs to cure.
Once the epoxy has cured, excess glue is cleaned up with a chisel.
And the carbon fibre rod trimmed off to length with a hacksaw.
Fingerboard is marked onto the neck.
As is the headstock shape.
The neck shape is then cut out on the bandsaw. First the fingerboard.
Then the headstock
The sides of the headstock are planed flat
And checked for a good fit with the headstock template.
The neck is sanded on both sides on the linisher so it is straight.
And fits the fingerboard template.
The upper side of the headstock is now sanded on the linisher with a fine grade of sanding belt ready for marking.
Now it is time to drill the holes for the tuning machines. First the position of the holes is marked on the headstock very carefully with a steel rule and fine pencil point.
The precise positions of the holes is marked with a steel point.
Here the position of the holes have been marked and the headstock is ready for drilling.
The holes are drilled with a brad point bit mounted in the drillpress, but are not drilled right through to the other side. The drill bit is precisely positioned over the marks while it is spinning to ensure the positioning of the holes is precise.
Once all the holes are drilled, the drill bit is changed to a normal twist drill and the holes are drilled right through to the other side. Drilling the holes in 2 stages ensures precise positioning and a clean entry and exit to the holes. A brad point bit does not exit cleanly, whereas a normal twist drill usually does, but a twist drill will tend to wander if used to start the hole and will thus not be precise. We are using the best of the two drill types.
Finished drilling tuning machine holes.
Now we start to shape the neck and fit the dovetail. Firstly remove some wood from the heel of the neck with the bandsaw.
Flatten the end of the carbon fibre and shorten the tenon of the dovetail to ensure there will be a gap in the joint just in case the neck needs to be removed later in the life of the mandolin. Without this gap, the dovetail joint is almost impossible to loosen.
A slight taper is chiseled into the tenon on the neck, checking so it fits the taper of the mortise in the headstock.
The neck is now shaped on the linisher. This is a very dusty operation, so a dust mask and the dust extractor running is essential, but I have found it to be the most effective way of quickly shaping a neck.
The underside of the headstock is also sanded flat and the headstock thicknessed to within 0.5 mm of the final thickness.
Here is the neck after being shaped on the linisher. Final shaping will be done with a scraper after the neck has been glued on.
The dovetail is now fitted. This is done by hand by shaving thin slices of wood with a very sharp chisel.
And also with a file. Do not fit the dovetail so the neck is fully seated, leave it slightly proud of it's final position. Make sure the neck is straight by dry fitting the top and sighting down the centre join of the top. Final fitting will be done later after the top and riser block are glued on.
A final check to make sure everything fits. The neck is now ready for the next step - installing inlay.