Making A Jazz Bass 

Assembling the Parts

Fitting The Neck

Micrometer Marker is a dye suspended in grease. It is used in engineering to mark the high spots in mating components. One surface is smeared with the blue and the components are brought together. Dye is transferred to the high spots of the second.
This is one of the most exacting parts of the job. The neck needs to fit snugly in its socket and point the right way in both planes. First, the neck socket floor needs to be flat. I routed my neck socket on the overhead router but on checking, it was anything but flat, at least in the context of a precision joint. 20180306 115405Measuring flatness in the confines of a neck socket presents problems and I resorted to mechanical engineering methods. I have in my arsenal of tools, various short straight-edges made from ground steel stock. I used two of these, one that would fit across the socket and one slightly longer than it, coated with a film of micrometer blue to mark the high spots. I took great care not to get the blue on visible parts. When I was happy that it was flat, I Installed the neck and clamped it with a G-cramp, I used a straight-edge to assess the accuracy or otherwise. The height above the body measured 12 mm adjacent to the neck and 13 mm at the bridge position. After two or three tries, removing the neck, trimming the sides of the socket and reassembling, I achieved similar accuracy in the transverse plane. I was happy with that so I drilled the holes for the neck screws and fitted the neck plate. I checked the measurements again. The height had to be revisited later in the assembly process.
 
Aligning the Neck 1
 Aligning the neck 2
 Aligning the neck 4Aligning the Neck 3
 

Fitting The Hardware

Marking Hole Positions may sound trivial but it has to be done accurately if the screw is to seat properly in its countersink.  Self-centering punches are available but I make individual punches for each size of hole.

 

The bridge has to be in the right place and it has to be perpendicular to the strings. With the neck in place, I positioned the cut-out template on the body and measured 34 inches (the scale length) from the nut and marked it on the template centreline. This would be the position of the centre of the saddles in their fully-extended position. With a large tri-square held against the reference side of the template, I drew a line across the template. I then placed the bridge (saddles extended) on the template and aligned it with the square, with the centre-line and with the 34 inch mark. The fixing hole positions were marked with a punch, the template removed and then drilled through on the drill press with the pilot drill for the fixing screws. Replacing the template on the guitar, taking care to aligh it, the holes were drilled through to the body.

Fitting the scratch-plate and control panel is straightforward, at least, it should have been. When I placed them on the body, I discovered that the control plate as the wrong size. I had not realised that there were variants. So, I bought the right size from Ebay and tried again. Then I discovered that the control cavity was in the wrong place. I checked it against the template and against the drawing and they were all the same. The drawing was wrong. Fortunately, the error would be covered by the plate, I just had to enlarge the cavity. I altered the template in case I ever make another Jazz Bass.

 Next came the machine heads. I bouught some rather nice Wilkinson machine heads. I had already drilled the holes to match the ferrules supplied with them so the job would e simple. I pressed in the ferrules, first by hand and then using a G-cramp and two wooden packers. Then I positioned the machine heads. They did not fit. the baseplates overhung the head. Another purchasing error! I seems that the modern Jazz Bass has larger ones the the vintage models. My drawing was for the latter. I could not find vintage-size machine heads of similar quality in the UK. Schaller make them but they are not available here so I bought some unbranded ones from Ebay. They are OK. They operate just as smoothly as the Wilkinson ones but the chrome plating is imperfect. However, the ferrules are smaller, both in bore and on the knurl. They are loose in the holes, not so loose that they will not centre but not tight enough to ensure that they remain seated. I resolved to fit them loosely for now and epoxy them in after applying the finish.Machine Heads 2


Machine Heads 1

 

I installed the pickups and fitted the strings and adjusted the truss rod. So the guitar was finished "in the white". Here is a picture:-

20180331 162225

With the bridge saddles in their lowest position, the action was slightly too high, the neck pocket required further adjustment. Minor issue! I would calculate the adjustment required and trim the pocket when I dismantled the guitar for finishing. In the meantime, I was desperate to try it out.

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