Building a Neck Contour Jig
This article introduces you to my interpretation of a guitar neck contour jig inspired by the original idea of Bill Scheltema. Feel free to download the plans and files further down to build one for your own guitar projects.
This neck contour jig is designed to be easily adaptable to different scale lengths. It should also not take too much space in my shop if it is not needed. Using a carriage which supports a plunge router, the depth of the router bit can be adjusted easily and – even more important – precisely.
The main idea is built around a 40 x 40 mm aluminium construction profile manufactured by item as center beam holding the guitar neck. The one on the pictures has a length of 900 mm. If you need different scale lengths, you only have to create a new neck rest with a different length and all other parts can be reused unchanged.
The profiles which are guiding the rotation of the center beam just slide into the Construction Profile and can be easily exchanged. The recess in the center of the profile which follows the aluminium profile keeps it safely in place and does not allow movement.
With the help of an adapter, the M8 machine screw is connected to the rod and therefore serves as rotation axis. It’s a good idea to secure the threated part of the machine screw by adding some glue to keep it safely in place. After that you cut off the head of the screw. You replace it with a shaft collar which prevents the springs from slipping away.
The inner shape of the profiles follows exactly the shape of the construction profile and on the upper side is has a nose to prevent it from rotating. The profiles just slide onto the beam there is no further fixture needed.
The outer contour of the profiles have an offset of 10mm to the reference curve. This is why I also engraved the original sized profile. I use this as a reference line to set the depth of the router bit precisely.
The center point of the rotation is exactly the middle of the top surface of the aluminium profile and the profiles are designed for a neck thickness of 25 mm.
If you design your own profiles keep in mind that you have to consider the positions of the profiles on your jig are not at the position where you might design them on your neck.
First I created curves for the 1st and the 16th fret and then I project the curves to the points where the profiles sit on the neck rest beam following the outer lines of the fret area.
The support plate offers 19 mm wide slots to hold the carriage rails. The slot in the center is one the one hand used as vertical guide for the axis if the neck rest beam and on the other hand you can screw the ball bearing mechanism into this slot.
I tried to make this jig as flexible as possible so I added a clamping mechanism as depth stop for the carriage rails. The initial setup takes a little bit longer due to this option but it can be very accurately calibrated.
I tried several ways to attach the bearnig ball to the support plate. At the end I found an axis which is normally used for smaller wheels. It has a diameter of 8 mm which fits perfectly to the inner diameter of the ball bearing (8 mm x 22 mm x 7 mm). I used some super glue to fix it permanently.
Two wing nuts are used for every depth stop because they have to withstand a good amount of pressure caused by the weight of the plunge router.
3M Stikit self-adhesive abrasive can help to increase friction between the two parts.
Carriage Rails and Spring mechanism
The top edge of the carriage rails are coverd with a u-shaped aluminium profile. This let’s the carraige slide with less friction.
I did not make any drawings or CAD files for the rails because they are basically just straight rectangles. I used some scrap wood which was left over from a shelf.
The springs are fastened with M8 machine screws. You can slightly adjust the spring tension by adjusting their vertical position. From my experience, the upper most position feels just right.
The position of the carriage relative to the rails is fixed by 6 ball brarings ball bearing (8 mm x 22 mm x 7 mm). Each ball bearing is attached with DIN 912 M8 Screws. They are easily accessible from the top with a hex wrench to fine tune the position and to prevent if from wiggling.
See it in action
Even if I could not list every single screw, because most of the parts were just laying around in my shop, I think this guide gives you a comprehensive understanding on how to build your own neck contour jig.
If you don’t have a CNC machine or a Shaper Origin, you can easily use the SVG files and send them to an online service to produce the parts for you.
Keep im mind: meassure twice, cut once.
Please check all drawings if they really fit to the parts you are using for your build before blindly cutting them. From my point of view, it is always best to meassure the real parts (for example the diameter of the screws) and to adjust the drawing to fit perfectly to their size. The meassurements worked fine for me, but this does not neccessarily mean that they will fit you needs.