My interpretation of a neck contour jig inspired by the original Idea of Bill Scheltema. I wanted to have a version which is easily adaptable for different scale lengths and also one which does 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.
40x40 mm Aluminium Construction Profile, Length: 900 mm
19 mm MDF for the base construction
10 mm MDF for the Profiles
U-shaped Aluminium for sliding rail
Some M8 machine screws and nuts
8 ball bearings 8 mm x 22 mm x 7 mm
The main idea is built around a 40 x 40 mm Aluminium Construction Profile 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 make the center part and the sides which are used as rails for the cartridge.
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.
Make some test-fittings while cutting the recess of the profiles to find the perfect fit.
the outer contour has an offset of 10mm to the reference curve. This is why I engraved the original sized profile additionally. 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.
I made the side rails height-adjustable by adding depth stop brackets. I'm not 100% sure if all of you will need this but I wanted to have a version which is very flexible. But this also means that the initial setup might take longer.
What I find super helpfull for this process is a digital depth gauge I normally use together with my router table. The goal is to have a unique hight on all 4 points where the side rail have contact to the base construction (I don't find a better name for it right now but I hope you all know which part I am refering to ;). And let the differenty sized profiles take care of holding the propper distance to the router bit.
It helps to make the base construction in form of a "L" shape because it is usefull to clamp these to a solid table. Because of the spring tension, the jig aloone will not stand very stable.
I did not include shaper files for the rails because they are simple recangular shapes. I added an "U" shaped aluminium profile on top of them. Together with the bearings on the cartridge it slides super smooth. I also added some Silbergleit on the aluminium which further reduces friction.
Initially I used a Kress router motor this is why the carriage has a center hole with a 43mm (Eurohals) diameter. I later decided to replace it with my OF1400 plunge router. It only needs 2 holes to screw it in place. They are unfortunatelly not part of the shaper file. The plunge router and especially this one makes it very easy to micro adjust the depth of the router bit. But make sure, you have a really long bit with a length of about 100 mm.
The Aluminium Profiles can be found from different suppliers. These are from the company Item. https://product.item24.de/produkte/produktkatalog/produktdetails/products/konstruktionsprofile-8-1001042794/profil-8-40x40-leicht-natur-2633/
On my website, you can find an article explaining more details about the design and the build process: https://www.on-guitars.com/blog/jigs/building-a-neck-contour-jig/
Feel free to join the thread in the community section about this project: https://community.shapertools.com/t/guitar-neck-contour-jig/5077