This is my interpretation of the jig designed by Gavin Brunton for setting up the McNaughton Center Caver Coring Jig.
The coring system is fantastic, but takes a lot of practice to get the optimal results. Gavin Brunton designed a jig and accompanying spreadsheet where you enter the bowl blank diameter and depth, and it calculates the optimal entry angle for the coring blade. The jig allows you to set this angle with precision.
Gavin created several YouTube videos describing his jig, and has generously shared the spreadsheet for the calculations as well. See the end of his design video for his e-mail address to get access to the spreadsheet.
In Action: https://youtu.be/ppbcVUdDAIc
I took Gavin's design and adapted it for 3-D printing using Fusion 360. With his permission, I am sharing these models for anyone to print. It is a work in progress, and I will update as I make changes.
Bolts are all the same as described in Gavin's videos (M5)
This design is for the standard set of blades, using the radii specified in Gavin's videos. These worked for me, but there is reportedly some variation. If you find some drastic differences, let me know and I could create a custom adaptor.
Red - 89 mm
Green - 137 mm
White - 176 mm
Blue - 275 mm
Updated connector between extension and protractor to fit better off the printer.
Protractor hash marks are now recessed.
Angle indicator now longer.
Create a Turret adapter and blade selector to fit the small blade set.
The Grain Doctor
Supports are necessary only on the protractor extension piece.
I used Prusa ColorPrint (https://www.prusaprinters.org/color-print/) to set a pause while printing the Protrator portion. This allowed me to change the filament for the top few layers of the protractor, then back again for the angle hash marks. This allows the markings to stand out visually.
If you did not switch filaments to accentuate the protractor markings, you can simply paint them carefully.
For the extension, you will likely have to sand the male prongs to get it to fit in the female slots on the main body of the protractor.
Connecting the protractor extension
For the extension, you will likely have to sand the male prongs to get it to fit in the female slots on the main body of the protractor. Once you get the fit, simply superglue the two together.