Fret Slotting Mitrebox

This is a 3d printable slotting mitre box designed for cutting fret slots for stringed instruments by using an indexable template.

NEW VERSION 3 - BETA 17/10/26

I am still documenting V3 but I decided to release early, this release brings genuine multi-scale capability and a template generator so you can make any template you want. Note I have increased the price slightly to match my listing on Cults (which lets me sell in £) but I think the multiscale template generator is worth the price of entry alone.

V3 is a complete redesign / rethink, while V1 and V2 are capable of cutting multiscale fanned frets it was proving quite an effort to make the slotting templates work as accurately as needed and there was too much repositioning of the fixture to cut each slot.

V2/V1 still work just fine so if you are only cutting single scale boards they will work as well as ever.

This time I completely redesigned the mitre box and have adjusted the way the template works instead of indexing on a side pin the fixture has a pair of dowels to index in slots in the centre of the template. This seemed quite an obvious way of fixturing the template to me and a search of the internet shows I did not get there first of course (when do you ever) but I haven’t seen anyone running commercially with this solution yet.– see https://www.projectguitar.com/forums/topic/48745-multiscale-fretboard-cutting-templates/ and https://www.projectguitar.com/forums/topic/52485-multi-scale-fret-slot-jig-for-tablesaw-take-a-look/for a similar approach

The mitre box is somewhat customisable so if you did want to use it with side pins, that can be done as well. The base and index pin system are also suitable for use with mitre saw or radial arm saw just mount it to your saw table with the dowls aligned to the saw blade.

Instead of heat set insets this time fastenings are simple M4 screws and Nuts.

ALSO INCLUDES MULTI-SCALE TEMPLATE GENERATOR!!!

There is a new version of my slotting template generator that will produce standard and multiscale slotting templated for use with this mitre box system I will be releasing it later for purchase separately but it is included with the mitre box now - This not the same version that I have made available for free so this is hopefully a big upgrade for those interested in multiscale guitars.

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Version 2.0 - Redrawn  12/2025 - insert holes are now Ø8.1 X 13 deep, sized to suit more common M6 inserts. Treat this one as a work in progress as I have not actually made one of this iteration but many people are having issues finding the correct inserts,  Version 1 files still available if you have the original inserts. The only inserts that require to be shorter than the common 12.7 long ones are the roller holders and you can either source shorter 9.5mm or 8mm inserts for these or file down the longer ones.

V2.01 - Revised The Screw Lengths - New non printed parts  BOM

• 1M2X10 Cap Head Screw

• 28M6 x 12.7mm Heat-Set Insert

• 8M6 x 9.5mm Heat-Set Insert

• 1M2 x 4mm Heat-Set Insert

• 2M6X50 Hex Head Screw Full Thread

• 8M6X14 Button Head Hex Drive Screw

• 12M6X20 Button Head Hex Drive Screw

• 8M6X16 Button Head Hex Drive Screw

• 8626ZZ Bearing 

Should now work with CNC Kitchen inserts and those available from McMaster-Carr amongst others, for example. See inserts.txt for links.

• https://www.accu.co.uk/brass-threaded-inserts/849042-HTBTEI-M6-BR

• https://www.amazon.co.uk/HANGLIFE-Threaded-Inserts-Printing-Components/dp/B0CS6YCWHD

• https://cnckitchen.store/products/heat-set-insert-m6-x-12-7-20-pieces

• https://www.mcmaster.com/products/inserts/threaded-insert-type~heat-set/system-of-measurement~metric/

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Version 1.04 - now with STEP files so you can make your own modifications. It has been noted that the inserts I originally specified may not be easily available so the STEP files will allow you to dimension the holes to suit any insert.

Full instructions are contained in the pdf attachment.

Bill Of Materials
3d printed parts, Approx. 400g material required, Print Time 14Hr.
• Base, Qty 1 225mm Long
• Side Plate, Qty 2
• Side Mirror, Qty 2
• Roller Holder, Qty 4
• Roller Holder Clip, Qty4
• Side Plate Clip, Qty4
• Clamp (Optional Experimental for angle cutting, Qty 2)
• Clamp Fixed (Optional, Qty 2)
• Clamp Face, Qty 2

•  Base Shorter (215mm)  V1 - Qty 1 Req (alternate for smaller printers)

All Printed parts can be made from PLA its stiffness is a benefit.
Sundries - Approx. Cost £20-27
Screws

• M6 X 14 Button Head Hex Screw, Qty 8
• M6 X 16 Button Head Hex Screw, Qty 8
• M6 X 20 Button Head Hex Screw, Qty 12
• M6 X 60 Button head Hex Screw, Qty 2
• M2 X 20 Cap Head Socket Screw, Qty 2
Other screw types of the right length can be used.
Inserts
• M6 Brass Push In Flanged Insert, Qty 34 – See Drawing for dimensions, source these from ebay or amazon
example 1
example 2
• M2 Brass Push in Insert, Qty2 (Option Qty 4) – Expected OD Ø3.6
example

Bearings
• 626ZZ Roller Bearings, Qty 8

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3D PRINTING SETTINGS

Print from PLA or other stiff material - default settings work but ensure minimum 3 perimeters.

The mitre box is 75mm wide but you can increase this width using the scale command in your slicer if you require a wider box a scale factor of 130% will give a width of 85mm. This will work fine with parallel fret templates as well.