Fret Slotting Mitre Box Extension Base

A recent addition to the ProjectGuitar.com workshop was a new mitre slotting box from Guitars and Woods (G&W). Like any tool, integrating a fret slotting box into your workshop and usage methods benefits from a few tweaks. Straight out of the box, it is a useful and powerful tool (read our review here!). What more can we do to it?

The base of the box is pre-drilled and countersunk to accept three screws or bolts so that you can affix it to your work surface or a larger baseboard. I opted to go for the second approach. The mitre box itself is just over 105mm/4" wide (I went for the wider base version) and 305mm/12" in width, which is shorter than most fingerboards. I drew up a rough sketch for the ideas I wanted to have. This was all very "back of a beermat" sketching....

Most dimensions were for reference or brainstorming purposes only....

I wanted the mitre box to sit in the centre of a wider board between a pair of risers which sit flush with the level of the base, thereby extending out the area underneath the fingerboard and/or template. The risers extend behind the mitre box so that a pair of toggle clamps can be added for securing workpieces firmly. One aspect of this "design" is very specific to my own working area. Specifically, that thing sticking out of the bottom....

My main "heavy" work area is a French Roubo style bench weighing several hundred kilos. It will go nowhere even if you put your weight behind it! Part of the Roubo design is a large "leg" vice sitting flush against a front leg:

Several of my more permanent working jigs (such as my router thicknessing jig) have a flange of wood fitted to the underside which I can clamp up in the leg vise, providing an extremely stable working area. Not everybody has one of these, however if you do then this type of mounting for work jigs is invaluable.

Bench mounting flange detail

The jig ended up being made on a base measuring 800mm x 150mm (about 31,5" x 6"). The outer risers (10mm thickness) were cut 150mm wide also, with equal lengths so that the box sits in the centre of the jig.

Detail of the flush-level extensions either side of the box

An added feature was three magnets glued into a free area of the jig. These retain the two Allen keys used to perform adjustments and settings on the mitre box. These are simply shallow recesses drilled and neodymium magnets superglued in. Epoxy might have been a better idea, but being a small job I opted for CA. Personally, I hate rummaging through piles of Allen keys looking for one that "might fit". Invariably you get the wrong side of the Metric/Imperial fence and round out the head of the screw you're trying to work. Your day then takes a turn for the worse and the job just doesn't get done in a hurry....

Toggle clamps set either side of the box provide strong hands-free workpiece retention: Bessey or Destaco clamps are great, but pretty costly. You can also score more or less the same kind of thing from any one of the many Chinese sellers on eBay for a tenth of the price. However you go about this, there's no need to go for massive clamps like the ones used to hold Drumpf's rug down.

Clamped down, the workpiece isn't going to go anywhere....

Finally, the extension boards were marked with lines used to ensure that boards can be lined up perpendicular according to the centreline. Extremely important when working with non-squared pieces without templates:

Construction

Your own mitre slotting box might be different to mine, especially if you go for a narrow 3" base or buy it from a different supplier to G&W. I opted for an 800mm (~31,5") length with 50mm (2") additional width on top of the box width of 105,5mm (just over 4"). The extensions were simply glued and clamped in place with the mitre box in situ. After these dried, the box's mounting locations were marked onto the main board. I pre-drilled these straight through using a drill larger than the screw thread diameter; these go through to the mounting flange underneath, so tightening them cinches everything together. If you're not using a mounting flange, use a smaller pilot hole of course so the box is secured to the base. Finally, the flange was drilled with pilot holes, glue added and the whole lot screwed together.

Mitre Box - 305mm x 105,5mm x (10mm base)
Baseboard - 800mm x 150mm x 16mm
Extensions - 245mm x 150mm x 10mm