Mitre Box MB3
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The Mitre Box MB3

The MB3 Mitre Box is an accessory that holds wood at angles to the machine face, either at 90° (up under the plate), or at 45° for mitring rails and boards, or vertical, and at any angle in between. It is essentially two large cheeks or plates, held apart by two threaded rods. The work goes between the cheeks and is clamped tight by the Cam Lock. You can make one yourself, but the MB3 has some special features and is made of HDF which is hard and designed not to bend.

Working with the MitreBox MB3

at 90°

The MB3 will hold work horizontally. This is a way to put a leg on a table with a sliding dovetail. Cut the dovetail with a large 1in6 bit. If it’s heavy you’ll need to support the end of the leg with a roller or similar. You can cut the rails for the table in the normal way for tenons. It makes for a very solid joint. 

at 45°

Whenever a decorative feature or functional profile goes around the corner of a box or frame, you will need a mitre.

Hold the wood at an angle and cut it square with the bit, and you get an angled cut. The obvious result is a 45° mitre, but you can enter the wood at any angle from vertical to horizontal.

Mitred Joints

Mitring boards to make Splined Joints. The spline and the recess for the spline can be made with mortising and tenoning techniques. A nice variation of this is to make a dovetailed angled spline set vertically in each mitred board. 

Making mitred Bridle Joints for framing: put the frame in at 45° to cut the mitres, and then vertical to make the bridle joint.

Mitering boards, but leaving an area to make Mitered Dovetails. This is a complex operation when done by hand, but easy with the MB3. With the board at 45° run across the edge and across the corner and then forward through the right-hand edge. Then place the board vertically and flatten the area for the dovetails.

Mitred dovetails can be made in the MB3 with the tails made vertical and the pin pockets cut with the piece inside face up and the bit brought in to a stopped cut, using the angled stop on the Guide Rail. 

The MitreBox MB3 also forms part of the Pathfinder. It combines with the Pathfinder Parts, and one of a number of Templates, to complete the Pf1 Pathfinder.