Construction techniques

Making bridle joints

Andy Standing  |  Oct 26, 2008

The bridle joint is also referred to as an ‘open’ or ‘slot’ mortise-and-tenon joint. This is because the mortise is open-ended and the tenon may be slid into it sideways. The joint can be used on corners, either cut square or mitred, where it’s signifi cantly stronger than a halving joint by virtue of its large gluing area.
Tools you’ll need to cut bridle joints:

• Try square
• Pencil
• Mortice marking gauge
• Tenon saw or Pullsaw
• Coping saw
• Router with straight cutter
It’s most useful, however, for connecting middle legs to continuous top rails on tables, where breaking the rail to form a pair of tenons would weaken the structure unnecessarily. This form of the joint is known as the T-bridle. It’s a relatively simple joint to make, with the slot being cut fi rst and then the tenon made to fi t it. The proportions used are the same as for a standard mortise and tenon, so when joining two timbers of equal thickness, the slot should be set centrally and should be no more than one third of the timber’s thickness.
This is also an easy joint to cut with machine tools. You could use a mortiser to cut the slot, but a bandsaw is the ideal tool. Using the rip fence, you can saw a slot in seconds with total accuracy. To remove the waste from the tenon component, use a radial arm saw or a sliding mitre saw.
Marking out with a square Marking with a pencil Extending mark around timber

1] Start by marking the position of the joint on the tenon member with a try square and a sharp pencil

2] Use the mortise member and the try square to mark the wood’s exact width on the tenon member

3] Extend the lines all round the workpiece using the try square. They should meet exactly if the wood is square

Marking the depth of cut Setting mortice marking gauge Centralising the mortice gauge

4] Mark the depth of the slot on the mortise member. You can make it a little deeper and then plane off the end once the joint is complete, to produce a neat finish

5] Set a mortise marking gauge to the width of your chisel. The wood is 19mm thick, so I chose a 6mm wide chisel as closest to one third of its thickness

6] Centralise the gauge and mark both sides of both components. Always work from the same face of the workpiece to minimise any inaccuracies

Pencil in marked lines Cutting the joint with a pull saw Using a coping saw to cut out waste

7] To make the marked lines more clearly visible before cutting the joints, run a sharp pencil along them

8] Fix the mortise member vertically in a vice. Using a fi ne-point saw, cut down on the waste side of the marked lines

9] Use a coping saw to remove most of the waste from the slot. Take care not to cut beyond the base line

Using a chisel Cutting accross the grain Using a router

10] Square off the base of the slot with a chisel, cutting down to the marked line and working from both sides of the wood

11] Now cut the matching tenon. Make sure the cuts are vertical and within the waste area. Don’t run over the gauged lines

12] You can use a router to remove most of the waste. Fit a wide straight cutter and plunge down to the gauged lines in stages

Cleaning up with a chisel Fitting the joint The finished joint

13] Clean up the base of the joint on both sides of the wood with a wide-bladed chisel held fl at to the surface

14] Test the fi t of the joint, and make any necessary adjustments with a chisel or abrasive paper

15] The fi nished joint. If you marked and cut the mortise a little over-deep, plane the projection fl ush for a perfect fi nish

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