How to Biscuit Joint a 45 Degree Angle

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Things You'll Need

  • Tape measure

  • 1-by-6 stock lumber

  • Compound miter saw

  • Combination square

  • Biscuit joiner

  • 4-by-4 block, 6 inches long

  • Clamps

  • #0 biscuits

  • Yellow glue with brush

  • Damp rag

  • Sandpaper

The biscuit joiner, sometimes called a plate joiner, creates a glued joint by cutting a half-oval slot in two pieces of wood. Football shaped biscuits glued into the slots align and hold the pieces together. Slots cut at the same angle as a mitered cut allow two pieces to join at an angle, but the biscuit joiner fence adjustment must allow for angled slots. The resulting joint appears virtually seamless unless viewed from the edges.


Step 1

Measure and mark two pieces of lumber 8 inches long for cutting. Set the bevel on the compound miter saw to 45 degrees. Align the blade with the mark on the board, start the saw and lower the blade through the wood. Cut two pieces in this fashion.

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Step 2

Place both boards on a workbench with the angle cuts facing each other. Align the boards so the edges are flush with each other. Set the combination square to 1 ½ inches and place the flat edge against the two boards where the cuts meet. Use the end of the square's ruler to draw two parallel marks -- perpendicular to the angle cut -- from one board onto the other. These mark the locations of the four biscuit slots.

Step 3

Clamp one of the boards upright to the edge of the workbench with the angle cut facing away from the bench. Set the fence on the biscuit joiner to 45 degrees and the depth adjustment knob to #0 biscuits. Place the joiner on the angle cut and set the height adjustment 1/8 inch above the end of the miter cut on the board.


Step 4

Align the mark on the board with the center mark on the joiner. Hold the joiner firmly with both hands, start the joiner and plunge the blade into the board. Repeat for the second mark and for both marks on the second board.

Step 5

Lay one board on the workbench with the angle cut facing up. Insert a biscuit into each slot. Fit the second board onto the biscuits. Set the combination square to zero inches and place it flat edge down on the bench with the ruler upright. Slide it against the upright board and adjust the board until it is flat against the square. Place the 4-by-4 block on the first board and against the second board. Clamp the block and the first board to the workbench.


Step 6

Remove the second board and the biscuits. Spread yellow glue with the brush into the slots on both boards and along the cut edges. Coat both biscuits with glue and insert them into the slots on the first board. Fit the second board over the slots and flat against the block.

Step 7

Clamp the second board vertically to the table and horizontally to the first board. Wipe up any excess glue that squeezes out with a damp rag. Allow the glue to set for one hour before removing the clamps.

Step 8

Sand the joint to remove any remaining glue that squeezed out and to smooth the joint.


This process works well for joining any angle, but on angles other than 90 degrees require a block cut to that angle. Don't try to center the slot on the angle, the blade will go right through the board. Focus on aligning the center mark on the joiner with the mark on the board.


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