How to Make Window Sash Joinery

Written by brian scudder
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How to Make Window Sash Joinery
A window sash is the framework for the window glass. (window with flowerpot image by Stanislav Pepeliaev from

Window sash joinery consists of precision-cut pieces put together with mortises and tenons. These joints provide structural integrity, allowing the sash to have the strength to support glass. Hand-hewn window sashes are time-consuming and fairly difficult to manufacture. But with innovations in woodworking tools, sash joinery can be easily made by using a set of sash router bits.

Skill level:

Things you need

  • Tape measure
  • Poplar wood
  • Mitre saw
  • Router table
  • Router
  • Window sash router bit set
  • Scrap wood, 24 inches long
  • Masking tape
  • Table saw
  • Wood glue
  • Rags

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  1. 1

    Measure the dimensions of the window sash frame -- the actual perimeter size of your window. Sides, or stiles, must extend the entire height of the sash. The top and bottom rails must be cut to fit between the stiles. Transfer the sash frame measurements to the poplar. Make the cuts with the mitre saw.

  2. 2

    Place the end cope bit in the router. Adjust it to the proper height.

  3. 3

    Run the 24-inch piece of scrap wood through the router bit to test for proper height.

  4. 4

    Cut the end copes on the rail pieces of the sash. Set them aside.

  5. 5

    Cut the entire length of the scrap piece with the end cope bit. This piece will be used as a template for safely cutting the mullion pieces.

  6. 6

    Change the bit to the groove bit. Adjust it to the height.

  7. 7

    Run the 24-inch test piece through the router bit and test for the proper height.

  8. 8

    Cut the rails and stiles by running the bit down the entire length of each piece. This will cut the groove for the glass and the matching profile for the end copes of the rails.

  9. 9

    Dry fit the perimeter sash together.

  10. 10

    Measure between the perimeter of the recess in the interior side of the sash frame.These pieces form a grid inside the sash and must be 3 inches wide to allow for safe cutting on the router.

  11. 11

    Cut the mullion pieces to length with the mitre saw.

  12. 12

    Place the end cope bit in the router and cut both ends of the 3-inch-wide mullion pieces.

  13. 13

    Replace the end cope bit with the groove bit and adjust to the height of the previous groove cut.

  14. 14

    Cut the 3-inch-wide mullion pieces by running the entire length through the bit.

  15. 15

    Rip the mullion pieces to width on the table saw by adding the profile sides together, while adding the width of the exterior of the mullion.

  16. 16

    Place the groove cut mullion pieces into the previously cut template piece.

  17. 17

    Tape the mullion piece to the template to prevent it from moving inside the template.

  18. 18

    Run the taped mullion piece through the router groove bit.

  19. 19

    Place the remaining mullion pieces into the template, tape them, and repeat the cutting process as before.

  20. 20

    Dry fit the pieces and check the dimensions of the sash.

  21. 21

    Apply wood glue to the coped ends of the mullion pieces and the coped ends of the sash frame.

  22. 22

    Assemble the mullion pieces to the frame and wipe off the excess glue with a rag.

  23. 23

    Place bar clamps on each end of the stiles of the sash and tighten, wiping off the excess glue.

  24. 24

    Square the window by measuring diagonally from corner to corner with each diagonal measurement being the same. This method of squaring is known as the "X" method.

Tips and warnings

  • Assembly of the sash requires a clean work surface to avoid obstructions in the joints.
  • Use push sticks to aid in machining the pieces. Always wear safety glasses and read operators' manuals and instructions for all tools.

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