How to make a miter jig

Written by david r. wetzel
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How to make a miter jig
Constructing a mitre jig (,,,,

Mitre jigs are handy for ensuring cuts are made as intended every time. This mitre jig is designed to ensure that 45-degree angle cuts are perfect, avoiding problems when fitting window, door and picture frames. If you have a mitre jig, you won't have to worry about how the corners look on these types of frames.

Skill level:

Things you need

  • Plywood base board, 1 by 12 by 18 inches
  • 2 wood mitre slot guides, 3/4 by 3/8 by 17 inches
  • 2 wood mitre fences, 1 3/8 by 2 inches by 14 inches
  • 10 No. 8 flush head wood screws, 1 inch long
  • Table saw with 1/8-inch blade
  • Framing square
  • Electric sander
  • Drill
  • 7/64-inch pilot drill bit
  • 5/32-inch shank hole counter sink
  • Screwdriver
  • Sandpaper
  • Wood glue
  • Ruler
  • Clamps
  • Safety goggles
  • Hearing protection

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  1. 1

    Use the ruler to find the halfway point on the 18-inch side of the base board, and mark this point with a pencil. Use the framing square to draw a line from this point to the other side of the base board. Then measure a point 7 1/2 inches along this line from one side of the base board and mark.

    How to make a miter jig
  2. 2

    Make a 1/8-inch wide cut along the line marked in the previous step, starting from one side of the base board. This slot is called the Kerf line.

  3. 3

    Mark one end of both mitre fences with a 45-degree angle using the framing square. Then cut these ends using the table saw along the 45 degree line.

    How to make a miter jig
    Carpenter's Square
  4. 4

    Find the centre of the 2-inch side of the mitre fences and mark 3 inches from either end of the mitre fences with the pencil.

  5. 5

    Drill a 7/64 inch pilot hole through the mitre fences at these points. Lay both mitre fences with their 45 degree angles facing each other to form a 90 degree angle. Next counter sink the pilot holes using 5/32 shank hole counter sink. Then set the two mitre fences aside for now.

    How to make a miter jig
    Drilling Holes
  6. 6

    Measure the distance between the centres of the mitre guide slots on the surface of the table saw and record this distance.

  7. 7

    Divide this distance in half and measure from the Kerf line and mark the distance.

  8. 8

    Mark a line from one long side to the other using the framing square using the points marked in the previous step on both sides of the Kerf line. These lines are used to determine the location of the screws to attach the mitre slot guides.

  9. 9

    Mark a point along these mitre slot lines 2 inches from both ends of the base board. Then find the centre of both mitre slot lines and mark the centre. There are a total of six points marked on the two lines, three on each line.

  10. 10

    Drill all six points using the 7/64 pilot drill bit. Then counter sink the pilot holes using the 5/32 shank hole counter sink.

  11. 11

    Sand the surfaces and edges of the plywood base board and mitre fences using the electric sander to ensure all surfaces are smooth to avoid splinters and snags.

  12. 12

    Place a thin layer of wood glue on one of the 3/4-inch sides of both mitre slot guides.

  13. 13

    Turn the base board bottom up and lay the glued side of the mitre slot guides over the 7/64 inch pilot holes. One end of each mitre slot guide must be even with the edge of the base board that does not have the Kerf line cut.

  14. 14

    Measure to ensure the mitre slot guides are the precise distance apart. Use the carpenters square to ensure the guides are straight and clamp in place. Then turn the base board face side up.

  15. 15

    Screw the wood screws using the screw driver into the six counter sunk holes to hold the mitre slot guides in place. Then remove the clamps.

  16. 16

    Measure and mark a point 3 1/4 inches from the edge of the base board where the Kerf line begins.

  17. 17

    Place the two mitre fences on the top side of the base board ensuring that the counter sunk holes are face up. They must be placed at the points marked in the previous step, leaving a 1/8 inch gap between the two boards. The mitre fences ends not cut on a 45 degree angle will hang off each edge of the base board.

  18. 18

    Align the two mitre fences with the framing square to ensure that both fences are at an exact 90 degree angle. Then screw the two mitre fences in place using the screwdriver and the wood screws. The mitre jig is now ready to use.

  1. 1
    How to make a miter jig
  1. 1
    How to make a miter jig

Tips and warnings

  • Measure twice and cut or drill once.
  • Read directions over before beginning construction of the mitre jig.
  • It is critical that he mitre slot guides be placed the exact distance from each other to avoid binding in the mitre slots.
  • Always use caution when working with power tools, especially the table saw.
  • Hearing and eye protection should be worn at all times when using a power tools.

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