How to Cut Long Scarf Joints in Plywood

Written by donna armstrong
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How to Cut Long Scarf Joints in Plywood
The measurements on the plywood determines the length of the cut. (construction ,measuring image by Greg Pickens from

A long scarf joint is a taper edge joint that is used to connect two pieces of wood. The glued edge of the scarf joint is much larger than edge of a butt joint, making the scarf joint the stronger of the two. Long scarf joints are commonly used in boat making where the boat is longer than one piece of plywood.

Skill level:

Things you need

  • 2 plywood sheets
  • Table
  • Measuring tape
  • Marker
  • 4 clamps
  • Straight edge or square
  • Sharp wood plane
  • Low angle block plane or belt sander
  • Wood glue

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  1. 1

    Lay the first plywood sheet on the table with the good or face side up. Place the other piece of plywood face down on top of the first piece. Slide the first piece back at least six inches.

  2. 2

    Measure five inches or the total length of your scarf joint from the edge of the bottom piece of plywood. Mark the measured length and draw a straight line across the bottom plywood piece. Measure the same distance on the top piece and draw a straight line across the sheet. Use a straight edge or square to ensure the lines are straight. The most common long scarf cuts are five inches.

  3. 3

    Line the top piece up with the line on the bottom piece of plywood and make sure it is perfectly straight. If the top plywood is not straight the joint will not be straight, thus making the joint weak.

  4. 4

    Clamp the plywood pieces together placing two claps on each side and tightening the clamps. The clamps should be as close as possible to the point where the top meets the bottom with room for the tools to make the cut. The clamps will make sure the plywood does not shift during the cutting process. If you do not have claps small screws can be inserted six inches from the edge of the top piece of plywood.

  5. 5

    Start removing wood to make the angle or tapper with a sharp wood plane. Angle the plane to so that the plywood starts at the edge and slowly angles up to the top piece's line at a 45 degree angle. The bottom edge of the plywood sheet should be 1/32 of the thickness of the wood. Check the angle every few minutes with a straight edge to make sure it is straight.

  6. 6

    Finish the joint with a low angle block plane or belt sander. This will leave the joint smooth. The belt sander works faster; however if it is not easy to make sure the edge stays at a gradual incline. The block plane removes a slim piece of wood making it harder to make mistakes than when using a belt sander.

  7. 7

    Remove the clamps and take the top piece off the bottom piece. Place wood glue over the scarffed cut section of the bottom piece and line the top sheet's cut section up with the bottom sheet. Use clamps to hold the joint together until it dries.

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