How to Make Spline for Flooring

Most wood flooring is designed with tongues along one edge and grooves along the other. These tongues and grooves fit together, creating tight seams between boards. Reversing the direction of the tongues and grooves part-way through the installation can help vary the wood grain, and it sometimes makes working around unusual spaces less challenging. To fasten the grooved edges of two boards together, you will need a separate tongue, called a spline, that fits into both grooves. This type of joint is similar to biscuit joinery, except a spline is one long piece instead of several small ones.

Measuring tape
Solid wood screen molding
Pencil
Table saw
Wood block
Handheld power sander
Medium-grit sandpaper
Wood glue
Mallet

Instructions

- 1
  Assess the depth of the groove in an uninstalled piece of wood flooring. This is easiest to accomplish by measuring across the short end of the board. The depth of the groove will be quite small, less than 1/2 inch.
- 2
  Mark the width of the screen molding at twice the depth of the groove in the flooring using a pencil.
- 3
  Measure from the pencil mark on the molding to the edge. This is the amount you will trim off the edge of the molding.
- 4
  Set the guide or fence on a table saw the amount to trim off the molding and turn on the saw.
- 5
  Lay the molding flat on the table saw platform with a long edge parallel to and against the fence.
- 6
  Push the molding into the saw blade with a slow, steady motion. As the blade nears the end of the molding that is closest to your hand, use a block of wood to finish pushing the molding through the blade.
- 7
  Test fit both edges of the spline into the groove of a piece of flooring. If it is too thick, sand down the top of the spline with a handheld power sander and medium-grit sandpaper to reduce some of the bulk. Stop sanding and check the fit often, as making the spline too thin will cause a loose, weak joint.
- 8
  Cut the spline to the length of the board that you need to join.
- 9
  Fill the groove in the flooring board that is fastened to the floor with wood glue. Tap the spline into the groove with a mallet.
- 10
  Squeeze glue into the groove of the next board that you will install and tap it against the spline until the two boards fit together tight.

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