Trim Carpentry Techniques:

Flattening A Cupped Board
With Multiple Saw Cuts

In This Article:

Multiple saw cuts are made in the back side of a badly-cupped cedar 1x8 to make it flexible enough to lay flat.

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Skill Level: 3 (Intermediate) Time Taken: About 15 Minutes

By , Editor



Cupped trim lumber. The top board on this stack of cedar 1x8's was badly cupped.

I knew this degree of warpage would make it difficult to force the board flat when it came time to install this piece of lumber on the porch trim I was repairing.

Note that these boards all have a narrow strip of wood attached to one edge. To match the existing material on the century-old house, I needed boards just slightly wider than the 7¼" width of a standard 1x8, so I tacked a strip of cedar to one edge on each piece of 1x8.

I could have simply bought 1x12 cedar boards and ripped them to the desired 7¾" width, but we couldn't find decent-quality 1x12's at Home Depot or Lowe's.

First I removed the blade guard/splitter on my table saw.

Then I adjusted the height of the blade so it would cut about half of the way through the board.

Since rough-sawn cedar is about 7/8 inch thick, I set the blade height at about 7/16 inch.

Setting the height of the table saw blade, guard removed.


I set up the fence so the first cut would be about 2½ inches from the edge of the board.

Most of the curvature seemed to be near the mid-section of the board, so I didn't see a need to make saw cuts in the outer flat strip of wood.


After cutting the first saw kerf (red arrow), I moved the fence over one-half inch and made another cut.


After I made each cut I moved the table saw fence another ½ inch farther away, and ran the board through again.


After cutting 8 saw kerfs the back side of the board looked like this. Cedar 1x8 with multiple saw cuts to allow cupped board to lay flat.


I could press on the board and force it almost flat against the saw table.

This made me confident that I could force this board to lay flat when I fastened it.

Caution: Be careful when using a table saw without the blade guard and splitter. Obviously it's important to keep your hands away from the unguarded blade. Without the splitter and the attached anti-kickback pawls there is a possibility that the board could bind in the blade and be kicked backwards. If your hand is near the blade when that happens your hand might suddenly come in contact with the blade. Keep your hands away from the blade area.

More Info:

Tools Used:

  • Table Saw
  • Roller Stands
  • Ruler or Tape Measure

Materials Used:

  • 1x Trim Lumber
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Written October 22, 2007