Marking Gauge for a Perfect Circular Saw Rip Cut

This easy to make tool is used to perfectly position a straightedge guide for a circular saw rip cut.
When I rip a long plank I usually use a straightedge clamped on both ends and slide along it with my circular saw. The problem is the accuracy of the position of the straightedge. Positioning the straightedge is a multi step process with some math first :

• measure the gap between the saw blade and the edge of the saw shoe
• add it to the size of the expected cut
• mark the result on both end of the plank
• position your straightedge and clamp it

Each of those steps may introduce errors or inaccuracy and you may end up with a cut that is not perfectly parallel to the reference border and has not the exact width you were expecting.

With this marking gauge, you:

• eliminate the math part
• make sure both ends are perfectly positionned
• can easily verify the position once the straightedge is clamped
• see exactly where the cut will be

optionally use it as a "regular" mortise and tenon marking gauge.

Materials:

• left over pieces of wood. (I used oak for mine)
• one 5mm screw
• one metal washer and small wood screw (optionnal)
• some glue

tools:

• saw (mitre saw is perfect)
• drill
• circular saw
• straightedge guide (I use a cheap aluminum masonry straightedge for those long edge rip cut)

Cut and sand a nice long square stick of wood (mine is 15mmx15mm and 25 cm long).

It will be the stem of the marking gauge

Next is the most critical part of the build...but it is easy.

Put the stem against the straightedge and hold it is place with some sacrificed plywood (the plywood has to be slightly thicker than the stem to allow the circular saw to slide nicely)

Adjust the circular saw to bite the stem...we do not want to cut it but just mark the stem.

Do this on the four sides of our stem.

Optionally you can turn around your circular saw and have a second mark (one for each side of the saw).

First, prepare the parts:

Cut a block of wood slightly bigger than the expected stock of the marking gauge (we will have two cuts in this block so the final size will be reduced).
Cut the stock in three pieces. One of them is slightly thicker than the stem (use the stem to mark for the cut) one will be the lower part of the stock the last one will be the upper part of the stock.

Cut into two parts the piece that has the same thickness of the stem.

Then glue, cut and sand:

Glue the lower part of the stock with the last two pieces and use the stem to have a perfect fit (see picture).

Remove the stem... let the glue settle down, sand and glue the upper part

Cut the edges of the stock to have a nice rectangle and sand it.

Drill a hole slightly smaller than the srew (I used a 6mm screw and drill an 5,5mm hole) in the stock.

I added a nice wood cap to the screw for easy operation. I used thermal glue.

Grind a washer and hold it with a screw on the other end of the stem.

This will allow to use the gauge has a marking gauge.

• Adjust the stem to the size of the rip cut you need.
• Place the straightedge with the marking gauge
• Clamp the straightedge
• double check the position of the straightedge with the gauge

You can now rip cut the plank and get a nice parallel cut with the perfect size.