Thin-Strip Cutting Jig With Micro Adjustment

How can you consistently rip-cut thin strips on a table saw to a precise thickness? How do you adjust the table saw fence to cut a groove with a precise width? Build this simple and inexpensive jig from easily available parts and you can get accurate cuts down to about 0.008 inches (1/128”) - at least in theory. That is more than you need for any woodworking project! I’ll show you how to build the jig.

5.25” by 10” by 1/2" Baltic birch plywood piece, dimensions flexible

A couple of hardwood blocks, 2.25” by 1.5” by 7/8” thick

1/4-20 threaded rod, about 12”

Two threaded inserts for 1/4-20

A few hex nuts 1/4-20

Wood glue

Table saw

3D printer if you have one, otherwise make the thumb wheel knobs and dial from plywood

A drawing of the jig is shown above and attached as thin-strip-jig.pdf.

Make a short piece (5 inches) of miter bar from hardwood, typically 3/4" by 3/8" cross section. I had a left-over piece from an aluminum t-track/miter bar which I used for this jig. Be sure the miter bar fits snugly into the table saw miter slot with no play. Attach the miter bar to the plywood board with recessed screws, about 4.75" from the short edge.

Cut a couple of hardwood blocks 2.25" by 1.5" by 7/8". Drill a 3/8” hole 5/8” deep into the wood blocks in the location shown in the drawing. In the same location drill a 1/4” hole all the way through. Screw the threaded inserts into the 3/8” holes. Then insert the threaded rod so that the two blocks are about 2.5 inches apart. Glue the two blocks to the plywood board while the threaded rod is in place. This insures proper spacing between the two threaded inserts.

3D print the dial wheel and a couple of thumb wheels, stl files attached. The thumb wheel lets you fix the dial wheel in a preferred position during use; for example where the main tick and handle is on top. The dial wheel has 8 tick marks. Each tick mark represents a 0.00625" adjustment of the threaded rod in or out. Accurate enough for wood working projects! Insert a short 3/16" dowel into the dial wheel for a crank.

An acorn nut fixed at the end of the threaded rod makes the contact with the table saw fence; and prevents scratching the fence.

First make sure that your table saw is properly tuned and adjusted; i.e. blade parallel to miter slot, fence parallel to blade and miter slot.

To use the jig you should first determine the actual kerf size of the blade. You need to do this only once for each blade you are using. Cut a 1/4 inch deep groove the width of your blade into a test board. Then set the fence and make a rip cut to trim one side of a second test board. Without moving the fence, set the jig into the miter slot and adjust the threaded rod/acorn nut so it just touches the fence. Then back off the threaded rod by a number of turns, e.g. 5 full turns of the dial. 5 turns will move the rod by (5 turns) ÷ (20 turns per inch) = 0.25 inches. Now move the fence against the rod/acorn nut and lock it. Remove the jig. Make another rip cut on the second test board. You should get a thin strip. Test the strip in the groove of the first test board. Repeat this procedure until the cut-off strip fits perfectly into the groove in your first test board. Write down the number K = one-half the number of turns for this cut; this corresponds to the kerf size of your blade. Keep this blade kerf parameter K for future reference.

To illustrate with an example, let's say you make 4 full turns of the dial to get a strip that fits perfectly into the groove, so your number K = 2. This corresponds to the actual blade kerf of (2 turns) ÷ (20 turns per inch) = 0.1 inch, which is a thin-kerf blade. The spec of my blade says 0.098" for the kerf! Pretty close!

You may round your blade kerf parameter K up/down to the nearest eighth to make the adjustments mentally easier. Experiment to get the value that works best for you!

As a rule of thumb, a full-kerf blade is about 1/8" (0.125") thick for a K = 2.5; a thin-kerf blade is about 3/32" (0.94") thick for a K of about 2. This is a good starting point for your calibration.

Now you can cut thin strips to any desired thickness. I use thin strips for splines in cutting boards and boxes. Thin strips are also used when you make curved or bend laminations. I have included a table for common widths, be sure to add your blade kerf parameter K to the value taken from the table.

Let’s say you want to cut 1/16” thin strips. 1/16” requires 1/16" x (20 turns per inch) = 1.25 turns of the dial. So take a board and make a rip cut along the left edge. Don't move the fence yet. Set the jig into the miter slot and adjust against the fence, just touching. Then back out by K plus 1.25 turns. In our example from step 2 you turn the dial 2 + 1.25 = 3.25 times. Now move the fence over against the acorn nut, lock it, and remove the jig. Make the rip cut and you have your thin strip at 1/16”. For each additional strip turn the dial again 3.25 times, move the fence over, and cut.

Another way to use the jig is for cutting grooves or dados to a precise width with a regular saw blade, no dado blade required. First, set the fence and cut the left edge of the groove. Set the jig into the miter slot and adjust it against the fence. The number of turns for the groove width is calculated like so: W = (groove width in inches) x (20 turns per inch). Then turn the dial by (W - K), and move the fence against the acorn nut. This will cut the right edge of the groove. After this remove the wood between the left and right edge doing multiple cuts. For K = 2 as in step 2 above, a groove that is 1/2 inch wide will take 8 turns between the left and right edge setting. Do some test cuts first on scrap pieces to fine tune the settings.

Groovy!