Use this gauge for measuring the depth of dadoes, mortises, and other recesses where precision is critical.
I made my first rosewood gauge about a decade ago. The design is from an instructor at a woodworking course I took at the time. Since then, this gauge has become one of the most useful measuring tools in my shop; not a day goes by that I don’t use it. You can make a similar one in about 2-3 hours, spread over two to three days.
Select Your stock
Select a piece of straight-grained wood about 3/4″ x 1 1/2″ x 14″; I used Makore, a hard (39 lbs/cu. ft.) close-grained African wood. I chose Makore simply because I had some cut-offs that I had been saving for just such a project. Cherry, maple, or beech would also have been good choices. Even though the final size of the gauge is 2 3/4″ long, use long stock; it’s safer to mill. The 14″ stock is long enough to make 4 gauges. Use one for yourself, and the other three to give as gifts. I can’t think of a woodworker who wouldn’t love to receive one of these.
Mill the Stock
Ensure that your stock is square and uniform in thickness. Begin by bandsawing the blank in two, so that you have two pieces approximately 3/8″ thick. If you lack a bandsaw use a table saw. Next, thickness plane or joint the two blanks to around 5/16″ thick.
Rout the Channel
Now we’ll rout a channel in one of the blanks. Before doing this ensure that you have your ruler on hand. I use the 6″ Pocket Ruler from Lee Valley, as it’s extremely well made and not too expensive. I mark the approximate center of the blank, install a 3/4″ straight bit in my table mounted router, set the height to a hair’s breadth thicker than the ruler, then cut a test channel in a piece of scrap wood.
Run the ruler along the channel to see that it fits smoothly. Make any necessary adjustments, then rout the channel in your blank
Glue Up the Blanks
Now you’re ready to glue up the blanks. I use white glue. Don’t apply too much; you don’t want glue seeping into the channel. Clamp and let the blanks set overnight.
Drill Holes and Insert the Nut
Likely you’ll have to hand plane or joint the edges of the glued-up blank. Now you’re ready to drill the holes for the lock nut. Again, ensure that you have the brass bolt and nut before you start drilling. I used a 10-24 1 1/2″ brass bolt, which I cut in half. I used a shop grinder to round over the edges of the nut; it doesn’t have to be perfectly round, you just need to knock off the sharp edges. If you’re going to make four gauges, mark out four hole locations along the blank, allowing for a final gauge size of 2 3/4″ to 3″. If you are just making one, mark for one hole.
Drill holes for brass nut
Now you can drill 3/8″ holes the depth of the nuts. I find a drill press works best here, although you can use a portable drill. Next drill a hole slightly larger than the diameter of the bolt in the center of the 3/8″ hole. Only drill to the depth of the channel. Mix up a small amount of epoxy, lightly coat the sides of the nut, and insert it into the 3/8″ hole. Clamp and let it dry. When dry you can file or sand the nut flush with the blank. Now you can cut the body of the gauge to length. I like mine about 2 3/4″ long. Ensure that you cut the ends square to the body. Lightly sand the edges of the gauge.
Make a Knob
You need a knob to hold the ruler from sliding in the channel. I cut a piece of wood that measures about 3/4″ square. Drill a 1/2″ deep hole into the end grain of the knob the same diameter as the bolt. Mix up another bit of epoxy and glue the bolt into the hole. No need to clamp, but let it dry overnight. Then carve the knob to a pleasing shape.
That’s it! You can leave the gauge ‘au naturel’, or apply an oil finish. You’ll find this gauge fits nicely in your apron pocket, and is a lot handier to use than a hand held ruler alone or a measuring tape.