How to Set a Miter Gauge for 45 Degrees

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2 Responses to “How to Set a Miter Gauge for 45 Degrees”

Jay April 7th, 2020

So, here's the situation: I built 5 colonial spinning wheels per instructions from an article by W. Clyde Lammey in Popular Mechanics from 1934 ("Colonial Spinning Wheel You Can Build" - it can be found on the Web with difficulty). The large wheel itself (built from 61 individual pieces) is 19 1/2" in diameter, and the rim is made up of 3 layers of 12 trapezoidal pieces that are 5 3/8" length at the base and 3" wide. The trapezoid's angles are 15 degrees. So for each piece, there are two 15 degree cuts that have to be made "exactly" while maintaining the critical 5 3/8" length. How any of this could have been done using the available tools of that time period during the height of the Great Depression is another matter. But I have the advantage of digital tools, a router table, a 14" HF miter saw and a Sears 10" table saw with the usual miter gauge we all know and love. As each layer of 12 pieces is assembled, any error is potentially multiplied 24 times (2 angles x 12 pieces). Thus, the last piece never exactly fits well during a trial assembly and once glue is applied, it is even more off. I have tried making a "perfect" template and used it as a pattern on the router table, but it doesn't seem to matter since I can't make those perfect 15 degree angle cuts, the template moves slightly and the bit's bearing mars the template's surfaces during routing (and it's dangerous). On the table saw, there is too much play in the miter gauge slot to even hope for any kind of accuracy. The miter bar has to be slightly smaller than the 3/4" slot or it won't slide (a 3/4" dowel won't fit in a 3/4" hole!). Here's another situation: I have constructed several mitered, round, game tables with a 40" diameter. These consist of, naturally, 4 initially triangular pieces, 40" wide at their bases, cut at 45 degree angles. To get the angles correctly drawn, I use a good 24" combination square. The sizes of the pieces makes it too large for the table saw's miter gauge or the HF miter saw. Using a band saw or good jig saw and then running the cut edges (carefully) over a jointer doesn't get you the required exact 45 degree angles. The closest I can get is using a long, hard maple straight edge as a router guide. After the edges are cut, the router table is used to create the glue joint cuts so that the 4 pieces intersect along the 4 miters. But it's never perfect. Pipe clamps certainly help. (Afterward, the square table top is cut with a Rockler circle cutting router jig, etc.) That perfectly straight cut, the exact angle, the perfectly centered hole - they remain elusive in spite of laser guides, digital angle finders, planer, jointer, drum sander, drill press, various saws and routers. When you add to that dust and insects landing on your polyurethane finish and uneven primer and paint results, what a challenge to woodworking!

Gary April 6th, 2020

This works great if your framing square is actually square. Stamped out framing squares you buy tend to be out of square due to the heating and cooling of the metal. Check your square for square and if need be, square the framing square before you trust it for accuracy. A degree or two off square will create problems, especially with things like picture frames. A master carpenter friend of mine taught me how to do this. Knowing him to be a perfectionist, I had him square all of my squares. Never had a problem after that with getting accurate angles.