How to Set a Miter Gauge for 45 Degrees
George VondriskaDescription
Setting the miter gauge on your table saw to a perfect 45-degrees can be very challenging. And, if you’re planning on making picture frames, being just a tiny bit off will be a deal breaker. But here’s great news. You’ve probably already got a tool in your shop that will give you the precision you need to set your miter gauge perfectly, allowing you to get an exact 45-degree cut.
Angles from squares
The amazing set-up tool for this operation is……a framing square. Yep, the lowly framing square. Used correctly, it’ll allow you to pivot the miter gauge to just the right spot for a perfect 45-degree angle. Thanks to the size of a framing square, you’ll get excellent accuracy.
Accurate picture framing
This video will help you get the miter gauge correctly set so you can accurately cut angles, but remember that there’s more to good looking picture frames than simply having the angles right. You also need to be consistent with the lengths of your parts. Each side needs to be exactly the same length as the opposite side. The best way to accomplish this is by using a stop block on your miter gauge.
But wait, there’s more
This is just one nugget of a tip that WoodWorkers Guild of America has for you. Make sure you’re getting the most of out your shop and your tools by checking out more great shop tips.
If you're lookin' for a really easy and accurate way to set a miter gauge for 45 degrees, got you covered. All you need is a framing square. And here's what's cool about this, is the scale of a framing square is so large that's what makes it easy to be really accurate. Here's what we're gonna do. You need to use the same number on the inner legs of the framing square and set those numbers on the edge of your miter gauge slot. So it looks like this, I get one leg of the framing square against my miter gauge, pivot this, and the number I'm gonna use is eight. That means I'm gonna get the eight closest to me on the edge of the miter gauge slot, the eight on the other end on the miter gauge slot. And you're gonna have to do a little messing around back and forth here, sliding the framing square in and out, and pivoting the miter gauge until it aligns perfectly, and both spots looking for the hash mark on eight to be right on the edge of my miter gauge slot. When I have that in both positions, lock the miter gauge and we're ready to cut at 45 degrees. Now, if you want to be ambitious you could do a little bit of geometry. And, of course, if we use those numbers being identical for 45 we could do some math, and figure out where do we need to be? What numbers do we need to use for 30, 25, 20 for any angle you want to use? Just takes a little bit of trig to get that figured out. But the framing square makes this nice and easy and, most importantly, easy to be accurate which is, of course, really important, if you're gonna use your miter gauge for cutting miters.
Great, informative video!
That is assuming miter gauge slot is exactly parallel to blade.
As George says, for a 45-degree cut (for four miters) 8 inches and 8 inches works (as would any two matching measurements.) Here are numbers you can use for other angles: 60° (three miters): 12.125" (12 and 1/8th) on the near leg f your square, 7.0" on the far leg 36° (five miters): 7.5" on the near leg, 10.3125" (10 and 5/16ths) on the far leg 30° (six miters): 7.0" on the near leg, 12.125" (12 and 1/8ths) on the far leg 25.71° (seven miters): 6.0" on the near leg, 12.5" on the far leg 22.5° (eight miters): 5.0" on the near leg, 12.0625" (12 and 1/16th) on the far leg 18° (ten miters): 3.25" on the near leg, 10.0" on the far leg 15° (twelve miters): 3.75" on the near leg, 14" on the far leg Keep in mind that the farther you get from 45°, the harder it's going to be to set the measurement on the far leg of your square accurately, since it'll be hitting the miter guage slot at an increasingly steep angle.
I have drafting triangles in 30-60-90 and 45-45-90 that I use. I measure against the flat of the saw blade. For those that need "a little help with the math," use the tangent function available on your phone, computer, or calculator. tan(angle) = side opposite / side adjacent. This works much better with metric than English measurements if you are doing really odd angles, though. Unfortunately, I don't have a metric framing square :-) But I can take some scrap picture matting that happens to be 40" (1000mm+) on long edge. https://www.mathopenref.com/trigtangent.html
Great post. Thanks for the tip. I have a question though: If i set the pointer at 45 degrees using this technique, and then move the gauge to the 45 degrees in the opposite direction and the framing square technique indicates that I am still right on, does that mean I can trust the scale on the gauge for other angles?
I like your idea! A computer program to yield low integers defining our common angles would be fun to write. 22.5, 30, 60 would be fun to know in whole numbers on a framing square.
Setting the miter gauge to 45 degrees is not good enough. There has to be some play in the miter gauge slot or the miter gauge wouldn't slide. That play could be up to 1 degree, so you're going to be off for those long cuts. Even 90 degree cuts are problematic. You need some way of clamping the board to the miter gauge or it will move and rotate as you cut, giving you a very inaccurate cut. You can forget about using a miter gauge if cutting 45s on a wide board (or even 90 degrees, for that matter). Basically, the table and/or your arms are not long enough and you will not be able to either start or end with the miter gauge still in its slot. Lastly, using a miter saw, you can easily cut at 45 degrees, but that is limited to cuts of up to about 14 inches in saw travel and the longer cuts are just not accurate enough. To get really close on a 45 degree cut in a wide board, you will need a long combination square, and anything longer than 12 inches is expensive if it's any good. Next, you need a wide straight edge of at least 5-6 inches. Lastly you need a router with a flush trim bit that will follow the straight edge (clamped to your work piece) as a template, making sure it is 45 degrees with the combination square. It's best if your flush trim bit has a bearing on both the top and the bottom. Make sure that the grain is in the direction you are routing or the result will be a climb cut, potentially ruining your work piece. Using the router method, you can get really close to 45 degrees and you are not limited in the length of that cut. An example of where this came in handy: I was building a round game/card table, 40 inches in diameter. It had a 16x16" chess board in the center and the 4 sides mitered into the each other and the board. Glue joint were used for all joints (other than the chess board). The sides were red oak, the board hard maple and walnut. Until using the router method for the 45 degree angles, it was trial and error with a lot of pipe clamps!
This also assumes that your framing square is square. Most people don't check this very often and, when framing large items such as a house, the framing square being a little off is not usually a problem. However, for miters, it is. If you haven't checked the squareness of your framing square recently, now would be a good time to do so.
Eyeballing methods like these can get you close and if you're lucky, dead on. How all four corners of a mitered frame come together will determine if further fine-tuning is warranted.
Line up the numbers on the slot before sliding the miter gauge against it. This will save some trial and error.