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Miter Angles and Miter Saws

Miter saw gauges confuse a lot of finish carpenters for one simple reason—they aren’t designed for finish carpentry, they’re designed for framing and stairs. Let me show you what I mean.

When a framer builds a roof, they first establish the PITCH of the roof—4/12 or 6/12. That pitch is the angle the rafters follow. All of the cuts made to that rafter—the ridge cut, the plumb cut, and the birdsmouth are all measured off the BACK of the rafter—off 90 degrees to the angle of the roof.

(Note: Click any image to enlarge.)

That’s why most miter saw gauges are set up off 90 degrees to the back of the fence! In fact, some miter saws even include roof pitch angles on the miter saw gauge.

But those angles just confuse finish carpenters. Finish carpenters are always bisecting corner angles—which is easy to do with a protractor.

A 135 degrees angle looks like this:

A 135 degree angle is an OBTUSE angle. The miter for this corner is 67 1/2 degrees. That's easy to cut on your miter saw. Just set the saw at 22 1/2!

But the angles on a miter saw gauge are off 90 degrees to the angles on a protractor, which causes a lot of confusion. Some carpenters opt to use a Starrett Protractor. But I prefer to have the guys on my crew use a standard protractor, so they’ll know at a glance the difference between an acute angle and an obtuse angle. That means when they visualize the miter, they’ll be starting off on the right foot!

A 22 1/2 degrees angle is an ACUTE angle. You can't cut that miter on a miter saw without an acute angle jig.

Miter saws didn’t always come with miter saw gauges that were set 90 degrees off from protractors. Back before framers used miter saws, finish carpenters could use a protractor to read corner angles without any confusion.

Miter saw gauges like this one (see photo, right) were easy for finish carpenters to use, and didn’t cause another problem: Let’s say you’re installing base molding at a corner that measures 86 degrees. You first bisect the angle and determine that the miter should be 43 degrees. But when you set your saw at 43 degrees and cut the piece, the miter is NOWHERE near close! That’s because 43 degrees on a standard power miter saw gauge is really 47 degrees.

The easiest way to solve this whole problem is to use a Sharpie to mark your miter saw gauge with protractor numbers.

In fact, some manufacturers include protractor angles on power miter saws:

I just wish they all did!!!

• • •

AUTHOR BIO

Jesper Cook was born in Stockholm, Sweden in 1977. He grew up in family homes in both Sweden and Denmark until the age of 18, when he moved to Los Angeles, CA.  He has worked in the construction trade for over 10 years, gaining experience in everything from movie sets to tile installation.

More recently, he has focused on high-end finish carpentry. He is currently a Project Manager at Millworks By Design, a finish carpentry company located in Agoura Hills, CA.

Jesper enjoys SCUBA diving, mountain biking, and especially photography, which he practices in his free time. Recently married, he and his wife, Julia, spend their vacations traveling Europe and visiting castles, museums, and other historical sites. He often draws inspiration for his finish carpentry work from classical architectural details that he has photographed in cities throughout Europe, such as Paris, Rome, and Seville.

Comments/Discussion

29 Responses to “Miter Angles and Miter Saws”

  1. Fred stinard

    At this point in my career as a fine trim carpenter or any of the guys work for me can’t figure it out with out the tool telling them what to do it becomes time to hang up the tool belt. This is entry level at best.

    Reply
    • Marc

      Your implication is that NO ONE that has only entry level skills is/should be reading this article, thus it has no business being published…correct? I read a LOT of stuff that I know is entry level, doesn’t discount the quality of the content though now does it…especially if you are an entry level carpenter.

      Unless of course you are one of those mystical wood wizards who NEVER had to learn ANYTHING from ANYBODY. Seriously Fred, look back at your comment and tell me WHAT it contributed to the discussion of the article content.

      Reply
      • Dan

        Marc, i think you may have “hit the nail on the head” with your comments to “Mr.” Fred Stinard. i wish i had the way with words you have shown, i think we would both end up at the same point; but my comments would have been censored…lol

        Reply
    • David Luyendyk

      This article is categorized as “Building Basics”. It’s supposed to be entry level. ThisIsCarpentry is for anyone who wants to learn, regardless of where they are at. That’s what makes this a great place.

      Reply
      • Gary Katz

        What David said!!!! This is an INclusive magazine. Not an EXclusive magazine. Some of our readers will be drawn to the OTT articles, like drawing and carving a volute; other readers will be more interested in how to cut miters in casing! We make room for them all. That doesn’t mean we have to dumb-down the articles. If one of our weekly stories doesn’t interest you, wait a week or two.

        Gary

        Reply
    • David

      Fred, you suggest that you need no reliance on tools to calculate and cut angles in wood, right? Maybe–and more correctly–you are suggesting that you try to use your mathematical aptitude to determine angle measurements. Most trim carpenters I know are extremely detailed and reading blueprints has come easy to them over the years. If you read this article in detail like a carpenter would a blueprint, you should have noticed the target audience, which are those people desiring to learn basic carpentry. The category of audience was the first thing listed. A great trim carpenter rarely overlooks obvious details. If you were on my crew, I would offer you many challenges that I’m quite certain you would not be able to complete without generous assistance. There is always someone more knowledgeable and skillful than ourselves. The people I met of this caliber never gloated and always enjoyed teaching and sharing what they know. What prompted you to read this article anyway? Exactly!

      Reply
  2. Mike Hawkins

    Hi Jesper,
    Nice article. I have two different protractors, a starrett, and I forgot the name of the other one. Both have two scales, one shows the actual angle, the other shows the miter saw angle. I use it mainly to check corners when running base and crown to see how far off the corner actually is. I never think of rafter angles and miter settings in the same sense. I don’t cut rafters that often, so I usually lay them out with a framing square and then transfer the angle to the miter saw.
    Mike Hawkins

    Reply
  3. Laurie McDougall

    yup, this is pretty much what I do. I first heard of this several years back, when someone on a crew said to us “1/2 the reciprocal” it took me a while to figure that out, but when I did- wow! It was like what Dan said above, a light went on! This is the basis for my trim carpentry business. I often see trim work in people’s homes that was done by someone who does not know of this technique.
    I actually use a shortcut to get my settings. I measure the corner with my bosch miter finder, “whatever happens to one side of 90 degrees, do the same to the other side” so if my reading is 92 degrees, that’s 2 over 90, so two from 90 is 88- miter setting is 44. It takes longer to say than do,
    I kinda like what Jesper’s done with his saw though, putting the correct angles onto the saw scale, that could save me time.

    Reply
  4. Norm Miller

    Hmmm…no one mentions coped corners, which will forgive several degrees out of square. Where it really gets interesting is those very acute angles at the ceiling where you have to run large, often multiple piece crown and coping is not an option. I’ve tried several different gauges, yet it always seems to come down to several test cuts to find the right compound angles for the right fit. As to outside corners, the drywall bead & mud always puts the cut out of 90. I found years ago to get in the habit of setting the saw a tad over 45 for these and it usually worked out well.

    Reply
    • Gary Katz

      Norm,
      This article was really about understanding miter angles–which does play a part in cutting cope joints, too, but it wasn’t about coping. And the story wasn’t about cutting acute angles–though this article does play a part in figuring out the miter angles for acute angles–so you DON’T have to hunt-and-peck for the right miter/bevel angle! But Norm, those are great suggestions for future articles! Which one (s) do you want to do? :)
      Gary

      Reply
  5. Roger Gendron

    Hmmmn.. I am a little confused. An inside corner of 86 degrees bisected should be 43 by my arithmetic. Since 45 degrees is the one point that is the same on either scale, 43 using the “outside” or “factory” numbers appears to be the same as 47 on the “inside” or “hand written” scale. So why wouldn’t the cut join properly at 43 degrees? (did I miss something?)

    This debate has been going on for years, and why I was interested in a Festool Kapex, as overpriced as it is. The protractor, or angle finder, that comes with the machine, is essentially a tramel that moves the center leg in direct proportion to the outside legs, and will bisect most angles I run into; abtuse or acute. Take the angle off the walls, put the tramel against the fence, line up the laser and cut.

    You don’t need a Kapex to use this method either; a protractor will work against your miter saw fence almost as well, albeit there is the short extra step of bisecting the angle on the protractor (divide by 2, then reset the protractor to that number).

    Do we really need all those numbers on the machines?

    Reply
  6. Kevin

    As a basic article I think it is more important to teach the proper methods, not add crutches. Some miter gauges run from 0 and some from 90, know the difference and how to deal with it. Any time you can use a bevel gauge to get close that’s good but all of gauges that translate or marking it on your saw is just a way around understanding and knowing your craft and tools.
    Signed “Old School”

    Reply
    • roger

      “Proper” methods? “knowing my craft?”
      Old School, Old profits.

      Reply
  7. Sternberg

    I bought a machinest’s vernier protractor, and use it often, None of the miter saws or digital protractors are accuarate within 1/10th degree, which isn’t good enough for a wide crown. Incra or someone needs to offer aftermarket vernier protractors for some of these compound miter saws. They would save a lot of trial and error.

    Reply
  8. Mike

    I am not a contractor, just a semi handy homeowner who enjoys learning new carpentry techniques. I appreciate this sites comprehensive and inclusive wood working information! There are articles here that at this point are far too advanced for me, but I enjoy them and take from them what I can. Everyone learns new tasks in a variety of ways and this explanation was helpful for me. Thanks and keep up the good work.

    Reply
  9. Roger Gadd

    Boy! this is a real head scratcher for me. I’m good at math (or I thought I was) and don’t have any problem with almost anything to do with math. My mitre saw is on a job site so I can’t play with to see if I can figure out what you are saying. I do use the Starrett and would be lost without it. I’ve gotta spend some time on this one!

    roger

    Reply
  10. Roger Gadd

    Ahhhhhhhhhhhhhh! Now I get it!
    I never could understand on my mitre saw how a 90degree cut registered 0.
    Anyways I use my Starrett and it’s settings are based on a mitre saw so I won’t have a problem but I now understand if I use an ordinary protractor.
    On the job site today we all had an awakening when we took the time with the saw and what you described.
    Great article.

    Roger Gadd

    Reply
  11. Jesper Cook

    I’m glad you figured it out! That is exactly why I wrote this article – I figured there are many carpenters out there who don’t quite understand the scales on their miter saw. But once they understand it the tricky angles become a lot easier to work with.

    Jesper

    Reply
  12. Ed

    Jesper, thanks for a good article. I am a retired engineer and understand complementary angles and such but an article that puts it into simple perspective is a great help. Often people do things by rote without understanding what is actually happening. I am making jigs for my RAS to cut 45 and 67.5 angles for kitchen countertop edging and “googled” your article just as a sanity check to aid my preparations for the 67.5 jig.

    Reply
  13. Jackie

    Jesper,I was looking for an easy way to learn how to miter the baseboards for our basement. I’m more of a show me how and I can do it kinda girl. I think I need a class! Thank you for the info tho :)

    Reply
  14. John

    Thanks for this Jesper. I just bought my first miter saw to do some crown molding. After my first two cuts, I realized what had happened. I’m sorry I didn’t read this article first. Oh well… DIYers have to learn somehow. :/

    Reply
  15. Rich

    Not a pro, but I’ve installed over $6k of millwork in my house, and used a vintage Stanley No. 30 Angle Divider, a No. 358 Miter Box, and a shooting board with a Veritas (Lee Valley) low angle jack plane. Great combination of old school tools; the only downside is you have to know how to sharpen a handsaw, and keep your plane iron sharp as well. Most of the time I didn’t need the shooting board. Result is tight and accurate miters. The box is incredibly accurate, and by using the angle divider to transfer the measurements you eliminate calculation error. Great tool.

    Reply
  16. Dan

    This information is great for the weekender….I have the tools to do the honey do list, and get to make plenty of saw dust….but when you go for months or even years between moulding projects…its nice to have a resource to brush up on the old basic logic….

    Reply
  17. Robert

    Thanks for the information but you left off cutting 22 1/2 mitres. I am getting ready to install crown in a kitchen with a corner cabinet and have always just had to keep back cutting the cope to get it to fit. Is there an easier way?

    Reply
  18. Gene Henderson

    Wisdom is in the basics. The A-ha moment has come to me by falling back to basics to figure something out. If anybody becomes too sophisticated for the basics their work probably sux.

    Reply
  19. mike

    Iam still missing something in this article. Half of 86 is 43 but how does 43 become 47 on the miter saw.

    Reply
  20. Ken Ackerman

    Mike,

    Consider this explanation: The outside most (or lower if you prefer) scale shown on most miter saws starts at 0 degrees in the center. At 0 degrees, the angle you leave on the board cut is 90 degrees, as we all know. 90 degrees is the reciprocal angle of 0. All cuts on a straight board leave 2 angles as measured with a protractor. Those 2 angles always add up to 90 degrees, so the angles are always the reciprocal of one another. That lower or outer scale always describes the angle the saw head swings through, which is NOT the angle left on the board if you were to measure it with a protractor, that scale is the reciprocal of the angle left on the board.

    As Jesper pointed out, the scale on the older miter hand saw box starts at 90 degrees in the center and decreases to either side. That scale always shows the angle left on the board and that’s why trim carpenters were never confused by it.

    Here’s a picture of my Incra miter gage that has both reciprocal scales as Jesper’s mark up showed. I zoomed in so you could see the actual numbers. The upper scale starts at 90 and decreases angle wise from there (both sides) it’s the scale that tells you the angle left on the board. The lower scale starts at 0 and increases angle wise from there (both sides).

    As you can see from the 1 degree marks between 50 & 45 degrees on the lower scale, the yellow line at 47 degrees points directly to 43 degrees on the upper scale. Maybe it’s easier to remember the upper scale as the angle-angle-on-wood scale and the bottom scale as the angle-the saw blade-travels scale. Reciprocal numbers. That’s how 43 degrees becomes 47 degrees.

    My Swedish carpenter grandfather used to tell me that Loki the Norse God of tricks invented the zero centered scale to confuse every one.

    Reply

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