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  • Calculating crown molding angles

    Is there a formula to calculate the plumb and miter cuts on outside crown corners from the step angle of the crown?

    In his book, Gary uses a Bosch tool to figure this out; I do not have said tool.

    Thanks

  • #2
    Re: Calculating crown molding angles

    Buy this book:
    http://www.compoundmiter.com/

    From them you can also purchase their "true angle" tool which will give you accurate inside and outside angles. Their true angle tools are plastic, but will get you started.

    You should eventually upgrade to a Starrett Protractor, which you can get below:

    http://www.amazon.com/Starrett-505A-...6?ie=UTF8&s=hi
    Last edited by MiterMaster; 12-15-2006, 03:04 PM.

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    • #3
      Re: Calculating crown molding angles

      Crown Math Thread
      "I cannot teach anyone anything; I can only make them think." - Socrates

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      • #4
        Re: Calculating crown molding angles

        Get said tool. It's well worth it. The 2 seconds that you have that thing in your hand saves losing your hair by scratching your head like me. I waited and waited and thought and thought and finally got it a few weeks ago. It's one of those tools that when you need it the expense is an afterthought.
        Just riding down the road throwing chicken bones out.

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        • #5
          Re: Calculating crown molding angles

          I run a lot of crown, use the Bosch Angle Finder, and also the plastic angle finder previously mentioned (they come in at least 3 sizes, the longer length you can use, the better), along with a Miter/Bevel chart. I insist on extra material, so can make up samples into each corner, long enough to obviate the hump of drywall mud in the corner.........................steve
          When I get a little money I buy books; and if any is left I buy food and clothes.
          Desiderius Erasmus

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          • #6
            Re: Calculating crown molding angles

            Any reason you are not cutting the crown at angle? You understand that if you simply install crown stops and stand your crown against the fence and the base then you cut a 45 degree angle everytime (if you cope) or within one or two degrees if you don't.

            -Allon

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            • #7
              Re: Calculating crown molding angles

              Big crown or small saw?

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              • #8
                Re: Calculating crown molding angles

                This http://www.hartvilletool.com/product/12201

                and the small starrett have replaced my BAF. It never comes out of the van anymore.
                Greg.

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                • #9
                  Re: Calculating crown molding angles

                  You can find the angle of a wall corner with just a bevel square and using the angle scale on you miter saw. This link shows the process. http://www.josephfusco.org/Articles/...wnscript.html#

                  Granted that this might not be as nifty as BAF or some other gadget but it will be just as effective. If you know for sure that your crown is a 52/38° or a 45/45° you can just download a chart from the web. Here is one: http://www.josephfusco.org/Articles/...rownChart.html

                  If you are using a crown with some other angle than you can always use one of the many online calculators to figure the miter and bevel cuts:
                  http://www.josephfusco.org/Articles/...ownscript.html

                  You could also just plug the numbers into any scientific calculator using this formula:
                  miter = tan-1(( sin(crown angle) / tan( wall angle / 2 ))) for any angle of crown or wall.
                  bevel = sin-1(cos(crown angle) * cos( wall angle / 2)) for any angle of crown or wall.
                  www.josephfusco.org
                  www.constructionforumsonline.com

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                  • #10
                    Re: Calculating crown molding angles

                    Joe,
                    Great info. On the math for figuring crown angles. I've always carried a small cheater card in my truck for bevel and miter angles derived from the spring angle. But I am always more comfortable knowing where the numbers come from My reg. calculater is long lost. do you know what the equivalent sequence would be on a construction master?
                    Thanks a bunch
                    Andy

                    BTW if anyone is interested in a great book on understanding trig on the job look for Math To Build On, A book for those who build.
                    by Johnny and Margaret Hamilton. Invaluable

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                    • #11
                      Re: Calculating crown molding angles

                      Thank you for all your comments and suggestions. I can work my way through the formula until I feel the cost of the Bosch tool is cost effective.

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                      • #12
                        Re: Calculating crown molding angles

                        Amazon users gave the Starrett tool mixed reviews for accuracy. Some loved it; others found it off by 1/2 deg or more. Quality control in mfg?

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                        • #13
                          Re: Calculating crown molding angles

                          Originally posted by kiptewksbury View Post
                          Amazon users gave the Starrett tool mixed reviews for accuracy. Some loved it; others found it off by 1/2 deg or more. Quality control in mfg?
                          First time I've heard anything bad about the Starretts. I wouldn't rely too much on the reviews at Amazon, could be anybody reviewing it.
                          Greg.

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                          • #14
                            Re: Calculating crown molding angles

                            Originally posted by kiptewksbury View Post
                            Amazon users gave the Starrett tool mixed reviews for accuracy. Some loved it; others found it off by 1/2 deg or more. Quality control in mfg?
                            1/2 a degree? That is too minor to be an issue, but it begs the question: How did they know the Starlett was off by half a degree? There are a variety of ways to calibrate, but I think they all have more than a half-degree of tolerance outside of using manufacturing tools for calibration.

                            But still, is there a reason you need to cut the molding on the flat?

                            -Allon

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                            • #15
                              Re: Calculating crown molding angles

                              I bought the BAF a long time ago... First I did the math thing for a few years, but that got old really fast... Best 100.00 I ever spent. Its Also great because I can give a quick 10 minute lesson to the aprentice and off he goes to start cutting my corners...
                              "any society that puts equality ahead of freedom will end up with neither. But the society that puts freedom before equality will end up with both greater freedom and great equality. "

                              Milton Friedman

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