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  1. #1
    Join Date
    Aug 2004
    Location
    Brattleboro, Vt & Arlington, MA
    Posts
    17

    Default 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. #2
    Join Date
    Nov 2005
    Location
    Chester County, PA
    Posts
    251

    Default 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 at 03:04 PM.

  3. #3
    Join Date
    Mar 2005
    Location
    Sol III
    Posts
    1,935

    Default Re: Calculating crown molding angles

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

  4. #4
    Join Date
    Nov 2006
    Location
    Atlanta
    Posts
    152

    Default 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.

  5. #5
    Join Date
    Oct 2004
    Location
    San Marcos, CA (Northern San Diego County)
    Posts
    491

    Default 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

  6. #6
    Join Date
    Jul 2006
    Location
    Agoura Hills, CA
    Posts
    195

    Default 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

  7. #7
    Join Date
    Oct 2006
    Location
    Western Mass
    Posts
    25

    Default Re: Calculating crown molding angles

    Big crown or small saw?

  8. #8
    Join Date
    Jul 2006
    Location
    N Ft. Myers FL
    Posts
    227

    Default 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.

  9. #9
    Join Date
    Jun 2004
    Location
    Staten Island, NY
    Posts
    534

    Default 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.

  10. #10
    Join Date
    Nov 2006
    Location
    Calyfornia
    Posts
    751

    Default 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

  11. #11
    Join Date
    Aug 2004
    Location
    Brattleboro, Vt & Arlington, MA
    Posts
    17

    Default 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.

  12. #12
    Join Date
    Aug 2004
    Location
    Brattleboro, Vt & Arlington, MA
    Posts
    17

    Default 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?

  13. #13
    Join Date
    Jul 2006
    Location
    N Ft. Myers FL
    Posts
    227

    Default Re: Calculating crown molding angles

    Quote 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.

  14. #14
    Join Date
    Jul 2006
    Location
    Agoura Hills, CA
    Posts
    195

    Default Re: Calculating crown molding angles

    Quote 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

  15. #15
    Join Date
    Dec 2006
    Location
    San Jose, Ca.
    Posts
    238

    Default 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...

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