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17th April 2020, 01:12 AM #1New Members
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Need help calculating proper miter angle
While under quarantine during the pandemic, I’d like to take some time to build wayside chapel pillar in the style of those in my parents’ Lithuanian homeland as a sort of a memorial to the event. I’ve attached some sample pictures to give you an idea of what I am talking about. I could use some advice on one part of the project—that is determining the proper angle to use to miter the roof panels. As you can see from the attached pictures what I am trying to do is construct a hip roof with 4 equal sides that come together like a pyramid—just unsure how to calculate the angles of the miters to make this happen. Any guidance would be greatly appreciated! Thanks.
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17th April 2020, 02:16 PM #2GOLD MEMBER
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time to break out the maths
What are the dimensions (roughly, or exactly if you like)? Basically the key will be the "aspect ratio", the height of the peak from the bottom edge, so that you can start to work out triangles and from that angles. Oh, and we work in mm here, none of that imperial guff... even though my name is one of those
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17th April 2020, 02:32 PM #3
There is an easy way depending what type of saw you have: table saw, mitre (chop)saw or SCM (sliding compound mitre) saw
The person who never made a mistake never made anything
Cheers
Ray
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17th April 2020, 06:31 PM #4
The attached spreadsheet should sort you out. Sorry it's in metric rather than feet & inches, but if you use inches & decimals you'll be OK.Compound Mitre Angles (version 1).xls
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17th April 2020, 09:07 PM #5GOLD MEMBER
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If it’s a 4 sided figure, the angle of the mitre on each side is always 45degrees.
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17th April 2020, 09:19 PM #6
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17th April 2020, 09:21 PM #7
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18th April 2020, 07:55 AM #8GOLD MEMBER
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So, it’s 45degress, like I said initially. But then those 45 degree cuts are at an equal angle to the base, whatever angle that may be to get the desired pitch of roof, meeting at a point at the apex, forming a pyramid. Did you even look at the little roof over the statues in the photos?
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18th April 2020, 09:26 AM #9
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18th April 2020, 09:39 AM #10GOLD MEMBER
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Number of sides 4 (cell b1 - data entry) Angular bend (degrees) 90 (cell c1 - calculation). Formula: =360/b1 Tilt angle (degrees) 75 (cell b4 - data entry) Cross cut angle (degrees) 14.51 (cell b9 - calculation) Formula = DEGREES (ATAN(COS(RADIANS(B4)) * TAN(RADIANS(B2/2)))) Blade tilt angle (degrees) 43.08 (cell b10 - calculation) Formula=DEGREES(ASIN(SIN(RADIANS(B4)) * SIN(RADIANS(B2/2))))
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that's from Alex's spreadsheet (which opened fine for me)
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18th April 2020, 10:04 AM #11GOLD MEMBER
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Unless you are cutting by hand you don’t need to know the compound angle.
As Riverbuild and RWbuild have said. Set your saw of whatever variety to 45 degrees and then cut to your pitch angle and you have created your compound angle
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18th April 2020, 10:11 AM #12GOLD MEMBER
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18th April 2020, 01:52 PM #13
Thanks Brett. Here's a screenshot. If you type the things in cells F2, F9 &F10 into cells B2, B9 & B10 of your spreadsheet, without the inverted commas, it should work. The things in blue are the numbers you enter, the things in yellow are the numbers you need.
Screen Shot 2020-04-18 at 12.42.26 pm.jpg
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19th April 2020, 10:12 AM #14GOLD MEMBER
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19th April 2020, 10:53 AM #15GOLD MEMBER
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neither? Building a birdhouse basically Or sending it TO the moon. I'm sure you need at least two other formulae to get it back as well
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