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Author Topic: Math question for collar beam angle?  (Read 719 times)

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Offline Lennyzx11

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Math question for collar beam angle?
« on: September 14, 2023, 06:15:49 PM »

Whats a math or framing/speed square way to solve for the
Collar beam to principal rafter angle in order for it to end up level?
Id like to cut the 1 housing appropriately also.
Do I cut the mortise square to the rafter or also angled? 
With 45 degrees such as braces it works itself out but Im having trouble converting to the 9:12 pitch Im using.

This coincides with making the post to rafter connection plumb but I think that just means cutting the top of the post at the 9:12 slope/pitch.



 

Thank you,
Lenny

Southwest corner of Vermont

Offline GRadice

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Re: Math question for collar beam angle?
« Reply #1 on: September 19, 2023, 09:31:10 PM »
If I understand your question correctly, the angle at the end of the collar tie is also 9/12, the same as the roof pitch and the same as the angle on the top of the vertical post.

I can't answer your question about the mortise and tenon since I have no experience with something like that.
Gary

Offline Don P

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Re: Math question for collar beam angle?
« Reply #2 on: September 22, 2023, 09:20:27 AM »
There's several ways.

Math;
Pitch angle= atan(rise/run)=36.86
Deduct that from 90 to get the complimentary angle=53.14
Remember the sides of a triangle add up to 180

Framing square, this is the real way in the field. 12" on the blade, 9 on the tongue. The tongue is the plumb cut, the blade is the level, seat cut.


 

With a speed square you can pull angles from the framing square layouts and read degrees;


 

 


Draw it to scale and use a protractor, or in software a protractor function;


 

I'm sure there are more.
The future is a foreign country, they will do things differently there - Simon Winchester

Offline Lennyzx11

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Re: Math question for collar beam angle?
« Reply #3 on: September 22, 2023, 07:37:32 PM »
Thanks DonP. 
Thats what I was looking for.
That way(s) seems much more efficient than cutting the d*** thing three times wrong.
Southwest corner of Vermont

Offline Prizl tha Chizl

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Re: Math question for collar beam angle?
« Reply #4 on: September 27, 2023, 01:07:46 AM »
Dont worry, weve all been there. (At least I have-more than once, usually on those valley  rafters.)

My uncles adage
I cut it three times-and its still too short!
The Woods Is My Church


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