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Thread: compound mitre angles
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16th September 2009, 11:23 PM #1New Member
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compound mitre angles
I am building a wood frame house in france which is very complex in design. it is basically a single pitch roof (back higher than the front), but its front and back walls are higher at one end than the other (a 2.8° angle). I need to set up my compound mitre saw to cut the tops of the wall posts to generate the same angle as the roof pitch. If the front and rear walls were the same heights at each end it would be a simple cut the same as the pitch in the roof, but the roof joists dont run off the wall at 90°. The joist angle from above is 76.5°. the roof angle at 90° to the rear wall is 11.2°(not the final pitch). do I set my saw at 11.2°from 0 and 2.8° from 90/vertical or do i have to get into serious maths? I have the plans in sketchup for measuring angles etc, but doesn't the one angle effect the other when setting the saw? any help would be appreciated as i now feel i have bitten off more than i can chew.
Last edited by drphoto; 16th September 2009 at 11:24 PM. Reason: spelling
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16th September 2009 11:23 PM # ADSGoogle Adsense Advertisement
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17th September 2009, 12:07 AM #2Golden Member
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Hi drphoto, welcome to the forums.
Could you post the sketch-up or a diagram of what you're describing? That should help understand the challenge.
Cheers,
Af.___________________________________________________________
"The things I make may be for others, but how I make them is for me."
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17th September 2009, 01:10 AM #3
if you cut each post to the correct angle before installation you have to get them all the "right" length and orientation — no easy task
I suggest it would be easier to install all the posts over length by say 50mm and then use two or more string lines to mark the angles required directly onto each post.regards from Alberta, Canada
ian
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17th September 2009, 09:34 PM #4New Member
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axo diagram of the problem
i hope the file has attatched and it is openable. They are pdfs so they should open ok, and thanks
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18th September 2009, 12:13 AM #5
Looking at the file axo 01.pdf
I suggest that you lay each wall out full scale on the floor or slab and build the frame horizontal before standing each section up. Then it's relatively simple to scribe each post with the correct angle on adjacent faces – then cut
Normally rafters would be notched to fit the top plate — you wouldn't try to angle the top plate so taht the rafters don't require notching.regards from Alberta, Canada
ian
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18th September 2009, 05:21 PM #6New Member
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Thanks, I have been building the shorter rear zig zag walls flat and lifting them as you said, it works well. I got someone around yesturday to look at the the slopes etc. I think we are going to build a low wall from scrap wood and experiment until we get the right slope. We have found a 11.5° slope in one direction and a 2.5° along the length of the wall doing the math. we are going to tap the saw off square for the small angle, and hopefully the joint will look ok, at square there would only be a 2mm gap on the one side of the joint. Thanks again for the advice. I will be probably be back soon with a new dilemma.
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20th September 2009, 09:16 PM #7Awaiting Email Confirmation
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so the correct pitch is 20°?.. the roofing for this is surly running parallel with the rafters?
so i would just work off that at the 76.5° angle to the walls, just determine the run at 76.5° to the wall and calculate the rafters to suit, what your saying about cutting the wall posts? im not sure exactly what or how your making this, but the angle will be the same as the pitch of the roof even if the rafters then run 76.5° to it, the rafters will end up being another pitch..
ive done a roof like this before, except the rafters ran 45° to the walls which makes things alot easier.
its hard to see what your trying to figure out.. if there's any calculations you need doing just ask and ill be happy to help
(with more information i could tell you what heights to do the walls and all angles ect)
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20th September 2009, 09:29 PM #8New Member
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the pitch is 20% , which is 11.5° off the top of my head. A friend has done a few calculations. They seem to make sense to me so I will build to those and find out in a month when I start placing the roof beams if he was right. I might make a test piece and check it out at ground level just to be sure.Thanks again
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21st September 2009, 05:23 PM #9Awaiting Email Confirmation
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hey, sorry you got my curiosity going
the pitch of the roof going 90° off the bottom framing [or what ever was 76.5°] is 11.095° appose to 11.307°/20% which is the rafter line
anyways hope its all going well, and good luck
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22nd September 2009, 01:05 AM #10New Member
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Luckily I can't measure the angle that accurately, and i feel that 11.1° and 11.3° is the same in my book. They are rafters and not a delicate inlay, a few millimeters here and there shouldn't cause much of a problem. And I think I need all the luck I can get.
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