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 CJB143 01-16-2012 05:56 AM

birdsmouth rafter cut

I am fairly new to rafter cutting, but i have always marked my first common and cut it and used it as my pattern. cutting each rafter one at a time. i recently watched a roof framing video where they were gang cutting the birdsmouths. 12 on 12 pitch with a skillsaw on a 45 degree angle for both cuts. my question is how did he figure how far apart to make those two cuts. if anyone knows this can you also explain diffrent pitch roofs too

 Just Bill 01-16-2012 06:27 AM

Framing squares come with an instruction manual. This will tell how to do the birdsmouth for any set of roof pitches. Too much info to put here.

 CJB143 01-16-2012 06:50 AM

i understand how to do birdsmouth cuts for common and hip rafters. its just gang cutting all.

 titanoman 01-16-2012 06:53 AM

Like Bill said, it would take a long description and pictures to make you understand.
Just keep cutting them the way you are.
(they probably had a bunch standing together on edge with their saw set on a 45° if it was a 12/12 they were cutting. Measure the depth of one you already cut and set blade depth accordingly).

 abracaboom 01-16-2012 09:16 AM

Quote:
 Originally Posted by CJB143 (Post 824173) my question is how did he figure how far apart to make those two cuts.
Length of plumb cut (or level cut) times the square root of two.

Quote:
 Originally Posted by CJB143 (Post 824173) if anyone knows this can you also explain diffrent pitch roofs too
Unless you have a saw that can tilt more than 45 degrees, there's no point.

 CJB143 01-16-2012 09:40 AM

i have a worm drive skil that goes to 53 degrees... i think that is a 16/12

 titanoman 01-16-2012 10:06 AM

Quote:
 Originally Posted by abracaboom Length of plumb cut (or level cut) times the square root of two. Unless you have a saw that can tilt more than 45 degrees, there's no point.
Length of plumb cut times the square root of two?
Makes zero sense to this roof master.

 abracaboom 01-16-2012 03:53 PM

Quote:
 Originally Posted by CJB143 (Post 824374) i have a worm drive skil that goes to 53 degrees... i think that is a 16/12
I would still cut them one at a time, if you care a bit about precision.

The "no calculations" method to know the distance between the two lines would be to lay out the birdsmouth in one rafter as always, and use a tape measure to measure the distance between the lines.

 abracaboom 01-16-2012 03:55 PM

Quote:
 Originally Posted by titanoman (Post 824403) Length of plumb cut times the square root of two? Makes zero since to this roof master.
With what do you associate the square root of two?

 Willie T 01-16-2012 04:17 PM

Guys...... Root 2 is a math joke. :whistling2:

 BigJim 01-16-2012 04:56 PM

Quote:
 Originally Posted by abracaboom (Post 824347) Length of plumb cut (or level cut) times the square root of two.
Made me do a little head scratchin there, but that will only work on a 12/12 pitch, oh wait it will work on a 14/14 pitch won't it.:whistling2:

 Joe Carola 01-16-2012 05:15 PM

Quote:
 Originally Posted by CJB143 (Post 824202) i understand how to do birdsmouth cuts for common and hip rafters. its just gang cutting all.
Once you mark your birdsmouth ....you have both marks on the bottom edge of the rafter pattern which represents the seatcut and heel cut. Rack you bench with the rafters on edge w/bottoms facing up and take the pattern with the birdsmouth and mark both sides of the rack with the two birdsmouth marks...(seatcut and heel)and snap the two lines. Those are your lines that you will cut.

Some full time framers do this but they use a saw that has a swing table on it from Big Foot tools that cuts up to 75°....the saw is actually called Big Foot.

It's easy when the pitch is 12/12 because both cuts are 45°. When the pitch is 5/12 for example..the heel cut would be 22.62° and the seatcut would be 67.38°. This is where the bigfoot swingtable saw comes in. Here is a link to their website.

http://bigfootsaws.com/swing_tables.html

 joed 01-16-2012 05:15 PM

If you know how to mark a single birds mouth then try this. Mark a rafter on the side like normal. Bring the mark around the side to the edge using your square. No need to actually measure it at all.

 Joe Carola 01-16-2012 05:49 PM

1 Attachment(s)
Quote:
 Originally Posted by CJB143 (Post 824202) i understand how to do birdsmouth cuts for common and hip rafters. its just gang cutting all.
Here are the two marks that you use to gang cut on the rack with the bottom of the rafters facing up. I used a 5/12 pitch for the example.

 titanoman 01-16-2012 06:48 PM

Quote:
 Originally Posted by abracaboom With what do you associate the square root of two?
What are you talking about? Is that a real question or are you making jokes that are going over my head?

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