How To Cut Birdsmouths for Rafters: Speed Square and Framing Square Methods Explained

i'll show you the speed square method the rafter square method or you could print a template from an online generator and i'll link that below the bird's mouth is made out of two cuts the seat and the heel the seat cut sits on top of your double top plate and the heel is the end to start you need to know how steep your roof is going to be in carpentry this will be stated as some number in 12 for example 4 and 12 which means for every 12 inches you go over the roof will go four inches up speed square has a ledge to get you flat up against boards is 90 degrees square on these two edges has inch markings on this edge and when you make angle cuts you pivot where it says pivot on this corner when you're marking angles for rafters use the numbers marked common on this slot these numbers are the inches in 12 that refer to the slope or pitch of your roof very commonly it's either 4 in 12 or 6 inches and 12 and i'll show you 4 and 12. to make your heel cut put the square flat up against your board and while pivoting at the pivot point move the scale so the common number in this case four lines up with the edge of your board and then you can make your mark while i don't believe there's a standard for the length of the seat cut i like to use the width of my top plate which would be three and a half in this case for two by four construction so i go to the three and a half mark put that on the edge of my rafter and then square up the speed square to the heel cut mark i made then i can mark that straight line and that will be my seat cut the speed square is of course reversible so if you need to go the other way you can flip it around mark your angles this way too to use a rafting square you find four inches on one end 12 inches on the other and then put both those marks up against one edge of your board marking this line will make your heel cut note that you need to be consistent and both numbers need to be either from the outside or the inside otherwise your triangle will be messed up similar to the speed square you put the length of the seat cut you want on the edge of your board and then put your square up square against the heel cut you just made and then make your mark however you make your marks the fastest way to cut it is with a circular saw i put the blade as deep as it goes to cut away the most depth of material for the length the blade travels if you cut the notch completely with the circular saw you'll end up with overcut into the remaining rafter all the pros seem to do this but if you don't want to have extra material cut away unnecessarily you can finish the cut with a hand saw or a jigsaw or cut the whole thing that way note that the ridge cut the heel of the bird's mouth cut and the rafter end are all parallel to each other so you can use the same method to get the angle for those lines too and once you have one rafter done you can trace around it on new boards to make new rafters if you want to know the angles or how to calculate them i did that on this slide additionally if you have trouble wrapping your head around angles like i do i made this conceptual diagram that might help

Channel: David Pratt

Views: 360,608

Keywords: Rafter, Construction, Roof, Birdsmouth, Angle, Cuts, Layout, Speed Square, Framing Square

Id: lqH-RhQdWEI

Length: 3min 10sec (190 seconds)

Published: Sun Nov 22 2020