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Posted by Harry K on February 29, 2008, 10:39 pm
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> > >> >I have a 3/12 pitch roof (3 inch's of rise for each 12 inch's of
> > >> > run). =A0I am installing Facia Board (1x8 pine) and my question con=
cerns
> > >> > the proper angle cut at the ridge of the roof. =A0The right angle
> > >> > triangle by definition of the 3/12 pitch has a 90degree angle at th=
e
> > >> > top plate center, a 14degree angle at the eave and a 76degree angle=
at
> > >> > the ridge (for a total of 180degrees in the right triangle)
>
> > >> > Vision a gable roof and the two right triangles would fit against e=
ach
> > >> > other and form the gable. =A0The two 76degree angles would be toget=
her
> > >> > at the ridge of the roof. =A0What would the plumb cut be in degrees=
for
> > >> > the facia board on the ridge? =A0I thought that with two 76degree a=
ngles
> > >> > combined that I would split that in half for the cut, but obviously=
> > >> > that is wrong. =A0The angle cut is not 76degrees and my miter saw
> > >> > wouldn't cut that anyway. =A0I think the angle cut may be 14degrees=
for
> > >> > each of the facia boards joining at the ridge on the two 76degree
> > >> > angles, but I don't know why I think that or how the angle is actua=
lly
> > >> > calculated.
>
> > >> > Thanks for any assistance with the angle cut.
>
> > >> > David
>
> > >> 90 minus 76 =A0=3D 14
>
> > > 14degrees makes sense, but why am I subtracting from 90degress when
> > > the angle is 76 degrees? =A0Guess I should have paid more attention in=
> > > school huh?
>
> > Probably need a blackboard so I can draw you a picture. =A0A miter saw m=
akes a
> > 90 degree angle with the fence. =A0To cut a 76 degree angle on the board=
you
> > set the saw to 14 degrees.
>
> What most carpenters would do is hold their speed squares on the 3/12
> mark, and look down and see what angle the plumb cut corresponds to.
> Mathematically orientated carpenters can use a scientific calculator
> and enter 3 / 12 INV TAN. =A0 Which I guess is technically the angle of
> the rafter to the ceiling joist, but it is also the angle that you set
> your miter saw to. =A0Like Pat said.- Hide quoted text -
>
> - Show quoted text -
Or use a bevel gauge to set the saw to. That's what I do and it
avoids the problem of odd angles. Been a long time since I actually
read degrees of angle on anything.
Harry K
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