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Snips... ;-)
Rafters and Such
Excuse me while indulge on your patience. Mr. John Manners and I
have been having fairly intelligent conversation about rafters and
such. This is my take on the matter. I am not a final authority on
this matter and would appreciate any other input or all-out
correction if I am wrong, even though this train of thought has kept
me alive and well for this long, I am willing to listen and change
if need be.
The question was: I've been looking at an octagonal rotunda type
structure and the rafters are exposed. This has given me
opportunity to notice that the cut angles of the shorter rafters
that meet the hip are not 45 degrees or 22 1/2 degrees, but look
more like 30 degrees. I would have thought that the angle of the cut
would have been one of these figures, 45, 22 1/2 or some divisible
of these, since there are 8 sides to the structure. : This is not an
exact quote by the way. Nor do I imply that Mr. Manners is not
intelligent in any way. He has presented a question that average Joe
would NEVER DREAM of asking. Worthy of response IMHO.
Mr. Manners,
I've been trying to convince my computer to scan a few pics; but, it
is a stubborn and unpredictable thing. The reason for the confusion
about the angle looking like it is somewhere between 22 1/2 degrees
and 45 degrees is caused by this. The hip divides two panels that
are not planar to each other. If the two panels were flat even with
each other, i.e.. a flat roof, the shorter rafters coming from the
middle area of the hip rafters would be 22 1/2 degrees or a
divisible thereof( trying not to lose my train of thought). But
since the two panels are not on an even plane, there is another
angle between the panels, to further compound the intersecting
rafter angles.
If you were to take all of the existing panels, strip them off, and
lay them in order as they came off, then you would see that the
panels will all touch in the center BUT, the panels will not touch
at some point around the outer edge.
There, then, you have seen where the angular relationship changes by
shortening the outer edge of the panels. By shortening the outer
edge OR by extending the length of the panels from the point, to the
outer edge; You raise the pitch of the roof. And you change the
angles (of the panels) at the center point where all panels
intersect.
The reason for the flat (no bevel) 90 degree cut at the King Post
(very heavy center piece where all of the hip rafters meet) is
obvious, but the angle of the cross-cut would be the same as any hip
rafter top cut.
Man, my head hurts now.
Tom Ford in KY,
I may have to try some of that KY bourbon someday.
December 18, 2005 |
