It's kinda funny (coincidental, perhaps) that you would pose that
particular question at this time. There's been a thread running for a
few days on long miters and the difficulties of cutting them precisely.
I'm pretty sure that what you're looking at are miters that are both
quite long (several inches) and compound.
For an octagonal roof, that's going to require that each section be cut
at 45deg along the X-Y axes and then angled along the Z-axis, perhaps
10-25 deg. or so, depending on how much pitch you want and how big an
area you want to span.
I'd suggest cutting the octagonal sections first (that may require quite
a bit of T&E) and getting them fitted. Then, angle them upward and make
the undercut. Having not thought thru the project completely, I'm not
sure just what you'd need as supports underneath when you put it all
When you angle them up, it changes the angle of the miter needed to
get them to fit properly. Hence my web page, which tells you the
right angle for the *final* upward angle.
As for *making* the cuts, I use an Incra 5000 and t-track clamps.
I plugged in
number of sides 6
angle of sides 45
just to see if I could figure out what this is all about. This is what I
cross cut angle 22.2
blade angle 20.7
So if I set the blade at 20.7, and set a mitre of 22.2, and cut pieces to a
sharp point, and arrranged them in a circular pattern I'd get a roof?
I have never used a chart, nor understand it (them). Is this a specific type
of chart for circles, or is this the same type of chart you would likely see
at the back of textbooks?
I'm gonna try 0 and 90 with 6 sides:
0 (flat) gives 30,0
90 gives 0,30
I definetely don't understand.
Yes. Assuming you're using plywood for this example, you'd end up
with six triangles with square edges, which form a flat "circle" when
90 means they're all standing up. If you cut out big squares with 30
degree bevels on each edge, you'd end up with, essentially, a
six-sided box, without a top or bottom.
To avoid confusion, consider a four sided box with mitered edges.
You'd use a 90 degree setting on the crosscut miter, and the blade
would be angled 45 degrees. Nice box, yes? But if you set the miter
at 45 and the blade at 90, you wouldn't get a box, you'd get a picture
You want something halfway between a box and a picture frame :-)
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