Tapered angles

Michael Allen · 07-22-2012, 08:18 PM

Greetings. I am a fairly experienced woodworker who has made tables, craft items, TV stands, and other such projects. I would like to make a cedar birdhouse. The bottom part will be straightforward, 8 sides, with a diameter of about 9". The top, however , presents a challenge. I would like the "roof" to be conical, consisting of 8 segments (panels) 9" diameter at the bottom, tapering to 1 1/2" diameter at the top. My question is: How do I figure out the proper angle (mitre" ) to cut on the sides of each piece ?

Thank you

jlmran · 07-22-2012, 11:26 PM

Edit: deleted

GBrackins · 07-23-2012, 02:07 AM

if I am understanding correctly you are talking about an octagon shaped (either sides) with an octagon shaped roof. The angles would depend on the measurement from the 9" diameter to the 1-1/2" diameter sections of the roof. What is that distance? Will the edges of the roof overhang the sides of the birdhouse or be flushed? A sketch of your intent would help.

danpik · 07-23-2012, 07:23 AM

If I get a chance, I will draw it up in Autocad after lunch and get the angles.

JulieMor · 07-23-2012, 08:10 AM

I would probably use dollhouse roofing shakes. They are small and therefore easier to mold around the curves. In order to get them to mold to the curvature, put them in a steamer for a few minutes. That's how the pros do complex cedar shake roofs.

Since the wood will shrink and swell, make sure you leave a small gap between the shakes. You may want to use a flexible adhesive to secure them too.

woody4249 · 07-23-2012, 10:40 AM

Now that's a real good question.............mathematically speaking it is beyond my comprehension.
I would make a disc of the diameter you want at the peek. I would then mount this on a piece of dowel and temporarily locate it in the center of the bird house at the desired height.
Then take a piece of roof material and place it against the eaves and the peek and mark your bevels and angles.
I have an idea that trial and error would be quicker than determining the following equation.

A9+B1.5 (X3.172) / Height X today's date-95.4 = pitch angle[jk]

I didn't give my house addition roof this much thought

danpik · 07-23-2012, 01:26 PM

If you want the roof to be a 45 Deg angle Ie: 12:12 pitch, then here are the dimensions you need to use.

Don't forget to put the 22.5 deg taper cut on the sides too.

This will give you a 9" diamater circle at the base around the points. The top cut i gave you should yield a 1.5" dia circle around the points. By not cutting it to that dimension and letting the two sides meet at a point will close up the circle at the top

JulieMor · 07-23-2012, 04:14 PM

Quote:

Originally Posted by Michael Allen

The top, however , presents a challenge. I would like the "roof" to be conical, consisting of 8 segments (panels) 9" diameter at the bottom, tapering to 1 1/2" diameter at the top. My question is: How do I figure out the proper angle (mitre" ) to cut on the sides of each piece ?

Oops! My bad. I read conical and a cone shaped roof, rather than octagonal, stuck in my mind when I answered.

I just did the roofing on a cupola I built. I laid down one course then marked the cut at the ridges, took the shake to the bandsaw and cut it. Then I did the next course above that until I got to the peak. It works for any roof pitch.

The peak presented another challenge but I was looking at the waterproofing aspect of the installation. I'm not sure the birds care.

Aesthetically, you will probably want to lay ridge shakes on it too. Not sure if you want to put that much detail into it but here's how it's done on human roofs: