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Topic: How to calculate bevel angles for cutting combined compound
angles?

Replies: 1   Last Post: Mar 10, 2013 5:06 PM

 James Waldby Posts: 536 Registered: 1/27/11
Re: How to calculate bevel angles for cutting combined compound
angles?

Posted: Mar 10, 2013 5:06 PM

On Sun, 10 Mar 2013 13:38:12 -0700, Christoph J. WALTHER wrote:
> On Sunday, March 10, 2013 7:55:45 PM UTC+1, James Waldby wrote:
>> On Sun, 10 Mar 2013 10:09:02 -0700, Christoph J. WALTHER wrote:
>>
>>
>>

>> > With a miter saw I want to cut the end of a beam (fig. 1 in the sketch I posted here: http://goo.gl/6Fqtk )
[big snip]
>> Question: Why is your main angle 54.4° instead of 54° ? It appears that
>> 54.4° gives you an arrow angle of 180-2*54.4 = 71.2° instead of a proper
>> pentagon angle of 72°.

> Many thanks for all the good help here. I shall try it out asap (living in a residential area, it might not be the best idea to use a high powered miter saw on a Sunday evening... ).
>
> @jiw: This is about constructing a geodesic dome and the angle value came from one of the many sites on the web offering respective calculations. Certainly something I will keep in mind further pursuing my project ? thanks for pointing it out.

Actually, in my question I might be wrong about the arrow angle being
180-2*a; if the 54.4° angle is in the position shown in your figures,
then the arrowhead angle is 2 * 54.4° or 108.8°. Do you actually set
your miter angle at 54.4°, or at 90-54.4 = 35.6°? Also, when the
arrowhead angle is measured in a plane perpendicular to the angled-back
front edge (the "knife edge") instead of in a horizontal plane, it is
slightly larger.

--
jiw