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.