A fellow LJ member(Belg1960) was asking about designing an Octagon Birdhouse a while back. He recently contacted me and asked if I would show him how I would do it in SketchUp. I thought I would make this public for all to see. The method that Jim Jakosh provided was certainly a good one. Every woodworker would benefit from understanding math as much as Jim does. Me, I tend to lean more on SU to do my math.
The SU method I am presenting here is but one SU approach. There are other ways to do this in SU, but this is the first one and the easiest one that came to mind for me.
Let me say that my purpose with this scenario is to use SU to tell ME the dimensions and angles rather than me having to tell SU those values. This is most often the case with me when using SU during the design.
The constraints given to me to dimension the Gazebo Bird House(GBH) were as follows:
8” diameter base
7” base height
10” diameter roof line
6.7” roof height(derrived from Jim’s scale)
1” hole at the top(for finial placement)
(arbitrarilly chosen on my part)
And YES, he requested a Hexagon, not an Octagon. :)
I begin by drawing a side view profile-triangle of the roof using the given constraints(I rounded the 6.7” to 6.75”):
Note the 1/2” line on the bottom left corner. This represents the radius from the center point to the inner edge on the top where the finial will go. I also make all of this a ’Component’ so it doesn’t STICK to the other parts I’ll be drawing.
I then lay up the profile of a 3/4” board profile where it would lie against the roof profile-triangle:
Next, I rotate the bottom end out to the bottom edge of the roof profile-triangle:
SU tells ME that this is 28.4 degrees. Incidently, this is the cut angle for the top & bottom of the roof panels.
Note how it intersects with the triangle, thus keeping space for the hole in the center and not exceeding the roof diameter. It is not just a parallel fit to the triangle.
Now I convert this roof-panel profile into an actual 3D board by flattening the top & bottom, and pushing/pulling the front and rear faces to give it depth. The goal here is to extend it in both directions further than it needs to be. 5” ought to do it. These will be trimmed off in a later step.
I’ve shown it transparent so you can see how it intersects the profile-triangle. The panel itself is also made into a ’Component’.
Next, I rotate to an arial view to do the real magic. I will be copying(in a circular fashion) that panel 5 more times at 60 degrees(360/6 sides[a hexagon] = 60 degrees). Note the point of rotation around the tip of that line sticking out to the left of the profile-triangle.
And here’s what you end up with:
It actually looks to be a jumbled mess doesn’t it.
Lets come down a bit from the arial view and hide 4 of the panels. I also added a wooden color to the panel we will be working on:
By the way, since these panels are ’Components’, then any changes I do to one, gets replicated on ALL the other panels.
Now comes the math part, but with no math at all. I draw an intersecting line where the two panels cross, from the inside intersection to the outer intersection. This is done on the top AND bottom beveled edges of the panel.
I now edit the wooden panel itself to connect the upper intersecting line to the lower. And then remove the excess just as if I had cut it off with a saw. I have no idea at this point what that bevel angle is that I just created. Later I’ll just measure it using SU. And here’s what I’m left with:
Note that I also hid that one remaining blue panel to help eliminate some confusion to the non-SU users.
I now repeat the beveling for the other edge using the adjacent panel on the opposite edge:
But what am I looking at? Because these panels are ’Components’, any change I do to one, happens to them ALL. Even if I have them hidden.
I can simply copy that one beveled face(now shown in wood veneer for easy identification):
Then paste it onto my all-wood panel:
BTW, I do this using one of the most unused, but most useful features of SU, ’Paste In Place’.
I finish up the panel by simply removing the excess on that other edge of the panel. And what I’m left with is a perfectly formed panel. In fact, if I unhide all the panels, they are all perfectly formed, and with precisely correct beveled edges:
So now, how do we cut these panels? More accurately, how do we measure the bevels? I simply make a copy of one of the panels, lay it down on a flat surface and measure the angles using the Protractor Tool in SU. We already know that the top and bottom bevels are 28.4 degrees:
The side angles for the panels are 15.3 degrees:
And the bevels themselves are 26.1 degrees:
And all the other pertinent dimensions:
OK, now for the base. We are looking for a 8” diameter base at a height of 7”. So we do a similar procedure, but it is easier because we don’t have to tilt the panels. I won’t bore you with the details of this, other than the differences. For the base, I build it extra long, then raise it up into the roof until the top of the inner edge touches the roof panel. I then draw lines that can be used to bevel off the side panels. It is easier to do when having just one roof panel, and one side panel visible:
And with most panels in place:
I drew a 7” vertical line from the base of the roof, downward. This gave me a general idea of how tall to make the actual sides. They need to stick down below the lower roof line 7”, but they are actually taller since they go up into the roof where they attach.
Well that’s about it. Any comments, criticisms, and suggestions are welcome. I hope this gives you some new ideas on how to use SU in your future projects.
Oh, and that bevel angle for the tops of the side panels, well that would be 90-(the bottom angle of the roof panel: 28.4 deg.), ie. 61.6 degrees, right? And the side bevels of any hexagonal box are 60 degrees.
And with the finish applied:
-- Backer boards, stop blocks, build oversized, and never buy a hand plane--