Reciprocal roof, advice needed

Good day everyone,

I need some advice regarding a reciprocal roof a friend of mine wants to build in his backyard.
Someone else made the drawing and to be honest it’s quite a mess…
A lot of geometry was not on the default layer, I have corrected that.
All of the logs have weird geometry and I don’t know what caused that.
Maybe both those problems come from importing a .DWG to SketchUp.
Also the logs weren’t notched yet, Booltools2 made that a breeze. Great Extension!!

My friend asked me if I knew a way to get the measurements he needs for making the cuts (notches) that doesn’t take too long because I believe all 83 logs are different.
The measurements he needs are these:
1 total length of the log (easy)
2 length from side of log to middle of first notch.
3 length from side of log to middle of second notch.
4 miter angle of first notch.
5 miter angle of second notch.
6 angle of difference between first and second notch. (seen from the side of the log)
7 depth of first notch.
8 depth of second notch.

I’ve been breaking my head over this for 2 evenings now and don’t see a way of doing this easy, also because the logs have been placed before making them a component which gives them a big bounding box with the axes not alligned with the logs themselves…
I copied one log and tried to rotate it to the world axes, that sort of worked exept for the last rotation which should put one of the notches horizontal…
All of this is taking a long time to do and I still can’t figure out how to make some of the measurements.
Anyone has some tip and advice?

herman bewerkt.skp (2,6 MB)

The axis orientation could be corrected. so the bounding boxes fit the geometry. Change Axes for that.

If I were charged with the task you have I think I would rebuild the model so components have the correct axis alignment and no excess geometry. It would be a lot of work but probably easier and faster than fixing what’s there.

I wonder if every piece has to be unique.

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Whow, what a structure for the back yard.

To quickly find the direction of the central line of a log, use the ‘Tape Measure’ tool and double click on its end face to get its ‘face normal’ guide.
Move the guide to the center of the circular face.
Use the component’s context menu > ‘Change Axes’ to set one of the axes along the guide (the central line).

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With Fredo6 Tools > MoveAlong
hb-01 (SU17).skp (2.6 MB)




This reminded me of an ancient old plugin for creating lamella roof frames. It still works in SU2021.

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That’s a good idea and much faster than trying to do it my way!

I guessed that would be the smart thing to do…

This is also one of my big questions about this structure. I think there would be some kind of symmetry in it, that would make things repeat. That would make the task a lot easyer as there would be less different logs.
Unfortunatly it is not easy to see if this would be true as I would have to measure every log first to see if there are identical ones…

Yes, he has a very big backyard. He already has a Yurt we build 3 years ago. We made a bathroom from an old polyester silo for the yurt. At the moment he is building an outdoor kitchen from steel panels that form a pumpkin shape.
The reciprocal frame is to be covered with willow branches, then straw for insulation. EPDM for weatherproofing and then soil. It’s going to be a guesthouse.

thank you for this tip, didn’t know it yet!!

This is not easy as the “ends” of the logs are not circles anymore…
Offcourse if I rebuild the logs this would be an easy task!

@mihai.s As usual your video’s are stunning and fast! I see you rebuild the structure with just 2 different lengths of logs. I counted 12 different lengths in the original…
Unfortunatly the video’s are so fast that I don’t understand what you are doing in them. I’ll have to watch them more.
I just downloaded Fredo6 Tools which include MoveAlong. What did you use it for? I don’t see you use it in the video…

Another thing I am concerned about is the depth of the notches. I’m not a structural engeneer but almost halving the diameter of thee logs would weaken them considderably in my eyes. My friend says he wants to do it this way because it is saving time. This way every log has only 2 notches instead of 4 (half) notches which I suggested him…
Offcourse he is right about the timesaving aspect, both in measuring and making. But because of the heavy loads he is going to put on the stucture I think it would be a better option.
Another plus on the half notches is that they interlock and can’t slide as his notches can.
What are your thoughts on this?

Hi @tweenulzeven,
The structure consists of a few different types of logs depending on their length. I created only two components in the first phase for the two visibly different lengths (the short and the long).

As you saw in the second gif, once you have all the cylinders replaced with components, with the help of the two components placed horizontally, you can make the number of copies that correspond to the number of cylinders in the structure (which are placed in different directions).

Then, two by two, one horizontally and one in the structure, you create unique components, because there may not be two elements alike in the whole structure.

After preparing these, you can intersect all the cylinders in the structure with each other (BoolTools), and the changes will appear to those that you have aligned horizontally. You will be able to add dimensions to them more easily.

Fredo6 Tools > MoveAlong



@mihai.s It is slowly getting more clearly to me now. I will have to watch some tutorials on MoveAlong before being able to replicate your steps…
Thank you very much!

I suspect he really wants a geodesic dome but has created something more random.
Laying it out properly would save money and effort, but would be less ‘artistic’ if you know what I mean.

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If he wanted a geodesic dome it would have been much easyer, there are online calculators for that and you would have only an x amount of different triangles depending on the dome frequency. A reciprocal roof is very different from that in the way that it is easyer to manipulate into very different shapes.

You just need a little practice. After you select the tool, activate the Copy and Align functions and pick the center.


Wow, that saves a ton of work!!
Thanks again.

I was playing around with reciprocal roof frames a few years ago, and I uploaded a YouTube video demonstrating how I drew the frame and then figured out the angles for all the intersecting cuts. Subsequent to this video I did posts a couple more demonstrating more complex reciprocal frames. So, for what it’s worth, here’s a link to that first video:

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Thank you for the link, I’m going to watch them!