Dome build: A better pair of segments.


After much sawing and checking yesterday I made another pair of segments today to my own dimensions and angles. It is vital that the dihedral angle between segments causes each segment base strut to follow the base ring. No problem there.

The adjoining ribs between each segment must also lie perfectly flat against each other without any distortion. Any gaps between the ribs in the image are due to protruding screw heads. I did not bother to countersink the screw holes just for this quick assembly check.

 As I was checking the angles for the final time, on the second segment, it occurred to me that I had moved the goalposts. By reducing the width of the segment, the squareness of the lowest sheathing panels was lost. So I decided to make them square again. This required a reduction in strut spacing.

The result can be seen alongside. Where I have added new struts lower down without removing the originals. This ensured the successful geometry of the segment was not changed. The effect can be seen in the other image once the original struts were removed.

And then it all went completely awry!😖 I had my drawing with angles and lengths of strut beside the saw.  So I busied myself sawing out enough pairs of struts for two segments. The problem was using a pre-drilled rib as a pattern but using the wrong holes. Grr?

Now I need to use a new pattern with only active guide holes or just mark the active holes. It only means the loss of a few minutes work but I was hoping I was setting up a routine for churning out segments. Making lots of struts the same length would be far more sensible than changing the saw settings for for each one. I just need to make sure I have the correct settings and strut orientation.

With the four segments to play with I placed two of my builder's straight edges against the outside ribs to the center to check where they crossed. About 155-160cm radius as near as I can judge. This is with the segments standing on uneven ground and held only by clamps. But it seems close enough not to worry about the dome being far too small or much too large. It is odd how small the dome seems when viewing from outside with it down on the ground. I wouldn't want to carry it far but I can manage to lift the four segments.

Click on any image for an enlargement.

No comments: