Celestial sphere models

[THE DC]

So is this latest version the most up-to-date, with the corrections you mentioned?


Thanks again!


Great contribution!

[Laurence Finston]

Originally Posted by THE DC

So is this latest version the most up-to-date, with the corrections you mentioned?

Thanks again!

Great contribution!

Yes, it's the latest version and I made all of the corrections I mentioned. There are still a couple of unsolved problems (see below). I don't think they will prevent me from getting the model assembled, though.

In order for the stitch markings to match on the long "tab" and the opposing face, and so that the paper won't bunch up when they start to curve, they have to follow a meridian of right ascension. The consequence of this is that the stitches get close to the edges as they approach the ends of the biangles. I'm not yet sure how to handle this.

One approach would be to use a different meridian for the stitches near the ends. On the other hand, it might be possible to glue or tape them. In addition, I've already printed the plans as they are out on the heavy paper and started testing them.

I've found that keeping the biangles aligned while stitching them together is harder with the new version. I've only just started working on this. It may be enough to make sure to leave enough slack when stitching. Otherwise, doing small sections and alternating the side you work on may work, or using temporary stitches ("basting"). On the old version, I had to stitch each tab separately and could make sure it was aligned before starting to stitch. It may turn out that this was a better approach.

The very ends of the biangles, where they come to a point, are also a problem. On another sphere model I made pyramidal "caps" for the ends. However, I never tested these plans.

I've found that the 170g paper is possibly too stiff to curve much in the east-west direction. The partially assembled still looks good (in my opinion), just a little boxier than I'd imagined it. It may look better when I add the last section.

I think a lighter but stronger paper would be better, but I don't think there is any really good copy paper, certainly not anywhere near as good as artists' papers.

Thanks again for your feedback!

[Laurence Finston]

Finished assembling the prototype. The photos show the model after threading the last tabs, each one individually, and before and after pulling the threads tight.

Sewing the model together was very easy and pulling it together at the end went very fast, after the preparation of threading all the tabs with separate needles. The threads could have been much shorter.

For this model, I think sewing is much more practical than gluing. It would be hard to get the two surfaces to match up and not slip and it would be difficult to clamp them. However, gluing could be used in combination with sewing. In this case, I don't think it's needed, though.

I used a previous version of the plans with the stitch markings only on the tabs and no markings on the triangles at the top and bottom of the biangles. It required a lot of work transferring the markings to the opposing faces. These problems have been solved on the current version of the plans, with timestamp 18 Oct 2021 5:32 p.m. On the current version, the triangles are meant to be sewn together; there are no tabs.

With the current version, the single, long tab at one edge of each biangle should probably be cut at intervals and one probably shouldn't sew a single seam along the edge. It will probably work better to sew small sections, as I did with the prototype in the photos.

The model doesn't look as spherical as I would like. It might help to attach the triangles at the ends together. I didn't do this for this version. It might also help to use more biangles, e.g., 16 instead of 8, and/or to make pyramidal caps for the top and bottom.

The copyshop I go to has 120g paper. I've printed out the current plans on it and will test whether it works better than the 170g paper.