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Posted: Sat Feb 01, 2014 1:39 pm
by Peter Kane
This might help:

Top image shows the two faces of the front of one star arm, plus a "dart". I've drawn lines to show the tabs.

Middle image shows the two faces cemented together with a pin sitting in a blob of balsa cement at the outer vertex. A non-decapitated pin is shown alongside.

Lower image shows how the dart holds the pin more securely (normally I'd make the dart the same colour as the face). It also shows the back section of the star arm attached and one extra example alongside so that you can see it better. Note that the white star kite-like section has no tabs on its pointy end.

In practice, I would start by joining all five back (white) start arms together first to form a complete star back. Then I would cement the section shown in the middle panel (complete with dart) onto one of the star arms. Then I would rotate the free (yellow) tab over and cement it to the other side of the white (back) star arm. Then its just more of the same.

Pete K

Posted: Sun Feb 02, 2014 10:58 am
by robertw
Thanks for the pictures Pete. Now how did you put the last of the 12 sections in? That is, where the pins poking out of the main body, or out of the final section itself, and how did you slot them into the other part?

Posted: Sun Feb 02, 2014 1:19 pm
by Peter Kane
Ho ho, I should have guessed that you would ask about that. I nearly explained how, but I thought my post might time-out if I took any longer.

I used a variation on a technique that I'm sure we have all used before, but it was so effective that I intended to make it the subject of a separate posting. Here's the approach that I settled upon eventually (it can easily be adapted to other last-piece scenarios):

Situation: All of the pointy-bits of the star are assembled except for the last one. This leaves us with two coloured triangles yet to do. The two coloured triangles are cemented together and attached by one edge to the remaining white star-arm back (just like the lower section of the previous diagram, except that the white bit is already attached to the rest of the back star. Now spread glue on all five the remaining tabs (I generally spread glue on both surfaces to be joined). Just push them in place and hold them for a bit. It is surprisingly easy - provided that you use the following trick, which I call "Hinged Tabs" :

A Hinged tab is just a bit of card which is lightly scored, but not folded (this will be the hinge). Spread some glue on the fat end of the card, but not quite as far as the hinge. Stick it in place as shown in the following diagram.


Note that the hinge does not quite coincide with the scored line for the tab and the edge of the hinge does not project as far as the end of the tab. That's all there is to it. When the tab is folded back, the hinge rotates in the same direction, but adds enough resistance to push the two joining tabs together. In other words, it gives you something to push against.
In this instance I used four Hinged Tabs, placed on the two pairs of edges that were coming together. They weren't needed on the edge that joined the back of the star, because I can get my fingers around the back. This technique works best if you put the Hinge Tabs in place before you come to the last piece, otherwise they can be difficult to align on the part that is almost complete.

Posted: Mon Feb 03, 2014 12:06 pm
by robertw
Hmm, I've never tried anything like the hinge method. I just hope the two tabs spring enough to hold while the glue sets.

But actually I wasn't asking about completing one of the 12 stars. I was asking about putting the last of the 12 stars in place. How to slide the pins into the right place for that last star.

Posted: Mon Feb 03, 2014 1:42 pm
by Peter Kane
The answer is that only the first star is built completely - with five projecting pins. The second star can be built almost completely, but the last arm of the star must be assembled as described in my previous post, because the final vertex has to wrap around the projecting pin of the first star. As more stars are added to the assembly, you will find that more of the vertices need to connect to (and wrap around) pins in the assembly, so these vertices cannot be completed in advance.

Pete K

Posted: Mon Feb 03, 2014 1:54 pm
by Peter Kane
On the matter of the hinges, I myself was surprised at how well it worked; just be sure to score the hinge only lightly. For similar situations in the past, I have used strips of card that stick at two or more sides of the opening (almost forming a base for the final piece to attach to), but you need to get the reinforcements just the right size and depth. This technique is a lot easier and gives good results, because the hinge WILL push back as far as you need it to, while still providing adequate resistance.

Try building a couple of Pyramids without bases and then join them together using hinges on all tabs.

Pete K

Posted: Mon Feb 03, 2014 8:52 pm
by oxenholme
I would be nervous about using hinges if only because in time the cement would cause the card that I use to distort.

Maybe this is because balsa cement is a tad powerful?

Posted: Wed Feb 05, 2014 8:04 am
by Peter Kane
oxenholme wrote:I would be nervous about using hinges if only because in time the cement would cause the card that I use to distort.

I only use balsa cement at the tips of the vertices - to hold the pins in place. Elsewhere I use UHU gel. When attaching the final piece of a model (or section) in many models, you have no choice; you need to add reinforcement of some kind. I find this way to be simpler and better than any other approach I've used in the past. The hinges are typically smaller and simpler than other alternatives. There really isn't much to them.

Maybe this is because balsa cement is a tad powerful?
Indeed. I might be wrong, but I think you were one of the people who suggested it way back when I tried my first vertex-connected model, so a belated thanks.

Pete K