How do you use 75937 Parabolic Rings?

[NathanR]

I’ve been experimenting with 75937 “parabolic rings”, or “plate 2x2 with bar frame octagonal”, as bricklink describes it.  I’m struggling to understand how it can connect to other elements, so I was curious - what connections are legitimate, and how do you use this part in your own MOCs?

From what I can see, in official lego sets the parabolic ring is typically restricted to detailing like on the rathtars in 75180 Rather Escape, or the base for legs of Destroyer Droids:

However, the ring can also be used as a structural element for brick built cylinders.  You can connect 61252 plate 1x1 with clip horizontal and the studs will line up perfectly (left) and you can extend the assembly with bricks and remain “in system”:

Changing the clip to 15712 tile 1x1 with vertical clip, it turns out the parabolic ring is 9 plates high, or 11 with two clips attached (left).  Curiously, mecabricks says this is impossible, but it appears to work in real life.  It turns out that in LDD and real life, the 1x1 tile part of 15712 has a slightly lower height than a standard 1x1 tile - why??  To keep this kind of attachment "in system"? It is certainly a useful feature, because if you add an extra two plates top and bottom, the entire assembly exactly matches a 6x6 plate (right).  At least, it does in LDD (unable to test in real life and I'm not sure what CAD programs to trust any more).

The two clip types are also equivalent.  15712 + two 1x1 plates matches the height of the 61252 (Left). The gap between them appears to be two and a half plates (?), but I’m not sure. The cylinder with the tile clips can be extended with bricks, but the plate across the top must be an odd length of studs.  I assume this is like with technic triangles, where you count the gaps, not the studs, from mid-point to mid-point (right).  So in this case it's a half plate from each of the parabolic rings, + 9 plates = 10 plates = 4 gaps:

Now this where things get a bit crazy for me.  If I build using the 15712 vertical clip, the whole assembly goes “out of system”.  Zooming in between the 1x1 brick and the black tile, you can see a hairline gap - quarter, maybe eighth plate thick? What causes this gap?

As a result, the separation between  the two rings is slightly less than 6 plates, resulting in a collision at the halfway point:

I’m not sure if this counts as being within lego tolerances.  But how would you go about getting this kind of assembly back "in system". Is it even possible to close this gap?  Does this even matter in real life?  An answer is kind of important to me because I've been using it as a key component in a particle physics detector MOC that's taken me some months... I was just about to order parts when I discovered this "flaw", and I'm not sure how disastrous it is:

 

Anyway, I'd love to hear your thoughts on these geometry issues.  And do you have any other ways of building with parabolic ring? Are there any other interesting features of this piece that I've missed?

[knotian]

I use some as wheels to turn valves in an industrial setting.

[koalayummies]

First off I admire you using LDD to check for 'legality' or in-system connections, I couldn't count how many times I've stopped building just to load up the program and check that at least LDD says its legal. That being said there are times where it has errors, like allowing an illegal or outright impossible connection and it also occasionally shows errors for connections that would be legal.

Not sure if that piece has been discussed in this or any of the previous threads discussing LDD brick and bug errors, but it was mentioned in these threads as having some errors but not sure if its similar to the error of plate fractions that you're experiencing (control F and the piece # should take you to the posts discussing it):

I love seeing complex builds around interesting parts like what you are doing. All of my uses of this piece are very basic compared to what you've been constructing. Not sure if any of this helped but it does appear others have had LDD errors with that piece.

 

[NathanR]

47 minutes ago, koalayummies said:

First off I admire you using LDD to check for 'legality' or in-system connections, I couldn't count how many times I've stopped building just to load up the program and check that at least LDD says its legal. That being said there are times where it has errors, like allowing an illegal or outright impossible connection and it also occasionally shows errors for connections that would be legal.

Actually I build the other way round... I do everything in LDD, and then when I'm reasonably certain it will hold together I order the bricks to try in real life! 

LDD is usually pretty good at catching errors, but I have seen some funny "illegal builds" that it allows.  My favourite is if you surround a 4070 1x1 angular brick with regular 1x1 bricks... the side-stud collides with a brick so you could never do this in real life.

Thanks for the links.  I couldn't find the 75937 and 15712 "error" referred to, but I've been wondering if this is actually a property of the Lego bricks. I did try a few tests with real bricks, but the hinges move so easily and the gap is so small that I couldn't really see it.  Real life seems to let this work ok, but I'm not sure if it works because of the tolerances in Lego bricks or because it's putting a strain on the pieces (which might do long term damage, something I'm keen to avoid).

[Marishka]

Thank you for intresting investigation! I have some of that parts and have no good idea how to use them, hovewer, they may allow nice functions.

[Peppermint_M]

I would suggest working with the physical parts, LDD is never as good as the real thing. 

Also on the subject of "in system" or "legal" : while some connections might stress parts, you have to keep in mind that other enforced limits are in place as they are too complicated for children or do not withstand the more "robust" play typical of the target market.  

[NathanR]

9 hours ago, Peppermint_M said:

I would suggest working with the physical parts, LDD is never as good as the real thing. 

I grant you that!  It's just that I always keep sets as sets, all neatly packaged and sometimes stored by bag number. I don't have many other bricks available to hand, so I rely on LDD and the like to make my designs, then I order the parts.

9 hours ago, Peppermint_M said:

Also on the subject of "in system" or "legal" : while some connections might stress parts, you have to keep in mind that other enforced limits are in place as they are too complicated for children or do not withstand the more "robust" play typical of the target market.  

Actually, if it was just for me I probably wouldn't care so much.  Unfortunately, the models I'm designing at the moment have attracted interest from work colleagues... in fact, I'm aware of at least one instance where one of my MOC's even got ordered as a kid's birthday present.  So I find myself trying to think and work like an actual Lego designer, following the same guidelines and rules they have to... it makes things very difficult for me...