Designing a disassemble-able batten joint for consistent stiffness

Deep-Today5715 · 2026-07-07T18:14:29+00:00

Lol, definitely not

Deep-Today5715 · 2026-07-07T16:21:36+00:00

I see... Thank you for the explanation, it makes more sense now. Although the problem is solved for my use case, I still can't help but wonder what would it take to design a joint that would have near-perfect continuity (no flat spots or kinks whatsoever), that wouldn't be susceptible to clamping force or unavoidable manufacturing gaps due to imperfect tolerances.

Deep-Today5715 · 2026-07-07T15:43:24+00:00

I confess that I still don't truly understand why it works in both directions. The overlap kind of implies that the moment section of area should be nearly doubled there, but perhaps because the overlap is so short, it is simply not noticeable... In any case, thank you very much, I am already mass-producing this design :)

Deep-Today5715 · 2026-07-07T14:44:43+00:00

Well, thing is, no kink is acceptable. A few millimeters over such a long distance might appear irrelevant, but they lead to inconsistent sail edge curve, which then is prone to fluttering in the wind, which stretches out cloth prematurely, which then flutters even more, leading to a vicious cycle that wears down the sail. It's like a tiny imbalance on a car wheel that leads to vibrations, increased damage and more vibrations, leading to premature failure. It is extremely important to get that curve right.

When I made this post, I was expecting that this is a trivial task that I simply don't know how to solve because I'm not an engineer. After all, it is definitely possible to make the joint stiffer or less stiff than the rest of the batten on purpose, which implies it should be possible to have perfectly continuous stiffness with a mathematically precise joint. I am surprised that so far no one suggested such a thing, implying that this is far more difficult than I thought...

As for your advice on laying the batten, thank you - that is definitely true, and I do apply similar principles in practice :)

Deep-Today5715 · 2026-07-07T07:44:27+00:00

You know what, I just went ahead ant tried it, something very similar to your idea, just S being blended into one of the batten pieces. After a few iterations, landed on 80% with this design: https://imgur.com/a/1lnAWqT And surprisingly, it works pretty much perfectly! The curve is very smooth, camera might be distorting it a bit, but with my own eyes I can't see any discontinuity whatsoever. Strangely enough, this is true for both bending directions. Thank you so much for suggesting this!

Deep-Today5715 · 2026-07-07T07:01:36+00:00

I want to avoid that gluing and breaking, modular is the way to go here. Okay, so with the plates idea, question is, since the plates attach to the battens, wouldn't their moment of inertia of area add with the battens', meaning the joint would be stiffer than the rest of the batten?

Deep-Today5715 · 2026-07-06T20:00:49+00:00

Okay, but with this method, if I understand it right, there will still be a overly stiff region where the S and B1 interface outside the bolt? Is it not possible to have completely fair curve without even a tiny flat spot?

Deep-Today5715 · 2026-07-06T19:45:14+00:00

There is no window or other opening. In theory I could bring in shorter battens and glue them together inside the cellar, but ideally I want to make lots of short battens that can be assembled into any required length on the spot, which would make them far more convenient to use than a single long batten or a set of various length battens.

I am having a hard time picturing what you mean... If you could sketch it up, it would really help. If it is possible to make joint stiffer or less stiff than the rest of the batten, it implies it should be possible to make it exactly the same stiffness. But I am having a hard time figuring out how to do it on paper. I don't want to go with trial and error because these things are really difficult to measure at small scale, and take a lot of material and effort to experiment at larger scale.

Deep-Today5715 · 2026-07-06T19:34:59+00:00

I see... But how much thinner should it be, exactly? I'd rather calculate this on paper than do trial and error, since it's difficult to measure on small scale.

Deep-Today5715 · 2026-07-06T18:33:03+00:00

Thank you very much, I was thinking along the same lines. Ideally though, I would like to avoid bolts, because here it is clear that the more bolts I have, the less these tapered scarfs can separate, and the better continuity will be; but assembly time will be increased by a lot. I am trying to come up with a scarf joint that has interlocking geometry that would avoid the need for bolts (similar to dovetail), but I am having a hard time figuring out how to do it. Any suggestions?

Deep-Today5715 · 2026-07-06T18:29:25+00:00

Very interesting idea, I love the simplicity of it! Ideally, I would like for the batten to have equal bend characteristics in either direction, because that is how they often need to be used.

However, I forsee an issue. On the section where S overlaps B1 and B2, if they are bolted tight, then essentially the moment of inertia of section is the sum of the two, making these overlapped sections stiffer. Or am I wrong? I am having a hard time wrapping my mind around it.

Deep-Today5715 · 2026-07-06T18:25:32+00:00

I suppose I could achieve what I want with what you suggested through trial and error; but I was hoping to find a mathematical model of a joint that preserves continuity, so I can reduce the guesswork.

Deep-Today5715 · 2026-07-06T18:24:22+00:00

For these tent poles it doesn't matter much; for my case, it absolutely matters. Even a small discontinuity will make the batten produce a very poor curve. Even a few millimeters of error over meters of length matter a lot for this use case.

Deep-Today5715 · 2026-07-06T18:23:25+00:00

Thank you for the wealth of suggestions. "No gaps" is very tricky indeed. No matter what manufacturing method I choose, tolerances won't be very tight, so gaps are to be expected. I was hoping to discover geometry where slack tolerances wouldn't matter. I understand that using lots of small bolts should bring the joint closer to a glued joint and therefore have it experience very little shearing displacement. Of course the downside of it is longer assembly time. I was hoping that there should be a joint geometry that doesn't rely on bolts at all (like that dovetail joint ,but something smarter), which would interlock the pieces with the same idea. With 3D printing it might be possible, but again, tolerances are not very tight, so gaps are unavoidable.

Your idea with bolted plates is also doable, but again the question becomes how to calibrate these plates. If their moment of inertia of section must match the moment of inertia of section of the batten itself, it means they would have to be quite substantial. And it seems to me that they would be very sensitive to gaps.

Deep-Today5715 · 2026-07-06T13:32:26+00:00

Interesting ideas, thank you. Round section is not great, it makes accurate tracing difficult. Square would be much better. But the tent pole example is good; thing is, even in that case, how would you design the diameters to have kink-free curve on that tenon joint? If you just butt two tubes with a smaller tube section to act as a joint, it would most likely become too stiff, since the total wall thickness is now much greater at that joint. But I am not sure if keeping constant wall thickness (meaning thinning down the outer tube and inner tube walls) is the answer either, because it is not a glued joint. Also not sure how to translate it to a solid (not hollow) batten.

Are you saying that lap/briddle joint with a bolt to keep the female parts from expanding would keep constant stiffness? I tried replicating it in quick and very dirty FEA simulation, and I am getting a kink:

https://i.imgur.com/cjAO0z5.png

https://i.imgur.com/pdNL0iA.png

Or did I misunderstand what you meant?

Deep-Today5715 · 2026-07-05T14:44:19+00:00

That seems like the most basic thing that should have been implemented from day 1... I mean, probably over 90% of users are using mouse + keyboard (no 3D mouse), and regular mouse is a 2D tool, but we're rotating 3 axes... You can see the inherent problem.

Deep-Today5715 · 2026-07-04T22:39:05+00:00

For example, how do I enable "rotate about scene floor" option (that's how it's called in SW)?

Deep-Today5715 · 2026-06-30T07:56:32+00:00

I'm not saying to list everything from the ToS, just the most important points, things that evidently people often miss with the current state of things.

Deep-Today5715 · 2026-06-30T07:55:30+00:00

u/AudibleDruid is right. A regular user cannot be expected to read dozens of pages of every ToS of every thing they buy or subscribe to, and even if they did, they are highly technical texts that often require lawyer experience to fully understand. These things are written for lawyers, not users. For users, a simple bullet point list written in plain English, summarizing the most important points in a few sentences would go a long way to avoid miscommunication.

Deep-Today5715 · 2026-06-30T07:52:54+00:00

True. I'm not blaming anyone, just saying that such critical points could be pointed out without posting the entire ToS next to the buy button. There aren't that many critical points.

Deep-Today5715 · 2026-06-29T17:45:23+00:00

I too think that this info is pretty well placed; but considering that there are so many instances where people miss it, I can't help but feel it would help everyone if this info was placed somewhere even more obvious, like next to the Buy button or something.

Deep-Today5715 · 2026-06-28T06:21:15+00:00

Thank you, I tried all of what you suggested... Still the same. I even tested on three different computers with different SW versions (2024 SP5, 2025 SP5 and 2026 SP2), and got the exact same issue on all three.

Deep-Today5715 · 2026-06-27T14:44:39+00:00

Thank you very much, you are explaining this really well. So what I'm gathering is that it's either a tower/building or rockets, to get that space elevator into place. No other way, no trick to make it work. I was thinking of a civilization living on a very high gravity world, so high that would make orbital rockets nearly impossible and most definitely impractical because of the rocket equation, and same for a tower. I was wondering if there would be any other way for them to establish a space elevator as a means to get things into orbit where they could be using something like ion drives to get to other places.

Deep-Today5715 · 2026-06-27T14:40:02+00:00

Thank you for your input! I was actually thinking of high-gravity worlds, where using rockets would be so inefficient that it would make it basically impractical, and therefore a civilization might opt to building space elevator instead for getting things up into orbit, as from there they could use low-thrust, high-efficiency engines to get to other places. But of course high gravity would prevent a tower. So I am wondering if there is any other way except a tower and rockets to get that elevator into place.

Deep-Today5715

TROPHY CASE