Injected joinery for modular construction
The joinery consists of 3 parts connected by one single bolt and the structure can be continued in 12 directions. I made two moulds for the joinery as two of the three parts are the same. After injecting, holes need to be drilled at the connection points with the help of a template. The joinery’s thickness is 9 mm, so you have to cut out the negative shape from the beams that have the same length. For now its in testing phase, it seems strong enough to build bigger structures, like a green house or a tent. Let me know what you think of it, how could it be more simple and if you have a different structure in mind:)
That really looks great. A library of these designs would be a great resource. Have you calculated the load capability of the joints? Looks like the bearing load at the bolt to plastic interface would be the first yield point. Maybe a larger diameter bolt or pin, or a locally thicker pad.
Again, great work
Great injection mold design. With some changes on the truss angles, this type of connectors could potentially be used to build large scale geodesic structures.
Keep us updated on progress, this opens up a large number of application including house building.
ohhhhh, that’s just what i’m missing to create geodesic structures 😀 !!! awesome !!!
Hi all, I’m Kit, working on the structure with Adam.
In the last few weeks, there were 125 ‘cups’ of the joinery were injected, over 200 wooden beams are prepared and both CNC and injection ‘plates’ of the joinery were tested.
The injection took 12-15mins per a joinery part, with 8 hours of working, around 30 parts could be produced per day.
The original plan is to build a 4-leg-structure, like a pyramid, however, the structure is already strong and sturdy after 2 legs were built.
The injection ‘plate’ was broken during the pressure test, while the CNC part stays tough. Due to the design of the mould of the ‘plate’, the plastic meets after the holes and it causes a weakness point to the ‘plate’. The quick solution should be pre-heating the mould before injecting, which still has to be tested.
One of the beams is replaced with a plastic beam made by the extrusion machine, and it works as good as the wooden beam.
This is super interesting stuff, great work with a lot of potential!
Coincidentally I’m currently researching geodesic structures for a client. The project will probably be made out of cnc-machined plywood but my research might be of help for figuring out the hubs of the structures. Some of those geodesic structures can be made out of just 2 pieces, similar to the system you’ve made.
Oh but I’m certainly open to offer help and share my findings if there are questions regarding the mathematics or 3D modeling of it. I’ve read that an issue with diy outdoor geodesic domes is sealing them properly from wind and water.
Buckminster fuller has made some amazing stuff, especially knowing he didn’t have access to computers to do the math and calculations. Pretty insane.
Good to know. Will most definitely hold you to your offer 😉
Re sealing: That’s what I liked about the shapes you showed, they offer space for proper sealing. And PP of course takes DIY to a whole other level!
I recently watched an episode of Fuller House.
Boy was I disappointed!
Thanks for sharing the project @siemenc. It is interesting to see CNC version of the geometric dome.
I also working on the geometric dome direction right now. There is a reference called Hubs from the UK. Their flexible “ball joinery” is really interesting to give a try, as it gives variety to the geodome design, like door, tunnel, leg or window. They also allow people to download the simplified 3D model on their website.
We 3d-printed the parts in the last two days and tried to build a pentagon of the v2 geometric dome, 22 “balls”, 1 “5-way-connector” and 5 “6-way-connectors” were printed. The result of the 3d-print parts are nice, the “connectors” lock the “balls” really tight. However, it is not easy to make these with the injection machine, as there are undercuts.
A pentagon was built early today, with the Hubs parts, and the result is fascinating.
The length of the beams can be found on their website. The assembly process is simple, quick and easy after the “balls” are screwed to the beams, it just takes 5 mins to build a pentagon.
However, the joineries are too flexible, it does hold the shape when it is picked up and the “5-ways connector” could be rotated in a certain amount. Maybe that is why Hubs said the structure is not for climbing ;).
Open for Discussion:
Should we give up variety to have the strength? Or the other way round?
Well, the structure of course isn’t complete like this.
Linking pentagons together will limit the flexibility of the whole structure, basically becoming sturdier as it becomes larger.
Plus, you are of course missing a layer as the other layer would also strenghten the trangles.
Think of it this way: it is easy to lift a brick. Harder to lift a house.
The parts make up the whole. You now only have a part…
So I say moot.
No need to give up strenght nor variety.
Yes, of course, the structure is not finished and it is not sturdy. I would like to build one more level of the structure to test, but it will take one week to print everything….
And I also wanna try the previous approach to test although there is no variety but it is strong enough to climb on it.
The Hubs parts are Acetal. They can probably preload the locking plates a little higher than your 3D parts.
I think the weakest point of the Hubs design is the screws in the end grain of the wood. This is generally regarded as bad practice by woodworking types, screws do not hold well in end grain and are more likely to split the wood.
I like the slot with the cross drilled bolt design much better, you can see the plastic failed before the wood, it also aligns the beams nicely which the Hubs do not. I suppose you could adapt the ball part of the Hub and put a square socket or a flat tongue on the end of it instead of using a screw.
Nice! I’ve seen those hubs during my research, it’s a quite clever solution that allows for adjusting for tolerances. But I agree it would be better to tweak the design to not have that screw in the end grain to allow for a more solid structure.
However, it is not easy to make these with the injection machine, as there are undercuts.
Not sure I see the undercuts? Is it because of the hole in the center of that peg?
Myself, I’m looking at two types of joinery now which I’ve tested on small scale using the lasercutter (one is based on the great work of Robert Clark). Seems to work well but I’m a bit concerned with how tolerances might affect the assembling on a larger scale.
I have been thinking of ways to get rid of the need of cnc milling machines in the mold making process. Mold making is always the difficult of part of IM and expensive.
Look at this article: it may be helpful. https://www.3dhubs.com/knowledge-base/3d-printing-low-run-injection-molds#why
If you use conformal cooling channels connected to a water source like a tap you could get some interesting results. You should be able to cool the mold down enough to do 100 of units. If you could get a desktop extrusion printer to print molds it would be a powerful tool to increasing product development and outputs.
let me know what you think!
I’m also a Product Designer for PP and am excited to help develop this project further! adamtoth is no longer at headquarters working on his initial structure, but chuwaikit and I are continuing to work together on a geodesic dome hub. We’d like to hear more about why people are interested in this concept and what they might use the domes for. Whether you are a prospective dome owner or part producer, please take a moment and fill out this 5 question survey to help us create the best product possible!
Thanks! Looking forward to collaborating with all of you more on this!
One of the parts of the joinery topic is the strength capability of the resulting part and whether it achieved the prediction based on typical material properties. It would be great if the team set up a test rig to get quantitative data. For example, at what load did the part shown in Kit’s May 28 post fail?
Test rigs can be built fairly easily/cheaply. This build is general purpose and probably provides more data than you need https://www.youtube.com/watch?v=uvn-J8CbtzM . The simplest form would be one of the generic 300Kg or 1000Kg hanging digital scales, a simple load frame, and video capture of the break point. A step up would be a load cell and arduino as used in the test machine video.
There are plenty of online tools for estimating geodesic joint loads. An example here, with links to tools in the description https://www.youtube.com/watch?v=TqxarO-5igc .
On a side note, I hope @sarahg ‘s profile photo implies that conditions in Eindhoven have improved from the February wool hat, double hoodie, ski jacket outfits to large chocolate dipped ice cream cones. Good choice.
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