3-tube Wavy Joint

I designed a 3D-printed joint for three 20mm diameter wood sticks. It has wavy edges on the top and bottom of the tubes and holes on the side for the bolts to hold the wood sticks. The attached .stl file is attached for your reference.

This post will introduce the following:

1. Experimenting and Modeling
2. Deciding the Model I Will Later Work on
3. Refining the Model
4. Adding Holes to hold the Wood Stick
5. Slicing
6. 3D Printing on UltiMaker
7. Post-processing
8. Producing Another One

• Sufficient PLA Filament
• UltiMaker
• 20mm Diameter Wood Sticks * 3
• M5*16 Bolts * 3

As the first picture shown, I thought of several ways to connect the wood sticks, three cylinders, three cuboids, or one cylinder with two cuboids. I wanted to work on a coordinate axis style of joint first because they seem firm and easy (wood sticks are joined together along the x, y, and z-axis). I set the diameter of the circle to be 20.4mm to leave some space for the wood stick to go through. I then thought about, maybe I can join one cylinder wood stick with two 30mm*30mm wood sticks, so I modeled another one as shown in fig.3 and fig.4.

I also fillet the edges of the joint to make it more smooth and pleasing to the eyes. But I am not quite satisfied with the result.

Getting inspiration from the first picture, I decided to model another one that seems more interesting to me. Instead of joining three cuboid wood sticks, I joined 3 cylinder wood sticks. I just want to see how would the three tubes join together, without falling apart, overlapping, or crossing the borders.

I created a tube with a 20.4mm inner diameter and 77mm height. Replicated and rotated them to make them join together. Although the joining mechanism is already quite interesting and delicate, I'm not quite satisfied with how it looks. It's kind of raw and not artistic enough.

I used "surface-rail revolve" to create the beautiful flower-like plane and selected "cap planar holes" to make it solid. I then split them and trimmed the unnecessary parts. I tried several directions and organic solids but they just don't work well on my tubes. The trimmed tubes are like "broken" ones and are not as organic and beautiful as I thought. I then decided to try some regular solids to make my tube more elegant and wavey, and the final product looks good.

And since the structure of this joint can't hold the wood sticks as fixed as those closed ones, Prof. Garcia suggested adding small holes on the side to help hold the wood sticks later. I thought the size would be 3mm radius, but it turns out to be 3mm diameter. Luckily, this mistake can be fixed if I use a larger bold (but the proportion of the bolt may not look good on my joint).

On the slicing application, I set the profile's default to 0.2, and the infill (%) to 20%. I also selected support and adhesion since my model has a wavy (not flat) bottom as well as a tilting structure. (The red part indicated the body of my model and the cyan part indicates all the support that will be removed after printing).

I then copied the file to the USB drive and plugged it onto the UltiMaker Printer. It is shown on the screen that it would take 3 hours 40 minutes to print.

After completion, I removed the complete model and pass it onto the post-processing stage.

I first removed the bottom of the model by hand and then sanded it with the tools we have in the lab.

However, the support inside the tube is too strong to remove, so I could only print another one with no support inside.

Also, when I checked the inside of the tube, I found out that some parts at the overlapping surfaces are missing (no materials in-between). I checked the original project file and realized two of the three tubes I have are open-polysurface. I did relevant changes in the .3dm file and it is now a closed solid!

Although the newly-printed one still has some flaws, it is strong enough to be a joint for 3 light wood sticks. The M5*16 screws also work well for the holes. So yeah, this is my 3-tube wavy joint.