In the last few months, every time I’ve gone kiteboarding and looked at the line splitter (now V1), I’ve had the feeling I could do much better. After watching this video about compliant mechanisms I encouraged myself to design a new version of it.
The improvements I want the line splitter to have are the following:
- Single part solution
- Keep itself shut while not in use
- As minimal support material as possible
V2.0 – Return of the LineSplitter
Instead of commencing with V1, I started from scratch by designing a 1mm thick “Ribbon” that will act as a spring to keep the mechanism shut while not in use. The rounded parts will take the stress of the bending while the flat parts will compensate for the bending moment. The shorter the flat bits, the stiffer the spring will be. Opposite from the first version, this time, the moving part will have the “L” shaped grooves, while the outside will have the straight slot. I’ve also added a tab connected to the inside so it can be pushed in to make the grooves align. To avoid support material this tab will lie on the printbed.
Taking advantage of the free simulation module of Fusion360 I created a custom material with PLA properties which I got from here . I simulated a displacement of 4mm and a force of 5N acting on the tab
As it’s seen on the first simulation, the misalignment of the force over the spring will tend to make the inside part rotate therefore I’ve had to add some chamfers on the inside to only allow axial movement. From the second simulation, it can be seen that I’ve still got a safety factor of around 1.5. All good. Let’s print!
Lessons learnt from V2.0 :
- A throw of 4mm is on the low side, increase if possible
- The spring works great, at 4mm of travel the force is low, however, it can be maxed out no problem
- When printing, the starting point of each layer has created a small seam between parts, next time set to random in Slic3r.
- There is some displacement on the upper side, copy the “railing” technique of the lower side
- Set some sort of stop/detent to avoid skipping the point where grooves match.
V2.1 – A new hope
For V2.1, I’ve increased the travel to 7mm, consistent with a 5N force, for this I’ve had to increase the center part around 12mm. I’ve also added a top chamfer to act as a rail and a physical stop on the tab to avoid overshooting the alignment point. If this design works I think I will have reached a functional point and the next step will be adding more superfluous features
Prototype V2.1 design
Lessons learnt from V2.1:
- The overhang over the central groove is too large
- Would be nicer if the spring was a bit stiffer
- The design is getting very long
- Problems of Ver 2.0 have been solved!
V2.2 – The rise of the line splitter
There are only two main issues to solve. To avoid the overhang, the part will have to be flipped on the print bed; for this to work the side of the “Push tab” will have to be inverted. To make the spring stiffer I have removed a “coil”, this way the spring will compress more per unit travelled. This has also the side effect of making the unit shorter. I have also taken the opportunity to fillet the edges where the line will rub with to avoid line damage. I’ve also filleted most other edges that don’t interfere with the manufacturing in the 3d printer.