Source: Pexels

27 / 2 / 2019

WEEK 3: For this week, we had to design, laser-cut, and document a (parametric) press-fit construction kit, which could be assembled and made into a 3D (card) model.

I started off by deciding that I’d be making a water mill out of 4mm MDF. I did so because I thought that the construction and mechanism of a water mill would be interesting to design, and I decided to use 4mm right at the start so I could account for all the design dimensions. So first up I did a rough sketch in my notebook which includes potential pieces that I’d need to cut out and a rough overall idea to refer to.

 

First rough notebook sketch

To find out the tolerance, I’ve cut out a piece of MDF on the laser cutter with different sizes of slots starting from 3.99 to 3.91, each one sized -0.02 from the previous slot, sketched out on Fusion:

I fitted the two test pieces by placing them together with their respective sized slots. Based on how they fit together, I found out that 3.95mm was the best fitting slot where it’s not too tight that it comes apart easily with a bit of force, and not too lose that it is still secure.

 

Afterward, I started working on fusion to make all the pieces required. When I was making the parts, I decided to use filleted slots with a 3.95mm width. When I did a first test run, the filleted slots didn’t work well enough for smaller parts and those that need to have a tighter fit. Therefore I alter the slots into regular rectangular ones instead except for the two wheels and the parts in between them as the filleted slots work better in this case – the connecting parts would stick out instead of laying flat which I think fits better with the look of the water mill.

In the process, I’ve made many errors and iterations along the way:

One main issue was how I would make the wheel turn without using a dowel in the middle. My approach was making an ‘X’ joint in the middle of the wheel and slotting that onto a hole on the two legs of the water mill. It took about 4-5 tries to get the diameter and the spacing of the slots right so that the wheel could actually turn when it’s assembled.

Another issue I had was the dimensioning the supporting leg bar that would go in between the two legs of the model. Since the distance between the two legs was a bit difficult to calculate because of all the parts connected, at last, I simply measured the distance with a physical model and return back to the computer to design that final piece, which worked out in the end.

Templates on Fusion 360

Templates on Illustrator for laser-cutting

I exported the templates on Fusion as a .dxf file, then reopened it on Illustrator to get a .ai file (it was a workaround for some issues we collectively were having with the laser cutter). Then on Illustrator, I simply duplicate the pieces to the number I required and imported that file onto Ethos. Since I’ve had experience using a laser cutter before, I simply followed the steps eg. setting up the origin, area of cutting, material thickness, and cut my pieces out.

cut-outs and parts

To get to the final model it took about 20-25 iterations on Fusion and 5 different tries on the laser cutter.

Onto the assembly process, it was quite easy to do so after getting the design and dimensions right, here are some snapshots and a video of me assembling the model.

Overall this week, it was a good challenge trying to design this press-fit construction kit and a nice opportunity to practice more on Fusion 360. I’m quite satisfied with how my model turned out but there are definitely improvements to be made on multiple places such as improving the mechanism of how it turns, stability of the legs and most importantly, experimenting with more styles of slots. Currently, I’ve only made one type of slot which is the most direct approach. I got carried away with the design of the model itself and haven’t done a lot of experimentations on the slots themselves, so hopefully, I’ll be able to work on that in the following weeks!

Final model

Nonetheless, I’ve still learned a lot during the week by just tampering with dimensions, fitting and tolerances (which resulted in many scrap pieces of MDF sitting in my locker) – and it was fun, enjoyable and rewarding!