Sander van Vliet

Fabacademy2016
@Fablab Amsterdam


Computer Controlled Cutting

Week 3 (10 - 17 February)


Lecture

We were introduced to the principles of cutting by the use of tools like a:
-knife (you know this!)
-hot wire (polystyrene-, polypropylene- and polyethylene foams)
-waterjet (textiles, rubber, foam, plastics, leather, composites, stone, tile, glass, ceramics, metals)
-vinylcutter (self-adhesive vinyl/aka plastic sticker)
-lasercutter (plastics, woods, rubbers, fabrics, foams, papers and thin metals)
-wire EDM which stands for Electrical Discharge Machining (Any material that will conduct electricity)
All Fablabs have a vinylcutter and a lasercutter and some also have a wirecutter (hot wire).

Assignment part 1

Design, make, and document a parametric press-fit construction kit
For this we will be using the lasercutter and we are provided with 3mm cardboard pieces of 1000x1400mm. In Fablab Amsterdam there is a BRM laser with a bed of 1200x1600mm.

Designing it
I started off looking into designing a lamp which would have a front consisting of parts with several different shapes. These shapes would affect the way the light would be directed and maybe generating shaped shadows. After a while I put something together, but I did not find it very nice looking.
Another idea I tried was a pyramid constructed of equilateral triangles (all three sides are equal). The official name for this type of pyramid is Tetrahedron. The pyramid could be scalable by adding more pieces although I came to the conclusion that if you scale it up it might not be strong enough because there is no inner structure to keep the sides from caving in.
With cardboard I tried out how both ideas could work, but in the end I did not like either of these ideas enough for creating a press fit kit.

After I had seen my children play with a dollhouse recently, which has all kinds of miniature furniture, the idea of making a bookcase came to me. I thought of a simple design and made it out of cardboard. In my drawing and product I wanted to make a rear panel too so it would be closed and this would also make it more stable, keeping the parts together. This could be upscaled to real dimensions and would not need any screws or glue to stay together. The press fit slots could be drawn parametrically so that I could change the width of all joint openings according to the real life dimensions with not too much effort.

Drawing it
In Rhinoceros I drew all the parts and the press fit slot and made it parametrical by saving them as separate files (blocks) which I then inserted in the main drawing file. If a block file is changed afterwards, all instances of this block in the main file can be updated automatically at once.
For the slots to fit well (meaning to go in smoothly enough, but not come out too easily) I needed to account for the kerf (amount of material taken away by the laser) in my drawing. The width and the height of a slot is each formed by two lasercuts so I needed to subtract 2x the kerf width from my slot width and height dimensions. To know the exact kerf of the lasercutter in combination with the material used I created a test file containing the different slots in 5 different slot sizes ranging from 2,5-3,0mm. I also created 5 different bookcase files with these different slot dimensions so I would not have to spend time on creating the final lasercutter file during my lasercutter time slot. In Rhino I selected all lines and used the Export Selected function with the default export scheme and created a .dxf file which can be imported by the software which connects to the lasercutter: Lasercut v5.3.

Making it
I placed the cardboard on the lasercutter bed and set the origin point for the laserhead. I also fixed the cardboard with tape because it was not 100% flat. If lasered when the material is not lying flat, the effect of the laser will not be consistent and could well mean that the material is not cut all the way through at some points.
Then I made a test run to decide which settings for the speed and the power of the laser would be best to use. In the lasercut software I drew several squares and set a different speed and power to each of them. The one cut with 400 speed and 60 power looked fine so that was the setting I then used to cut my test pieces. Although the settings were fine for the small squares, they were not for bigger parts. Apparently the laser head speed is being built up so the longer the line it moved along, the more it accelerates. Because it came to a higher speed, the side of the bigger piece was not cut through and I needed to tear it off. I could still use this piece because the side with the slots was cut out well. I lowered the speed to 350 and it did not happen anymore.

I assembled the five partial bookcases and it was clear to me that the one with 0,15 correction of the kerf was working best for this press fit slot. I imported the corresponding .dxf file of the complete set of parts for the bookcase and have the laser cut that out.

And here it is, my own prototype miniature bookcase!
I am happy with the result because all parts fit really well. Also I am surprised how sturdy it feels, it will probably be able to have some (tiny) real books in there =)
press fit cupboard source files - rhinoceros

Versions of the bookcase
I had some time left and wanted to see if I could make other versions based on the drawings I had of the first bookcase. Below you can see an L shaped version and one where I removed the extending part of the shelves on the sides of the bookcase. This makes it look a bit more sophisticated I think, but the sides do come off more easily this way. The assignment said to work without any screws etc. but when fabricated of wood the parts could be fixated with glue.
I then put them next to each other which makes a tv drawer. The book collection was made on a lasercutter by my girlfriend as a present, what a nice surprise!
press fit cupboard v2 and v3 source files - rhinoceros

Assignment part 2

Use the vinyl cutter to make a sticker
While working in Fablab Amsterdam I noticed someone talking about the dishes in the little kitchen sink there. She seemed to be a bit frustrated about people placing their dirty cups there instead of in the dishwasher. She had put a note there already, but I thought it was not really clear and also noticed it was not clear enough for other people. When she heard this she replaced it with a clearer but quite unfriendly note. I thought this was a good opportunity for making a few stickers! (and she did too, as it was quite a fun discussion)

I created three sticker designs in Inkscape and opened them in Illustrator on the vinylcutter pc, but the fonts were not recognized! I could try and copy the fonts from my pc to the vinylcutter pc, but it was quicker to go back to Inkscape. All I had to do was apply the function Objects to path, which changes the letters from a font type to just paths or lines if you will. Then Illustrator was able to open the document correctly.
The first try of cutting the stickers did not go very well, the letters were peeled of by the knife of the machine while it was cutting them out. When she gave the result a closer look my instructor saw that it had cut three lines! She reminded me that I forgot to change the stroke width to a hair line, like 0,001px. After I did this the machine cut the sticker perfectly! I used speed 20cm/s and force 80gf.
I used transfer adhesive to apply the stickers and I hope that they will have a positive effect on the situation =)
stickers source file - Inkscape