Week | 4
Computer-controlled Cutting
How I’m making a parametric construction kit and learning how to use the laser and vinyl cutters.
12 February 2018 15:26:
This week’s assignment will be to design, make and document a parametric press-fit construction kit, and also to cut something on the vinyl cutter.
To put it very simple there are 3 main parameters to keep in mind when you’re using a laser cutter and these are Speed, power and frequency. Another important aspect to consider is the Kerf, which is the actual tolerance from what you draw and what you get in the end, because you are cutting by burning.
We were also asked to document information about the existing laser cutter here at Fab Lab Barcelona, and this is documentation I’ve been able to consolidate after our brief introduction to the equipment last week:
There are two Laser-cutting machines that can be used at the moment at Fab Lab BCN.
The small one that handles pieces with maximum size of 60 x 30 cm:
The bigger one that handles pieces with maximum size of 100 x 60 cm:
These are the steps to use the Laser-cutting Machines:
0 - Choose and measure your printing material (cut to fit machines if needed).
1 - Check under honeycomb for material leftovers. If so, ask instructor to clean.
2 - Ask Instructor to turn on vacuum system;
3 - Turn on machine and wait for it to self-calibrate;
4 - Open lid and use arrows (on touchpad) to move up the honeycomb so you can place material plate;
This is the touchpad:
5 - Put the material plate making sure it’s as flat as possible. If not flat enough, fix the corners with masking tape or send the print job in multiple (smaller) parts;
6 - Focus the laser - Place the focus tool/guide and move up the plate until the object falls. The acrylic one for the big machine and the metal one for the smaller;
7 - Move machine laser manually (using the arrows on touchpad again) either to “0-0” point or to most appropriate point in the material plate;
8 - Close the lid;
9 - Go to computer and import your file from Fab Drive;
10 - Draw something to do a print test to evaluate the 3 basic parameters of Speed, Power and Frequency. You should also look for the best direction to print, considering that, in cardboard or wood, using the natural direction of the material could help;
11 - Setup printing options in Job control (this part requires specific and detailed documentation, I guess. I couldn’t take many notes far from the screen, but we will update it as part of the group assignment).
12 - Send out to print by choosing the appropriate printer;
13 - Wait for the print job to be completed, open the lid and evaluate results.
14 - Adjust printing setup accordingly and test again if needed.
15 - After setting up final parameters, send the actual job to print.
Remember:
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Printing software will only read and print according to your color definitions, it is mandatory to define those and assign your colours to layers.
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In the big machine, don’t go more than 1 in speed because of a problem in the belt (range should be 0.5 to 1).
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Use low frequency on materials that are more likely to burn.
If you notice any fire spark or excessive smoke during the operation, do one of the following on a top-down order: Press pause on touch pad; or Press stop on touch pad; or Turn off pushing red button; or Open lid.
So, after this preliminary documentation I was set out to do the actual tests as part of the group assignment.
For my personal assignment, I wanted to create a simple press-fit construction kit that could have some purpose, rather than just making a point that I’ve learned how to model parametrically and use the laser cutter. Nevertheless, there isn’t much time to work on this task so I decided to stick with something simple. Inspired by this image here:
I thought of making a much simpler flying saucer lamp, that could be sliced and printed in cardboard or plywood.
So, having this as an initial reference of a “minimalist” design:
I have, then, used Fusion to make this model:
As you can see here I have input the size of the main circumference as a parameter and made all other parts adapt to this, so they are relative and if that changes, everything else does (apart from the hole to pass the wire, which should be constant):
Once it was ready, I have exported it to Slicer , a very useful add-on to Fusion 360, that allowed me to slice the model for printing:
Slicer has several modes in which you can slice your 3D model and the choice I made was the interlocked slices, so that I could print the assembling parts for press-fit kit.
The software is very useful and intuitive, it allows you to test different types of slicing, orientation, amount of parts, offers instructions on how to assemble, etc. But it has some bugs. I’ve had several issues trying to save models and adjusting the thickness of materials. Here are some screenshots:
Here’s the model at Fusion and here’s the Slicer model.
I have realised that, since I have used Fusion to design the object parametrically and, then, slicer to export it, I haven’t really proven that I can design a parametric joint, so, I am planing to do a simple one on Inkscape or Grasshopper and post it here.
13 February 2018 22:26:
After several tests on the smaller laser cutter, I have chosen the following parameters to laser cut the cardboard: Power: 31. Speed: 1. Frequency: 5000hz. I have also noted that the best thickness to be considered was 2.7mm, taking into account the kerf.
Here are some samples and the chosen parameters (circled):
The power, speed and frequency seem to have worked well for the cardboard cutting:
But, there were many take aways from the process of making this and the main lessons to me were:
1 - Have a wider safe area on the material plate. I have measured and cut the cardboard to 60X30 cm and input these properties at Slicer, so it could automatically arrange my parts in the sheet. In order to save material, I avoided using too many sheets, but I noticed some parts were too close to the edge, what eventually made the 3 last parts on the sheet to be cut, and I had to print them separately. Here’s what happened:
2 - Take into account the natural direction of the material for better finishing. The cardboard has a corrugated interior, which means that when you cut you will you will always show this interior. If you choose to distribute and print your parts randomly, taking into account only the better use of the sheet, you might end up with a uneven finishing. See the difference here:
3 - The final size of the object is directly connected to the material chosen. Having chosen cardboard to make this project, I didn’t consider that the size of some parts and their ends would be so small that would actually bend, due to the flexibility of the material. An it would avoid proper fixation. You can see this happening in the tip of the cardboard below, if it was ply wood, it probably wouldn’t bend:
4 - When choosing the kerf on a flexible material, keep in mind the amount of connections and adjust accordingly. Since my piece had many connections, I have realised that the insertion of a piece in a slot slightly pushes away both of its walls. Meaning that the next surrounding slots will have less space to insert a piece and so on and so forth. This means that, though I have measured the kerf of the material correctly (2.7mm in a 3mm material), I have made it connecting only one piece, not several pieces connected to the same part.
5 - Pay extra attention to the assembling moment. I assembled my pieces in a somewhat noisy environment and, with so many parts (32) I have skipped one gap right in the beginning, which influenced my whole design. Since it was hard to assemble everything due to the kerf comment above, I couldn’t go back and reassemble everything from scratch, because the cardboard had been compressed to fit in. So I left it as it was. Though it sounds obvious, it’s very important to pay a lot of attention to the right order and positioning of each part. I ended up with uneven ends because I missed one gap at the start:
So, this is the object I ended up with. Instead of an Unidentified Flying Object, it looks more like an Unidentifiable Flying Object : ) :
Not impressive, but a decent prototype and useful exercise. Time permitting, I might do it again in plywood.
Another part of the assignment is to cut something with the vinyl cutter and I have decided to cut a sticker with the logo of my final project, so that I could use it in the future. I have done the logo on Photoshop, using basically text (since the design is just the name “Feedblocks” and a cube with a pixelized question mark, which is also a text”), imported it on Illustrator and converted layers into objects, then exported an .svg.
The vinyl cutter we have at the lab is the Roland GS-24 and the steps to cut were:
Put the vinyl in the cutter (in our case we only had black sheets);
Align and pull the lever down;
Choose “Piece” from the “Select Sheet” menu (the machine measures the length and width of your sheet);
Import the .svg file at Cut Studio;
Press “Cutting”.
I have also repeated and documented this vinyl-cutting process for my final project, which can be seen here.*
A big part of the assignment, which I have mentioned above, was to do a parametric part. Up to this moment, I had made a parametric model of the UFO that would scale proportionally according to the input of various dimensions. Apart from the UFO model I posted above, I have also made now a parametric part: a laser cutter test done at fusion following this very nice tutorial here. to make a parametric model, you have to input a series of measurements that will be later referenced by the model, so, if anything changes in the parameters, the model changes accordingly. I did this by adding parameters such as the slot_depth, spacing and a thickness from which the slots would vary incrementally (also added the increment as a parameter):
This is my model, where I can change the thickness and the models adapt accordingly:
Each slot has in the center the input thickness and every new slot to the right subtracts 0.25 mm and every new slot to the left adds 0.25mm:
The parameters for the laser cut I’ve used where found out and documented during our group assignment, which are: Power: 80. Speed: 1.7. Intensity: 1000hz.
This laser cut test helped me realising that the best kerf for the 3.1 plywood (picture below) is roughly 0.1 mm, meaning that the best cutting size for press fitting plywood would be 3mm.
Here’s a video showing me trying to press-fit with the different dimensions:
Here’s the page for the group work assignment I’ve taken part.