WEEK 3: COMPUTER-CONTROLLED CUTTING
Objectives
Group assignment:Individual assignment:
Have I...?
For vinyl cutting:Vinylcutting
For my first try with vinilycutting I have been followed and suggested by Flavio Lampus and Pietro Rustici who work in my Fab Lab.
I like Piaggio Vespa, the italian iconic "scooter" (I don't like to define my Vespa as a scooter), so I decide to cut the Vespa logo. I search on Google image and I find this one:
I could have used this image, but I preferred to try to vectorize it in order to document everything and to be able to view again it in the future. So I open the logo in Inkscape in order to vectorialize it and prepare the image in the best way for cutting. As I said in Week 2, I had previous experience with 2D raster and vector image software. To vectorialize an image I proceeded in this way. First of all I launched Inkscape and I open the image. Than, selecting it with left mouse button, I choosed Path - Trace bitmap (In italian is Tracciato - Vettorializza bitmap) I you can see the option I choosed on the screenshot below.
In the new pop-up menu I left unchanged all the parameters since I already had a satisfying result from the small preview in the right side. But you can try changing the parameters to find the best result for the image you have chosen. Basically my image was very simple and lacking in complex details.
Inkscape created a new vector image above the original, so I simply moved the vector one and deleted the raster one.
Now I resized my image. I selected mm as a unit of measurement and I setted to L: 80 and H: 30. So I think that my cutted figure will be 8 x 3 centimeters.
The final step in Inkscape was to resize the work plane with the image size. With the combination Shift + Ctrl + D I opened a new pop-up menu and here, opening the Ridimensiona pagina a contenuto drop-down menu (you can see on the screenshot below) I add 1 mm to all directions of the plan.
Than I saved it as PNG raster file (Cairo PNG format) in order to be compatible with my Fab Lab's Vinylcutter.
Here is the result.
Saving this image on a USB drive, I trasfered it to the PC connected with the Vinylcutter (a Roland CAMM-1 GS-24) and I opened it with the software CutStudio using the command Import. For these screenshots I used the project of my colleague Eleonora Piccinelli (we worked togheder for this part and we made screenshots just once), so the image is different but obviusly the process is the same. Searching online I've found the official user manual of this Vinylcutter, translated in Italian language. If you want to take a look you can find the PDF at THIS LINK.
Once selected the image with the left mouse button, I clicked on it with right mouse button and than Image profile. In the new menu I clicked on Extract Contour Lines.
On the work plan, CutStudio created cut lines over the original image. I simply deleted the image and leaved only the cut lines.
So I decided the cut parameters. I went to File - Cutting Setup and in the new menu I press on Get from Machine in order to send the machine cut parameters to the software.
At the same time I insert the vinyl sheet inside the Roland Plotter.
I press the button Enter to calibrate the knife to the origin.
And than finally I click on File - Cutting. After that I removed the surplus material.
I covered my shape with a transparent adhesive film. After few minutes I put the adhesive vinyl in his final location (my phone's back) and I removed the transparent film. Here is the final result (you can download simply saving the image from your browser). I'm very happy about that: I really like how it came!
--> Download week3_vespalogo.png (2 KB)
Finding Kerf
The kerf is a sort of "margin of loss of material that occurs during laser cutting". It is a very important measure to take into consideration especially when designing joints. Me and my group, as first thing, calculate plywood's kerf making a 1 x 1 cm square in Adobe Illustrator and than cutting it with our lasercutter (a Trotec Speedy400 flexx). Settings and method in which we cut are explained in our Group Page.
We removed the little sqare and we measured it with a digital caliper. The measurement is:
And then we calculate the kerf:
We found that the kerf of this sheet of plywood is 0,09 mm, less than 0,1 mm. But it's important to remember that the kerf varies not only from material to another, but also for the same material must be verified every time.
Parametric design with Fusion 360
As I said in Week 2, having a Mac I use Fusion 360 as software for parametric CAD. I suggest this software also for Windows user because it has a simple graphic interface and it's easy to comprehend and learn. I've also followed some tutorials and guides; you'll find links at the bottom of this page under Useful Links.As firts try, I build a parametric shape representing a sort of "male/female" 2D joint, just for understand better kerf and how to predict it. For first operation I setted up my Parameters, the fundamental part of a parametric project. In this way, if in the future I will have to change a measure, all the other ones will adapt automatically without having to do it manually.
Using parameters in Fusion360 it's easy. The funcion to search is under
Modify - Change Parameters (I bring it as first function using the little button close to it) and is represented by an icon with the ancient greek symbol sigma "Σ". In the new window, to add a new parameter I had simply to press the + button, adding a name and a value or an expression. I didn't have to follow particular rules to write expression, just basic mathematic sintax. I summarized the main functions of the window in the following image. For this example, I used two parameters, Parameter1 = 2mm and Parameter2 = 5mm. But it would be, for example, Parameter2 = 2 + Parameter1, creating a dependency between them, as I made for Function = 2*(Parameter1*2) + (Parameter1 + Parameter2).
For this work, parameters I used were:
kerf = 0.09 mm
d = 10 mm (the measure I want the joint will be)
male = d + 2*kerf
female = d - 2*kerf
For this first try I did not take it into account about kerf for the other edges: I know it must be considered for every of them but for now I'm only interested about the joint.
Than I create a new Sketch, drawing a random joint without any values with the feature
Sketch - Line
After I set the measurements of the sides. I used both fixed measures and the parameters previously set. I use the feature
Sketch - Sketch Dimension (I set it as first function too). I just click on every side and wrote the measure I wanted.
I transform it in a solid extruding both shapes. The process is the same I used during my first experience with Fusion last week, so I don't repeat it again. It is a superfluous step in this case because now I am only interested at this two-dimensional vision and not at other possible faces. To make it somthing that I can cut I have to export it as
.DXF file. For doing that, I click with the right mouse button on Sketch1 (left hand side) and I choose Save As DXF.
The .DXF format save my shapes inside a file that could be opened, for example, in Adobe Illustrator. Suggested by my instructor Matteo Sirizzotti, I investigate about this file format.
DXF (or AutoCAD DXF) is a format developed by Autodesk with AutoCAD 1.0 for enabling data interoperability between this softwares and others. If you want to know more about DXF I suggest to take a look to the Wikipedia page and the File format summary.I made some try. The first one I cutted with 0.09 mm kerf. The result was acceptable: it fits well and resists enough when moved.
I did other tests to improve the result. I tried with 0.03 mm kerf, value resulted from a wrong measurement (infact the joint was too large and pieces did not remain attached togheder) and also with 0.1 mm (but in this case the value was too high and a piece was broken a little bit). So I decided that 0.09 mm was a good value and I tried to use it for a different joint, creating invitations to facilitate the joint and the resistence. The result was good but unfortunately I notice after the cutting that I wrote a wrong measure on Fusion 360 and one side was slightly smaller.
I need to pay more attention to values when I design my pieces: I tend to do things too quickly because I want to see immediately the final result!!!
Second try
Than here is my second try to make something to be composed. My idea is to make a sort of nameplate, something modular which may be useful to the Lab, for example during conferences or workshops. Here is the sketch:
I started creating the CAD design setting these new parameters:
base = 50 mm
kerf = 0 mm (for now...but I can change after)
d = 10 mm
spessore = 0.8 mm (depth)
male = d + 2*kerf
female = d - 2*kerf
altezza = 30 mm (height)
radius = 15 mm
Than I preparate principal pieces of the base, the two final pieces and the central one that can be cut several times.
Now I extrude them, making complex solid. I did this to try to assemble the pieces (following the suggestion of my instructor Matteo Sirizzotti) to make sure that they fit perfectly. Once I extruded my shapes, I clicked with right mouse button every
BodyN voice I found under Body lateral menu and then I selected Create Components from Bodies.
Than I clicked on
Joint (under Assemble menu), I selected faces that I wanted them to match and I go to the Top visual to see if there were any overlaps: each face fits perfectly!
Now, changing the kerf value from 0 mm to 0.09 mm I noticed that there was a slight overlap between male/female joints: that's what I am looking for because this difference should disappear by actually cutting the piece on the material. This is the power of parametric design: without this, I would have had to requote every single measure. Now I can continue being (almost) sure to proceed with the right measures.
I continued creating the cut extrusion and the nameplate. Here new parameters and the final solid vision on Fusion 360. I introduced a new parameter
incastro1 = 20 mm
for the nameplate's joints.
So I export in DXF format, modified in Illustrator setting 0,001 mm red line (RGB 255 0 0) for cutting and black (RGB 0 0 0) for printmaking. Here's my try with some values for depth and kerf:
But only after my third try I notice that I wrote wrong parameters for the nameplates! Infact some values are 1 cm longer than what the base's joints should and therefore they not fit together! So I modified again those parameters in my Fusion sketch. I change material for cutting so I modified again kerf, depth and other adjustments. For example I add another parameter:
distanza_denti = 29.915
for distance between joints of the nameplate.
And after some other adjustements (for example for the teeth's height of the plate I inserted the function "thickness (spessore) + kerf" while the correct one is
thickness - kerf) on the CAD sketch (thanks to Silvia Palazzi, a 2017 Fab Academy student), here is the final sketch:
And the final result! The measurements are not exactly 100% accurate because the wood used is not uniformly flat, but the joints are firm and the seal is strong.
--> Download nameplate.dxf (5 KB)
--> Download nameplate.f3d (Fusion 360 - 126 KB)
Useful Links
Fusion 360 guides: