3. Computer controlled cutting¶
This week we had to do some tasks that helped us learn about 2 different cutting techniques.
Vinyl Cutting¶
To cut vinyl stickers at FabLab Bahrain we have 2 machines. I decided to use the Silhouette Cameo, which is used in conjuction with the Silhouette Studio software.
How to Use the Machine¶
After installing the software (and pressing skip on everything) you can import images to be printed by going to the bar on the top and clicking on file then open. Make sure that the image is a .png with a transparent background, this will make the following step a lot easier.
For this assignment we were allowed to use designs from external sources so I used this batman logo from Klipartz.
After importing the image click on it and then open the trace panel from the right:
From this panel select the trace area by drawing a rectangle around your image. You can adjust the trace quality to determine how small the details that will be detected and traced, typically the default setting is good.
After you are done press trace under trace type. When you move the image you will see that a traced outline of the image will be under it. You can click on and delete the original image now.
When you click on the outline you will se its dimensions, you can make it smaller or bigger by dragging the dots on the corners. Note that the default units are in inch, you can change them by going to edit then preferences.
You can also move the outline around or copy it, I made another copy of it for my friend.
Think about what the machine is going to cut and make sure that the lines present are the ones you want to be cut. In this case, the image has another outer circle that I don’t want. To delete only a single vector you must use the eraser tool from the left tool bar, and erase a small portion of the vector in question, when you do this the program will treat it as its own entity and you can click on it and delete it on its own.
You can also do effectively the opposite of this by selecting two entities then right clicking and selecting create compound path.
After you delete something make sure to move the image close to the corner to minimize material waste.
Next is interacting with the machine itself. You must first choose a vinyl sheet color that matches the thing you are trying to print. I went with yellow since that is the color of the batman logo background.
Then you must cut a piece slightly bigger than your design and paste it on the cutting mat. These mats are sticky and even come in different grip strengths depending on the material to be used (we use the mats based on availability).
The types of materials used for each mat can be seen below:
Add tape to the corners to make sure that it won’t move.
After the vinyl is secured on the mat, insert the mat inside the machine slightly, make sure you align the mat to the line drawn:
If it is inline then press Load Cut Mat:
It should get inserted and secured inside the machine, pull on the mat slightly to ensure that it is fixed.
After it is fixed connect your laptop to the cutting machine via USB, and then go to the send tab on Silhouette Studio:
In this tab you can set the type of cutting operation and the type of material used. Based on these inputs the software will automatically set the blade depth, force, and speed. In this case we are doing cutting on glossy vinyl.
After setting the parameters, press send and machine should start cutting.
After it is finished do not remove the mat yet, instead test if the design has been cut or not, if not, simply increase the blade depth and try again. Due to the blade getting dull I had to go up to blade depth 4. If it has finished cutting press Unload Cut Mat, remove the tape and the vinyl, then carefully extract the design.
Maintaining Complex Designs¶
If the design is intricate or has some separated parts that are hard to extract while keeping the same distance, use some transparent self-adhesive sheet and paste it on the design after removing the outline (you can keep the outline but it will make things harder later, so it’s better to remove it now).
I did not encounter this issue since my design is simple, so I am using footage I filmed of Ahmed Alaali.
Before starting make sure you only use as much adhesive sheet as you need based on your design’s size:
Removing outline using various tools:
Result:
Pasting the adhesive sheet:
Smoothening:
You will be left with the design stuck on the adhesive sheet, you can then remove the bottom layer and paste the design on your desired location.
Final Result¶
The vinyl was placed a bit too low on the mat, hence, a little from the top part did not get cut properly.
Nevertheless, I settled for the logo itself, even though I find it looks a bit weird being yellow.
I placed the sticker on my calculator so I feel like batman pulling out a special gadget every time I have to do some calculations on it.
Laser Cutting¶
FabLab Bahrain has a laser cutter hidden away on the top floor. It is a 100w CO2 laser cutter, but we are only supposed to go up to around 65w because the machine has been used for some time and defects may pose safety risks when going to the limit.
This machine is the Nova 35 from Thunder Laser, it has a working area of 900mm x 600mm, but can hold parts up to 1000mm wide and basically unlimited length if the pass through is open (we usually leave it open).
Laser Cutter Characterization¶
As a group assignment we were separated into 3 groups of seven to work on the tasks, we were sent to the laser cutter first to test it out and characterize some of it’s parameters.
Focal Point¶
The first test we did was to identify the correct elevation of the laser’s nozzle in order to get proper beam convergence (Focal Point).
This was done by placing a rectangular piece at an angle and cutting a line through it:
This line is not consistently cut, the location of where the cut is best can be identified by running a finger along the backside of the piece. This location is determined to be where the laser’s focal point is. The elevation of the focal point in this laser cutter is conveniently the height of this Lego piece of around 7mm.
The elevation can be adjusted to this correct setting by using the Z up and Z down buttons.
Power & Speed¶
By using the software (RD Works V8) that comes with the machine, we can create a grid of squares each with a color assigned to it. The colors can be set to represent different operations with different speeds and power.
After creating the shapes just click on them and then click on the colors on the bottom. Then click on a color from the right to set its parameters:
Here you can set the operation to be either cut or engrave, and you can set the speed and power. Make sure you set the Repeat num to 1, also make sure that you set Min Power and Max Power as the same value for a more consistent result.
We continued assigning colors to squares until we ran out of colors, then we customized each color with a different speed and power value ranging from a speed of 5mm/s to 40mm/s and a power of 10% to 65%.
The test did was on 3mm thick Acrylic, these were the results:
We used the software to create text to engrave it to indicate the speed and power of each square. Engraving is done by using lower power and faster speeds. Also note that the engraving must be set to be done before the cutting happens so that the piece does not move and mess up the engraving. It was hard to read at first, so we just used a marker to highlight it.
To identify the most suitable setting for cutting this material we look at which squares were actually cut, because others only had a small engraved outline instead of a cut. Next we assess the size of the squares, using the software we made the size of each square 10mm x 10mm, so by using a vernier caliper we can measure which setting achieve the closest value to this, i.e. taking off the least amount of material to achieve a good cut.
The best setting for cutting 3mm Acrylic was 20mm/s speed and 65% power.
Kerf & Joint Clearance¶
Since laser cutting is considered subtractive manufacturing, it takes away material based on the width of the laser, meaning that holes that need to be a certain size in order to fit something in them must be adjusted to account for this. This is important because we are using press-fit to construct our designs.
To find the appropriate allowance we perform a kerf test. We took a test in dxf format from a online website and printed it.
After printing, we tried fitting a piece into each hole and seeing which one gives the most secure fit.
For 3mm Acrylic the best fit was achieved with a 2.45mm slot.
Parametric Press-Fit Construction Kit¶
Designing¶
I used SOLIDWORKS to design a cardboard teddy bear like creature, that can also be assembled to make different shapes.
I used equations to make the design parametric in order to accommodate for different material thicknesses and quickly change them.
I put in the parameters from the experiment performed on cardboard:
To use the same variable parameters for different parts I exported the variables as a .txt file and then imported them. When doing this the link to external file tickbox should be automatically ticked, this indicates that changes made to the variables file will automatically affect the designs.
To use these variables, you must write =”Variable Name” in place of the desired dimension, the resulting dimension should have the greek symbol Sigma in red next to it, indication that it is linked to a variable.
I also assembled the individual parts as an assembly in order to view the completed kit and change any dimension as needed. This was actually immensely helpful.
To convert the sketches to a .dxf file for cutting SOLIDWORKS can be used by just opening a new part a copying each part’s sketch and then pasting it into the new part. This will allow you to save the file as a .dxf with all the needed data.
Another option is to import the individual parts into fusion and then use the project feature from the sketch tab. This takes longer because you need extrude and import each sketch, but it does give you more control since you can position and duplicate each sketch in a more controlled manner making the work you have to do on the computer next to the laser cutter less (it’s hot up there).
To do this you must open the data panel (the 9 dot square), navigate to you desired project, and then upload the models.
After doing this you can also right click on each model you uploaded and import a new version incase you made changes to them.
After importing the models you just drag them from the data panel on the left onto the workspace. This will insert them into the current document, allowing you to use the move function to position and copy the models. Make sure to space the components very close to each other to reduce the material waste.
Just make sure you select components (or bodies if you are working directly in Fusion) as the object you are moving.
After you move the duplicate and components as you need, just click on a face of one of them and create a sketch. This will only sketch the face you clicked on, we can sketch the others by using project from the sketch tab:
You can then select the other components by clicking on them from the workspace.
This will create 1 sketch with all the required sketches in their desired quantities with controlled spacing between them, which you can then export as a .dxf by right clicking on it from the browser on the left.
Since I have SOLIDWORKS installed I can open this dxf file to ensure that it looks good.
This is what my sketches look like when I open them:
You can download my design as .dxf here.
Printing¶
After the dxf file is ready we send it to the computer next to the laser printer via email. In our case multiple students sent in their files and printed at the same time.
To open the files to be printed, we go to file then import. This allows you to bring in dxf files, since using Open only allows you to use the software’s proprietary file type.
The software allows you to edit the imported files by copying and moving objects as needed. This is important to reduce the distance between pieces to reduce the material waste.
After you finish importing, copying, and moving any designs you determine the cutting speed and power. All the different pieces are to be cut from cardboard, so they are assigned the same color. The color’s cutting speed and power is then set to 80mm/s and 55% respectively, which were found to be the optimal parameters for cutting the 2mm cardboard.
Afterwards we can start printing directly by pressing start on the software, but this assumes everything is already perfect, so what we do is press download to send the file to the laser cutter after naming it.
Next we interact with the cutter itself. After sending the file, we select it by pressing file and then navigating to the sent file and pressing enter.
Now that the file is loaded, we press frame to identify the size of material needed to cut the pieces.
In this case, the cardboard sheet to be used is large and has an uneven surface, this may mess up the focal point that we already set as per the focal point test. To remedy this we can weigh down the areas that are not cut (expert supervision required) or tape down the ends to secure it.
Now that the surface is even we can set the focal point using the z controls and the lego piece that is conveniently the right height:
After everything is set, move the laser to the starting corner of the sheet and press origin. Press frame again to confirm that there is enough material, if it is ok press the green start button and then the magic happens.
Be careful after the cutter has finished when removing the cut pieces, they should fall easily but some pieces may need some convincing to come out. When doing this be careful not to drop any pieces in inaccessible areas, this actually happened to one of my pieces and I had to add it to the next person’s print.
Final Result¶
The final result turned out as expected:
And because the “teddy bear” is made of simple shapes they can be assembled in different ways.
Such as a tea cup holder (because normal coasters are for peasants).
It can also be used as a crown for your cat!
