Assignment 03

This week's focus in FabAcademy was on computer-controlled cutting, including the vinyl cutter and the laser cutter. Compared to previous weeks, this week was the first week with a group assignment! It was really exciting to see the expertise of my fellow students and it was a lot of fun to work together even though it was quite a big workload. We had to complete the following assignments:

• Group Assignment
  • Characterize your lasercutter's focus, power, speed, rate, kerf, joint clearance and types
• Individual Assignment
  • Cut something on the vinylcutter
  • Design, lasercut and document a parametric construction kit
    • Accounting for the lasercutter kerf
    • Which can be assembled in multiple ways
    • For extra credit include elements that aren't flat

The documentation of the group assignment is hosted on a different website. You can find it here. However, I would like to evaluate, what I have learned this week.

In the first part, where we focussed the laser correctly, we were cutting multiple lines with the lasercutter with its laser head at different heights. It was surprisingly easy to focus the laser. I have done lasercutting before, but changing the focus was something only the "Profis" (the professionals) were allowed to do. Maybe it is also due to the lasercutter. Previously, I only had worked with other lasercutters but the Fusion Epilog machine made focussing really easy.

Additionally, during focussing, it was very much visible to see that only one or two millimeters can make a difference between cutting and not cutting. Setting the focus slightly too high or too low can also cause very unclean, thick and dirty maybe even burnt cuts.

The Focus Tool and the Laser Head

Determining the Focus

When characterizing the speed, power and frequency, I learned a lot about what these parameters mean. A high frequency for example mean more "heat". For example for plastics that only melt at higher temperatures or for other materials that require a high heat for being cut, like MDF, the frequency needs to be high. Plain wood however requires a lower frequency as it can be easily cut and rather burns in case the frequency is too high.

The speed and power are relatively self-explainatory. A small speed and a high power is needed for materials that are not cut easily. Usually if the speed is high, the speed can be reduced by increasing the power. This is however only true if the lasercutter's power and speed is linear.

Determining the kerf is also very easy. However, I was not aware that it is depending on the material and the settings for speed, power and frequency. It makes sense though! Characterizing the kerf is nevertheless really easy an the workload was manageable.

Test Grid for Different Speeds and Powers for Plywood 4 mm

Test Cut for Determining the Kerf

Last but not least of the group assignment were the joint clearance and types. It was easily done with combs where each slot has different properties. Clearances can vary with your preference. Some might prefer a tighter fit for their design and hence need less clearance, other however might like a looser fit and need more clearance.

Comb for Testing the Joint Clearance

Comb for Testing the Width of Flexures

The individual assignment is split in two parts, where we are asked to use the vinylcutter and the lasercutter. I had already worked with both, but during both the global and the local lecture I got more background information about both machines, about how they work and what I need to keep in mind when working with them.

For last week's assignment of CAD, I used the part of modelling in 2D already for this week's assignment as I did not know how I can make use of it for my final project. Therefore, I designed already the file, I wanted to cut on the vinylcutter: The outline of a frog.

The vinylcutter in the lab is a portrait 2 from Silhouette. Before cutting the outline of the frog with it, the material setting however have to be determined.

The Portrait 2 from Silhouette

Accessories for the Vinylcutter

I started the preparation by sticking the material onto the cutting mat and slid it into the vinylcutter. Then, I opened the vinylcutter's software Silhouette Studio and plugged the vinylcutter into my computer. Fortunately, the Portrait 2 was identified by the software and I did not have to set it manually. In the software, I drew a small test piece consisting of a square with a side length of about 16 mm and a triangle using the polygon tool.

Design of a Small Test Piece

Then, in the "Design" tab I selected the "Sticker Paper, Clear" and let it cut with the default settings. Unfortunately, this resulted in a very deep cut reaching to the cutting mat. Therefore, the first change was setting the passes to one instead of two. However, after doing another test cut on a different place on the cutting mat, I discovered, that the cut was still relatively deep and I set the blade depth to one instead of two. I continued with this procedure until I found the optimal settings which were blade depth of one, one pass, a force of 20 and a speed of nine.

Default Material Settings for "Sticker Paper, Clear"

After finding the perfect settings, I was able to start my actual cut of the outline of the frog, which I designed already for the 2D modelling part of last week's assignment. For this, I firstly exported the Inkscape file (.svg) to a supported format, i.e. to .dxf, and then opened it in Silhouette Studio and scaled it down.

.dxf File Opened in Silhouette Studio

Next, I sent the cutting job to the vinylcutter that subsequently cut the outline of the frog with the optimal settings on a new piece of sticker paper.

Lastly, I was only left with weeding which I did with a pair of tweezers after. I did this while the sticker paper still adhered to the slightly sticky cutting mat with a pair of tweezers. It was in general relatively easy for the body of the frog but tricky for the hands and feet. Here, I tried to peel the film off from the palm to the fingertips which was relatively easy. However, sometimes I accidentally lifted the parts where the material forked to build another finger but I was able to repair it. Maybe slightly more force or a lower speed would have resulted in an even cleaner cut and thus easier weeding.

Cut Outline of the Frog after Weeding

After weeding, I wanted to stick the sticker to a locker that I use in the lab, just to personalize it. For this, I used a piece of transfer paper that is bigger than the sticker itself. I stuck the transfer paper on top of the frog sticker and gently pressed it down. This part did not require a strong adherence as the transfer paper is really sticky. Hence, I also had no problem removing the bottom layer of the sticker so that I was left with the frog sticker on the transfer paper, the sticky sides facing the same direction.

Sticking the Transfer Paper On Top of the Frog

Sticking the Transfer Paper and the Frog to the Locker

Lastly, I placed the frog sticker with the transfer paper at the desired position on the locker. As the sticker paper was not that sticky and the frog's outline is relatively thin pressing the sticker strongly to the locker's surface was crucial. Here, I used the flat part of a finger nail and rubbed it over the frog sticker while strongly pressing down. Then, I removed the transfer paper by peeling it off with the possibly lowest angle. However, it was still tricky to remove the transfer paper from the sticker without lifting the sticker. Sometimes, a pair of tweezers holding the sticker on the locker's surface came in handy.

In the end, I managed to remove the complete transfer paper. It was difficult but not impossible. Potentially, a slightly thicker outline with less sharp corners would definitely make the transfer easier.

The Frog Sticker on the Locker

For the part of the assignment using the lasercutter, I was not sure what to exactly fabricate. For my final project, I will need some lasercut parts, i.e. the lasercut frames. However, cutting them on the lasercutter does not fulfil all requirement as it cannot be assembled in multiple ways. Instead, I decided to design an organizer for my drawer next to my desk.

In this drawer, I have various desk and office related things like sticky notes, a hole punch, a stapler, adhesive tape, sticky notes, coasters, paper clips and so on. However, it is so unorganized as every time I open and close the drawer the things got shaken up. Therefore, I wanted to design an inlet dividing the drawer length- and cross-wise into multiple compartments. You can see a preliminary design of the division made by four parts as a sketch below.

Unorganized Drawer

Preliminary Design (Dimensions in mm)

To design this drawer organizer in the CAD software of my choice, Fusion 360, I defined four parameters, namely "thickness" equivalent to the thickness of the material, the "clearancefactor" which is determined by the clearance necessary for press-fit joints, the "kerf" of the laser and the parameter "height" which is the height of the parts. Their values are preliminary and can be adjusted anytime.

Parameters: Name, Value, Unit and Description

Next, I created four different sketches. I started with the longest part running lengthwise, namely part 1. This sketch is drawn on the YZ-plane and consist mainly of a rectangle with a length equivalent to the length of the drawer (362 mm) and the height of the parts determined by the parameter, which is visible with the "fx:" tag before the actual value of the dimension. On its top end, the rectangle has two slots to build press-fit finger joints. Their height amounts to half the height of the total part whereas the width is determined by the multiple parameters: The width is the "thickness" plus the "clearancefactor" times the "kerf". By this, it is accounted for kerf and the clearances for the press-fit joint.

As for this part and for the others, I did not include chamfers which were recommended by actually everybody. However, I decided against it because I did not want them to be visible at the joints. Instead, both parts that build a joint should be flush at the top without any step in the height. I could have included the chamfers in the bottom but in case I turn the organizer upside down for a different design, I would have the chamfer visible again.

Sketch for Part 1

The second part is also constructed within the YZ-plane and consist of the same rectangle an its slots but ends directly after the second slot from left to right as it does not traverse the whole volume of the drawer. The height of the part, the slot width and slot depth are again a parametric dimension as indicated with the "fx:" tag before the actual value of the dimension. If you look closely, these three dimensions are also parametric for the remaining parts making the construction parametric.

The third piece is drawn in the XY-plane and thus orthogonal to the first two pieces as it runs cross-wise through the volume of the drawer and not length wise. Additionally, the slots are now open to the bottom building the opposite part or the finger joints.

Sketch for Part 3

Similarly, the fourth and last piece was also constructed in the XY-plane with slots opening to the bottom. The rectangle around it has a total length of the width of the drawer (235 mm) and a height of 40 mm which is equivalent to the parameter "height".

Sketch for Part 4

For visualization purposes, I wanted to assemble the pieces. For this, I extruded all four sketches to become a 4 mm thick part.

Extrusion of the Sketches

Next, I selected all bodies, right-clicked and clicked on "Appearance". This opened a dialog, where I assigned the material "Bamboo Light - Semigloss" to all parts. Additionally, I created components from all bodies, which allowed me to assemble the pieces. For this, I used the tool available at Assemble > Joint and selected the midpoint of the bottom face in the first slot of part 1 and the midpoint of the top face in the first slot of part 4. I continued to create a joint between part 4 and part 2 and a joint between part 2 and 3.

Selected Snap Point on Part 1

Selected Snap Point on Part 4

In the end, I rendered the assembled parts. This is how it looks:

Rendering of the Assembled Organizer

Rendering the assembly was however only to provide a 3D view onto the design for better visualization. For lasercutting, the assembly is not necessary but the sketches are enough. They only need to be exported to a .dxf format, which can be easily done by right-clicking on the sketch and selecting "Save As DXF". This opens a dialog where I selected to save the file on my local computer with a specified name and location. Before exporting, I however checked, whether the parameters have the correct value. In this case, I did not have to change them.

After I had exported the .dxf files from Fusion 360, I opened them in Inkscape in a single file and gave them different colors each. This allowed me later in the lasercutter's software to selectively switch the cutting of one or multiple paths on and off. Additionally, I adjusted the page size of this Inkscape file to the content.

Saving a Sketch in .dxf Format

Sketches in Inkscape for All Four Parts

With the Inkscape files being ready, I used a flash drive to open the file in Inkscape on the computer that is connected to the lasercutter. Here, I pressed Ctrl+P and clicked "Print" to send the files to the lasercutter's software.

In the software, I selected a "vector" cut for all paths, as well as a speed of 17, power of 90 and a frequency of 20. These settings were found to be optimal for the material I am cutting, i.e. plywood with a thickness of 4 mm, in the group assignments. Next, I sent the job to the lasercutter via pressing "Print".

At the lasercutter, I firstly had to set the focus using the focus tool. For this, I mounted the focus tool on the laser head and then used the arrow buttons on the right of the control panel to navigate to "Focus". Now, I was able to control the z-axis with the joystick. After moving it to the right position, I set the z-axis to zero by pressing the joystick. Lastly, I removed the focus tool again.

Next, I set the zero of the x- and y-axis by going to "Jog" in the menu. Then, I again set the position to the desired one with the joystick and pressed it for saving the current position as the zero. This position was in the top left corner of the material such that the laser head can do the cutting towards the front and right of the bed.

Control Panel and Display of Lasercutter

Before starting the job, the extraction system and air assist had to be set up. For the latter, the valve behind the computer had to be turned. The extraction system is started by pressing the on/off button on the system with is located immediately on the right of the laser cutter.

Once, I had zeroed the axes of the lasercutter correctly and had started the air assist and extraction system, I navigated to "Job" on the control panel with the arrow buttons. As it already displayed the job name of the job I sent to it eariler, I pressed "Go" and then it cut all parts.

Lasercut Parts

As a last step, I only had to assemble the parts according to the design.

Hero Shot: Assembled Parts

The assembled parts can then be integrated into the drawer to organize its content. I like it a lot because it organizes the drawer really well. It also keeps everything in place when opening or closing the drawer so that I do not have to worry about organizing and sorting things anymore!

Before

Afterwards

• Vinylcutting Sketch (.dxf): Vector graphics of the outline of the frog
• Lasercutting Sketch (.svg): Vector graphics containing sketches of all four parts for the drawer organizer