These past two days, I have been working on making a laser cut box with sides that snap-fit together. My homework buddy for this project was Raeedah 🙂

This is how my box looks!

Do you want to know how I did it?

1. Before starting anything, I put tape to a little more than half of my plywood to avoid charring in the place where I was going to laser cut the box.
   

   Tape on the plywood

2. Then, we needed to figure out what the kerf for the laser cutter with our desired settings was, before starting the box.
   1. To do this, we recreated using Adobe Illustrator, the box with 10 lines that was recommended to use in the instructions . This was done by drawing a bigger rectangle with a smaller one inside it and 10 lines (using the Shift key to make the first one vertical and then copying it) within this smaller rectangle:
      

      File made using Adobe Illustrator to calculate the kerf

   2. The first time that we tried to print it, we used 5 speed in the laser cutter, but it was a bit hard to separate the pieces which caused the ends of them to not be completely straight. Since the wood was 0.2 in thick, we based the speed on what the guide seemed to indicate and increased it to 4 speed (at first I did some math to try to get a better number but we were not able to insert decimal numbers, so we chose 4 speed in the end).
   3. After a couple of tries (see Improvements section), a useful kerf file was printed, and we were able to take the small rectangular pieces and push them against the side of the small rectangle. Then, we measured the gap formed with some calipers (0.06 in) and divided this value by 10 to obtain the kerf (0.006 in).
      

      Measuring the kerf with some digital calipers

3. I measured the thickness of my plywood to be 0.2 in with some calipers.
4. I then went into MakerCase and added the details for my box: 4-thickness (4-0.2 in = 3.8 in) for the width, height and length; selected ‘outside’ for dimensions; added the material thickness (0.2 in); selected ‘closed box’; selected finger joints; modified the finger size based on how the picture looked (0.525); and pressed download box plans. I was then able to change the kerf to 0.006 and download the file as SVG.
   

   Settings chosen in MakerCase

   

   File obtained from MakerCase

5. After I had the file, I opened it in the appropriate file for Laser Cutting in Adobe Illustrator.
6. I then removed the ‘front’, ‘back’, etc. tags. I also then used the shape building setting as mentioned in the instructions, but I am not sure if this actually did anything because the boxes seemed already separated into six.
7. I then also added a text box with my name, course, semester and date on to the back side; Jones’ (my college) crest on to the front side. I then added the Rice owl, the OEDK logo, a drawing of the Sally port from the Noun Project, and a drawing of a representation of “Art” from the Noun Project too.
   

   Images added to the six box pieces using Adobe Illustrator

8. After that, I chose the appropriate raster and vector settings for the Stroke, for the inside images and the box outlines respectively.
   1. One thing that happened here was that I was not able to add a Stroke for the college crest. While discussing this issue with the TA, I tried downloading an online image of the college crest instead, and converted it to a vector image using Adobe Illustrator. The option that seemed to look the best was the ‘Low fidelity photo’. I then added that one to my box instead and while I was not able to add it very big since the photo had a background, and while it was not a 100% representation of the original image, it ended up working!
9. I then followed the instructions in the laser cutting manual to laser cut my box.
   1. As for the settings to print the box, I chose the following basing the ones for engraving in the little speed vs. power chart available at the OEDK.
      

      Printing settings chosen

   2. Then the box got laser cut!
      

      Laser cut pieces of the box

10. I then went on and removed the blue tape (I did decide to leave a bit on the owl from the logo though).
    

    Removing the tape from the box pieces

11. And these are all of the faces from the box:

 

1. 

The final result:

Room for improvement?

•  Some things that can be improved includes the use of resources
  • I added a lot of tape, which could be optimized in the future with more experience.
  • I also did not use the wood space super well. The reason for this was that I thought that the origin was where the printing would start at first, but that actually corresponded to the corner of the file!
• The first day that we worked on this project, we had a lot of issues with the project and we had some difficulties when using the machines. In my case, for example, even though I had set the origin at the top, the cutting started about the middle and this occurred twice, etc.
• The kerf calculation also gave us a few issues. At first, we used 5 speed and some of the pieces were not cut super well. Then, on the second try (which we stopped), we realized that the outside rectangles were being cut first which would negatively affect the calculations. By cut and pasting in Adobe Illustrator, we added these last per the TA’s instruction so that the laser cutter would cut the smaller pieces first and then the rectangles. So, the third trial at obtaining the cut was the one used.
• Another issue with kerf was that even in the third trial, the pieces where not completely straight, so the top of the gap was wider than the bottom. We decided to measure at the middle, but this was not totally accurate. After printing the box, it was very hard for me to put the pieces together, to the point that I used the bottom of my metallic water bottle to press the sides together. This is probably because of the kerf calculation.
• Also, I realized that I had written ‘Fevruary’ instead of ‘February’ right after printing the box! (It was a typing error; I know how to write the word…). I decided not to reprint it though because I thought it was kind of funny, and it would also be a waste of time and resources.
• The last issue were the sizes of the box!!! At first I was confused my the instructions and I thought of adding 4 x 4 x 4 directly into MakerCase because in the worst case scenario I would have a slightly bigger box. However, I then understood that I had to subtract the thickness myself so I used 3.8 in instead… I had not realized until I thought about it on my way home later and asked Raeedah if she could check the size for me. Yep, it was under 4 in… At least I learnt how it works.
  

  Measurements of box

Calculating the cost?

There are several components that go into the cost calculation:

Raw materials

• We used plywood as the main raw material for this assignment (tape was not included in the calculations)
• To calculate the amount of material used, I included the following (actual cut wood plus any extra around that is probably not useful – did not include area with mistake in printing above because it might be useful on the other side since its only a bit of engraving):
  

  Plywood included in calculations for raw material cost

• Total material used = (12.9375 + 29.546875 + 20.4921875 + 97.5)in^2 = 160.4765625 in^2
• A piece of plywood of 0.197 in thick (almost my wood thickness) and 4ft * 8ft costs $26.78 [1].
• Thus:
  • 160.4765625 in^2 * (1ft^2/144 in^2)*($26.78/32ft^2)= $0.932630717

Labor time: 300 minutes or 5 hours

• This includes all of the time spent working on the project. However, this is actually an overestimate of how much making a box like this should cost. This is because a lot of the time was spent on troubleshooting and having a few difficulties, as well as on working on the kerf calculation which should have been a lot simpler. However, since these things can happen, and it was difficult to estimate how much time was spent on what, I decided to include the full work time into the calculation.
• I feel like a wage of $14 per hour (as compared with my previous two projects) is good for this task.
• Labor cost = 5 h * ($14/h) = $70

Machine time: 17 min 43 seconds ≈ 17,71666667 min

• This is the time that the laser cutter was operating. This includes the two full attempts to make the kerf files as well as the laser cutting time for the box. I was at first thinking of excluding the first or both of these kerf cutting times from this calculation. However, I decided not to in the end, since the kerf depends on many factors such as the settings chosen, so this step is important when making this box. It can also go wrong and might need for the setting to be changed and try again which is why I left the first time there too. However, there was a second attempt done between these two, in which the laser cutter was stopped after cutting the two big rectangles and one of the smaller ones since we realized that the order in which it was cutting was wrong. The time for this is not included because I failed to make note of it, however, it should be under a minute.
  • Time for full attempt 1 at kerf file cutting: 1 min 18 s
  • Time for full attempt 2 at kerf file cutting: 1 min 39 s
  • Time to cut the box: 14 min 46 s
• The power of a laser cutter varies depending of the application. That of a laser cutter that at a high power is able to cut our type of wood uses 30-40 Watts [2]. Since it can, however, also cut thicker wood, I will use 40 Watts as my value.
• I again used the electricity cost/kWh calculated in the sewing project blog post ($0.1638695652 per kWh) (https://engi210.blogs.rice.edu/2023/01/22/paulas-apron/).
• Adding this data into the “Electricity Calculator” [3], we get a cost of $0.00 per day (0.012 kWh) when the machine time was inserted as ‘per day'(rounded) or $0.71 per year (4 kWh), which equals $0.71/365days = $0.001945205 for the total machine time.

Total cost = $0.932630717 + $70 + $0.001945205 = $70.93457592 ≈ $71

 

References:

[1] https://www.lowes.com/pd/RevolutionPly-5mm-Poplar-Plywood-Application-as-4-x-8/50121135

[2] https://hummalaser.com/which-power-of-co2-laser-cutter-to-choose/

[3] https://www.calculator.net/electricity-calculator.html?appliance=&power=40&powerunit=W&capacity=100&usage=17.71666667&usageunit=mpd&price=0.1638695652&x=67&y=4