Laser cutting Plexiglas boxes

Arduino Plexiglas Enclosure

Arduino Plexiglas Enclosure

I have completed my first small scale production job with my modified laser cutter. I volunteered to help out with a project involving the use of RFIDs. We want to offer RFID stickers so that people can “check in” to a number of stations throughout an event and show at the end of the day that they in fact made it to all of the different displays. This demonstrates the function and usefulness of the RFID, and shows that a little sticker can accomplish this task.

We used Adafruit shields with Arduinos to accomplish RFID read and write functions. I offered to make cool looking clear Plexiglas (a brand name for acrylic sheet material) boxes that would let people see the circuitry and blinking LEDs while enclosing them to improve their functionality. I found out pretty quickly that it takes a lot of iterations and some trial and error to learn the details about manipulating certain materials to successfully produce nice looking, durable, and functional items.

I started the project by cutting out an Adafruit enclosure intended for the “Raspberry Pi” computer. This enclosure can be found on Thingverse at the following web address.

Adafruit Raspbery Pi Enclosure

I downloaded the DXF file, converted it to a PLT file, and “tricked” Moshi Draw in to cutting it out as a series of vectors. As I have described previously, Mosh Draw is intended to be an engraving program, and my laser was not sold as a cutter. Using the following steps, I was able to successfully cut out the Adafruit box.

1. Download the DXF file for the object you want to cut. This is a 2D drawing. You can create your own DXF using Autocad or other commercial (and some freeware) applications.
2. Open the DWG, DXF, or probably a large number of other format 2D drawings using Corel Draw.
3. Select all of the objects in the drawing.
4. Select “Arrange,” “Group,” then “Ungroup All.”
5. Re-select all of the objects in the drawing.
6. Select “Join Curves.” I used “Gap Tolerance” of 0.01”
7. Export the drawing as a PLT file. I understand that this is related to the old HPGL format used by desktop pen plotters.
8. Open Moshi Draw.
9. Select “File,” “New,” and create a 200 x 200 mm drawing space.
10. Select “Output,” “All.”
11. Even though the PLT option is grayed out, check the box next to it. The PLT file button will appear.
12. Open the PLT file that you just created.
13. Select “Output” using cutting speed 3 (I need cutting speed 1 for ¼” Plexiglas).
14. Your 2D drawing will be cut out of the plastic!

After successfully cutting out a copy of the Adafruit design, I drew the box for our own project using CAD, and followed the same steps to cut out my own design. My final design is shown in the picture below.

Arduino RFID Box

Arduino RFID Box

 

If you are interested in cutting out this box yourself, please Right Click and Download. Rename the extension to DXF

 

If you want me to cut one or a few out for you, I can also do that and list the parts on eBay. Leave a comment on this post and I will contact you to set it up. I am also happy to answer questions to help you do it yourself if you want to try.

 

I purchased a bunch of 11×14” Plexiglas sheets from Home Depot. Their thickness is 0.093” and they cost $4.24 each. Each sheet made two of the boxes I needed for the project. The laser cutting speed you need to use depends on your laser power, material thickness, and material type. The tradeoff is that if you make the laser move slowly enough to definitely cut through your material, I found that it is tougher to cut very fine details. I think more edge material ends up being melted. If on the other hand you do not cut almost all the way through your material, you need to try to snap it apart afterwards. When you have corners with fine details, they are just as likely to snap off as they are to separate from the waste material. This is the main example of the trial and error part of production that I mentioned above.

Since I have added air assist to my laser cutter, I have been able to increase cutting speed and maintain finer cutting detail. Since the final focus lens is protected from the cutting process by compressed air, it is less often covered with cutting debris or residue from smoke. Some materials produce more smoke than others e.g. wood versus Plexiglas. That job turned out to be easier than I thought it might. I just needed to add a nozzle over the final focusing lens, run a thin tube from the head to the outside, and adapt the tube to a regulator and fittings to attach to my compressor.

I have also added a support mesh to my laser cutter so that I don’t need to worry about the cutting order. Previously I had parts dropping out since the outside cuts were sometimes made before the inside cuts. Now since the laser cutting process puts no mechanical force on the part, and since it is held up everywhere by the mesh, I can let the cut proceed in any order. My laser cutting mesh is 6.5″ x 10″. A picture of the mesh and the air assist head is shown below.

Laser cut mesh and air assist

Laser cut mesh and air assist

Important lessons:

1. Lexan does not laser cut, but only burns! It apparently also produces poison gas! I have very good ventilation to the outside world on my system – good thing! Plexiglas cuts very cleanly.

Lexan does not laser cut!

Lexan does not laser cut!

2. Plexiglas likes to crack just for fun! Especially the .093 inch stuff is very delicate. Home Depot did not sell 0.125” sheets, but only .093 and .22
3. Find the laser cutting speed that just barely penetrates the plastic, and you will be able to snap out your pieces but also cut fine details.
4. Make any feature that is supposed to be flexible e.g. a retainer hook very long to give it more flexibility. You can see this in both the Adafruit box and my final design.
5. The little shock of the initial “snap” when the box goes together is the moment when the plastic is most likely to break. Try to ease parts together by holding off the flexible parts with your fingers as they go through their mating slots.
6. Home Depot sells a plastic sheet scoring tool for less than $5. That seemed better than using my bandsaw, but the tool had really bad reviews! I did not open the scoring tool and will be returning it to Home Depot next time.
I know there is a pretty large community of people out there who like the K40IV due to its low price. I have shown here that you can build parts that rival those produced by laser cutters with a price tag at least 10x higher! You need to be ready to make some modifications on your own, and struggle a bit with software, but the results look great!

At speed 3, each box takes 17.5 minutes to cut.

Laser cut Plexiglas box home production

Laser cut Plexiglas box home production

Draw one, make many!

Draw one, make many!

Boxed Arduino and Adafruit RFID shield

Boxed Arduino and Adafruit RFID shield

Plexiglas box end detail

Plexiglas box end detail

Completed RFID Reader/Writer Enclosure

Completed RFID Reader/Writer Enclosure

I also laser cut boxes for a “Simon Says” game that required more binding clips since the walls were larger. Buttons were also added to this game box. One great thing about laser cutting is that design iterations can be implemented very quickly. I was able to reach a design that I liked with just a few tries. Making drawing changes on my computer and printing modified parts is much faster than manual machining.

Simon Says Plexiglas Box

Simon Says Plexiglas Box

Simon Says Plexiglas Box Bottom View

Simon Says Plexiglas Box Bottom View

 

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One response to “Laser cutting Plexiglas boxes

  1. Pingback: Laser Engraving Marble « G. P. Le Sage Blog·

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