Making Almost Anything <-> MAS.863 <-> Fall 2011

Kristopher Dos Santos <-> Personal Robots Group

Week 2 <-> The Cardboard Lantern

Dinosaur skeletons!

Yes, you remember, those balsa wood kits you could put together at home, and you could have wooden skeletal replicas of T-Rex and Brontosaurus facing off on the battlefield that was your dresser top.

Well, at the very least, I remembered them, and once this assignment went out, this was the first thing I could think of building. Designing a cardboard kit for a dinosaur would be perfect! Except, when I thought of it, the project sounded so unoriginal. However, it made for a good test run, so I decided to do that first.

Rather than try to "draw" a dino skeleton in SolidWorks (my DXF program of choice), I did a bit of searching on the Internet for some pre-made DXFs (again, this was a test). I found this forum for milling called, and the user "ger21" provided this nice Triceratops skeleton shown below.

Imported DXF of Triceratops skeleton

However, this was designed for the mill, and so I had to make the slots myself. Thankfully, the center lines were all there, so I knew where to make the slots, and how deep to make them. I noticed that the drawing was made for 0.25" press fits in birch, so I decided to scale down the drawing based on the press fit size I would use. With a bit of testing, and help from previous years, the fit I wanted was a 0.145" gap thickness. The cardboard itself was 0.166", but I knew that its compressive nature would require more than just a couple thousandths for a tight press fit.

Creating the Gaps for Press Fit

Once all of the slots were created as shown above, I used the "Sketch Fillet" feature to round the edges using a 0.05" radius fillet. (Chamfering does not work well with round sketch features it seems.) I then divided the entities into two pages for cutting. This was going to be one big dino.

Triceratops on Two Sheets

From testing, I used a recommended setting for the laser cutter (100 PPI, 75% power, 15% speed) and got great results. However, this time around was not as successful, since some lines were not cut completely. Had I slowed the speed to maybe 12%, I think there would have been no problem.

Triceratops Front ViewTriceratops Back View

And voila! The completed Triceratops skeleton, in all of its glory! The press fits were nice and tight, so the structure held together quite nicely. This was a fabulous test, for now I have a huge cardboard dino in my office!

And now, for the real project, my Cardboard Lantern.

It arose from a simple idea, cardboard + LEDs = winning. I wanted to do some source of lighting involving a battery, copper tape, cardboard pieces, and one or more LEDs. What formed was a self-standing "lantern" of sorts with decorative "flame" panels.

I started with a coin battery, 3V, and designed a sandwiching mechanism that would allow me to adjust for error when clamping the battery to the copper tape pieces. This would ensure that there would be tight contact, allowing current to move through the pieces.

Solid Model of Cardboard LanternLayout of Pieces

The slots were designed with the same tolerance, plus a little extra to account for the copper tape (so the width came out to be 0.149"). The walls were designed with a bit tighter of a tolerance (0.31" for the tab, 0.28" for the slot), with a 45 degree chamfer of 0.03". Each two pillars have opposite contacts to either side of the coin battery, so that a LED could plug into the top base and complete the circuit, as shown below to the right.

Pieces Fitting TogetherDemonstration of Circuit

The copper tape adheres to the surfaces, then folds over the slots on the disk pieces and the triangle base, such that the pillars can make contact for the LEDs on top.

The Finished LanternLatern in the Dark

The press fits worked perfectly, and the contacts aligned very well. I am quite pleased at how this came out, and I hope you are too!

Workflow and Procedure for This Week

  1. Design your piece in Solidworks, with all of the necessary features. In the reference of cardboard, design slots to be 0.145" (or 0.149" if copper tape contact is involved). Alternatively, design the tolerance between your tab and your slot to be between 0.02" and 0.03".
  2. Take one piece of your model and select "Make Drawing from Part/Assembly" to pull the part into a drawing. Additionally, you can make a new drawing file, and insert the part (or any part for that matter). Make sure that when the part comes into the drawing, it appears on the sheet as if it is being cut out of the drawing itself.
  3. Once you have placed a part, go to your FeatureTree and right click your sheet, and select Properties. Here, set the dimensions of the page to be 32" wide and 18" high (the dimensions of the laser cutter bed). Also, set the scale to be one to one, so that once you import all the parts into the drawing, the scale of the part can be set to the sheet setting.
  4. Once that is set, place all of your parts onto the drawing. BE SURE TO REMOVE ALL HIDDEN LINES AND CENTER MARKS (for arches and circles)! Set them close together, but not too close (0.125" of space is good).
  5. Export this to a .dxf file. From here, this file can be imported into CorelDraw, and once the page is also set to 32" by 18", you can place the .dxf right on there.
  6. If everything is placed correctly, set up the laser settings in the Print menu. My settings for cardboard were 100 PPI, 75% power, and 12% speed on Black, with Air Assist on HIGH. Once that is done, click Print, and your job should show up on the laser cutter.
  7. Hit X-Y to set your origin on the job, and make sure that the lens is clean. Make sure your stock is placed correctly, and that the Z is set on the laser (ask John or Tom about how to do this properly). Once that is all done, select your job, and press the green button. Good luck!

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