First Day: Coin Traps

Start by emptying out some change onto the table in front of you (if you have no change, some may be provided for you, but it may be a very boring penny).

Our first-day 3D print will be either a Quarter/Nickel Trap or a Penny/Dime Trap depending on the contents of your pockets/bag.  These models are a good illustration of a design that is possible with 3D-printing but would be impossible with standard subtractive manufacturing methods such as milling. How does the coin get inside?

The answer is that we’ll pause the prints at the right time and drop the coin in, then let the 3D printer continue printing above and around the coin. The “right time” is when the model is about 60% or 70% printed; this ensures that the coin will sit below the printing height of the nozzle, which will help us not damage the machines!

Start your prints!

We have three different types of 3D printers in JMU 3SPACE, and each one operates a little differently. The Lulzbot Mini 2s and the Ultimakers are operated from their own screen an jog wheel, with files on an SD or USB card that were previously sliced the the software “Cura”. We’ll learn more about this later on; right now we just want to print something!

To start a Coin Trap print on an Lulzbot Mini 2:

• Turn on the printer.
• Push the dial on the front screen inward to get a menu and scroll down to Print from SD.  Push the dial again.
• The SD cards have been recently reformatted, so there are very few files on them making it easy to find either the cointrap or the pennytrap.
• Click on the one you are printing and sit back and watch the magic!

To start a Coin Trap print on an Ultimaker:

• The model should already be sliced and ready on an SD card or USB drive inserted into the front of the printer.
• The only thing you need to be careful with at this point is to make sure that the number on the outside of the printer (Ultimaker 2+, Ultimaker 2 Extended, Ultimaker 3, or Ultimaker 3 Extended) should match the start of the filename you are trying to print (they should be UM2, UM2E, UM3, or UM3E respectively).
• Move the jog wheel on the front of the machine to select Print, and press the jog wheel like a button.
• Use the jog wheel to select the filename that includes pennytrap to print a penny/dime trap or the filename that includes cointrap to print a quarter/nickel trap.  (At this point in the semester, these should be some of the only files on the SD or USB but it never hurts to double check.)  Press the button when that file is highlighted.

Pausing your print

The different models of printers in the classroom will be ready at different times. When you think it’s time to pause and insert the coin, let me know so we can stop class and do the pause routine for all of the printers of that type. Here’s how to pause, insert, and restart:

To pause a Lulzbot Mini 2 printer:

• Press the dial on the front screen inward and scroll to Pause print.
• This will cause the nozel to disengage and the plate to travel outward a bit..
• Insert the coin, being careful not to accidentally touch the hot end of the printing nozzle or to allow any part of the coin to be at or above the current layer height.
• When you’re ready to continue, press the dial inward and scroll to Resume print (or something like that, we just bought these printers and all I remember is that it was very user friendly).

To pause an Ultimaker printer:

• Move the jog wheel on the front of the machine so that Pause is highlighted, then press the jog wheel like a button.
• Insert the coin, being careful not to accidentally touch the hot end of the printing nozzle.
• When you’re ready to continue, move the jog wheel to Resume and press the button.

But how did this Trap get MADE?

In this class we’ll sometimes print other peoples’ models for practice, or start with other peoples’ designs for inspiration, but most of the time we’ll be creating the 3D models ourselves from scratch. So how do you do that??

The Penny Trap (which is slightly simpler than the Coin Trap) is a very simple model, and you could make it in lots of different design programs. We’ll talk more about this in the coming weeks, but as a preview, here are two walkthroughs of how the Penny Trap could be created.

First, with Tinkercad, you can drag and drop shapes and cut out “holes” from some shapes using other shapes. You can read about this at the MakerHome tutorial Designing a Penny Trap with Tinkercad, and tinker with the model itself in Tinkercad.

Second, with OpenSCAD, you can use simple code to place, rotate, and take “differences” of objects to make the Penny Trap design. You can read about this at the MakerHome tutorial Designing a Penny Trap with OpenSCAD, and take a look at the actual OpenSCAD code.

One of the great things about designing models in OpenSCAD is that they are parametric, which means that you can change features of the model very easily by modifying the values of its input variables. In the case of the Penny Trap, this means that we could write code that creates “traps” for any type or size of coin. Here is that very thing: the model Customizable Coin Traps on Thingiverse. Using the Customizer interface you can choose traps for coins from all around the world, or select your own unique coin size.  OpenSCAD is also great for mathematical designs because it is extremely precise.