When I was in the consulting industry as an engineer, I built a habit of prototyping everything, to get a feel for how things look and feel way before the finished product is due. So, today I made a plastic 3D print of the old design for the 1 millionth block commemorative coin! I will walk you through the process:

This is a Stratasys Connex - a silly expensive machine sitting in the additive manufacture lab that can print everything from remote control casings to dental implants. The materials loaded were a rigid clear and a rubbery black, so for this run I used the clear compound.

This is the printer on the job while running a mid-job nozzle cleanse. It's currently spraying material from the 8 print heads into that cavity on the build floor - pretty messy! The black circle is the (almost finished) print job of the coin, which is encased in a very rigid jelly. Total build time was 68 minutes.

To remove the jelly from the print, we use a pressure washer. You can see me holding the coin in the center, and the bar in the bottom right is a windscreen wiper to wipe the water and residue off the viewing port. Cleaning up the print is pretty fast, and the fine detail is finished with a toothbrush. This is the result (5cm diameter):

The 3D model for reference (credit to @me-shell and @joshoeah):

I may coat the coin in a brass-coloured enamel or something - not sure yet. Of course, this is only a test piece and I am waiting on a community decision on the final model. However, some things I learnt along the way:

• Some of the details on the original artwork/logo are incredibly fine. Even at this scale, the smallest details are only 0.2mm across. If the plan is to make these coins actual coin size, and to reduce the area taken up by the original art to about half, that means the details will be 0.05 mm. I don't know any manufacturing method that will cope with that nicely, so I may need to take some small modelling liberties.

• Printing these things is smooth sailing from here on out. I could whip up 100 of these in the next few days if we wanted as the print time does not scale linearly. The build plate could easily take 60 coins in one go.

• A uniform colour in either solid black or see through doesn't look as flash as I might like. I will enamel this and report back.

I have also done some experimenting with the CnC machine, and it will struggle with small details. The problem is that the super fine cutter tips taper to a point, and as you approach the tip the surface speed approaches zero. Therefore, it is very hard to get a nice surface finish on tiny details. I will do some experimenting. On the bright side, I did find a bunch of leftover brass bar we can use!

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Image credit, in order of appearance:
Banner, @joshoeah
All photographs taken by me on my NZD$100 phone (apologies for potato quality!)