fastbuild: 90 min, 10 revisions




Sometimes I have a project that I want to invest my time in.

But it's a wild idea. A new way to solve a problem.


There's a lot of uncertainty.​..and I don't ​want analysis paralysis​ to​ get in the way. Instead, I build an MVP, or minimally viable prototype. ​ It's a strategic way to find the answers I'm looking for. This way, I don't ​have to ​wait around until I have all the ​design ​inputs.

​ Recently, I was designing an accessory for a friend, a holster for his Insulin pump.

​ Start the timer 00:00 at 12:36pm


I couldn't keep the pump​ in my hands​ for long, because it needed to be connected to his body. I took it briefly, took a few measurements, and gave it back.


As I built my first quick CAD model, I knew what I was modeling was​ not perfect.


But I didn't ​have any way to test how wrong ​my dimensions were.


So to calibrate my CAD model (in virtual world) with the pump (in real world) I fired up my 3D printer farm.


The Prusa Mini+ time to first part is just a few minutes.

I uploaded the STL file and started the print on two different printers in parallel.

​ ​00:05 Basic CAD model is created, just for the inside mating geometry. Export to STL and send to printer. I left the printers running and grabbed a few bites of lunch. Hit power ON for the big Fortus, I'll need this to start warming up.

​ ​00:10 I didn't even wait until the build was complete. I yanked one part off the build sheet on one of the printers as soon as the outline of the lower surface is done.


I leave the other one to keep printing. I'll get back to that one later.

I know the geometry is wrong, but I'm sure I'll learn something else when it completes. Then I head back to check the fit of the shape. Quick test fit with a calipers, and I'm starting prints again, for rev 2. ​ Once again, I start it on two printers, with the first print still running. I'll check that one later.

​ ​00:18 Grab some more lunch. We're not 20 minutes into this, and we're already on Rev 2. 1:00pm rolls around and we're starting rev 3, with the slip fit confirmed, and now with the first hint of a clasp/snap.


00:25 I could spend a few hours optimizing the clip and running snap deformation simulations, or I could print and test. You can probably guess, I chose the latter.


00:35 Rev 4 and 5 are starting in parallel, while Rev 1 is just finishing. Parallel processing at it's finest! I'm slicing at 0.25mm, course layer slice, min infill, just to test only the outer geometry.


The fit between Rev 1-3 got progressively better. The snap on Rev 4 needed to be tested, but I didn't want to wait for the entire part to print. ​ ​00:50 For Rev 5, I chopped off the bottom, and just printed the top section that had the clip. Now just the top section is printing. I've already validated the fit of the bottom. No need to continue printing/testing that. ​ ​00:60 Second clip prototype (Rev 7) is off the printer. This one needs a bit of dremel work to clean up some extra material in the flexure region.

This is how I 'bookend' the design. First, make it too soft, then try to make it too stiff. Now we know the bounds of the clip design. We can back into the desired geometry with a finite number of iterations. ​ ​01:15 Rev 8 and Rev 9 on the printers, both testing different strain relief geometry. No need to test each in series when I can design both, and print in parallel. ​ Again, only printing the clip part, each build is ~10 minutes. ​ 01:30 Final design files ready to run a high-resolution build file in ABS on the big printer.


I start Rev 10 in PLA which will be done in 20 minutes. This PLA version will be done about the same time that the Fortus starts printing Rev 10 in ABS, so I will have one final chance to pull the plug.


We choose ABS for strength and temperature resistance, and PLA for prototyping for speed. Fortus is up to temp, so we can hit GO.


Glad I remembered to preheat. Turning off supports in Insight to reduce build time. Part is designed to be support-free, but GrabCAD Print still wants to include them... ​

01:50 PLA Rev 10 is tested, proven perfect fit.

No risk to letting the Fortus run for 1.5 hours. I know the part will be good. Let's roll.

​ ​03:20 Final ABS part is completed, tested, and fits well. 100% success on this first ABS print. ​ This is how we prototype in parallel, only checking features of interest. No need to wait until a part is fully designed to print it.


Faster is key. More iterations builds confidence in the design.

Time is our greatest asset in development.

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