I've started building the AR3 with some of the AR4 changes. I have both the Teensy 3.5 and now a Teensy 4.1. I have a number of encoders so I'm going to do it that way rather than use the StepperOnline motor/encoder pair. Same with a bunch of stepper motor drivers in the parts bin.
I've created Alibre PART files from the drawings which was a really useful way to learn how it was put together. Most of the bearings have arrived from various suppliers. And I'm pretty well done all the 3D printing.
To make the metal parts I'll first make patterns and then cast the rough blanks out of scrap aluminum. Then use my CNC mill and ELS controlled lathe to take them to completion.
Here are the first photos. I have my ducks in a row on the 3D printed parts.