I purchased all the kits that Chris Annin offered: aluminum structural parts, hardware, screws and bolts, etc. I also ordered everything he specified in the electrical components (most from Amazon), and the full AR3 stepper motor/driver kit from Stepperonline. I would suggest ordering an extra bag of bolts and screws (roughly $20) in case your first bag is missing something or you lose something.

A couple of suggestions for constructing the AR3:

1. there are several steps where you have to fit bearings or bearing races into housings, and because of the close machine tolerances, the fit can be very tight. Inserting one piece slightly crooked can result in the pieces locking, so be very careful. Chris suggested placing one piece in the freezer to shrink it slightly and the other in an oven to expand so the fit is less tight. You need maybe a half hour or so. This really works. Also, I believe holes shrink or expand as the rest of the piece does, which may not seem intuitive.

2. Related to this there's a step on page 183 of the assembly manual - inserting J6 motor into the J6 housing side post - that I think should be done before installing the J6 housing side post (page 166) onto the rest of the arm. In my case in trying to fit the J6 motor into its hole in the housing it got stuck, real bad. Since the housing was assembled, I couldn't heat one and freeze the other. Let's just say that in trying to get the motor unstuck I had to order a new J6 motor. So I put this one into the housing before installing the housing.

3. Joint 3 is prone to a lot of play, which can affect the AR3's accuracy, partially due to gear backlash. But if you're using an un-broached pulley sprocket on the J3 motor shaft, the set screws can only grab so much, so there's slippage. Best to broach the sprockets if you can (I don't have that capability). Chris said he will offer a better redesign of the J3 drive system at some point in the future.

4. For mounting the limit switches I would suggest only using the socket head screws, which use an allen wrench, not the pan head screws, which require a screw driver, unless you have a set of right angle screw drivers to use in tight spaces. You will more than likely need to replace a few limit switches, and you might find that difficult when the AR3 is assembled. I'm not sure if there is a sufficient number of socket head screws to use on all the limit switches, which is all the more reason to buy a second bag of screws.

5. In wiring up the Teensy controller and the +5V wiring read this post for some clarifications: https://www.anninrobotics.com/forum/questions/properly-wiring-the-teensy-the-5vdc-connector-mystery.

6. If you're planning to use a servo gripper rather than a pneumatic one, read this post: https://www.anninrobotics.com/forum/questions/tips-for-using-a-servo-gripper-instead-of-a-pneumatic-one?appSectionParams=%7B%22origin%22%3A%22member_posts_page%22%7D.

7. The +5V power supply doesn't seem to easily mount to the floor of the Enclosure (page 225), so I 3D-printed a substrate for mounting it. If you want the file, let me know.

Good luck in your construction. Chris Annin provides very good support along the way.