Gentleman, before I introduce myself I wanted to say thank you for all the knowledge you've put into the public domain with this thread. It has been extremely helpful and makes a lot of things very easy for my project, which I'll get to in a second.

So I'm Skid, new to the forums, and am based in the US. I have a BS in aerospace engineering have spent a lot of time in Part 23 aircraft over the years - both design and manufacturing. Currently though I run a small composites manufacturing facility where we do everything from tooling through final part fabrication for a variety of industries.

One of the big arrows in my tooling quiver is our CNC router table which we've been slowly upgrading and building. Due to capital availability we started small and have slowly been building the machine to really match our needs. It has a working envelope of 1600mm x 2500mm x 450mm. Primarily we machine medium/high density foam, tooling boards, high density urethanes, and aluminum. The big things that matter on the machine are smoothness and precision.

We started with a CNC Router Parts (Avid CNC now) 4x8 Pro machine. From there we did a lot of beef up the base frame and decked it with a single 1in MIC-6 plate full length. We've built a new Z-axis that gives us the travel we need along with a much stiffer cross section and higher quality components. We also swapped out the NEMA 34 steppers for 750W Technic SD Clearpath motors.

On the whole it does great but we're in the process of getting rid of the rack and pinion and moving to ball screws to get better precision and smoothness.

The x-axis I have ordered up a 1600mm, threaded length, 25mm screw with a 25mm lead from Thomson Linear so it's a 23um precision screw with less than .05mm backlash nut - I chose not to go preloaded for a couple reasons. We'll drive that screw with a 2:1 pulley reduction. That guy is pretty straight forward and I don't have any questions.

However, I do have a couple specific questions I'd like to ask about the y-axis which will be the same 25x25 screw and nut combination with a driven nut setup that I haven't found in the thread. I openly admit I may have missed them and re-reading the thread again to see what I missed. My questions are:

1) Are you doing anything unique at the screw supports to prevent rotation of the screw in the mounts? Keying, roll pins, set screws?
2) How much tension are you applying to the screws? Are you controlling this via torque on the end nuts or otherwise?
3) What is the preferred belt tooth profile and width these days? I know I've seen several HTD-5 references but some of those posts are a couple years old and I wasn't sure if some of the GTXXX profiles make more sense these days. Or something else?
4) Have there been any efforts at running double nuts to eliminate backlash in the system or are preloaded bearings the way to go here? My cutting thrust loads are fairly small when I'm doing the finish work which is why I forwent the preloaded nuts just to minimize running load on the system. A double nut on the X-axis is pretty straight forward but I wasn't sure what you guys have done with the driven nut setup or if you just back the second nut up to the other side of the bearing/pulley machining block.
5) Is there anything you didn't do but wish you had on your setups?

For the most part the drawings, models, and tech discussion makes it pretty straight forward for me to put together a bearing/pulley assembly with US sourced parts. I suspect I'll run into some more questions as I move forward but I think this gets me moving further forward. Again, thank you very much for all the information you've made public on this.