Hello everybody,

I'm Alex, nice to be part of this forum. First thread for me here after reading and reading and reading many other ones. Lots of valuable information that already helped me figure out a couple different things for my design, thank you!
I decided to start this thread for some specific questions where I could not make a safe choice yet but also some design advice. I would like to know if anybody could guide me in the good direction please.

So here we are with another router build!

First, what do I want to do?
I am designing a medium-sized CNC Router table to machine some Renshape boards, wood, but also aluminum (apologies for talking about this material in the wood forum ). No steel machining involved here.
The machine will have a work area of Z 900mm x Y 850mm x Z 150mm (machine itself is 1100mm x 1070mm).
I attached screenshots of my 3D design to this thread.

I read a lot of threads suggesting that the gantry assy should be the most rigid part of your build. As you can see, I am using a mix of aluminum extrusions and steel laser cut plates. I use one 4080 extrusion at the top and one 8080 at the bottom for the gantry beams. Also, linear rails with ball screws for linear motion (ordered from Fred at BST Automation based on recommendations on this forum).

My first question is regarding the movement of the gantry assy, the X-Axis. This whole gantry assembly, including the 2.2k water cooled spindle that I plan on using, should be around 40-45kgs (~100lbs) based on the current design.
I initially planned on using two linear rails with 2 carriages each + one central ball screw located under the table. But I am currently re-thinking this choice.
Based on what I could read on the forum, many people go with a dual ball screw/dual stepper design for larger routers. Some say that it is worth the extra investment to get two steppers controlling the X-Axis in order to fine tune the machine and that you will not have any moving parts under the table. Others (not as many!) seem to suggest that one stepper controlling one axis is the way to go to avoid any problems like missed steps on one side of the gantry, plus this is also what "commercial" machines use. However, you need a stronger stepper motor which is why I integrated a Nema 34 stepper motor for this specific axis in my design.
Now, I am undecided as to what solution I should go with for this build.
I am not aiming at building the fastest machine as it will only be used to make prototypes or composite molds, no production involved here. I am a little concerned about the inertia the gantry will have when moving and I was wondering if you would recommend going with two ball screws instead of one? The ball screws that I will be using are 1605 for X and Y (as I said, I don't mind slower speeds, hence the 5mm pitch) and 1204 for Z. They are already ordered but I am wondering if I should ask Fred to throw in an extra one in the package before it ships.
Is there anyone here who could guide me in the good direction considering the specifications that I am aiming for? Many of the threads that I read were started 7-8 or 15 years ago, what would you recommend in 2020?

Second question is regarding Z Axis height. I am aware that the higher you go, the stiffer and sturdier the gantry assy should be. I designed it with this in mind. The two aluminum extrusions will offer a good rigidity to support the spindle movements and the steel plates on the sides with 3 vertical stiffeners each should be able to do a good job transferring the moves from the ball screw/linear rails with minimal flexion. The goal is to make it stiff but also light. Looking at this design, do you think that I might be aiming for too much with 150mm considering the materials that I plan on machining?

Finally, my last question concerns the brain of the machine. There is a lot of threads about Mach3 and many users are using it. This being a new build, I was thinking about maybe using the newer Mach4. I planned on using one of PMDX motion controller.
Any reason why this would not be a good idea?
On a more specific point regarding wiring, I noticed that PMDX also offers an isolated speed controller board (PMDX-407) that works with their motion controllers boards. My question is: do you need one of these speed controller to control your spindle with a VFD and Mach4 or can you directly connect your VFD to the motion controller board?

That's pretty much it to start. Any help will be greatly appreciated.

Thank you in advance!
Cheers,
Alex