Am I heading in the right direction?....

[Lloyd]

Thanks Jazz,

Regards ballscrews then I wouldn't use 16mm diameter for the long axis because in my experience it's just a bit too long. Now you can get 10mm pitch in 20mm Diameter then your much better using them over 16mm at this length. The difference in performance is neglible and your far less likely to get whip so often can go faster than 16mm screws that whip.!Use 16mm Dia 5mm pitch for Z axis.
Also I recommend you connect steppers to screw with timing belts and pulleys to help reduce resonance and add some flexabilty with ratios if required.

i was going to use 25mm ball screws for all of them, but I see it would be better with 16mm on the Z... Pulleys idea - I hadn't thought of...

Regarding the gantry sides, I am using 20mm alu as the bracket, I thought this would be plenty rigid enough based on other designs I saw - how would you size it different?

the location of the ball screw - I accept your opinion on this... My thought was because at the max depth I'll be cutting just PU foam, and this is far below the ballscrew it should be ok, and in a simple location build-wise...

Where would you try set it otherwise?

thank you for the heads up on the motors from Zapp

i have heard that Mach 3 can be unreliable - what's the consensus experience with it?

anyway, regarding the hardwear, I'm definitely going for profile rails, circa 25mm, with ballscrews on X and Y of 25mm, and 16 on Z, each with 10/10/5mm pitch respectively.

motors - definitely digital sounds better... Power likely as advised

[JAZZCNC]

Regarding the gantry sides, I am using 20mm alu as the bracket, I thought this would be plenty rigid enough based on other designs I saw - how would you size it different?

20mm is ok-ish but I'd brace it more. Don't under estimate the power of steppers connected to ballscrews. If the cutter jams for any reason but doesn't snap straight away, which does happen with thicker cutters, then something will bend and those plates are directly connected to the screws so are first on the list.! Closely followed by the Z axis front plate( I've seen my front plate bend many times)

the location of the ball screw - I accept your opinion on this... My thought was because at the max depth I'll be cutting just PU foam, and this is far below the ballscrew it should be ok, and in a simple location build-wise...

It's a personal thing and while it's in simple location it's in a vunerable location for getting leant on or against while leaning into machine, crap hitting it etc.

Where would you try set it otherwise?

Tucked in at the sides lower down with some form of cover.

i have heard that Mach 3 can be unreliable - what's the consensus experience with it?

No not at all, yes it as some faults just like others do, inc Linux CNC, but in the main it's IMO the best control for begginers thru to advanced users. There's more support from a massive user base so if you do have any problems there will be someone to help.
The main or most problems with Mach comes from the PC parallel port and people over tuning there motors not the program.
This is why I recommend you invest in a motion control card if using Mach, they allow much smoother and faster performance along with much better reliabilty due to the very stable pulse streams they provide, unlike the parallel port.

anyway, regarding the hardwear, I'm definitely going for profile rails, circa 25mm, with ballscrews on X and Y of 25mm, and 16 on Z, each with 10/10/5mm pitch respectively.

DONT use 25mm ballscrews this is a BIG mistake.? The inertia from 25mm screws is too much for nema 23/4 motors and you'll end up with a very slow under performing machine. Like wise if you go with nema34 Motors then unless you use expensive high voltage drives you'll have underperforming machine due to the slower speed of the motors.

Also you won't need 25mm rails 20mm will be fine, even 15mm would be more than good enough. The main reason why 20mm is prefered is due to bearing size being better suited. Plus the cost differance is nothing. Where as 25mm bearings are just a little too big and then to a lesser degree you have the negative inertia affect and the weight while accelerating/de-accelerating. Loadings wise even 15mm profiled linear bearings can handle the loads you'll need with some to spare.

The combination of 3.1 or 4Nm Nema 23 motors run at 70Vdc connected to 20mm dia 10mm for axis over 1300-1400mm long is well proven if you move away from it you'll regret it when you see a machine that as it. The machine running 25mm screws on 25mm rails with nema 23 motors will struggle perform half as well.!!
At the length your building your even on the border of being able to use 16mm ballscrews for the long axis but 20mm are safer bet in my experience.
I would recommend 20mm for X axis if screw longer than 1400mm, 16mm for Y & Z. 20mm rails all round.