Advice on Mammoth CNC Router Build - Steel Framed - 2440mm x 1220mm cutting area!

[Boyan Silyavski]

What you miss with this gantry design is that the rails must be as low as possible, at least one of them. Otherwise is pointless. Now you are just making a big lever.
As it is now is weaker than normal gantry.
The big+++ of this design is eliminating overhang and stiffening at the bearing blocks and lowering the assembly and eliminate gantry twist.
But as i see it you just lengthened the lever and didn't eliminate twist. Ok, square z casing will be stronger but will push more the gantry beams and bearings.
Ideally 3 rails at the gantry will be perfect as i see it with this design.
But adding third couple of bearing blocks on a normal gantry Z will do the same, its easier and cheaper. And 2 beams soldered together will be stronger than 2 separate beams as is your case.
So, try to lower one of the rails.

The point being here is that this design needs to be done correctly cause it will allow high speed machining or deeper dig, but you will need as i see it at least 3kw spindle, or it will become the weak point. As Dean said before.

[Wejjmeister]

Ok well lets see the rest of the design for Z axis and work from that.

My suggestion for nema 34 on 2020 screws was mostly for the long (X)axis to keep screw speed down to reduce whip and still maintain 10mm pitch speeds but I've just noticed it looks like your intending to use rotating ballnuts which if correct then you could use nema 23 motors on 10mm pitch.
That said 20mm pitch would allow a ratio to increase torque and have a lower nut speed for same speed as 10mm pitch which if using 20mm dia screws (which I would use at this length) may be better with the larger nut on smaller motors.

This doesn't help the Y axis thou which will still need nema34 motor if you use twin screws on single motor. That said Mixing motor sizes isn't a problem if you use High powered drives because they run from mains AC so don't have a mix matched DC power supply which would be needed for the lower voltage DC drives running the nema23 motors.

Ok that makes sense. I will swap out the motors for 23's on the X axis and then install a 34 on the Y axis in the fashion you stated, with pulleys and dual screws. I had intended on using 10mm pitch on the X axis, do yoou think that 20mm would prove advantageous, or would it be a case of pro's and con's?

What you miss with this gantry design is that the rails must be as low as possible, at least one of them. Otherwise is pointless. Now you are just making a big lever.
As it is now is weaker than normal gantry.
The big+++ of this design is eliminating overhang and stiffening at the bearing blocks and lowering the assembly and eliminate gantry twist.
But as i see it you just lengthened the lever and didn't eliminate twist. Ok, square z casing will be stronger but will push more the gantry beams and bearings.
Ideally 3 rails at the gantry will be perfect as i see it with this design.
But adding third couple of bearing blocks on a normal gantry Z will do the same, its easier and cheaper. And 2 beams soldered together will be stronger than 2 separate beams as is your case.
So, try to lower one of the rails.

The point being here is that this design needs to be done correctly cause it will allow high speed machining or deeper dig, but you will need as i see it at least 3kw spindle, or it will become the weak point. As Dean said before.

Im not sure how I can get the gantry any lower without it interfering with the material on the bed? Can you possibly sketch something up to demonstrate what you mean, as I am not following. I could weld another box section piece below the existing long section of the Y axis, but these would then protrude down into the cutting area, and reduce Z height.

Also just to clarify, the Z axis will be inside the boxed section, not on the front, overhanging it, so the loads will be evenly spread across the frame as far as I can see?

Running a 3kw spindle would be nice, but to begin with I think I would opt for the 2.2kw as I can find out the limitations of the machine with that and then start to push things later on in the process. The option of quicker cuts would be nice, but quality is my first concern to begin with.

Help?