There are only a few DIY machines I have found that I was really super impressed with when it comes to performance cutting aluminum.
The first, is Linux_fan.
His thread is here:
https://www.cnczone.com/forums/uncat...aluminium.html
His gantry is aluminum plate, bolted together, filled with Epoxy.
The second is ThomConcept
https://www.usinages.com/threads/cnc...uminium.63531/
Both designs are worth looking at.
Recently I've been looking at the omio CNC machines, just out of interest sake, and I've found many YouTube videos of these cutting aluminum really well for what they are. I was really surprised. I think much of this has to do with bit choice, and it looks like people are using 3mm - 6mm single or double flute endmills. I'm curious as to what would happen if they used a longer bit in order to make deeper pockets in thicker stock.
IMO, the rigidity of your machine and your spindle choice will determine how aggressively you can cut with larger bits and at lower RPM's if that is what you're after.
in the video above, he's claiming a MRR of 3 cubic inches per minute with a single flute 6mm bit, which is super impressive to me.
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Would you be cutting sheet mostly? For example 10mm thick and less? Have you considered the height of a vise for your Z axis?
If you're going to go through all of the trouble of designing and building something special, then the dual powered X axis is what I would do. Otherwise I'd consider buying an Omio X8, and modifying it. It's so much darn work to make a machine.
The flat plate gantry risers and Z axis...... It looks like you are using thick plate, 16-20mm, yeah, that's thick, but even so, look at ThomConcept's design in my previous post. Box type instead of plate is stiffer. Also, he has a box section for the Z axis. You don't need a full box for your Z but at least you can bolt some angle on the sides of the plate to make it less bendy.
If you reverse how the bearing blocks and rails are mounted on the Z axis, you can get the bearing blocks further apart vertically and possibly squeeze out a bit more Z travel.
If you want to make a really gucci machine, for your gantry risers, I would consider something like two 1/4" or 3/8" plates with several 1/2" x 2.5" ribs bolted in between them and fill the voids with EG. Also check out Linuxfan's build thread to see what he did for his gantry....
In general though, I have nothing really negative to say about your design process.
If you can pick up some surplus bearings from a good manufacturer, Like Bosh Rexroth, NSK, Genuine Hiwin, anything made in Germany, Japan, and perhaps Taiwan, you will be happy with them. I think the Chinese linear bearings can be hit and miss.
You mentioned Nema 34 motors.....so you match your ballscrews (lead and diameter) with the motors to get the performance you want to achieve. Many Nema 23's will out perform a high inductance Nema 34 that has way more holding, or low RPM torque.
A low inductance or mH rating for the motor generally means that it performs better at higher RPM's
The acceleration you want is also a factor. Do you have any idea what kind of top speed and linear acceleration you want to achieve out of this machine?
The 10mm lead ballscrews typically allow for a better top speed at a given acceleration based on the rotary inertia math, even for a heavy gantry, when using stepper motors.
The 5mm lead is totally doable if you are careful about motor selection.
You can. If one ballscrew is significantly longer than the other one, this could be an advantage. But if they are approximately the same length, my preference would be to use the same motors and ballscrews on X and Y.
It depends on what you want to cut with it, and whether you want to be able to mount a vise or two to the table. It's different for everyone. I'd suggest drawing up a vise, putting a 3" tall block in it, and look at how that would work with a bit hanging 3.25" out of the spindle. Then look at using a bit with 1/2" of stick out all the way down to the table. Can your design do both of these things?
It should be fine. But must be considered when selecting your motors. Low inductance (mH) steppers perform better at higher RPM's with lower voltages. The higher the inductance, the bigger the difference in performance will be at higher RPM. When looking at a stepper motor, it is the torque that is available at the top speed you want to go to that is important as this is what is available to decelerate the machine. At lower RPM you have more torque.
Look at this graph:
Doubling the voltage doesn't change the available torque all that much. It's different for every motor.
On thing to consider is if you really want to do this. It may be a better use of your time to buy something and just get to using it. Sometimes these projects can drag on for a very long time.