moving gantery CNC sturdiness

[RonVais]

Thank you everyone for your fast response !

I'm currently designing the machine in cad but i need to choose my components for the design- so dont worry choosing the compontent doesnt mean that Ill buy the component tomorow before compliting the design

As for the items i have bought are pretty much general use - exept for the spindle that i have seen lots of builds with (also as far as i know plywood usualy is cut at high speeds and those chineese spindle do fine at and dont loss to much torque at high speeds) and for the other parts i just had them already (steppers and steel tube profiles)

The main tree questions for now are:
* Will 50*100*3.2mm steel frame (not welded frame) will be sturdy enough and not vibrate? (as I sayed earlier I intend to build moving gantery configuration CNC with the dimentions 1500*1500*300mm of the frame)

* Can i get off with the kit mentioned in the original post? it includes HGR20 rail and HGH15CA carts
and a 2005 ball screw ( i understand the 2010 will be faster though i can compensate with driving the steppers at higher speeds to reach 100mm/Sec)
a kit with 2010 ball screw at aliexpress is about 250 euro more exprensive

* Will a ball screw at such length unsupported be sagging? and what can i do about it? (i dont want to use the rack and pinnion systems cause they are more expensive )

Thanks!

[JAZZCNC]

The main tree questions for now are:
* Will 50*100*3.2mm steel frame (not welded frame) will be sturdy enough and not vibrate? (as I sayed earlier I intend to build moving gantery configuration CNC with the dimentions 1500*1500*300mm of the frame)

* Can i get off with the kit mentioned in the original post? it includes HGR20 rail and HGH15CA carts
and a 2005 ball screw ( i understand the 2010 will be faster though i can compensate with driving the steppers at higher speeds to reach 100mm/Sec)
a kit with 2010 ball screw at aliexpress is about 250 euro more exprensive

* Will a ball screw at such length unsupported be sagging? and what can i do about it? (i dont want to use the rack and pinnion systems cause they are more expensive )

#1 Yes it will vibrate for sure, the question is how much and this we can't answer because too many variables involved. However, your needs cutting plywood are not taxing so it will probably easily fullfill your main needs, Cutting aluminium on the other hand is different and here it could struggle with vibrations leaving a poor finish.

#2 It's not that simple I'm afraid which is what I was trying to tell you before in my post about the motors.
You can't simply increase the speed of the steppers because as the RPM increases torque drops and because you are using a 5mm pitch you'll need 1200rpm to reach 100mm/sec which those motors won't provide enough torque at those speeds to turn 20mm screws. There are other factors due to resonance and whip which will also come into play and make it not happen.
Again I'll say it because it's VERY important, the Drives and the voltage you run the motors at make a big difference to performance and they need to match to get the best from them.

#3 Pay the extra and get 10mm pitch or even 20mm. You think your saving money by buying 5mm but what your actualy going to do is waste money because you'll soon realise after it's too late you can't reach the feeds you'll need and then you'll be stuck with them.

Now the reason why a larger pitch is better is two fold,
#1 Is obvious in that It gives you the feeds you require
#2 It means you can reach the feeds at a lower RPM which means you have higher torque as the motor is operating lower down the speed curve while cutting and the screw speed is lower so less chance of whip.

These Kits are false economy and nearly always made up of cheap components or poorly matched components. DONT DO IT is my advise, buy separate components that are better matched.

Also Like A_Camera says and I failed to spot first time you have NO CHANCE of building this for 1000 euro's, you'll need at least twice this to make it worth the time and effort.