Aluminium FEA optimalized CNC router

[routercnc]

It's an interesting design and if you really want to do the Z axis that way then I would add a reinforcement panel on the front outer face of that RHS box to spread the load of the spindle out to the edges (I assume the spindle is mounted just on the front face and not sandwiched between the front and rear faces?). Say a 8-10mm thick aluminium plate as wide as the RHS and enough height to pick up on the 4 spindle mounting bolts. Otherwise the loads will go into the weaker membrane panel and not be transferred to the stiff edges. If you simplified your loading condition on the analysis this will not show up.

Same could be applied to the rails, I would add a thin strip of say 6-8mm thick steel, by 30mm wide on the inside of the RHS directly where the rails mount and screw the rail bolts right through into it.

Also in post#9, first picture, the upright bracket holding the ballnut to the Z axis is too thin. It needs to be approaching the length of the ballnut and then bolted down in 4 places. It should be a 'boss' not a 'bracket'. Also the plate it sits on is on the small side if you are trying to maximise performance. This needs a better connection to the upright Y axis plate. As drawn it will twist when loaded. Maybe a similar plate parallel to the current plate but above the ballnut would work trapping the ballnut in-between 2 plates.

Keep exploring, it's good to see something different every now and again.

[PotatoMill]

I'm currently considering making a stationary gantry design. Since the weight of the gantry pluss the z and y cart comes inn at 80kg (mostly in steel).
The cons will be;
-Longer machine
-Longer rails
-Potensial for sag in the bed

Pros
-Less weight to move for the steppers
-Simpler design
-Less twist on the z axis, the largest factor for displacement

The reason i'm posting this is because it probably a lot more pros and cons than I can come up with, that I hope someone here will add.

[PotatoMill]

It would probably be best to make a 3:1 gearing to utilize the holding torque best. Or is it possible to get cheap ballscrews with shorter than 5mm lead?

[remrendes]

It would probably be best to make a 3:1 gearing to utilize the holding torque best. Or is it possible to get cheap ballscrews with shorter than 5mm lead?

I would go for 10mm pitch and direct drive.
On 500rpm it is 5000mm/min, more than enough.

[PotatoMill]

I would go for 10mm pitch and direct drive.
On 500rpm it is 5000mm/min, more than enough.

Wouldn't I want shorter pitch? If not I would not get close to the corner speed at all. And waste a lot of usable torque.

[remrendes]

Wouldn't I want shorter pitch? If not I would not get close to the corner speed at all. And waste a lot of usable torque.

With steppers? No, not really.
What do you mean with a corner speed?

Here you can see a torque curve for both. You can calculate with a 0-500rpm range.

Unfortuantely it is Hungarian, but here you can see my calculation for my X axis with servo. This is the optimal for a dynamics, but I chosen 2.5:1.

[PotatoMill]

Here is some info on corner speed. https://www.google.no/url?sa=t&sourc...JAddXnAgnBfq5A it's more apparent on these speed torque curves http://www.sanyodenki.eu/IMG/pdf/Ste..._06.12.N_e.pdf

[remrendes]

Here is some info on corner speed. https://www.google.no/url?sa=t&sourc...JAddXnAgnBfq5A it's more apparent on these speed torque curves http://www.sanyodenki.eu/IMG/pdf/Ste..._06.12.N_e.pdf

Yes, it is on the speed/torque curve, where the motor starts to loose his torque. Approx 4-600rpm on a cheap steppers.

[Fenza]

Hi PotatoMill, I see you specced 10m/s^2 acceleration. Now I'm not too experienced with routers and steppers (Mills and Servos is more my thing) but 1g is kind of a lot! I did a quick calculation and a 20mm ball screw 1,200mm length 5mm pitch with 40kg load will require over 3Nm of torque at the shaft to accelerate all the moving parts at 10m/s^2

Cutting forces are only small but the force required to overcome inertia and accelerate a 40kg load is great!

I believe 2.5m/s^2 would be a good target to try and aim for, though It would be nice if someone experienced with steppers and routers could chime in and advise. I believe 50in/s^2 is considered not too shabby in Mach3 which would be 1.27m/s^2

Hope this helps! That Kollmorgen app really is a great tool once you get used to it

Fenza

[PotatoMill]

I think it's more clear to me now.

Requirements
Speed: standard 0-2000mm/min max 3000mm/min
RPM needed:
5mm lead; standard 0-400RPM, max 600RPM
10mm lead; standard 0-200RPM, max 300RPM

A stepper motor seems to lose it torque from 300-500RPM
A standard servo motor has full torque up to 3000RPM. However to utilize the whole range I would need a 10:1 or a 5:1 reduction.

5mm lead will put me over the speed where the stepper starts to loose torque but it will also give me twice the force of a 10mm lead. I'm not sure i'm going to machine over 2000mm/min but for rapids I need a higher speed.

The weight of the X and Y cart is 30Kg. The Z cart is 20Kg
Cutting force; max 150N

After reading more on servos the torque advantages are clear. If my machine was bigger it would be obvious to use them, with the size om my machine there is not so much of a difference.