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Re: Aluminium FEA optimalized CNC router
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.
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Re: Aluminium FEA optimalized CNC router
You could always use more powerful Stepper motors to negate the loss of torque at higher rpm. Also you could simply run your machine with higher rapids using servos so less of a gear reduction is required. 10mm pitch 10m/min rapids and a 3:1 reduction doesn't sound too bad! Ball screws have a maximum rotation speed so make sure you're not going to be over rotating them. 1,000 rpm is a pretty conservative speed but just be careful when it comes to spinning long ball screws at higher rpm.
If you'll be happy running at 3m/min then Open Loop Steppers will be a good choice. Rpm and microstepping both change the available torque so it'll be best to work out what torque will be required and choose the motor based on your calculations.
Cheers,
Fenza
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
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.
If you buy a not Chinese stepper, probably it is higher, like the price :) But yes, you should calculate up to 500rpm.
With 5mm lead from 2:1 to 3:1 usually enough with servos. On 2.5:1 ratio I can get up 6000mm/s no-load speed on 3000rpm. But some motors could do 4000rpm.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
Fenza
You could always use more powerful Stepper motors to negate the loss of torque at higher rpm. Also you could simply run your machine with higher rapids using servos so less of a gear reduction is required. 10mm pitch 10m/min rapids and a 3:1 reduction doesn't sound too bad! Ball screws have a maximum rotation speed so make sure you're not going to be over rotating them. 1,000 rpm is a pretty conservative speed but just be careful when it comes to spinning long ball screws at higher rpm.
If you'll be happy running at 3m/min then Open Loop Steppers will be a good choice. Rpm and microstepping both change the available torque so it'll be best to work out what torque will be required and choose the motor based on your calculations.
Cheers,
Fenza
Why not closed loop?
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
Why not closed loop?
Personally I'm not a fan of closed loop steppers... Open loop steppers are cheap and Servos are great performers, closed loop steppers are neither...
I think it is possible for you to achieve your desired level of performance using the cheaper open loop steppers. 3Nm stepper should probably be around about right directly coupled to a 5mm ball screw.
Servos you'd be looking at 100-200W I believe.
Hope this helps!
Fenza
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
Fenza
Personally I'm not a fan of closed loop steppers... Open loop steppers are cheap and Servos are great performers, closed loop steppers are neither...
Fenza
A bigger steppers is a good idea. You can get enough torque in a no-load operation. Just you will get higher inertia as well.
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Re: Aluminium FEA optimalized CNC router
I have heard open loop steppers is not good for point to point 3D toolpaths. They loose step easy and you cant push them very well.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
I have heard open loop steppers is not good for point to point 3D toolpaths. They loose step easy and you cant push them very well.
Closed loop steppers are a solution looking for a problem, correctly designed open loop systems don't lose steps, if that can happen on a machine then it's badly configured or broken.
Closing the loop doesn't make a bad machine good, using the correct motors & screws and running it within it's limits does.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
magicniner
Closed loop steppers are a solution looking for a problem, correctly designed open loop systems don't lose steps, if that can happen on a machine then it's badly configured or broken.
Closing the loop doesn't make a bad machine good, using the correct motors & screws and running it within it's limits does.
While this is true generally, closing the loop with servos definitely makes machine faster. I also am not fan of the closed loop steppers price wise.
But if the machine will be machining Metal i dont see why at all there is a discussion for sth else than servos and closed loop. Given the price of aluminum material that will be machined and eventually a mistake made.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
magicniner
Closed loop steppers are a solution looking for a problem, correctly designed open loop systems don't lose steps, if that can happen on a machine then it's badly configured or broken.
Closing the loop doesn't make a bad machine good, using the correct motors & screws and running it within it's limits does.
Well said.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
Boyan Silyavski
closing the loop with servos definitely makes machine faster.
But is this a function of the closed loop or is it the fact that the drivers are part of the package and this stops cheapskates buying inadequate hardware and then blaming low speeds and step loss on open the loop?
;-)
- Nick
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Re: Aluminium FEA optimalized CNC router
I thought selecting a stepper or servo should bee easy, but it seems like nothings easy here. So for each person I ask I get a different recommendation. Steppers, open loop, closed loop, no only servos is good enough. The common thing is that everyone recommends servos if I want to use the money. But they are waaaaaaaaaaay more expensive than normal steppers. And all the cheap servos and closed loop steppers is a pain to get information on, since the datasheets and torque curves is not easily available and I have to ask the sellers for it for every motor. But my logic is as follows, if open loop steppers is good enough for Tormach it's good enough for me. First to comment on how this is not a mill. Then I can use some higher quality steppers instead.
By the way can someone remember the good reason to not use overkill steppers like 8nm nema 34? It's not like they are a lot much more expensive. I read it somewhere but I can't find it.
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Re: Aluminium FEA optimalized CNC router
With nema 34 you will need mains voltage drives to get any decent results You won't go far wrong with decent 23,s from Zapp or CNC4you
With AM882 or similar drives and 68V power supply non linear
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
By the way can someone remember the good reason to not use overkill steppers like 8nm nema 34? It's not like they are a lot much more expensive. I read it somewhere but I can't find it.
I think Nema 34 steppers would be too large for your machine. The Load/Motor Inertia Ratio would probably be below 1:1 and therefore you're using more energy accelerating the motor shaft than you are accelerating the 40kg load!
I'm not sure about Steppers but for Servos a 5:1 Load to Motor Inertia Ratio is pretty normal, with 2-3:1 being higher performance and even 1:1 is used for super speedy machines.
A belt reduction gives you flexibility in the gear ratio. If you happen to under size the motors you can lower the gearing and get more torque with less speed, but if you over size the motors you can get some free speed!
I'm sure you can see how this becomes a hobby for many people... Haha!
Cheers,
Fenza
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Re: Aluminium FEA optimalized CNC router
How about fixed screws and rotating ballnuts?
No problems with whip from the screws and reduced rotating mass ;-)
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
magicniner
...or is it the fact that the drivers are part of the package and this stops cheapskates buying inadequate hardware and then blaming low speeds and step loss on open the loop?
;-)
- Nick
I couldn't have said it better.
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
magicniner
How about fixed screws and rotating ballnuts?
No problems with whip from the screws and reduced rotating mass ;-)
I'll just need CNC router to make it first
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
PotatoMill
I'll just need CNC router to make it first
Jonathan has made them for people in the past - worth an RFQ?
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Re: Aluminium FEA optimalized CNC router
Do someone have some opinions on this stepper http://www.aliexpress.com/item/Nema-...999.264.8phZye? 1.8mh seems nice, but the seller dont looks so professional.
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Re: Aluminium FEA optimalized CNC router
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Re: Aluminium FEA optimalized CNC router
But the price is higher and the inductance is higher
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1 Attachment(s)
Re: Aluminium FEA optimalized CNC router
The price is same or lower. You have shipping costs and eventually duty to pay. If you are saving on stepper motors, you will not go far with that build. The links i gave you are the cheapest in Europe
Attachment 18935
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Re: Aluminium FEA optimalized CNC router
Inductance is probably my biggest concern.
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Re: Aluminium FEA optimalized CNC router
This is the motor that everybody here uses for a step motor on their CNC. No surprises, works well at 70V. The motor you show has less inductance on paper, but how true is that...
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Re: Aluminium FEA optimalized CNC router
Quote:
Originally Posted by
Boyan Silyavski
This is the motor that everybody here uses for a step motor on their CNC. No surprises, works well at 70V. The motor you show has less inductance on paper, but how true is that...
That was kinda my question. Is there anyone who have tested this/looked into it before?
Edit. I see that cnc uk sells the steppers in a kit with a 36v supply. I asked if they would put on a 48v supply instead. According to the classic 32*sqrt(inductance) rule about 57v should be optimal. Why is they selling 36v supplies in their kits?
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Re: Aluminium FEA optimalized CNC router
Cause most people / not on this forum/ don't build their own power supplies. And a 70VDC non regulated 550W PSU for 4 motors is not exactly cheap or light to manage and ship. So they offer the typical stuff assuming if you are to build strong and fast CNC you are knowledgeable from where to buy and build the PSU
