Aluminium FEA optimalized CNC router

**PotatoMill** · 17-06-2016

The design is kinda crude, it was a fast iteration. I'll probably get some time in the weekend to upgrade it so the details is more understandable. The i'm going to add end plates to the large gantry square tube. Most of the machine will be welded. I have planned to bolt the gantry and base together at the bottom of the gantry legs. I guess I need to remove the aluminium part in the title of the post sinse it's mostly steel now.

Originally Posted by Lee Roberts

If you send them a msg Fred will be more than happy to help and send you what you need.

Thanks for the tips, seems like Fred is a helpful guy.

Originally Posted by magicniner

It looks like you have the rails on the base and the carriages moving on the X-axis.
If you have the carriages fixed on the base and the rails moving under the X-axis you can have maximum support and rigidity where you need it most at all times.

I agree, I changed it back and forth several times. It became a compromise. Rails on the base would make sure the support is maksimum and equal at all times. However the moving base would be longer and the leverage from the longer base would put more stress on the machine. The weight of the moving part would also be higher.

Originally Posted by remrendes

I can give some info about that. I have one 60ASM200 at home. My computer is not enough fast for this resolution, so that is why it looks slow on a video. The electric gear ratio is 1:1.https://www.youtube.com/watch?v=qyrEdBIpqx8

Nice video, you got any info in addition?

**remrendes** · 17-06-2016

Originally Posted by PotatoMill

Nice video, you got any info in addition?

I have eveything :) I can give a contact number as well, I have seen a factory in China. They are pretty good.
If I will not forget, I'm going to upload a training video what I have from them.

**PotatoMill** · 18-06-2016

The cost of servos is going to be quite high, so i'll probably for closed loop steppers instead. However the ClearPath servos seems tempting. Is there any good reason to use servos instead of closed loop steppers?

**Fenza** · 18-06-2016

Originally Posted by PotatoMill

The cost of servos is going to be quite high, so i'll probably for closed loop steppers instead. However the ClearPath servos seems tempting. Is there any good reason to use servos instead of closed loop steppers?

Closed loop steppers don't have the speed or torque capabilities of servos and are sold as an 'economical' alternative. The only good reason to use closed loop steppers is because they are cheaper.

Some cheap servos like the JMC can be similar price to most closed loop steppers, it'll be interesting to know if anyone has tested how their performances compare.

Cheers,

Fenza

**PotatoMill** · 19-06-2016

Thanks for the quick response Fenza and Remrendes

According to a quick estimate I did I dont think i'm going to need any more torque than what these closed loop steppers deliver; http://www.aliexpress.com/item/new-o...a-82b3fb4b4813

Estimates done with

-40kg weight of moving part
-130N force of cutter (excessive)
-20N friction
-85% efficiency
-10 m/s^2 acceleration (more than I think i'll need, but I haven built any CNC machines before so i'm not certain on this.)
-5mm lead

Using T = (F*l)/(2*PI*n) where F is total force, l is lead per revolution, n efficiency
I get 0.44N well within

However I do know that theory and experience dont always match up. And in real life there could be some factor that make the estimate wrong.

**Fenza** · 19-06-2016

Originally Posted by PotatoMill

Thanks for the quick response Fenza and Remrendes

According to a quick estimate I did I dont think i'm going to need any more torque than what these closed loop steppers deliver; http://www.aliexpress.com/item/new-o...a-82b3fb4b4813

Estimates done with

-40kg weight of moving part
-130N force of cutter (excessive)
-20N friction
-85% efficiency
-10 m/s^2 acceleration (more than I think i'll need, but I haven built any CNC machines before so i'm not certain on this.)
-5mm lead

Using T = (F*l)/(2*PI*n) where F is total force, l is lead per revolution, n efficiency
I get 0.44N well within

However I do know that theory and experience dont always match up. And in real life there could be some factor that make the estimate wrong.

Hi PotatoMill your math certainly is correct but it doesn't account for the full picture. I use Kollmorgen MOTIONEERING to calculate more precisely what kind of motors are required, it's a little tricky to understand in the beginning but sticking with it pays off massively! http://www.kollmorgen.com/en-us/serv...eering-online/ here's the link to their site. I use their older application at the bottom of that page, it looks like they have a new online tool available now.

Kollmorgen have a huge range of motors available and the MOTIONEERING app helps point you to which is suited for your machine, I just use the data from that motor to base my search for a cheap servo / stepper system off of.

Also always remember that steppers holding torque is not the same as a servo rated/max torque.

A good rule of thumb that I use (though I'm not entirely sure it's correct) is that a 3Nm stepper is roughly equal in power to a 100W Servo.

Hope this helps!

Fenza

**PotatoMill** · 19-06-2016

Originally Posted by Fenza

Hi PotatoMill your math certainly is correct but it doesn't account for the full picture. I use Kollmorgen MOTIONEERING to calculate more precisely what kind of motors are required, it's a little tricky to understand in the beginning but sticking with it pays off massively! http://www.kollmorgen.com/en-us/serv...eering-online/ here's the link to their site. I use their older application at the bottom of that page, it looks like they have a new online tool available now.

Kollmorgen have a huge range of motors available and the MOTIONEERING app helps point you to which is suited for your machine, I just use the data from that motor to base my search for a cheap servo / stepper system off of.

Also always remember that steppers holding torque is not the same as a servo rated/max torque.

A good rule of thumb that I use (though I'm not entirely sure it's correct) is that a 3Nm stepper is roughly equal in power to a 100W Servo.

Hope this helps!

Fenza

Great tool, very helpful. I'm trying both the new and old now, the old one seems better actually.

**remrendes** · 19-06-2016

Originally Posted by PotatoMill

Estimates done with

-40kg weight of moving part
-130N force of cutter (excessive)
-20N friction
-85% efficiency
-10 m/s^2 acceleration (more than I think i'll need, but I haven built any CNC machines before so i'm not certain on this.)
-5mm lead

With 5mm lead is not the best ballscrew for you. You shoud use the motors up to 500rpm. Under this, you nearly can get a full holding torque.

**remrendes** · 19-06-2016

Originally Posted by PotatoMill

The cost of servos is going to be quite high, so i'll probably for closed loop steppers instead. However the ClearPath servos seems tempting. Is there any good reason to use servos instead of closed loop steppers?

Both have a feedback to driver, so both are better than a normal steppers.
A cost of the servos is higher than what you think. E.g. you have to reduce the rpm, with 1:2 - 1:3 transmission. 1x zero backlash pulley is approx £30-40, one belt can be £15-20 and you need 3 set. With steppers, you just need a coupling.
Unfortunately I started with servos, but I could get a cheap set from China.