Aluminium FEA optimalized CNC router

[PotatoMill]

So I have been working on redesigning the whole machine. I'm currently going for a stationary gantry design.

Due to the fixed gantry design the heaviest moving part is now the base plate with 30kg. I'm going to use 20mm HIWIN profile rails on all axis.
There will be one lead screw on each axis, no need for two on the X any more due to the stationary gantry. Here i'm going to use 1605 ball-screws. To drive the axis i'm currently looking at using servos in the 200-400W range. There is not the same amount of information on servos av steppers so I hope someone here have some knowledge on servos. Seems like JMC produce the cheapest servos and drives, but I cant find a lot of data on them. If there servos from JMC are good enough i'm probably going to use them. BST automation also seems to have a ok selection on servos, but again there is little documentation to find.

[Lee Roberts]

BST automation also seems to have a ok selection on servos, but again there is little documentation to find.

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

.Me

[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.

[PotatoMill]

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.

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.

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.

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]

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]

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]

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]

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.

[remrendes]

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.

[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