[darko9000]

I am on my way to building my first DIY CNC

I am not that knowledgeable about paring right motors with right board ot transformers so i decided to purchase a kit from this ebay seller. Vince, very nice guy, he answered some of my questions and gave me a few suggestions.

https://www.ebay.com/itm/Gecko-G540-...IAAOSwJcddL0eq

Gecko G540 5 Axis Kit, 5 600oz 8mm Motors, 48v 12.5a PS, Ethernet Smooth Stepper

I am looking to build MDF CNC with a 24x48 working area to start. Once I have built and played with this thing, the plan is then to build the new frame out of aluminum and steel. The same components would then be transferred to the new machine.
The design is based on CR ONSRUD 5 axis. I want to build a sturdy frame and be able to machine the edge of hardwood planks.
I have uploaded 2 drawing in my album so hopefully they are there so you have the idea of wham i'm looking to build.

So this is what I'm thinking.

Y-axis 1500 mm rail and 2005 ball screw
Y-axis 1500 mm rail and 2005 ball screw
X-axis 1000 mm rail and 1605 ball screw
Z-axis 400 mm rail and 1605 ball screw

With the option to add a rotary axis later.

I'm not looking for super-fast travel speeds. I would prefer more accuracy and torque vs speed. The machine would be used for wood and aluminum cutting primarily.

Is a 1500 mm long 2005 ball screw ok or I'm going to have problems with whiplash?

The hardware would be from ebay linearmotionbearings2008 store and would be similar to this kit

https://www.ebay.com/itm/20mm-HIWIN-...gAAOSw4DJYiNIN

Any experience positive or negative you have encountered building your machine that i should be aware of?

Any feedback is greatly appreciated, since i'm not that super knowledgeable. Don't want to make to many mistakes on my first try, budget is tight.

Thank you very much

Please excuse my broken english

Darko

[machinedude]

i don;t think you will have much trouble with screw whip on a 20 mm diameter 1500 mm long ball screw at 300 or 400 IPM. screw whip can come from a lot of places and things can be done to improve performance of your drive screws. diving the nut rather than the screw is one way to remove the whip but is move involved if you want more traverse speed.there are all kinds of calculators online to get you a ball park estimate of when to expect screw whip with the screw length , diameter and bearing support block types. since the long screw is the bigger diameter that will help with whip as well.

being that the machine is not extremely large fast traverse is not going to be as important as it would be for a larger machine.

the gecko drives are a good drive choice, they make quality drives. i think the only limiting factor of the Geko 540 is the amperage rating of that drive which i think is around 2.5 or 3 amps? so you can only go so big with your motors before you need a different drive to handle them.

[ger21]

I think both 600oz motors, and 5mm pitch screws are a poor choice. When used together, they are a terrible choice.

Stepper motor's torque ratings are holding torque, when the motors are not spinning. The faster the motor spins, the less torque it has. Higher torque motors have higher inductance, and the torque falls off faster as rpm's increase than a smaller motor. Becqasue of this, a 300oz motor will likely have more torque at 1000rpm than a 600 oz motor.
With 5mm pitch screws, to get any speed at all, you need to spin the steppers very fast, where they have little torque left. 600oz motors might be OK for a rack and pinion machine, but I'd never used them with ballscrews. Personally, I'd never use motors larger than 380oz with a G540.

You get the best performance out of steppers, when the drive system gives you 10mm to 25mm of travel per stepper revolution. Go with 10mm if you want more precision, and 25mm if you want more speed.
I'd never use less than 10mm pitch screws on a router.

[darko9000]

deleted

[darko9000]

I think both 600oz motors, and 5mm pitch screws are a poor choice. When used together, they are a terrible choice.

Stepper motor's torque ratings are holding torque, when the motors are not spinning. The faster the motor spins, the less torque it has. Higher torque motors have higher inductance, and the torque falls off faster as rpm's increase than a smaller motor. Becqasue of this, a 300oz motor will likely have more torque at 1000rpm than a 600 oz motor.
With 5mm pitch screws, to get any speed at all, you need to spin the steppers very fast, where they have little torque left. 600oz motors might be OK for a rack and pinion machine, but I'd never used them with ballscrews. Personally, I'd never use motors larger than 380oz with a G540.

You get the best performance out of steppers, when the drive system gives you 10mm to 25mm of travel per stepper revolution. Go with 10mm if you want more precision, and 25mm if you want more speed.
I'd never use less than 10mm pitch screws on a router.

I was under impression that bigger the motor bigger the torque and smaller the pitch more precision

Vince is offering same kit with 300 oz motor for little bit less money 1145$

https://www.ebay.com/itm/Gecko-G540-...IAAOSwJcddL0eq

I will be upgrading to a spindle later.

I can change my ebay kit to 10mm ball screws before i order.

Just wanted to make sure that later when i build all aluminum and steel frame and transfer hardware over i can mill aluminum with no problems.

Thanks!

[darko9000]

i don;t think you will have much trouble with screw whip on a 20 mm diameter 1500 mm long ball screw at 300 or 400 IPM. screw whip can come from a lot of places and things can be done to improve performance of your drive screws. diving the nut rather than the screw is one way to remove the whip but is move involved if you want more traverse speed.there are all kinds of calculators online to get you a ball park estimate of when to expect screw whip with the screw length , diameter and bearing support block types. since the long screw is the bigger diameter that will help with whip as well.

being that the machine is not extremely large fast traverse is not going to be as important as it would be for a larger machine.

the gecko drives are a good drive choice, they make quality drives. i think the only limiting factor of the Geko 540 is the amperage rating of that drive which i think is around 2.5 or 3 amps? so you can only go so big with your motors before you need a different drive to handle them.

Thanks for your reply. I have seen a few videos of machines driving the nut and it is pretty cool but that system is out of my price range for now. The kit from ebay has double nut on all ball screws so i'm hoping this would help with precision and whiplash.

[ger21]

I was under impression that bigger the motor bigger the torque

Again, a stepper motor's rated torque is it's holding torque, when it's not spinning. The faster it spins, the less torque it has. Bigger motors lose more torque at higher speeds, and tend to have lower maximum usable speeds.

[pippin88]

You need the motor inductance to get a better idea.

A torque curve would be very useful also.

[darko9000]

You need the motor inductance to get a better idea.

A torque curve would be very useful also.

The 300 oz nema 23 are listed at 2.4 inductance and 600 oz are listed at 6.4inductance

[darko9000]

Again, a stepper motor's rated torque is it's holding torque, when it's not spinning. The faster it spins, the less torque it has. Bigger motors lose more torque at higher speeds, and tend to have lower maximum usable speeds.

Thanks, i will change my kit to 10 mm ball screw pitch

[ger21]

The 300 oz nema 23 are listed at 2.4 inductance and 600 oz are listed at 6.4inductance

According to Gecko, the 300oz motor will need 50V to get max performance from it, and the 600oz motor would need 80V. With a G540, you'd only get 60% of it's max performance.
You really need to see torque curves, to see how much torque each has at higher speeds.

[darko9000]

According to Gecko, the 300 oz motor will need 50V to get max performance from it, and the 600oz motor would need 80V. With a G540, you'd only get 60% of it's max performance.
You really need to see torque curves, to see how much torque each has at higher speeds.

I don't see the torque curves anywhere but power supply is 48V, if i go with 300 oz motors would that be close enough to be ok?

https://www.ebay.com/itm/Gecko-G540-...IAAOSwJcddL0eq

I'm afraid i would not know how to purchase and assemble the right components individually. Electronics is not one of my things i know alot about it. For that reason Kit like this is appealing to me.

BTW just saw your website, your program is exactly one of the things i want to do with the CNC.

I built myself the inlay dovetail tool box for work and holy **** it took FOREVER to complete.

[peteeng]

Hi Darko - You say you have a gecko G540 5 axis kit? A G540 only has 4 axis. If you require 5 axis then don't get the G540 it can't be used for 5 axis. I suggest you get the cheapest parts to build your MDF machine to get you through the learning curve. You want to cut metals and this is quite a step up from where your starting. Perhaps buy a small chinese kit to learn on then plan a serious machine after that. The current discussed parts won't grow up to where you want to be...cheers Peter

[joeavaerage]

Hi,
Gerry is right you need LOW LOW LOW inductance stepper that can go fast, especially with fine pitched (5mm) ballscrews.
6.4mH inductance is too much, the stepper will be absolutely gutless at 1000 rpm despite it having plenty of torque (600 oz.in) at low speed.
If you could get 300 oz.in motors with 1mH inductance they would have MORE torque at 1000rpm than the bigger motors.

If you want to cut, not just engrave, but cut aluminum then you will need a very rigid machine. It suggests to me that 1500mm screw and rails
are going to be to flexible to be considered accurate for aluminum. I would suggest that you concentrate on wood, and then try aluminum,
but don't be surprised if the machine is to flexible to do a good job.

Craig

[peteeng]

Hi Darko - The 20mm screws over 1500mm will whirl at 1400rpm. So I don't expect you will be running that fast. But 5mm lead is too fine. 10mm oe 20mm will be much better depends on what rapid speeds are needed. The screws will be rigid enough to cut metal, its the machine structure that needs to be addressed. Peter

[darko9000]

Hi,
Gerry is right you need LOW LOW LOW inductance stepper that can go fast, especially with fine pitched (5mm) ballscrews.
6.4mH inductance is too much, the stepper will be absolutely gutless at 1000 rpm despite it having plenty of torque (600 oz.in) at low speed.
If you could get 300 oz.in motors with 1mH inductance they would have MORE torque at 1000rpm than the bigger motors.

If you want to cut, not just engrave, but cut aluminum then you will need a very rigid machine. It suggests to me that 1500mm screw and rails
are going to be to flexible to be considered accurate for aluminum. I would suggest that you concentrate on wood, and then try aluminum,
but don't be surprised if the machine is to flexible to do a good job.

Craig

Thank for your feedback
This will be primarily used for wood cutting. Later when i upgrade to a more rigid aluminum frame i would like to cut some aluminum.
Just to clarify, it is a very small working area (24x48) I do not care about rapid travel speeds just my cutting speed.


If you want to cut, not just engrave, but cut aluminum then you will need a very rigid machine. It suggests to me that 1500mm screw and rails
are going to be to flexible to be considered accurate for aluminum. I would suggest that you concentrate on wood, and then try aluminum,
but don't be surprised if the machine is to flexible to do a good job.

I understand this, i will try to build a as rigid as i can.

Thanks!

[darko9000]

Hi Darko - You say you have a gecko G540 5 axis kit? A G540 only has 4 axis. If you require 5 axis then don't get the G540 it can't be used for 5 axis. I suggest you get the cheapest parts to build your MDF machine to get you through the learning curve. You want to cut metals and this is quite a step up from where your starting. Perhaps buy a small chinese kit to learn on then plan a serious machine after that. The current discussed parts won't grow up to where you want to be...cheers Peter

In the kit from ebay It looks like you connect two gecko G540 together and you can go up to 8 axes if you want, did not know that is even possible .
Originally i was considering buying ACORN board but i really wanted option of rotary axes later and considering im using two Y axis that was not possible with ACORN board

Thanks!

[peteeng]

Hi Darko - Better check this with Gecko. I don't think its that easy. Peter

[ger21]

In the kit from ebay It looks like you connect two gecko G540 together

The G540 do NOT get connected together, but you can certainly use two of them. Not the most cost effective method, though, IMO.

Just to clarify, it is a very small working area (24x48) I do not care about rapid travel speeds just my cutting speed.

You will as soon as you start using it. I've heard this a hundred times from new members, but I've never seen anyone that didn't wish their machine was faster.

[teamloks1]

from my personal experience go with bigger pitch i also using 5mm pitch but with servo motor which can spin until 5000 rpm even with 600mmx600mm working area i still want faster rapid i should go bigger next time