[ba99297]

Hi everybody
My name is Vagelis and I am from Greece

I want to build a cnc router with dimensions
X : 1000mm, Y : 1500mm, Z : 300mm

The router is for cutting wood, plastic and ali if possible.

The frame is from steel
The machine will be like that


Attachment 198762

Attachment 198764

Attachment 198760

Attachment 198766

Attachment 198768

These are not the final plans. I just upload them in order to give you a general idea of what i am going to build. The gantry will be about 60 kgr heavy

I have already bought the motors which are three Yaskawa 400 watt Sigma II with 3000rpm.
Do you think the motor are suitable for such a machine?
What cutting speed is possible to be achieved with these motors?
The servos and a 2,2 Kw spindle ( without the inverter) are the only things that I have already bought


Now it is time to buy ball screws and linear motion equipments
The basic question that i have is what ball screw is better to buy
I mean of what diameter and mm per revolution

Also it is important to decide the gear ration between the motor and the ballscrew

The basic restriction is that i already have the motors (3 Yaskawa sigma 2 400 watt)
These motors are rated at 3000 rpm
At fist i was planning to connect them directly to the ball screws .

After reading this topic

http://www.cnczone.com/forums/diy_cn...rew_speed.html

i realize that the ballscrews have a maximum speed limit , depending on the diameter , length and mode stabilization at both ends. So based on the following calculator

http://www.nookindustries.com/Engine...cCriticalSpeed

my own ballscrews (if i buy the 2005) could run

X axis length 1000mm maximum rpm 2478
Y-axis length 1500mm max rpm 1075
Z axis length 350mm max rpm 19739 ( this axis forget him )

That means with 1:1 gear between the motor and the ballscrew, the Y axis ballscrew would never run with 3000rpm because of the 1075 threshold.
I have many thing that i am thinking about but first i think it is better to hear your opinion
I repeat my questions

First question
Are the motors suitable for such a machine?

Second question
What cutting speed is possible to be achieved with these motors?

Third question
What gear ratio should i choose between the motor and the ball screw?

Forth question
What ballscrew should i choose?

I remind you that we are talking about a cncrouter 1000X1500X350 for cutting wood plastic aluminium , with 60 kgr gantry and steel frame
Have in mind that i want to get as much as possible from my motors. I would aprecciate if you analyze your answers

Thank you for you time

Vagelis

[louieatienza]

Motors are perfect for the machine. I would use at least 25mm for y axis. Note Nook's calculators are for max speed under ideal conditions. You will not get the most benedit from your servos if you mount direct. If it were me I would get at least 12mm or more pitch, to lower the screw RPM, and use 3:1 - 5:1 reduction. Remember 3000 RPM is Yaskawa's rated speed, the max speed is 4000 RPM and the peak torque will be around 540 in-oz. With 3:1 reduction and 12mm pitch you should have about 400ipm max cutting speed and 600ipm max rapids; so I would say 12mm would be the minimum pitch. Consider safety as you will be generating a couple horsepower or more per axis, at speed...

[ba99297]

Thanks for your answer
I think that 1,2 or 1,5 pitch ballscrew are hard to find and expensive
So i am very close to chooze
Y axis 2010 for 1500mm long axis 2:1 gear ratio
X axis 2010 for 1000mm long axis 2:1 gear ratio
Z axis 1605 for 350 mm long axis and 2:1 gear ratio

any opinion?

[louieatienza]

Go to automationoverstock.com and look into surplus NSK precision ground ballscrews. You can spin them at least 3x faster than the rolled screws, thus you can couple them directly to your servos...

[ba99297]

Thank louieatienza for your information
Indeed the site has good prices but it isnt obvious the shipping cost for EU countries ( i am from Greece ). Also i dont know the tax fees, so it a little bit difficult to find out the total cost.
Thanks anyway for your help

[keebler303]

If you operate your motors at 1000 RPM, you will get only 33% of the rated power. You want your motors to be near 3000 RPM when you are at your maximum linear speed. With a 10mm pitch on your screws, you could go 10m/min at 1000 RPM of the screw. That sounds plenty fast to me.

I'd recommend 10mm pitch for X and Y with a 3:1 reduction. That will give you the most power from your motors when cutting at 10m/min. If you expect never to be cutting faster than 5m/min, I would suggest using even more reduction, perhaps 6:1. That will give you a lot more torque which will enable you to accelerate more quickly. Often on smaller tables (like yours) you will hardly ever be going at max speed because by the time you speed up, you have to slow down because you are already at the end of the table. If you use a 6:1 reduction over a 3:1 reduction, you should be able to double your acceleration rate which means you will get up to the proper speed much faster.

Matt

[ba99297]

keebler303 thanks a lot for your answer
I think the most important for me is know what is the maximum cutting speed for my motors ( without having torque problems and with logical cutting depth per pass )
My machine is oriented for general perpuse. I am not a pro and i have no spesific job so i may cut from pvc to aluminium.
My gantry will be about 60 kgr heavy and i repeat that my motors are Yaskawa 400watt servo sigma 2 SGDA-04ad (if i remember )
I have no sense (as have never before had a cnc) what is slow and what is fast
I think rapids is just for show off.
The most important parameter is the cutting speed with the motors run with no problem of torque
Your sujestion for 10mm pitch and 3:1 gear is resonable, as i will have 1000 rpm at the ballscrew far bellow the threshold limit of the 1500mm ballscrew
I have two other option
1. To go with 2:1 gear and 10mm pitch (that will reduce the torque and also rise the ballscrew rpm over the threshold )
2. To go with 2:1 gear and 05mm pitch (that will X 4 torque and reduce final speed to 7.5 m/min )

As to change a pulley isnt big cost, the most important is to select the correct ballscrew pitch
I will be glad to hear any opinion

Thanks everybody
Sorry for my english
Vagelis

[ger21]

I'd go with the 10mm pitch and 2:1.
I've always read that you should run your servos at about 80% of max, or around 2500rpm in your case.
That would give you 12.5m/min

[keebler303]

Max speed is 4000 RPM.

The 80% recommendation is based on the maximum voltage the drive can provide to the motor. As long as you have plenty of voltage (calculated based on the voltage constant of the motor) you can go right on up to 3000 and beyond with no adverse effect.

[ba99297]

Ok then
3000*10mm/2=15 meters per min
I think this is a very good speed with no load on the spindle
The question is
Do i need such a big speed, or it is better to go

with 3:1 gear 10mm pitch -->10 meter/min
or 2:1 gear and 5mm pitch--> 7,5 meters/min

These two of course choises will rise the torque and acceleration.
And as Keebler303 wrote

"Often on smaller tables (like yours) you will hardly ever be going at max speed because by the time you speed up, you have to slow down because you are already at the end of the table"
I am very thoughtful about my choise.
Thanks everybody

[louieatienza]

Depends on what you are cutting. Doing certain 3D work will cause a lot of retracting and repositioning resulting in many rapids moves, so it can drastically slow down everything; the larger the piece the farther the pints can be between retract and plunge. If you do mainly profile cuts where the tool completes one profile before moving to the next it may not matter too much. Machining 3D finish pass on materials like foam may require high feedrates. Consider that the continuous torque rating of the 400w Yaskawa servos I believe is 179in-oz at 3000rpm, but is capable of 540in-oz intermittent and 4000rpm intermittent....

[ba99297]

Thank everybody for your help
I will be glad to hear any other advice