[Danny1978]

Im currently building a heavy cnc router and was after help on what system I should run,my gantry would weigh around 300 pounds.im looking to cut a fair amount of aluminum hence why I'm building it heavy. Im running 25 mm profiled linear rail on all axis and will be running rack and pinion on the x and y axis.i already have a servo system but not able to use it because I want to run dual motors on the y axis and the servo system doesn't allow for this(maybe a future lathe project) I am now thinking about a stepper system but have confused myself reading to many posts. I'm really not shore about what size motors or power supply to get maximum performance. I planned to use gecko 203 or 213v drives,now I've heard the bigger motors won't get as high a speed as the smaller ones,is that to do with the power supply size? I also want to run a rotary axis so I will need 5 motors and drives.i would like to have around a 3:1 reduction on the x and y axis to increase torque but still want reasonable speed say 600 to 800" a minute rapids if possible. It makes it hard when I have no idea what sort of speed I will get out of a nema34 motor,size in oz in" I don't no,what size? Any suggestions,is a 3:1 reduction for a nema34 to great if I want those sort of rapids? Will a 72 volt 20amp power supply be a good choice to run all 5 motors and drives .im in need of some real help here as I cannot continue my build till I have some idea of where I'm going .any help on this would be greatly appreciated . Thanks. Danny

[wayneb]

Hi
I'm half though my build, and I am using with ballscrews and spinning nut assemblies (for my X and Y axis)
3 x Leadshine HBS86 (8Amp Peak) Hybrid Servo Stepper Motor Drives with Encoder feedback.
2 x 8 N⋅m (1100 oz⋅in) Leadshine Stepper motor with encoders. (One each X and Y) 2 x 500W (63Vdc) Antec Power Supplies
(Z axis) 4 N⋅m (560 oz⋅in) Leadshine Stepper motor with encoders. 1 x 400W (63Vdc) Antec Power Supplies
I can achieve up to 4m/min on my Y axis. ( X is not finished yet)
Hope this helps
Cheers Wayne

[Danny1978]

Hi Wayne just had a look at the lead shine stuff pretty interesting have you used this stuff before. I don't no to much about the electrical side of cnc , I'm very interested to hear how it works out for you. My biggest issue is rack and pinion and ratio,if I use say a 1200oz steppers on y and x axis will I end up in a ****ty area of torque and speed, for example if the motor turns say 600rpm the 3:1 reduction=200rpm with a pinion of 20teeth module 2 = about 125mm travel 200*125mm=25000 mm a minute . I'm hoping with this sort of setup that even if the motor power is best around the 300rpm range ill still get 12500 mm a minute rapids, but it is a big what if , I just want a bit of verification before I start wasting money on my own math theory. Very interested in seeing your build progress havnt come across to many Aussies on here cheers mate Danny

[ger21]

i already have a servo system but not able to use it because I want to run dual motors on the y axis and the servo system doesn't allow for this

If you plan on using Mach3, then Mach3 can slave any motors. Regardless of the type of system it is, you can still have Mach3 slave them.

I am now thinking about a stepper system but have confused myself reading to many posts. I'm really not shore about what size motors or power supply to get maximum performance. I planned to use gecko 203 or 213v drives,now I've heard the bigger motors won't get as high a speed as the smaller ones,is that to do with the power supply size? I also want to run a rotary axis so I will need 5 motors and drives.i would like to have around a 3:1 reduction on the x and y axis to increase torque but still want reasonable speed say 600 to 800" a minute rapids if possible. It makes it hard when I have no idea what sort of speed I will get out of a nema34 motor,size in oz in" I don't no,what size? Any suggestions,is a 3:1 reduction for a nema34 to great if I want those sort of rapids? Will a 72 volt 20amp power supply be a good choice to run all 5 motors and drives .

You shouldn't have any trouble with your velocity goals, but the more important issue is acceleration. 800ipm doesn't do any good if it take t-3 ft of travel to get to 800ipm.
I've seen plenty of YouTube videos claiming 1000ipm, but it takes half the travel to get there, and the other half to stop. So you'd never actually see those speeds.

What you need to do, is calculate the required force needed to accelerate at a given rate, and then calculate the torque required to achieve that rate.
Most rack and pinion users use a 1" pinion, which will give you roughly 2oz of force for every oz of torque. (torque divided by pinion pitch radius). Personally, I'd want about .25G of acceleration, which may be higher than most. If you have a 300lb gantry, than in a perfect world, you'd need 75lb of force to accelerate at .25G. Add in friction, cutting forces, and efficiency losses, and a healthy safety margin, and I'd probably want closer to 125lbs of force, maybe even more.

Since your using 2 motors, you can divide that 125lbs in half, with each motor needing to push about 63 lbs.
63lbs = 1008 ounces. Divide by 2 and you'd want 504oz of torque at the pinion. With a 3:1 reduction, that would put you at about 170oz at the motor.
Now, a 1" pinion gives you 3.14 (pi) inches of travel per revolution. At 800ipm, the pinion is spinning at 254rpm. With the reduction, your motor will be spinning at 764rpm.
So, you need to find a motor that will have 170oz of torque while spinning at 764rpm. Now, getting this information is that hard part. Some manufacturers put out torque curves, that will show the torque at any rpm. However, unless you use the same drives, at the same microstep setting, and the same power supply voltage that was used to produce the torque curves, then you may see very different results. So you have to play a bit of a guessing game here, or do some trial and error testing.

Now, as motors get larger, especially with Nema 34's and bigger, the maximum rpm decreases, sometimes rapidly. Since your main concern is with torque at higher rpm, holding torque doesn't mean a whole lot. In a lot of cases, a 400oz motor will have more torque than a 960oz motor when you get up near 1000 rpm.

A motor like this would probably work for you, at 440oz.
http://catalog.orientalmotor.com/ite...prodid=3001048 Looking at the torque curve, it should have around 200oz of torque at 1000 rpm (1.5Nm) when run at 48Volts. Keep in mind, though, that if using Geckos, Gecko recommends a power supply voltage of 32 times the square root of the rated inductance. This would be 39Volts for this motor. IF you run it at 48Volts, it may run very hot. If you run it at 36V, you may run out of torque a little earlier than you'd like.
Power supply voltage and current ratings will be dictated by the motors you choose, and shouldn't be just some arbitrary choice,

Now, I can't guarantee that this post is correct. A good idea would be to use a motor sizing calculator. There's one at the Oriental Motor site I linked to above. You'll need to create an account to use it, but it should be able to tell you what size motors you need for the performance you're looking for. If you search, several manufacturers have similar motor sizing utilities. I'd try a couple different ones to get a reliable number.

Good Luck.

[Danny1978]

hi Ger21 in your calculation you suggest 125pounds of force then divided by2=62.5 pounds for each motor =1008 ounces I don't understand why you have divided it again giving 504 ounces, isnt the 1008 ounces for one motor. Also thanks heaps for the link,didnt no how to fill out all of the sections .so I don't no if im getting an accurate calculation. I understand completely what you said about a machine reaching its rapid rate, I would be happy with 500 ipm the machines travel is only 50" by 50" but I am chasing good acceleration. Also in the 125 pound does that take cutting force into account? When you mentioned about gecko drives would it be worth while if using different size motors on x and z axis to use a separate power supply closer suited to there motor inductance. ? squared *32. Thanks a lot for your help. Danny

[wayneb]

G'day Danny

Just curious, why so fast?

[Danny1978]

Hi Wayne to be completely honest im impatient I do want to setup a tool change spindle at one end of the table and don't want it to take forever to get there,the rapids im talking about are a wish not a must ,if I am using rack and pinion I thought I may aswell try to get some speed out of it aswell,i had a look at your build nice and solid very similar to what im building but im having a cut area of about 1200*1200mm. I was very intrested in your electronics done some searching on them lastnight have you tested them out yet? still a bit stumped over what system to use,as I said I have a servo system from low cost cnc retrofits 4 axis with 600oz in motors.Ger21 said I could use this in mach3 slaved for the y axis,i was told by somebody else I couldn't,does this mean 2 motors can run out of the y axis of the drive or do I have to use the a axis for the 2nd motor ?

[wayneb]

G'day Danny,
I have got my Y and Z axis working.

http://youtu.be/bOoCjS6bBpM

In my opinion, I think the most important speeds are at max cutting torque. In my case, I have approx 800 kg of cutting force at the tip. I come across this formula on the forum. Thanks josvanhout

F = E x M x 2 x phi / h
E = loss by friction ( I take 90% for ballscrew )
F= forward force generated by turning the motor
M= turning moment from the motor in Newton/meter
h=thread distance (0.005 meters)

F = 0.9 x 7Nm x 2 x 3.14 / 0.005 = 7912.8 Newton = 807 Kg

This is at 750 mm/min (150 rpm x 5mm), but with no load it can go about 2200 rpm

http://youtu.be/V8gN_Ve1x0I.

Although I'm only running the Y axis at 4m/min, the acceleration is high at 200mm/s/s. It's all trial and error.

Electronics

I highly recommend Ethernet Smooth Stepper, (but I have no run my spindle yet.) Despite the lack of information, it was relativity easy to set up. With 2 breakout boards from Holmann designs, more than enough inputs and output for everything.

Hope this helps.
Wayne

Did I mention, my accuracy is less the a micron.

I know I'm going to be caned on that comment.

[Danny1978]

Looks awesome Wayne but you have thrown a bit of a spanner in the works for me,I've spent my day looking at all different systems, I'm now thinking ballscrew due to the fact that I want to cut and engrave aluminiumand I'm just not sure i will get the stiffness I'm looking for in rack and pinion, my machine travel is about 1200mm by 1500 mm do you think I will get away with turning the thread not the nut and get pretty good speed,plan on using 2505 or 2510 ballscrews. I also emailed dmm tech today to see if they could work out a system for me, I gave him info on the weights of the z axis and x axis and an overall on the gantry also ballscrew size,I didn't mention what rapids I thought I would wait and see what they come back with. Your video got me all worked up to just try and make a decision ,I always end up searching and reading to many things some of which contradict each other and don't no which way to go

[wayneb]

G'day Danny,
Sorry to hijack your thread.
If you need speed, go for the 10mm pitch ballscrew. I'm yet to finish my X axis to work out my max RPM pushing the gantry weight.

Cheers
Wayne

[wayneb]

What power are your servos? I keep forgetting that servos don't loose any power at high RPM.

[Danny1978]

My servos on the low cost cnc retrofits unit are 600 oz

[ger21]

I cut it in half again due to the radius of the pinion, which gives 2 oz of force for each ounce of torque (assuming a 1" dia pinion).
As for the power supply, It really depends on how much different the inductance is.

[ger21]

Just curious, why so fast?

For a router, 600ipm isn't really very fast. On our machine at work, we cut at about 1100ipm, and the rapids are quite a bit faster. A lot of newer industrial routers cut at over 2000ipm.