[icur_raise]

I just built a 2x4 MDF CNC, I am able to get the motor tuning up to around 8 inches per minute tops before the motors stall. I used 1/2 13 all thread for the lead screws. The motors are 405 oz. How fast can i expect these motors to travel with these lead screws and if i want to go faster how fast can i expect different screws to run. I guess i mean is there a way to figure this out with a formula or something. Any help would be great. Thanks

[metal-surgeon]

Does the motor 'stall' or quit at 8" per/min or is the speed maxed out at 8" per/min? How do you know you are traveling 8" per/min? Is the '405 oz motor' a weight?

Inches Per Minute = RPM x Lead

RPM = Inches Per Minute / Lead

Lead = Inches Per Revolution

Anyway, if the if you are traveling at 8" per/min with a lead of 13 threads per inch or (.077 per/revolution), the rpm of the motor would be 103.89

Had to figure this out recently at work too
I would be glad to help you figure it out if you wanted to run faster, you just need a screw with a more aggressive lead, less threads per inch.

[louieatienza]

There are a few reasons.

Before anything, try to slow acceleration a little bit, and see if it helps.

Disengage your screws (or leadnuts) from each axis and make sure your gantry and carriage move freely without changes in "tightness." For the gantry, if you have a single leadscrew, make sure it does not rack.

At 8ipm your motor is turning at 104rpm, which should be in the meat part of the stepper torque curve. Depending on power supply and driver, the motor could probably spin at 300-400rpm before the torque drops. Unfortunately, that still means you'll be moving pretty slowly.

1/2"-13 can be pretty rough; I'd check to see that the threads are formed well and there's no binding with your leadnut. If you used a coupler for a leadnut, there may be steel-on-steel galling. Some lubrication might help.

Usually with finer pitched screws, lower torque motors arre used since they can achievev higher rpm before the torque drops. With larger steppers, multi-start ACME screws are commonly used to take advavntage of the larger stepper's low end torque.

There will always be a compromise in resolution with more speed as far as steppers are concerned since they're inversely proportional, but for most DIY projects, a 1/2"-10, 5 start (2tpi) gives you good speed and decent resolution (.0025")

[crane550]

Everything you need is right here:

Leadscrew Pitch Tutorial

[louieatienza]

Does the motor 'stall' or quit at 8" per/min or is the speed maxed out at 8" per/min? How do you know you are traveling 8" per/min? Is the '405 oz motor' a weight?

Inches Per Minute = RPM x Lead

RPM = Inches Per Minute / Lead

Lead = Inches Per Revolution

Anyway, if the if you are traveling at 8" per/min with a lead of 13 threads per inch or (.077 per/revolution), the rpm of the motor would be 103.89

Had to figure this out recently at work too
I would be glad to help you figure it out if you wanted to run faster, you just need a screw with a more aggressive lead, less threads per inch.

Actually, the motor would have rotated 8 x 13, or 104rpm!:stickpoke

Your drive, power supply are also other factors. Even the speed of your computer if you're using Mach3 or other computer-based controllers. 2600 times your microstep resolution is a lot, you can also try use a lower microstep resolution and see if that helps, since with your thread pitch, you may not need much of it...

[ger21]

Drives and power supply play a large part in the speed your getting.
What drives are you using?
What power supply voltage?
What are the specs of the motor? Amps, Voltage, Inductance?

Motors over 400oz typically have higher inductance, and need very high voltages to spin fast.

However, let's go back to screws. 1/2-13 is very inefficient, wasting about 65% of the motors power to efficiency losses.
Switching to 1/2-10 acme will probably triple your speed, for two reasons.
One, it's more efficient. Two, it has fewer turns per inch, so for the same rpm, the machine will move faster.
For even more speed, going to multi start acme is the best choice. Most use 1/2" acme with between 2 and 4 turns per inch. For a 4ft travel, the 2 turns/inch (usually 1/2-10 5 start) will whip less at higher speeds.

But please provide the motor and drive info first, as they may not allow you to take advantage of the better screws.

[metal-surgeon]

Actually, the motor would have rotated 8 x 13, or 104rpm!:stickpoke

Same answer just a little different way to figure it out. But, since i got you hear Louie, can you help me understand the '405 oz' rating? I never heard of that before. I know a bit but have a lot to learn.

[louieatienza]

Same answer just a little different way to figure it out. But, since i got you hear Louie, can you help me understand the '405 oz' rating? I never heard of that before. I know a bit but have a lot to learn.

True, but my way is the easier and more obvious way! If it were exactly 8ipm, then the stepper is spinning at exactly 104rpm! If it spun 103.77rpm, you'd be off position by .1%.

The listed torque ratings of steppers are always the stall torque, meaning it's torque rating at rest, at the stepper's rated current and voltage. It's also measured in newton-meters (N*m) and I think it's about 141inch*oz = 1 Newton*meter.

Since we probably are more concerned with the stepper's power while spinning, you'd have to look at the manufacturer's website to find the torque curve of the particular stepper, and see if it's torque at the rpm you need it to be at will suit your particular application.

[msimpson99]

With motors attached and power removed from the motors, can you turn the screws, this moving your gantry with your fingers. If you cannot then you are binding the screw. This is very easy to do with standard threaded rod.

Did you oil the threaded rod?

[icur_raise]

Thanks for all the info guys really helps. I know that the 1/2 13 rod is the cheapest roughest way to go but i was trying to stay as cheap as possable.( not always a good thing.) The electronics kit i bought was from buildyourcnc.com. I did manage to do some tunning today and when i set up the calibration i maanged to get the speed up to around 15 IPM and acceleration is set to 2. It runs really well just a little slow for my likings. i did some test cuts to cut a 1 inch square and the results were .987 on both directions so some more tunning is in order i guess. but thats pretty damn good i guess for mdf and all thread. i figured i would try to change the micro stepping and see what that does have is set to 1/16th. is lower faster i will have to think about that. my steps in the tunning are around 12000 steps per inch give or take. thanks again for the info guys still learning.

[ger21]

Adjust the steps per inch to get .987" closer to 1".
Microstepping shouldn't really have any effect on speed.

[TrickyCNC]

Microstepping shouldn't really have any effect on speed.

what about computer system speed / latency ?

(just reading the EMC2 manual last night had reference to this )

[ger21]

I know next to nothing about EMC.

[TrickyCNC]

basically there is a limit to how many signals the computer can send to the BOB/drivers per second.
when microstepping , you are needing more signals per second per revolution.

Latency is the time from when the software says to send a signal, to when the CPU actually puts that signal at the output port. If this gap in timing is too large, then you have to slow down the signal rate (step rate)

That's my understanding of it anyway.

That's why some laptops and computers with on board graphics chips can be unsuitable for real time control. the cpu has to stop responding to the software requests whilst it looks after other jobs it has to do, like working the graphics , swapping memory about , etc. then it carries on the the software for a bit, and so on..