Question about Microstepping - Resolution+more

[Aryantes]

I've done a few searches through the forum and have noticed a few different posts on microstepping.

Some posts say that it is not a way to increase the resolution of your machine and some say it is perfectly practical to use 1/10 on a gecko drive to make your resolution 10x more precise.

I'll either be using a rack and pinion setup or a chain sprocket setup (#25 roller chain)

It seems like micro-stepping is in general a good thing.

My question is, what are the downsides?

I'm running off of a 3ghz p4 and Mach3 seems to run stable at 75 khz kernel frequency and even at 100 khz it says "System: Excellent"

If I am using a controller with 1/8, 1/10, 1/16 microstepping, any reason not to use it?

[Fastest1]

Speed is the reason. It would take 10x as many steps to move the same distance. Also though your system tests @ 75 & 100 khz, I am not sure it really uses anything past 45 khz. Does your controller have 1/4, 1/2 and full also? How much accuracy are you looking for? Lets say a stepper has 200 steps per rev X 1/4-20 lead screw, if in full step (200 X 20= 4000 steps per inch with a resolution of .00025 ) if in 10x (you guessed it 40000 steps per inch, resolution theoretically would be .000025). BTW I think a human hair is .002". A few people here are really into production so speed is very important. Even a slow machine can break tools and parts! Dont ask me how I know.

[Jesse B]

You'll want to find the fine-line between speed and accuracy. There's no point in making your machine 0.000025" accurate if it takes 10 hours to machine a small piece. And on the other hand, there's no point in having 0.1" accuracy and having the piece take minutes.

[ger21]

Microstepping is usually more important in reducing resonance than increasing resolution.

[Aryantes]

Isn't the effective speed the same?

If I set it to full step, then 1 revolution of a stepper motor takes 200 pulses.

let's say 1 revolution is 1 inch.

so, 200 steps = 200 pulses. In 1 second, moves gantry 1 inch.

If we set it to 1/16 microstepping, then...

200 steps * 16 microsteps per step = 3200 pulses = 1 revolution = 1 inch.

but then, you simply send 3200 pulses in 1 second, to move the gantry 1 inch, right?

It's just a matter of pulses? Assuming your computer can send enough pulses, isn't the effective IPM the same?

If it removes resonance, that is a good thing. I was wondering what the downsides are, torque?

[Jesse B]

Micro-stepping can also cause *some* loss of precision. The motor is being held somewhere between where it feels comfortable at, so each 1/16th step may not be EXACTLY the same. Mind you this works itself out throughout a full rotation, but it's just some food for thought.

[Fastest1]

The Z stepper on my lathe is around 101,000 steps per inch. It has a gear reduction (that I would or will remove if feasibly possible) that was probably needed in its time. I dont know how the speed is affected just yet but I do want to do threading via just an optical trigger on a pulley (like I am using on my Sherline). My Z might not be able to keep up. On my Sherline, I could thread at 400 rpm. I wonder if the Dyna will be able to move that fast. There will be cures if that is the case.

[ger21]

It's just a matter of pulses? Assuming your computer can send enough pulses, isn't the effective IPM the same?

Yes, if the PC is up to it, then speed would be the same.

[allen00se]

Intersting thread...
I am using EMC2 on my machine with a 10 microstep gecko drive and steppers that are 200 steps/revolution. So with my 1/4-20 rod I am in the category mentioned earlier of 40,000 steps per inch. I agree that I don't need that precision, but is there any way to make the gecko not have 10 microsteps? If i just change the setting in EMC2 it makes the machine think its going an inch but it really only goes 1/10 of an inch. Am i just stuck with 40,000 steps/inch?

-Krys

[Jack000]

emc2 has a setting for microstepping, does that not work? I'm using emc2 with the gecko g251 and microstepping works just fine.

[allen00se]

yes there is a setting for microstepping when configuring your machine, however... if I change that setting to take out microstepping it just results in my machine going 1/10th of the distance it is supposed to (unless i am talking about the wrong setting). I think the culprit here is the driver board, my gecko540 uses 10 microsteps, and I was asking if there was a way to make it not use those microsteps. I assume there isn't.

[Fastest1]

Sorry the G540 is not adjustable in regard to micro stepping. It is 10x. They have other drivers (Gecko) that are either adjustable or full step. I dont think they offer anything with the built in controller/bob like the G540. I would probably be running the 210s otherwise.