Steps per unit daft question

[dcrowder]

I know that this is a daft question but.... :)

When I am asked by mach3 how far I would like to move when using the 'set steps per unit' am I entering in mm or cm? I have just tried 50 and it moved close to 50cm! not quite what I expected!

Cheers


Dave

[komatias]

I know that this is a daft question but.... :)

When I am asked by mach3 how far I would like to move when using the 'set steps per unit' am I entering in mm or cm? I have just tried 50 and it moved close to 50cm! not quite what I expected!

Cheers


Dave

mm or inches, whichever you have set.

Again, more info needed to help you fix this. e.g. what are you using to drive the stepper motors, what is the lead screw pitch how many microsteps....

It really helps if you take the time tell what you are using to begin with.

[dcrowder]

bear with me 10 minutes and I'll tell you :)

[dcrowder]

All 4 x motors are 4.2A Nema 23 1.8deg Model Number 23HS2442B

X & Y Drive is Rack and Pinion Mod 1.0 with 20 tooth Pinion from here......... https://www.cnc4you.co.uk/Rack-and-Pinion (Datasheets available too)

Z Drive is using a 10x3 Trapezoidal Thread from here........... http://www.zappautomation.co.uk/mechanical-products/trapezoidal-leadscrews-and-nuts/trapezoidal-leadscrews-270/kue-class-100-steel-leadscrew/right-hand-280/kue-10-a-r-tr-10x-3-trapezoidal-screws.html

My Stepper Drivers are ACT Motors DM542. I initially had my microstep settings to On-On-On-On which I believe is software controlled, speeds were rather tame, i tried an alternative setting of 2000 microsteps (On-Off-Off-On) and the machine is a lot faster and scared the life out of me when I first jogged it :)

I tried the Set Steps Per Unit for both of the above settings with different results. My frame is about 1mx1m I had the X axis set about 250mm from Zero. Using On-On-On-On Mach3 asked me how far I want to move so I entered 50 thinking 50mm but it moved over 500mm. Using On-Off-Off-On from a similar position but slightly further away from Zero than my previous attempt the X axis charged off and stopped at my limit switch - twitchy bum moment :)

I'll be honest I'm a little bit overloaded with information about the switch settings I should be using and not sure if I'm setting them correct - any advice on this would be appreciated too!

I hope this information is what you're looking for! Thanks for your time :encouragement:

[dcrowder]

Also.. if it makes any difference... I don't plan to use the machine for any one specific purpose, I want to work with a range of materials, some work will be on a small scale and other will be using the whole working area which is approx 750x800 (I think)!

Also I am using a Y axis motor on each side of my gantry.

[dcrowder]

Oh... and also if it makes any difference - I'm using 2x48v PSU's, 2 x steppers per PSU

[cncJim]

Hi Dave,

I think I asked a similar question before (So I think its not a daft one!) and this was the general advice I was given:

The "Steps per" setting in mach3 motor tuning is how many steps are needed to move one unit of measurement (as set in Mach3) so if using mm units, its how many steps to move 1mm.

This is determined by a calculation taking the drive Microstepping amount and dividing by PITCH of the ballscrew or how far ONE revolution moves that particular axis.

So as an example (with ballscrews), assuming 10mm pitch ballscrews and 1600 micro steps the STEPS PER 1mm would be 1600/10=160

This will mean 160 steps moves 1mm so you would set the "Steps per" in Mach3 to 160.

As for which microstepping amount you should set your drive to... I dunno! it should be set to what works best for your machine/needs :)

I tried many different settings on my drives, some worked OK others seems to create resonance in the machine and made it shake! I settled on the value that that made the machine run smoothest while allowing the speeds I needed.

Cheers,
Jim

[dcrowder]

Cheers for that Jim... Just reading through formulas and working out pitches at the minute :) mind bending!

Quite a good explanation here... http://rlab.org.uk/wiki/Project:Large_CNC_Router ....but it still twists my mind - although it'll soon seem like common sense and I'll wonder what I was ever confused about!

[cncJim]

Cheers for that Jim... Just reading through formulas and working out pitches at the minute :) mind bending!

Quite a good explanation here... http://rlab.org.uk/wiki/Project:Large_CNC_Router
That's very funny because that's my wiki page! :) I am a member of rLab (http://rlab.org.uk) and I use the wiki page to document projects and stuff and hopefully "inspire" me to maybe finish some of them!! Google really does get everywhere.... :hypnotysed:



although it'll soon seem like common sense and I'll wonder what I was ever confused about!
Nah, if you are anything like I was (am?), you will file the information away somewhere "safe" and the next time you need the same info you will forget where you put it and ask the question here again! :)

Cheers,

Jim

[dcrowder]

A fine piece of work! It's really helped me get my head around what is going on.

Once I had read through that and also had confidence in the units I was entering in the axis calibration, it enabled me make some progress today :)

The machine is all zeroed, calibrated, motors smooth.. I went with 10x steps for the X & Y - and 4x steps for the Z as the motor would stop rotating at higher speed using 10x - my thinking behind this is that I get more torque the lower the steps....... Correct me if I'm wrong there though please!!!

I've just strapped a marker pen on to the Z and managed to draw an alien face so I'm rather chuffed right now.

On a lighter note... I also want to point out (this post being made shortly before the referendum) that we should be thanking the EU for getting us to use metric instead of imperial. I can't imagine how hard it is for our yankee chums working all this out in Inches :excitement:

[cncJim]

Glad it helped Dave. I can't take the credit though, that info is all from the many many many posts on this forum.

It can take some digging (the search functionality doesn't always make this easy) but often you will find what you need.

[dcrowder]

Glad it helped Dave. I can't take the credit though, that info is all from the many many many posts on this forum.

It can take some digging (the search functionality doesn't always make this easy) but often you will find what you need.

you can say that again!

[cncJim]

Yep, I have pretty much given up using the forum search. Much easier to use google to directly search the forum like this:-

"site:mycncuk.com microstepping mach3"

Works really well and is much faster! :)

[dcrowder]

1am and I've already learned something new for the day :)

[JAZZCNC]

I can't imagine how hard it is for our yankee chums working all this out in Inches :excitement:

No harder just decimal point is in different place.!!


I went with 10x steps for the X & Y - and 4x steps for the Z as the motor would stop rotating at higher speed using 10x - my thinking behind this is that I get more torque the lower the steps....... Correct me if I'm wrong there though please!!!

Well your sort of correct but like most things in CNC it's not that simple.!!
Resonance is big factor in stepper performance and lower micro stepping often make the motors run in area that they get affected by resonance. This cripples the performance.
Jim mentioned it briefly but playing with micro stepping can drasticly increase performance. Every machine resonates different so there's no one setting that suits all machines. ~However rule of Thumb is that higher MS runs smoother but at the cost of stress on the pulse engine. Basicly many more pulses are needed. So if your using the Parallel port some times running high MS can tax the parallel port which struggle to cope with supplying consistant train of pulses. This degrades the quality and frequency and all sorts of strange things can happen. Things from missed steps to poor performance or stalling motors.

That's why External motion controllers are much prefered if running machines at higher feeds. like routers. Small machines like mills etc can get away with using PP and lower MS because they rarely run in Mid band or higher speeds which is where steppers/drives get affected most.