Mach 3 - correlation between steps per MM and size of the table

This is my first post, so hello to everyone. I'm less than a newbie when it comes to this, but my friend asked me if I could help around his table. He has a custom build 2mx1m table with plasma cutter, running mach3. Now he bought it used and we can't reach the guy he bought it from. We don't have any manuals or names of motors. The machine is moving in all axis, so there's that.

So my problem is here - when I set the steps per MM on X axis, the units change. For example, when I home the machine, and I set steps per MM to 13 - it takes 2000 units on X axis to get to the end of the table (which is good). However, the machine 'shakes' when I jog through X axis, it's not a smooth movement. I figured out that I probably have the wrong amount of steps set up, but when I set steps per MM to a higher value, it does work more smoothly - but (and that's my problem/question) it takes far less units on X axis to get from home position to the end of the table (let's say 1000 units). So when I try to cut a circle, it's actually an elipse (Y axis is correct and runs smoothly).

I have a couple of questions and would be more than grateful if anyone could help me out or point me in the right direction - I googled extensively, but I probably word the questions wrong so I can't find the right answers.

1) How do I tell mach software that I have 2000mm x 1000m table?
2) I used the "set steps per unit" thing in settings, and after couple of times it set the steps to 267 - and it runs smoothly, but there is a problem I described above. How do steps per MM correlate to these values ?https://gyazo.com/9eb04445199581b3b16b26c20ef95468

I can provide photos of the machine, but there is nothing to identify which motors were used in building this table. I can also provide screenshots of mach3 settings, but that would be tomorrow, when I get to the workshop.

When I run some G code for a circle with 'correct' steps per MM on X and Y axis ( meaning, steps per MM that were set up by mach3 settings) - say the circle is 50mm in cambam, it's actually far bigger in reality. But when I set up steps per MM on X to 13 and 26 on Y, it makes a "perfect" 50mm circle, meaning it really takes 2000mm and 1000mm to travel through the table - it just is shaky, not smooth. How to manage that?


I'm very sorry if anything here is not clear, english is not my primary language. Please ask any further questions about things I didn't think of if it helps.


Thank you all for taking the time to read it and (eventually) help.

(As I had no idea where to post it, I posted it twice, once here and once in general forums. I am sorry if it's not fitting in one of the categories, please remove the faulty one).

The steps per setting is ONLY used to make teh machine move exactly the distance you program for. That part set you then set teh Accel and Vel of each axis that sets haow fast it gets up to speed and HOW fast it will move MAX.

Try resetting teh Accel & Vel settings 50% lower and retest.

(;-) TP

So I'm right that steps per milimeters tell the software how big my table actually is? Your advice is to remain at 13 steps per MM and adjust the velocity/acceleration? I tried that a bit (no extensive testing) and it still shaked the whole table when it moved.

Would you mind telling me why at 13 steps per MM my is actually 2000mm wide, but when I tell mach3 to program steps for me, so we go the whole "how much do you want to move" and how much does it actually move" questions a couple of times and I finally get it right and it moves 5cm when I tell it to move 5cm, it sets steps to 267 per MM? Where's logic in that? I'm sure it's logical, I just don't understand it. Why does mach3 set up incorrect steps?

Is this the only way to tell mach3 the size of the table?

Thanks!

You don't tell Mach3 the size of your table. Mach3 doesn't care.

The only thing you may do is setup soft limits, which tell Mach3 where your table border is.

Thing is, if I program a circle to be 50mm in diameter, I need mach3 to move correctly, as in movement in X has to show distance of 50 value. I have set up soft limits, they all work fine in my current setting. But my current setting is not optimal, because my X axis 'shakes' when it starts moving, it's not smooth.

And what do you mean "mach3 doesn't care"? If 1mm in reality is not the same as 1 unit in mach3, my cuts won't be accurate, my soft limits won't actually work. That's my problem, because when I add steps per MM to make it smoother, 1mm =/=1 unit in mach3 and my drawings are far from accurate.

Maybe I worded it poorly, as I said, my english is not that good - do steps per MM influence in any way the ratio between 1mm and 1unit in mach3? How do I set up my mach3 to match 1mm to 1unit in the program, so I could draw precise shapes?

That wasn't my advice. Mach does not care about overall table size because it's irrelevant to accurate movement. If 13 steps makes an accurate movement, then that is likely the correct setting, but I'm not there to measure it myself, so we take your word for it.

What are your velocity and acceleration settings?

Setting the Steps per is what tells Mach3 how far to move for each step it issues. NOW you do also have to make sure of the UNITS you are setting it up as IS what you will normally run in.

NOW that has nothing to do with how big teh table is as Mach3 does not know or care how big it is . It simply follows teh Gcode. NOW IF you tell it how big it is from teh softlimits setup it will then know how big it is BUT it will still not know exactly WHERE it is. For that you need to Reference Home the Machine so it knows where to reference the size to. Once it knows where Machine 0,0 is it THEN knows where the rest of the table is based on how you setup the softlimits.

You jerkyness could be coming from several different areas. It could be from motor tuning. It was suggested to reduce teh Accel and Vel. Did you do that ?? It could be from you running teh code in exact stop mode. In that mode teh machine will come to a full stop at each point of the code and can make it very shaky as on each line it has to start and stop.

Try switching to ConstantVelocity mode . In that mode the motion is blended together as best it can be. Lines of Gcode get blended together so it does not stop on every line and it can smooth out the motion.

(;-) TP

Here is the other thread on the same topic, I thought this was going around in circles...

http://www.cnczone.com/forums/mach-s...-software.html

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That's my problem, because when I add steps per MM to make it smoother, 1mm =/=1 unit in mach3

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The problem is that you don't add steps to make it smoother. Steps per unit is was dictates the distance moved. There's only one correct setting, and it can NOT be changed once set.

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Originally Posted by Stnq

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1) How do I tell mach software that I have 2000mm x 1000m table?
2) I used the "set steps per unit" thing in settings, and after couple of times it set the steps to 267 - and it runs smoothly, but there is a problem I described above. How do steps per MM correlate to these values ?

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Read the Mach3 manual.

http://www.machsupport.com/wp-conten...all_Config.pdf

It explains everything, from the software installation and Mach3 configuration to hardware design and considerations. Even if some of it is outdated and is definitely too wordy in my opinion, it is worth spending time on it and read basically every page of it, especially if you are "less than newbie". If you just want to concentrate on your questions then read only from chapter 5.5 to 5.5.4.1. Those pages explain everything you need to know about your questions.

There is a short version also, which is basically only about configuration.

ftp://machsupport.com/Docs/Mach3%20Setup%20Tutorial.pdf

Really, there is PLENTY of information about how to configure Mach3, not only on this forum, but all over the Internet.

As other already said, Mach3 does not care about your table size. "Steps per" is a setting which tells Mach3 how many step pulses it must send to your stepper motor to move 1 mm or 1 inch, depending on the units used, based on your lead screw pitch, or belt/pinion pitch. Mach3 handles instructions in G code, so if it finds for example an instruction like: "G1 X10" then it will send a number of step pulses which it believes necessary to move your X axis to 10 units distance measured from zero. If you have "Steps per" set to 200 it will send 2000 step pulses. If you want to move X to 5 then you just tell Mach3 "G1 X5", not changing "Steps per".

"Steps per" is set up based on your machine and is never changed once you have done the configuration right. Configuration includes even maximum speed and acceleration considerations. If your steppers don't run smooth then maybe those parameters are wrong also. It is a huge difference if you have a very fast machine or a slow one. If your PC sends those pulses too slow then it is OK, except that the move will be slow, but if it sends too fast your steppers may stall, start to vibrate or just skip steps. How fast the pulses are sent depends on the speed and acceleration values. Once you have that right, the maximum speed can never be overridden, so if you have for example a maximum speed of 1500mm/min then the above example could be complemented with an "F" value, for example "G1 X10 F1000" would mean that X is moved to position 10 with a speed of 1000 mm/minute, but if you enter "G1 X10 F2500" then it will be moved with 1500mm/min speed because of the maximum speed set.

Of course, you have to define your X,Y,Z zero coordinates every time you start a new job because the machine never knows where your work piece starts and ends. The table size is not important for Mach3, it is only important for you because that tells you the maximum size of material you can work on. If Mach3 gets an instruction to move in any direction outside your table limits it will continue moving until it hits a limit switch, which will indicate you that something is wrong, either in the G-code or in your configuration.

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Originally Posted by ger21

The problem is that you don't ad steps to make it smoother.

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Well, yes and no. You can add steps to make it move smoother but not without also changing the motor driver configuration and set micro stepping.

A stepper run without micro stepping takes 200 steps per turn, and that's not very smooth. To make it smoother you change microstepping from 1 to something better, for example 10, resulting in 2000 steps for the same turn, making it run smoother.

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Originally Posted by ger21

Steps per unit is was dictates the distance moved. There's only one correct setting,...

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Right. According to the above example, if his lead screw has a 5mm pitch then without microstepping he should set 40 in the "Steps per" and with micro stepping set to 10 he should set 400. That would result in the same distance, but would move smoother since Mach3 would generate more step pulses for the same distance.

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Originally Posted by ger21

... and it can NOT be changed once set.

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It can be changed, but not without changing the motor driver configuration.

I know you know all this, but it seems that he didn't understand the previous discussions.