[Stnq]

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.

[1875]

A stepper motor generally has 200 steps per one revolution. The number of steps depend on the pitch of your screws and any other drive reduction. For example, my screws are 5 turns for one unit of linear motion (inch) and my motors are geared 1:1 to the screw. That means steps per unit of linear motion is 1000.

If your stepper motor driver is using micro-stepping, then you need to multiply by the micro-stepping number. For example, my drivers are using 10 micro-steps, so I actually set my steps per inch to 10,000.

Vibration may be a different issue, but stepper motors will vibrate when run slow because they have discrete steps. Micro-stepping can smooth this out.

It seems your screw ratios are not the same. If you set one axis to 13 steps/mm and the other to 26 steps/mm, then you might have a 2:1 reduction on one axis relative to the other, or you may have a 5 and a 10 pitch screw. You want to set this so that Mach will move the table the right amount.


You tell Mach your table size in the soft limits settings.

There is also motor tuning to set your step pulse width (depends on your motor driver), motor acceleration and speed...

[Stnq]

Thank you for your input. However, like I said, I'm new to all this and please explain like you would to a three year old (heh). What screws do you have in mind? Where would I find them and how to measure how many turns they have?
How would I check if it's using micro stepping? And if it smooths things up, is there any way to enable it?

How can I set it in mach to get my table just right?

And how on earth is this normal that you have 10000 steps per inch and I have 13 steps per mm? I mean, at 13 steps per MM it gets the right distance (200cm) and at 26 steps per MM on Y it gets the right distance too (100cm).

About the soft limits - I'm sorry if it comes out rude, it's not my intention - I don't know if I word it badly or something, but soft limits are not the issue. The issue is, how do I make mach3 to move 1cm both in reality and in program on X axis, while it being smooth? Is 13 steps per MM something normal or is it totally wrong? Because when I run the "set up steps per unit" in mach3, it sets 267 steps on X axis. And it runs super smooth, but then if I tell mach to make a 50mm circle (where 1mm=1 unit on x and on y axis, like I want it to) it'll make something like 150mm+ elipse on X axis.

If it's on my side, that you cna't understand what my issue is - please ask, I'll try my hardest to clarify and answer any questions. But again - I know how to set up soft limits, they all work fine. The issue isonly with motor stuttering at 13 steps per MM. The question too is how do I make mach3 know how much 1cm is in axis units?

[1875]

Soft limits was just to answer your question of how to tell Mach your table size. Mach does not need to know the table size otherwise.

I think 5 and 10 pitch screws are typical metric screws. That would be 5mm and 10mm travel per rev of the screw. So, with 200 steps per motor rev and a 1:1 pulley ratio, then you'd have 10 and 20 steps/mm, respectively. You said with 13 and 26 steps/mm, it makes a perfect circle. These seem like odd numbers to me, but if the table moves the right amount, then you don't need to know any of the parameters I've mentioned. Try 10 and 20 and see if the table moves the right distance. If so, then it's done.

The motor stuttering is probably due to motor tuning. If you change the steps/mm, that will affect how fast the motor needs to turn since velocity is correlated to motor rotation speed. Set the steps/mm properly, then go to motor tuning and increase acceleration lower velocity. You have to trial and error on acceleration and velocity to find out where you motor starts to stall, and then back it off some.

[greggv]

screws can be what is driving your table, or a rack and pinion, a chain or a belt. Before you can estimate your steps per unit, you have to know the total gear ratio of your motor to the drive element. Are the motors driving a belt reduction unit? That would be the first reduction gear ratio. You need to find out how the table is driven, and figure out all the gear ratios. Then someone could help you. If you are using Mach 3 , I think there's a section in it where you tell the motor to go so many steps, and measure how far the axis moves, then you tell that to Mach 3 and it figures out your actual steps per unit.

[Stnq]

Greggv:

Yes, I used this as I mentioned. I put in 5 cm, it moves say 1cm, so I tell it it moved 1cm, then I do it twice more just to be sure and it sets my steps per unit to 267. Thing is, if it's 267 steps per unit, and I home my machine, it takes for example 700units on X axis to travel 2000mm (till the end of the table). What I need is for it to travel 2000 units, so it would be 1mm=1unit on axis. How can I achieve that?

I'm not sure about the reduction, could I take some photos of the machine so you'd take a look at it and maybe figure it out? It would be a giant help, if that's ok.

But the most important is the answer to my unit question.

1875:
Thank you for your input, but where are these screws? Yeah with 13/26 steps for x/y respectively it makes a near perfect circle (well it would be perfect but the x axis stutters and shakes so it's not 'ideal'). To be exact it's 13.546 and 26, if I recall correctly. Currently for X axis I have 7900 velocity and 1000 acceleration (something around that). What would be typical speed, I mean am I right with thousands or should I go much lower than that?

[1875]

Mach does not move in "units" it should be metric or inch. So you are using the wizard to set up steps/mm and you get it to move 5 cm when you tell it to move 5 cm, and that comes to 267 steps/mm? Then you tell it to move 700 cm and it moves 2000 cm?

Ponder this:

if Mach thinks it takes 267 steps to go a mm, it will send 2670 steps to go a cm. That is a lot of steps.
if Mach thinks it takes 13 steps to go a mm, it will send 130 steps to go a cm. That is not very many steps.

Both moves will happen in the same amount of time since the velocity setting did not change. I suspect the table is vibrating because the motor is being driven too fast. Slow it down to 1000 and slow the acceleration down to 100. Then try 267 steps/mm. The table may move slow, but verify the distance is correct and then move to increasing the velocity until the motor stalls, then slow it down a bit. Then work on the acceleration until it stalls, then slow it down.

[Stnq]

Will try what you said, but I'm not sure I explained my issue correctly.

There's this window where the "zero x/y/z" and units are, right? When I home the machine, it all says 0 and everything is green. With 13 steps per MM, when I jog the machine from home position to the end of the table, it shows 2000 and 1000 for X and Y respectively. Not sure how to call these things, so I call them 'units'. it's here: https://gyazo.com/9eb04445199581b3b16b26c20ef95468

However, when I run through the wizard and it sets my X axis motor to 267 steps (and I make it move 5 cm and it moves 5 cm in the wizard, so it should be correct), when I jog the machine from home position to the end of the table, it does not show 2000 for X. It shows different number (don't remember what exactly, I can check tomorrow if it's important). Because of that any of my g codes are wrong (because when I tell X axis to X50 it should move 50mm, it moves a lot more though and instead of a circle I get an elipse). How should I work around that?

I made the acceleration to 150 and velocity to 300 and it still shaked/stuttered, but I will try what you said.

[1875]

For the steps/mm, if you have it set to where you start at the home position, usually the lower left corner, and then move all the way to the opposite corner and the DRO displays 2000 and 1000 from 0,0, then it sounds correct for your table. the shaking might just be motor tuning. Make sure you first select the axis, then save the axis settings after changes.

[Stnq]

Well I set up the steps/mm in motor tuning section, no? Oh that's called DRO, ok. So yeah, if I set up 13/26 for X/Y steps, DRO displays from home to 2000/1000. But when it's set by the mach3 setting wizard, it sets up 267 steps. Where does the difference come from? And which setting is correct? How do I even know if it's the correct steps/mm value? Is it correct because it displays the good amount on DRO?
If I recall correctly, in motor tuning I have steps/mm - 13,547 / velocity 7800 / acceleration 1000. And when I jog, it kinda jerk it (meaning it's too fast, right?), but when I home it, X axis goes much slower and actually smooth. Then, I use for example F500 and it stutters/shakes on arches.

I had similar problem with my Y axis, it kind off shook in one place, but that was a loose belt, I tightened the X axis today and it helped a bit with the 'egg' shape, now it's much more circular (still not an actual circle due to jerking).

So...could you please explain how can I set up so mach3 uses the ratio 1mm in reality = 1mm/unit in DRO? Or am I being stupid right now and it's set up through steps/mm?

I'm going to sleep right now, 2am here. Thank you for your time and all your help, I hope you don't mind explaining a bit more.

What program do you use to write Gcode from dxf projects? I'm trying to use cambam, but I don't know how to set up some things such as pause when it should begin the cut (say I want to cut three circles, lead in tangent I would want a pause there for 1 sec so the plasma has time to cut through the metal - I know how to do it manualy, G4 P1, but how to set it up automatically? M codes are for turning the plasma on and off, right? If I cut something like this : https://gyazo.com/5f40b5d5e95400409774e1689e01f691 I would want to start from the circle in the middle, cut it out, turn plasma off, move to other circle, turn plasma on, wait a sec for it to burn through, then proceed, turn it off etc. Would you know anything about it? As I said, it wasn't really my thing, I never learned or played with gcodes or cnc or plasmas, so I'm being a newbie. I read a lot, but there's a lot of stuff that's not said in most manuals because it's "obvious" such as M3/M5 to turn the torch on/off, I couldn't find anything about it, found out by accident in some sample G code, heh. Thing's hard to learn, but very rewarding when you actually see that thing works

Have a good day!

[1875]

Did you get it worked out?

[Stnq]

Not exactly. I was digging through documents in the workshop to see if I can find something about the machine and I found a note about the motors. Would that help in establishing steps per MM/velocity/acceleration? If yes, I have no idea how to use data from this thing. Maybe you can make some sense out of it? Here it is. http://i.imgur.com/6ym5oHp.jpg

[CNCMAN172]

Stnq,

These are standard 200 P/R stepper motors. How do you know? Read the specs and you will find step angle 1.8, that means 1.8 degrees/step. Now take 360 degrees in a full rotation and divide that by 1.8 and you will get exactly 200 steps to turn one full revolution. You need to post a picture of your machine so people can see how the stepper motor is connected to the table. There is usually a ball screw or a cog rail or a belt. Something converts the rotary motion to linear motion you need to know that before you can calculate the steps per unit.

Russ

[Stnq]

I'm gonne get a picture of the machine and post it here sometime tomorrow/day after that, when I get to the workshop. Thanks for the explanation!