Author Topic: Mach3 Axis Calibration Mystery  (Read 8421 times)

0 Members and 1 Guest are viewing this topic.

Offline Werdelin

  • Active Member
  • Posts: 17
    • View Profile
Mach3 Axis Calibration Mystery
« on: February 20, 2017, 04:48:04 PM »
Hello,
I have just put a 3 axis router table together, and I am now fighting with the axis calibration in Mach3.

The Mystery is (so far) about the X-axis and the Y-axis. They have the same stepper motor, Nema23, the same Microstepper drive, Leadshine M542, with the same setting for microsteps (=16) BUT the screws do not have the same pitch. The pitch for X axis is 5, for the Y-axis is 10.

Wouldn't you expect the Steps Per in Config>Motor Tuning to be the DOUBLE for the X-axis compared to the Steps Per for the Y-axis? I mean, to move a bolt 1 mm takes N (number) of steps on the Y-axis,
for the X-axis it is 2 x N , since the pitch is half of what is on Y-axis?

Or am I just totally on the wrong path here?

Any help will be much appreciated,

best regards

Anders

Offline Tweakie.CNC

  • Global Moderator
  • *
  • Posts: 7,637
  • Super Kitty
    • View Profile
    • Tweakie.CNC
Re: Mach3 Axis Calibration Mystery
« Reply #1 on: February 21, 2017, 01:58:44 AM »
Hi Anders,

You are on the right track.

There is a calculator here : http://www.machsupport.com/forum/index.php/topic,16315.0.html
And an example here : http://www.machsupport.com/forum/index.php/topic,12512.0.html

In addition, on the Settings (Alt-6) page there is an axis calibration feature.

Hope this helps,

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Werdelin

  • Active Member
  • Posts: 17
    • View Profile
Re: Mach3 Axis Calibration Mystery
« Reply #2 on: February 21, 2017, 09:40:49 AM »
Hi Tweakie,
Thanks for your reply. It cleared out one mystery for me. Observing my screws a little closer, I discovered that they have the same pitch, and they have the same number of starts (2), however the diameter is different. But diameter does not play here...

I used the axis calibration on the Settings Screen in Mach 3, and now I have my axis calibrated. Now the Steps Per are appx exactly the same on both axis:

X : 160.00209

Y: 159.8356766

which I guess is a question of poor measuring. Might as well set them both to 160?

However: If I compare with the example that you sent me in the link, my Steps Per are ridiculously LOW. I've filled in my values in the quote below:

"Here is how you do the math. I will give you mine as an example. What we need to know is, How many pulses from Mach will it take to move the machine 1 mm? This is how I came up with the number.
My steppers have 200 pulses per revolution. ( 360 degrees divided by 1.8 degrees = 200 )
Micro stepping = 16. So 200 X 16=3,200
Motor to screw gearing is 1-1. So 3,200 X 1=3,200
Screw lead is 10 mm (pitch x starts). My screw will have to turn 0.1 rounds to move the nut 1mm. 1.0 divided by 0.100=10. So 3,200 X 10=32,000."

If I do the calculation myself, I come up with a value 200 times higher than that of the Axis Calibration on the Settings Screen?

best regards

Offline Tweakie.CNC

  • Global Moderator
  • *
  • Posts: 7,637
  • Super Kitty
    • View Profile
    • Tweakie.CNC
Re: Mach3 Axis Calibration Mystery
« Reply #3 on: February 21, 2017, 09:55:24 AM »
Obviously you have some of your machine information wrong (maybe microstepping ?, maybe pitch ?).

The last line in your calc. (Screw lead is 10 mm (pitch x starts). My screw will have to turn 0.1 rounds to move the nut 1mm. 1.0 divided by 0.100=10. So 3,200 X 10=32,000) should be 3200 / 10 = 320.

However, the important thing is that you have it sorted.  ;)

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Werdelin

  • Active Member
  • Posts: 17
    • View Profile
Re: Mach3 Axis Calibration Mystery
« Reply #4 on: February 21, 2017, 04:50:50 PM »
Hi Tweakie,

In the Excelsheet "steppercalc_alenz_rev1" the lead is a multiplication of pitch and thread starts. I have measured the pitch not just once - the pitch being the distance from one crest to the next, regardless of number of starts (see attachment) - and it is 5 mm. With 2 starts it goes 5 x 2... It can't be that.

I will definitely have to verify the microstepping...

But what's the impact of this very low Steps Per? I have set the Velocity to 6000, but around this value my stepper motor trips out, not even being very fast, and with a default Acceleration value of 25, slow starts and slow stops. If I set my Steps Per higher, then the axis will travel longer than they should. Also, if you look at the second attachment, which is actually made from a gcode of a SQUARE with a CIRCLE inside it, the result come out slightly longer on one end, and the circle is dragged to an uneven oval? Does this mean that my motors lose steps?

[The last line of my calc is copy/pasted from the link you sent so the mistake is in Chaoticone's example, but I ought to have seen it. But maybe it should be corrected]

Anders

Offline Werdelin

  • Active Member
  • Posts: 17
    • View Profile
Re: Mach3 Axis Calibration Mystery
« Reply #5 on: February 21, 2017, 04:52:33 PM »
sorry, wrong attachment

Offline Tweakie.CNC

  • Global Moderator
  • *
  • Posts: 7,637
  • Super Kitty
    • View Profile
    • Tweakie.CNC
Re: Mach3 Axis Calibration Mystery
« Reply #6 on: February 22, 2017, 01:42:12 AM »
Hi Anders,


Following the example calculation you have “1.0 divided by 0.100 = 10” it should be “1.0 divided by 10 = 0.100”

For motor tuning…
Start at 3000 and increase Velocity in steps until you find the place at which the motor stalls. Reduce the Velocity by 30%. Set Acceleration to 10% of the Velocity figure. You may be able to further ‘tune’ the set-up to increase speed but don’t risk destroying accuracy and reliability.

Check your machine axes mechanically as it could be a loose grub screw, coupler, etc. or mechanical binding that is causing that lost motion.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Werdelin

  • Active Member
  • Posts: 17
    • View Profile
Re: Mach3 Axis Calibration Mystery
« Reply #7 on: February 26, 2017, 05:25:50 PM »
Hi Tweakie,
I have tightened the motor block of the x-axis, and thereby I have improved the square and pocket above to be almost quadratic / circular. So you where right, the mechanical binding was indeed the reason

Still, for the steps per, the calculation even with the last value ends up being 320. Whereas I with steps per set to 160 get the table to cut the square depicted above in exactly the right measures? The big question for me is of course: Will I be able to tune my motors to the best performance possible with the present equipment, or will a steps per of 160 limit the possiblities when it comes to torque, speed, etc.

Another question I have for you is about limit switches. The limit switches and the home switches have been working fine, until recently, when I extended the cable for the limit switch of the Z-axis. Now, only the limit switch of the Z-axis is working, the home limit switch for the X-axis and the Y-axis seems dead. I have disassembled the plugs for the extensions to see if if I had made a rotten soldering, but verything seems to be OK. They all seem to be wired to the same pin, is there a way that I can test them individually? I have been looking at Config > Input Signals, but even with the Z-axis disabled (Home, Z++, Z--) the limit switch is working?

Do you have a clue?

best,
Anders

Offline Tweakie.CNC

  • Global Moderator
  • *
  • Posts: 7,637
  • Super Kitty
    • View Profile
    • Tweakie.CNC
Re: Mach3 Axis Calibration Mystery
« Reply #8 on: February 27, 2017, 01:23:57 AM »
Hi Anders,

Obviously your drives microstepping is set to 1/8 which is just fine.
You are very unlikely to achieve any higher resolution or performance if you change microstepping to 1/16 so it would be better to leave it as it is.

I assume your switches are normally closed circuit (n.c.) connected in series. With everything switched off, use a multimeter (on continuity) at the breakout board to test your switch wires which should show closed circuit - operating any switch should show open circuit. If this is not the case then you may have made a mistake in your wiring of the extended switch.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline Werdelin

  • Active Member
  • Posts: 17
    • View Profile
Re: Mach3 Axis Calibration Mystery
« Reply #9 on: February 28, 2017, 08:20:02 AM »
Hi Tweakie,

OK I'll leave it as it is, which is:

Steps Per =160     Velocity = 6000     Acc 60       Step Pulse 5       Dir Pulse 5

I will buy a multimeter one of these days.

However, when i click the GO TO ZERO, the X-axis is moving to its ZERO at a far higher speed than I can obtain by the motor tuning without the motor stalling? What is the explanation for that? Of course if I could imitate the tuning that the Mach3 is using for the GO TO ZERO command, then I'd be much better off speedwise...

Anders