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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

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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.
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

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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.
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
Re: Mach3 Axis Calibration Mystery
« Reply #5 on: February 21, 2017, 04:52:33 PM »
sorry, wrong attachment

Offline Tweakie.CNC

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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.
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

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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.
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