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Steps per unit strange trouble
« on: August 30, 2018, 04:22:39 PM »
Hi all,

I have been using Mach3 for 6 years now and have had no big troubles with it, all has worked well with a little help from the manual or by reading others questions and answers. But 2 weeks ago, I change the motor drivers of my CNC router and also made a change from inches to millimeters in my configuration, and now I am having a very confusing trouble....

I calculated and configured my steps per unit and the machine is acting very strange, you will see, to fine tune the steps, I have sent to cut 6 small squares of 10, 20, 30, 40, 50 and 60 mm but the smaller ones are cut a little small and the bigger ones are cut bigger and bigger. Below you will find a small table with the measurements I have got in my last attempt to calibrate.

Sent square       Dim X          Dim Y
10x10                 9.89            9.89
20x20               19.92           19.97
30x30               29.93           30.08
40x40               39.98           40.1
50x50               50.03           50.25
60x60               60.15           60.3

As I understand, all the measurements should be smaller or bigger by the same proportion (or ideally, correct!), but I am having some small and as the piece gets bigger, then the measurement is bigger and bigger......

If i adjust the steps per unit to obtain a 10 mm cut from a 10 mm drawing or gCode instruction, all the rest of the squares are each one bigger than the previous an the same happens inversely, if I adjust to get a 60 mm cut from a 60 mm gCode, all the rest of the squares are each one smaller than the previous one and if I adjust to get a 30 mm cut from a 30 mm gCode, the smaller cuts are increasingly small and the bigger ones are increasingly big

I have double and triple checked the diameter of the endmill, I have used Aspire to generate the gCode an have write it by myself, and made any other kind of revisions and the results are always the same and consistent, I really hope that someone could help me sending some light in this confusing results.

Thank you for your time and knowledge!!!

Offline ZASto

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Re: Steps per unit strange trouble
« Reply #1 on: August 30, 2018, 04:50:35 PM »
Settings steps per should be checked/verified on maximum possible dimension of your machine.
And, maybe you have a lot of flexing?

In the attached picture you can see the results of "springy" Z axis on a friends DIY machine.
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Re: Steps per unit strange trouble
« Reply #2 on: August 30, 2018, 04:58:48 PM »
Thank you for your info ZASto, The machine has been working fine for several years and has had no visible spring effect (also, the test cuts are being made at 0.5 mm deep on pine wood with a 2mm bit). Will try to recalculate with the max. dimension of the machine.

Thanks again!
Re: Steps per unit strange trouble
« Reply #3 on: August 30, 2018, 05:31:36 PM »
I did calibrate against 1100 millimeters, adjusted the steps per unit and then try to corroborate with 50, the measure was 48.28, 1.72 smaller than it should be, but at 1100, I get 1100.... still dont understand

Offline ZASto

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Re: Steps per unit strange trouble
« Reply #4 on: August 30, 2018, 05:33:38 PM »
Take a steel ruler. I calibrated another, chinese machine with 1005mm steel ruler made in CCCP :)

Do you have any backlash in your axes?
Make no mistake between my personality and my attitude.
My personality is who I am.
My attitude depends on who you are.
Re: Steps per unit strange trouble
« Reply #5 on: August 30, 2018, 08:08:40 PM »
I have verified the possibility of backlash, nothing moves noticeably, and have made measurements with 4 different rulers and flexometers, all show the same, at 1220 millimeters you can get real 1220 mm, but with the same steps per unit, if you ask for 50 mm, you get 48.2 to 48.3 (these last measurements taken with a calibrator)

Offline RICH

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Re: Steps per unit strange trouble
« Reply #6 on: August 31, 2018, 07:27:51 AM »
I would suggest you use the calibration feature of Mach3 to set the correct steps per unit for the axis. You can use one of the calculators in Member's Doc's to manually find the steps per unit. The distance moved should be the longest possible for the axis being calibrated. Make sure that backlash is removed before actual moving the axis.

Lets say that you calibrated the axis with a 10" move then any error of the axis will be very small for short moves like .010 .1, 1.0" move.

The user should know what backlash they have and  all axes have backlash it's just a matter of degree. One should also know just how linear
their axis is in movement in both directions of movement and in incremental distances over the complete axis movement.  Understand that
the mechanical parts that make up an axis define how accurate / linearity of movement you will have. As an example you have a ball screw
and the specs say that it accuracy is 0.012" per foot. What they don't tell you that the 0.012" can evenly distributed or even just in some spot
along the 12". So check to know what you have.

RICH
« Last Edit: August 31, 2018, 07:30:14 AM by RICH »
Re: Steps per unit strange trouble
« Reply #7 on: August 31, 2018, 03:48:08 PM »
OK, I will keep trying things following your guidance and of course will keep you posted, if anyone have more ideas, they will be very well accepted!

Offline ZASto

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Re: Steps per unit strange trouble
« Reply #8 on: September 02, 2018, 04:36:21 AM »
Check backlash.
You wrote nothing about circles. Are they round, stepped at 0, 90, 180, 270 degrees, ...?
Does your machine have screws/nuts or rack/pinion drive?
Have you tried yur squares in diferent positions on your table?
Make no mistake between my personality and my attitude.
My personality is who I am.
My attitude depends on who you are.
Re: Steps per unit strange trouble
« Reply #9 on: December 26, 2018, 09:32:55 AM »
I just discovered that my machine is acting in the same strange way.  >:(  I haven't been jusing the machine lately because I had a cable issue. Now, having replaced some cabling, I discovered that the traveling distance is totaly wrong. I want the machine to travel 1000mm on the Y-axis, but it moved much to far, so I adjusted the steps per unit. tested it some times and adjsuted the X-axis as well. Now I want the y-axis (only) to travel 250, 500 and 750 mm. but instead the machine moved about 260, 519, 758 mm (no exact meassurements). but traveling back to zero is no problem at all. I (tried to) check every possible adjustments and even went back to the original settings, but nothing seems to solve the problem.  ???

@ludara: did you solve your problem. keen to know what this strange behavior is comming from.