Machine axis calibration question

[minimillaidan]

Hi,

so I ve been calibrating my machine recently.

One thing i noticed is that I can calibrate my machine in the positive direction and get it within 0.01mm at various points (50mm/100mm/150mm/200mm/250mm) i have a figure in the backlash section to allow for the backlash I have in the ballscrew/nut.

so the issue I have is if I move the axis to +250.00mm in increments it all moves like I say within 0.01mm of what I ve asked it to, however if I move it back towards the - 0 I get an error of around 0.06mm so say I move it from +250.00mm to 150.00mm it is actually moving to 149.94mm which totally defeats the whole object of dialling the machine in.. as in one direction I can get it perfect but then if I move to a position the opposite direction it s out! Which would make it difficult to accurately machine parts, does the backlash figure not get taken into consideration when it s moving in both directions or is it only in the positive direction it is taken into account? No matter what I ve tried I get the same result.. everything on the machine is tight and has no play etc.

anyone else noticed this? Surely there must be a way to elminate this.. I understand I could use the double ballnut option however I don t have space to do that so it s not an option.

thanks in advance

 

[breezy]

@minimillaidan

Aidan,

Could you supply your settings files so that we test you setup.

Regards,

Arie.

 

[minimillaidan]

Hi Arie,

Please find attached my machine files

Thanks

 

[cncnutz]

Hi Adam,

Can you tell me what version software you are running on your machine so I can load it into the correct software for your files.
I know it's mill 3 axis but is it 3,49, 4.0 or 4.01

Cheers Peter

 

[minimillaidan]

Peter,

I am using 4.0 currently

thanks

Aidan

 

[cncnutz]

Hi Aidan,

I have had a look at your settings and something doesn't seem right about them.
The movement is unbelievably fine. A ballscrew with a lead of 0.4mm does not sound right.
The distance per step of 5 ten thousandths of a mm or 2 one hundred thousandths of a inch.

Can you provide more information on your machine. Maybe a photo so that we can understand the setup.

=============X-Axis=============
- Motor: Distance per revolution: 0.400110
- Drive: Pulses per revolution: 800.000000

Cheers Peter

 

[minimillaidan]

Peter,

I have the motor drivers set to 800 steps. The ballscrews i am using are 1605

The 0.4mm figure is what the wizard calculated when I ve run it and measured movement etc

thanks

 

[cncnutz]

Hi Aidan,

That sounds a lot better but something is still wrong.
I'm using 1605's on my Z axis
If your using a 1605 ball screw and your motor is set to 800 pulses per revolution then you should he 5mm in the Distance per revolution and not 0.4mm.
The calibration is out by more than a factor of 10.

• Is it direct drive between the motor and the ballscrew?
  
• Have I got the correct figures for your X axis drive setting?
  

Cheers Peter

 

[minimillaidan]

Peter,

yes I understand what you are saying.

yes I am driving the axis directly off the end of the shaft. And I have checked they are not slipping etc not that they would be slipping that much, but I still checked it.

like I say this was what the wizard outputed when I calibrated the axis so I am at abit of a loose end with it

thanks

 

[minimillaidan]

Also I forgot to ask the backlash figure used is that taken into account in the positive and negative direction? As like previously mentioned in the positive direction the backlash figures to be taken into account however in the negative direction it doesn t seem to be taken into account?

thanks

 

[cncnutz]

In normal operation backlash work in bot the forward and reverse direction.

I honestly don't know if backlash is taken into account when calibrating but I personally would not use it until I had finished my calibration.
I would simply calibrate it in such a manner that backlash did not figure into the process and then measure the backlash value and enter it once calibration is complete.
I don't believe it is the problem.

We need to start from the beginning and pick on one axis. eg the X axis.
Have I got the correct figures from your setting file or have I done something wrong?

With the ball screw you have and the motor set to 800 you cannot possibly be moving the correct distance if the figures I have below are right.
By not right I mean that if you asked it to moving 100mm it would move 1250mm.
If the figures below are correct then we are missing something huge in you drive train.

=============X-Axis=============
- Motor: Distance per revolution: 0.400110
- Drive: Pulses per revolution: 800.000000

To solve this we need as much information as possible.

Did you follow the calibration process shown on this page?
https://docs.masso.com.au/wiring-and-setup/setup-and-calibration/axis-calibration-wizard

You mention measuring the distance moved in your first post of 250mm and you measured it to within an accuracy of 0.01mm. What instrument do you have that is capable of measuring that distance to that accuracy?

Can you also confirm if the distance reading you give in our first post for the 150mm move of 149.94 and back to 0 is a reading from an measuring instrument or the DRO reading? we might be chasing ghosts here if you are quoting DRO readings rather than actual measurements.

Cheers Peter

 

[minimillaidan]

Peter,

I normally do as you say calibrate the axis and then work out backlash and input that figure.

It is defiantly moving the correct distance.. I ve checked multiple times, I came up with a fixture to accurately hold a vernier calliper I set it at zero and move to the required positions. Everything is solid and I ve checked the setup on machines at work.

the 150mm movement -149.94mm that I was mentioning in the first post was checked with a the measuring instrument not the dro as the dro still read 150mm

i followed the calibration setup as listed on the masso website

 

[cncnutz]

You still haven't confirmed this is the setting you have on your X axis.

I know that is what the setting file I looked at said but I need you to confirm it. Maybe I looked at the wrong file by mistake.

=============X-Axis=============
- Motor: Distance per revolution: 0.400110
- Drive: Pulses per revolution: 800.000000

Cheers Peter

 

[minimillaidan]

I can confirm you have the correct settings yes.

 

[cncnutz]

Then there is only 2 options.

Either your Ballscrew has a 0.4mm lead or your motor drive is more like 10000 steps per revolution.
There is no other explanation. Maths doesn't lie.

I have no problem believing your Ballscrew is a 1605 so lets look at your drive.

Please tell me what drive you have and maybe a link to the documentation for it.
If it has dip switches maybe a photo showing their settings.
If you are using servo's what settings do you have in them. Maybe a screen print if you configure them from a PC.

Cheers Peter

 

[minimillaidan]

Peter,

I agree that math doesn t lie this is what was throwing me in first place.

right I will check everything and get back to you.

the driver is -
hss86 hybrid servo driver

thanks

aidan

 

[minimillaidan]

Peter,

so ive reset everything and reloaded software and everything seems to have improved even now the 0.49 is 4.99mm strange really maybe a glitch when I loaded the last update in and it threw everything out.

Thanks for your help once again.

aidan