Accuracy issues after upgrading CMP 3020 to Mach3

[rob_bits]

Hello everyone!

I have upgraded an old CMP 3020 CNC to work well with Mach3. I have removed the original electronics and leaved the power supply, stepper motors and chasis. Replaced the spindle into a 500W DC controlable motor.

To drive the stepper motors I selected TB6600 stepper motor driver, like this:
https://core-electronics.com.au/tb66...or-driver.html

For bob I selected a Mach3 compatible usb 100KHz controller like this:
https://www.buildyourcnc.com/item/el...ach3-USB-Board

I put together everything, did the wiring and all axis seemed to work fine. And I could cut out some simple stuffs.

But when I measured the dimensions I got very bad results. I read some topics on the forum. In lot of users sugested calibration of the steps per/mm unit for other user problems. But I do not have an offset error. For shorter distances the error is bigger as bigger distances. For example around ~80mm dimension the error is ~1% but for dimension of 4-10mm it is between 3-10% which is very big. Now I think I can do milling with +-0.9mm precision which is very bad. See the attached measurements.

Regarding the steps per/mm unit I run the calculation and based on my mechanic it must be 400 steps/mm.

Currently I am using microstepping of 8. For first try it was 32 but I lowered to expect improvement but nothing happenend...

What can be the issue?
If the mounting of the spindle has +- some degree error can it introduce issue like this?
Or I have not replaced the syncronous belts on the stepper drives. If they streched can it be an issue?

I think steps are not missed beccause when it runs multiple times on the same path then it does not go off.

Thanks in addvance!

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[mactec54]

Hello everyone!

I have upgraded an old CMP 3020 CNC to work well with Mach3. I have removed the original electronics and leaved the power supply, stepper motors and chasis. Replaced the spindle into a 500W DC controlable motor.

To drive the stepper motors I selected TB6600 stepper motor driver, like this:
https://core-electronics.com.au/tb66...or-driver.html

For bob I selected a Mach3 compatible usb 100KHz controller like this:
https://www.buildyourcnc.com/item/el...ach3-USB-Board

I put together everything, did the wiring and all axis seemed to work fine. And I could cut out some simple stuffs.

But when I measured the dimensions I got very bad results. I read some topics on the forum. In lot of users sugested calibration of the steps per/mm unit for other user problems. But I do not have an offset error. For shorter distances the error is bigger as bigger distances. For example around ~80mm dimension the error is ~1% but for dimension of 4-10mm it is between 3-10% which is very big. Now I think I can do milling with +-0.9mm precision which is very bad. See the attached measurements.

Regarding the steps per/mm unit I run the calculation and based on my mechanic it must be 400 steps/mm.

Currently I am using microstepping of 8. For first try it was 32 but I lowered to expect improvement but nothing happenend...

What can be the issue?
If the mounting of the spindle has +- some degree error can it introduce issue like this?
Or I have not replaced the syncronous belts on the stepper drives. If they streched can it be an issue?

I think steps are not missed beccause when it runs multiple times on the same path then it does not go off.

Thanks in addvance!

The only way to see if your steps /per are correct is to run the Mach3 axis calibration, you can never guarantee that a calculation of the steps / per are correct

So in Mach3 Settings page above the ReSet button you will be able to calibrate each axis

[rob_bits]

The only way to see if your steps /per are correct is to run the Mach3 axis calibration, you can never guarantee that a calculation of the steps / per are correct

So in Mach3 Settings page above the ReSet button you will be able to calibrate each axis

Thanks. I will try it.
By the way I could reach improvement by setting the 4 microstepping instead of 8. But the accuracy is approximately +-0.2mm.

[mactec54]

Thanks. I will try it.
By the way I could reach improvement by setting the 4 microstepping instead of 8. But the accuracy is approximately +-0.2mm.

Any changes you make you will have to recalibrate

.2mm is a big number

Your Calibrating has to be done precisely to get any positioning accuracy, look up some videos on how to set the steps / per in Mach3

[rob_bits]

Any changes you make you will have to recalibrate

.2mm is a big number

Your Calibrating has to be done precisely to get any positioning accuracy, look up some videos on how to set the steps / per in Mach3

Okay, and what about assembly error? I think there is an angle error in the mounting of the spindle over the Z axis (see attached pic).

But what about other angle error? So what if I have mounting error on the X and Y axis as well, can these introduce accuracy issue?

[mactec54]

Okay, and what about assembly error? I think there is an angle error in the mounting of the spindle over the Z axis (see attached pic).

But what about other angle error? So what if I have mounting error on the X and Y axis as well, can these introduce accuracy issue?

Yes you are supposed to tram the spindle before you start work, look for some videos on how to tram the spindle