March 9, 2021

Need Help! Accuracy issues after upgrading CMP 3020 to Mach3

2 min read
Hello everyone! I have upgraded an old CMP 3020 CNC to work well with Mach3....

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:…or-driver.html

For bob I selected a Mach3 compatible usb 100KHz controller like this:…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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