Need Help!- "Y minus" loses steps on accelleration

[Mal Buckmaster]

I have been using my "Hobby CNC" based router for several years during which it has cut hundreds of balsa wood components for model airctaft kits and models using Desk CNC software.

The machine has recently developed a rough-sounding and erratic movement at the first reverse direction motion on the Y axis. This varies in intensity and creates the effect of progressively forshortening the toolpath to the extent that the return to zero/zero at the end of a 20 minute cutting file, the cutter can be up to 30 mm from the initial Y zero point.

This is a very simplified description of the condition which has been posted to determine if someone may recognise what is happening from personal experience and provide assistance in diagnosis and correction.

I have attached a picture if the machine for reference.

I reallize this may require much more detail if the problem is difficult to diagnose, but a simple starting point is probably the best means of introducting my plight to this vast forum for examination.

[bigalow]

If you have a mechanical issue(slipping coupling ect...) in a feed back system your axes can come up short(encoder on motor shaft). If you can I would seperate the motor from the Y axes. Jog the motor forward and reverse and see if you experience the same noise and while it is apart check the lead screw, couplings ect...

If it is a stepper motor the motor will give a ratcheting sound if stalled. Again this can account for a deficiency in position.

[Mal Buckmaster]

Dear Bigalow

Thank you for your response to my subject request for help

I reallize that as the possible causes for my problem are explored, it may be necessary to elaborate in more detail the components of my machine and the areas I believe I have covered in my own investigations so far.

I am not using a feedback system as the stepper motors are operating in "half step" mode via the driver board.

I have checked for any excessive mechanical binding in the leadscrews and guides and have verified that the "Y" axis is working freely and smoothly.

(I have obtained an opinion in recent peer discussions that the problem sounds like a deteriorating capacitor which could be in the power supply. I have noticed occasionally that when I switch on the power supply-which is a P.C. type-the stepper mototrs do not all "lock in" with full holding torque. This feels like the driver board is not getting a true d.c. input and is disrupting the initial triggering of the step/dir. pulses from the controller board. However I have no informed basis for this idea and include this comment purely as a possibility)

If there is an obvious need for a more detailed description of my machine and its operating components please let me know on this thread and I will oblige with as much info. as I can supply.

With thanks and regards.

Mal Buckmaster

[Mal Buckmaster]

I should tie off this thread.

I have recently installed a new Driver Board and Mach3 Software, re-configured the steppers from uni-polar to bi-polar and run my old DeskCNC G-code files with Mach3.

This has totally removed all problems, the machine now "sings" its way around the table, and the cut parts are the most accurate I have cut in the last three years.

Mal. Buckmaster