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General Mach Discussion / GANTRY RACKING

« on: January 17, 2012, 06:32:58 PM »

I'm running a home made CNC with separate steppers on the 'long' axis: with A slaved to X.
Once or twice, due to my cabling/construction (not MACH3), one of the ballscrews has got out of step with the other and the gantry has racked badly.
I'm thinking of fitting quadrature shaft encoders to the A and X axis to raise an E-STOP if the A and X axis move different distances.

I'll probably use some quadrature decoder chips and a microprocessor to do the job.

Before I start the work, am I re-inventing the wheel or is there a better/simpler solution?

I'm a 'hobby type' CNC user and don't have the means of making a 'rock solid' mechanical solution so an electronic safeguard seems the way to go?

regards Bill Legge
In Australia

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General Mach Discussion / SLAVE AXIS PROBLEM

« on: January 01, 2012, 06:36:42 AM »

I have a machine with two slave steppers on the main axis.
I have slaved X and A and installed home switches on both.
I have set the A axis to linear.
Using manual control the pair of slaved axis move OK and remain in step but:

1.  When I use to 'Go to Zero' command, the axis remain in step but move in 'bursts' of about one second/30mm.
2.  When  using 'REF ALL HOME' the Z and Y axis do the correct thing (touch the home switchs and then back off) but the X and A axis do odd things - one touches/backs-off, the other touches,reverses and keeps going in the wrong direction.

I have very carefully checked:
1. Pulse rate and varied it from 25KHz to 100KHz and it makes no difference.
2. All the ACHIVE_HIGH/LOW, DIRECTIONS, PINS and PORTS.

Any help would be very welcome.

Regards Bill Legge