GANTRY RACKING

[Bill Legge]

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

[ger21]

Wouldn't it be easier to fix the issues with your cabling/construction??
Also, decreasing acceleration and velocity may also help.

Basically, you get racking because at least one motor is losing steps.
What exactly are the issues that are causing the racking?

If you really want to go the encoder route, you can just buy this. http://romaxxcnc.com/encoderinterface.html

[rrc1962]

You could connect the two screws mechanically and run a single motor.  Any time you run two motors slaved, you stand the chance of the two going out of sync.

[hollydog]

       Just read your thread about gantry racking, I have two screws with two steppers on my gantry with a notched belt connecting the two together both steppers are connected electrically in parrel  driven from one stepper board.  To actually set up the squareness on the x I turn one screw slightly measure across corners of a large engraved or proffiled cutout.  Notched belts can be joined to make any length you require but do loose a little strength. See Cambam one and all machine .

                                               Hope this may be of some help.
                                                     Hollydog