pitch for z axis

[badassdevil]

what kinda pitch is every one using im trying to get a rough idea im using m16x4 trap but its been surgested its to fine and thats why im losing steps on the retract cause the motor it having to do to many steps

[wbegg]

You'll have to run your Z axis at a lower feed rate. This will prevent your motor from losing steps.

[wildwestpat]

Are you using open loop stepper motors? If so the available torque falls rapidly with speed. On retracting the head at the end of the cut check that the motor has enough torque for the speed and acceleration demanded by your code. Try reducing the demanded speed and setting the acceleration to a modest level. (The acceleration would be part of the code to stepper motor software and is the means of taking into account the dynamic inertia of the axis.) If the axis maintains register at the lower speed and or acceleration then you have to accept the increased machining time or upgrade the drive with a motor capable of more torque at the demanded RPM (see next paragraph). If you are using close loop drives then you run the risk of over demanding torque and this may result in drastic over heating of the motor and risk to both the motor and drive amplifier but I am assuming you are not using closed loop as you are losing registration.

There is of course a link between the motor required torque and the screw pitch to the axis speed. The stepper motor is unfortunately speed limited so that the gearing relationship with the axis lead screw pitch and any gearing needs to be treated as part of the compromise between pulses per second / RPM of the motor and torque. Use one of the online calculators or copy a design that is known to work - OR - accept the reduced speed. Please note that with stepper motors bigger is no always best as the stepper motor can induce resonances as it drives in steps and the magnetic snap from one step to the next has its own resonance which if coincident with the axis resonance can cause problems. Very fast axis movements are the province of closed loop servos and the attraction of open loop stepper drive is the low cost and the torque constraints.

Regards - Pat