Emco PC Mill 55 question regarding ball screw drive

Hi All, wonder if anyone can enlighten me.
I am concerned with how the drive of the Y axis works, just this one at the mo as this is the one that is causing issues. Please bear with me while I try to explain.
I took the stepper motor off to find a toothed pulley on the end of the ball screw. Thats fine but then I was suprised to see that this pulley simply unscrews to remove? I could not see any way this could or should be fixed in place apart from screwing it on as far as it goes. Now I am no expert engineer but would this pulley not turn back and forth on its thread before actually driving the ball screw?
So when changing direction the pulley would turn so far until it locked in place (clockwise) or until it hit the stepper motor plate (anticlockwise). I hope this makes sense and someone can explain if I am missing something.

I've never had mine apart, but there is no nut or screw to secure the pulley to the ballscrew? That seems very odd. But yes, without securing the pulley, it would try to unscrew when turned. There must be a part missing.

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Originally Posted by DesignRR

Hi All, wonder if anyone can enlighten me.
I am concerned with how the drive of the Y axis works, just this one at the mo as this is the one that is causing issues. Please bear with me while I try to explain.
I took the stepper motor off to find a toothed pulley on the end of the ball screw. Thats fine but then I was suprised to see that this pulley simply unscrews to remove? I could not see any way this could or should be fixed in place apart from screwing it on as far as it goes. Now I am no expert engineer but would this pulley not turn back and forth on its thread before actually driving the ball screw?
So when changing direction the pulley would turn so far until it locked in place (clockwise) or until it hit the stepper motor plate (anticlockwise). I hope this makes sense and someone can explain if I am missing something.

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Quite a simple setup, you need to make a 2 pin wrench to hold the timing pulley, set the preload on the axis bearing than hold the timing pulley with the wrench and lock the center screw

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Originally Posted by mactec54

Quite a simple setup, you need to make a 2 pin wrench to hold the timing pulley, set the preload on the axis bearing than hold the timing pulley with the wrench and lock the center screw

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Thank you, that makes sense. Where it was loose it has worn the pin in end of pulley and end of threaded sensor thing screwed in to stepper bracket. Any tips regarding setting axis preload?