Replacement rotor for CNC spindle drive CNC 3020/3040

I've a 3040 Chinese CNC router. The spindle motor has a plastic part on the top of it. To my understanding it has a role of cooling the motor. the rotor blades in it are completely vertical ones what only helps to gravitational cooling (the warm air moves upwards) and not forcefully cool the motor. My other problem that the motor I have (230W one) has no integrated encoder, so I can't measure the rotational speed.
I designed a replacement of this plastic part with fan blades in it and an encoder ring around it. The encoder ring has exactly 60 holes, what allow to measure the rotational speed with a frequency counter without modification.
Notes:

1. The part's height is smaller than the original one, because I've no double extrusion 3D printer to print support material.
2. I haven't printed it yet so I've no idea if it has any design flow.
   Update 07/03/2014:

• Created a model of the whole thing
• Tweeked the rotor based on the model
• Added the opto holder ring