Hello Andy
The small coupler screws coming loose are a known issue with the sharks.
You may want to consider using cap screws in the couplers instead of set screws, as they allow the use of a larger wrench and you can get them tighter. I belive NWA may now be selling them as parts as well.
thread lock will also help.
For best results, the leadscrew should have a flat on it like the motor does. if it does not, putting a flat on it with a file or grinder will help also.
you may find this thread helpful.
http://www.cncsharktalk.com/viewtopic.php?f=9&t=1422
bob
My circles are not round
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