Well here goes... Aluminium frame router design

[CharlieRam]

Hi, I have a few questions about the BK12 bearing supports, I've tried two of the supplied ones so far and the both exhibit end float, so after searching the forums I have tried placing the bearings back to back, packed with grease and reassembled but I think I need to shim them, the problem is how do I know what to shim, the ID or OD and where can I buy the shims from?
Also when the ballscrew is pushed fully into the bearings, it doesnt spin freely even with the nut slackened off, I assume I should be able to give the ballscrew a spin and the momentum should keep it spinning for a while, It may be the seal because it occasionally spins with the ballscrew but I have tried pushing it in a bit and pushing it out but it makes no difference? Any advice or help greatly appreciated.
Thanks, Charlie

Edit just checking this is Back to Back?