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re things on the end of ballscrews
top one is a split ring about 3/8 inch thick that has a set screw that will make it clamp down on the 12 mm shaft so shaft is snug againt a bearing. I do not know...

the industrial hobbies link link on lapping is at
http://www.industrialhobbies.com/howto/mill/mill_tips_index.htm
It is down the page about half way.
I just wet sanded with wet-dry sandpaper like...

Here is link to a photo of mounting bolt hole layout that I pulled from a sieg manual. I have not checked it for accuracy yet.
http://multimediaspot.com/mill/x3-sx3-mounting-holes.jpg

this guy...

REAL dimensions on Harbor Freight 93885 Mill
I am a proud owner of the Harbor Freight Sieg X3 mill. [Harbor Freight #93885 . I brought it home from the freight dock today. Harbor Freight got Yellow...

I dug around a bit and found that the Europeans would not likely use 1/4" 20tpi threads because your metric-conversion errors would make a mess. Direct drive to a 20tpi screw in full-step gives...

Your photo looks like the stepper motors are not direct drive so both drive pully ratio and tpi of ball screws will set how many turns your motors do to move 1 unit inch-cm?? One of the Mach videos...