Originally Posted by newtocnc1  Sorry, completely new to CNC. Got a quick question. Have anyone used product from hobbycnc? I want to get the controller board and motors from them. I also decided to go with ball screw design. I'm a bit confused on its mechanism..the motor moves the little screw on the screw shaft? Or the motor moves the long screw shaft while the little screw pinned onto my moving part? If my coupler is 5/8" outer diameter and inner is 1/4" diameter..what size of ball screw do I buy? Thanks a lot |
I'll answer the other half of the Q because i know nothing about Hobbycnc.!
With a ballscrew the most commonly used method is to rotate the screw with the motor attached to a plate which then attaches to the screw either by direct connection with a flexible coupler or off setting the motor mount and connecting thru timing pulleys and belts.? . .The later enable's gearing option's.
The screw rotates at both ends in bearings one of the ends needs to be fixed so the screw can't float, this is often done by machining one of the ballscrew ends with threads to accept a locking nut and a portion that goes thru a angular contact bearing.
These bearings are then held in bearing housings or machined directly into the machine, again depends on machine design and there's lots of differant ways to do it.? . . . Personally i like the BK/BF bearing blocks that you can buy they make the job very easy but add to the cost's.!!
The Ballnut is then fastened to the gantry or moving table depending on design with either a dedicated ballnut mount or bracket plate again machine dependant and various ways to do it.!
The other way but no so common is to fix the ballscrew at either end and put under tension then rotate the ballnut. This is usually done by using timing pulley/belt connection to the motor which then travels with the ballnut again either on the gantry or moving table.
This way is good if the screws are long and thin which may cause whip at speed but it's also slightly more complicated to impliment, thou IMO the best way if your you want faster speeds with long thin screws.?
To answer your Q on coupler size.!! The OD doesn't really come into it, you use a coupler who's ID is the same as the screw at one end and the same as the motor the other.
Again there's lots of ways to do it but i like the Lovejoy type couplers and you can buy them ready made to match your setup.? . . . . Take your pick.!!
Hope this helps.
Dean
08-07-2010, 09:15 PM
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