model of ball spline available from engineering company in huddersfield

http://www.reliance.co.uk/shop/products.php?10282&cPath=656_657_658
refactored the main code and moved the z carriage into its own file

it was becoming a bit unwieldy. re-wrote parts - now uses bearing
dimensions as parameters for the main block. need to continue with
modifications to allow parametric bar clamp bits.
added information for ball splines
major work done - z axis re-worked, and its code refactored into its own file. y axis has a solution using ball splines. bracing dimensions modified to make sure it fits when the briefcase is closed.

Z motors moved off center to allow for enough room for the z carriage,
currently experimenting with ball spline shaft position and y motor
position.