Hi im new here and was wondering if a kind soul could assist me in understanding how I would assess wether a certain ball screw would work with a certain motor. In other words I see stuff on ebay all the time but I have no idea if it will be compatible with each other .I own both the large 33686 round column and the red gear headed mill from harbor freight and I want to retrofit one .it doesnt matter which. I have been to jeff davis website manytimes. I dont know how to pick out the right size ballscrews. do they have to be 5/8,or can I buy any one off ebay and fit it to one of these mills. Ifso is there a rule to coupling one to any servo/stepper? Thanks in advance for your help!

Try using a 5/8 .5 (5 threads per inch) ballscrew. use a spring couper or belt drive.

The 5/8 .5 is generally used for our hobby type works as it is the cheapest when buying new. Now haveing said that, you have not indicated what you are going to use this on. If it is outside the envelope of a typical mill/drill or simular sized router, you may need to visit one of the manufacturers sites and dig into the engineering formulas to see what the minimum size that is recommended.
Without getting rediculous in size, bigger is better:}), but you need to have an idea of the loads to be generated and size accordingly.

Bubba

where is the cheapest place to order the 5/8?

I used www.roton.com

YMMV:})

Bubba