Ball screw Question

[rodzilla]

I was wondering for those of you who CNCed your Rong-Fu mill what size ball screws did you use. I have a Harbor Freight Model 33686 Round Column mill that i converted to CNC but have not done the ball screws yet i have some 5/8" ball screws laying around from another project and was wondering if this was what everybody else was using or are they using 3/4" ball screws. I see the machine has ACME Lead screw of 1" and was wondering if the 5/8" ball screws were going to be under powered. I mostly machine steel and sometimes the occasional aluminum

[Bubba]

rodzilla,
When I did my RF31 (same model as yours), I used 5/8" ball screws like most other people I have seen.The size of the screw has not given me any problems as far as I can tell. I have more problems with the operator (ME) than anything else! For the distances we are involved with and the speeds we typically run, I don't see us pushing the limits at all. There are more problems with the rigidity of the machine than the strength of the screws and that will limit speeds and loads more.

Bubba

[rodzilla]

Thank you for your answer that was what i was looking for. When you did your machine di you have to create new mounts to go on the machine as the diameter of the mounts coming out of the machine where the hand cranks go is about 5/8" - 3/4" or did you make reduced bushings for it. I'm also assuming that you had to make new blocks for the ball nuts to attach to and remove the existing ones. Any good ideas on how to do the Z axis other than with the fine down feed some pics would be helpfull and greatly appreciated

[Bubba]

If you look at my web page:

http://bellsouthpwp.net/A/r/Arts_home_page/DRO/

it should give you some ideas on how I went about it. Yes, I made new mounts for the ball nuts (pre-loaded). For the bearing housings, I modified the existing mounts to replace the original thrust bearings with AC bearings. NOTE: be sure to cut a counter bore to allow preloading the bearing or they will rub the bearing mount. As for the Z, I did the fine down feed thing and tighted up the pinion to rack (there is a little slop that can be taken up) and dumped the return spring and put another roller thrust bearing on there to locate the pinion shaft to one place (this keeps the worm from riding up and down the worm wheel) and put a heavy counter weight on the axis.