Which Ball Screws to use?

[Willyb]

Hi Guys

I need some help Guys? I am trying to decide which size of Ball Screw I should be installing in the Mill that I am converting to CNC? You can see a picture of the Mill below. The Mill will be used mainly to machine Aluminum with a little Steel. I do plan to use the Mill allot. So it’s either 5/8” or 3/4” Screws? I was originally planning to use 5/8” Screws but have been told by more than one person that I should be installing the 3/4” ones. What do you think about this?

Here is a list of the other components I will be using:

(Servo Motors)
C23-L55 Poly-Scientific.
Peak Torque = 430 oz.in.
Continuous Stall Torque = 50 oz.in.
Rated Torque = 40.5 os.in.
Rated Speed = 1700 rpms.

(Ball Screw Nuts)
Pre-loaded Ball Nuts with Wipers. (Uses two single circuit nuts per screw)

(Ball Screws)
Linear Error per foot = 0.001 to 0.003
Screw mounted on double Angular Contact Bearings

(Drives)
Belt drive with a 2:1 ratio between Servo Motor and Ball Screw.

(Mill Sliding Surfaces)
Original Cast Iron Ways.

Thanks for the help.

Willy

[balsaman]

I am using 5/8", as have many others. 3/4" would of course be better but more money.

Eric

[Willyb]

Hi Balsaman

Approximately how many hours do you think you would have on your 5/8" Ball Screws? Have you noticed any wear (increased backlash) on the Screws since they were installed? Approximately how often do you lubricate your Screws?

I guess what I am trying to figure out here, is the benefits for going with a 3/4" Screw instead of using the 5/8” ones? As far as the maximum load difference between these two Screws, it’s only 125 lbs. 5/8” Screws are rated at 825 lbs. and the 3/4” ones are 950 lbs. I guess for the same applied load, the 3/4” Screw will more than likely last longer because it has more area to carry the load. I can’t see machining pressure being anywhere close to the 825 lbs. rating of a 5/8” Screw, especially when working with Aluminum. Maybe I am missing something here, but I just can’t see that much of a benefit by going with the larger Screws? Price difference between the two is approximately $250.00 which is a little more than half the cost of the 5/8” Screws. Anyway’s, I need to make up my mined soon and would be interested in hearing any and all comments with either setup. Thanks for all your help.

Willy

[balsaman]

I am just doing the conversion now: Mill/Drill conversion coming right up!

Eric

[sendkeys]

try http://www.nookindustries.com/ball/BallCharts.cfm