Re: [CAD_CAM_EDM_DRO] Re: bridgeport ballscrew question

We went thru this a while back with ballscrews displaying a springing action when the table is locked. Bridgeports are all like that. Its low radial resistance in the ballnut and deflection of the yoke and endplates that are the culprit. One has to realize how much force we can apply to the axies lineally by rotating the handcrank. The application of 1lb of force upon the handcrank handle represents approximately 50 lb. force lineally upon the axis. Its a simple equation: 3" dia handcrank circle X 3.14 /.200 per revolution= approximately 47 lbs. Imagine applying 20 lbs of force to the handcrank, then look at the endplates with their large moment between table and screw axis. Its easy to see why they are springing/deflecting. And I wouldnt do that a whole lot because the ballscrew having very low resistance and the amount of mechanical advantage is apt to distort something permanently. The machine during normal use will never see these types of forces.

Ron


John Delaney <jdelaney2@...> wrote:


I recently fitted my BP with a retro kit from Rockford Ball Screws.
The screws and the nuts are great. Class A stuff. I have not put the
motors on it yet. Now, I may have done something wrong too, not sure.
I'm new at ALL of this. But when I run the Y all the way back or lock
the saddle down, I can feel some spring in it with the manual crank.
It reads about .002 - .004 on the dial. X is fine but there's no
lever arm to flex there. The C/L of the screw is almost lined up with
the table.

So I may be making a new yoke myself or finding a way to sister up
the existing one with some plate or something like that. Again, not
sure yet.

I saw a beefier one than the one I have at Elrod machine.

http://www.elrodmachine.com/yoke.htm

Unfortunately my bolt patterns and nuts won't fit that one.

I have no affiliation with Elrod. I haven't even bought anything from
them yet. They do have a nice Quill drive too.







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