Z axis -cnc conversion

[devincox]

I am starting on the z axis now and wanted to get some advise on how to proceed.

For those that have converted their IH to cnc or installed the cnc kit, how did you support the bottom of the Z axis ball screw?
Did anyone use the exsisting bearing from the original hand crank assembly?
Did anyone forgo the use of a bearing on the free end?

Thanks,
Devin

[devincox]

I just browsed this site:
http://wardscorner.net/cnc_conversion01.htm

and from the looks of the ballscrews, IH does not put a support bearing on the non-driven end. At least, not on this kit.


Does the diameter of the ballscrew negate the need for support bearings on the free end? I am using 7/8" ballscrews, is this large enough to NOT require a support bearing on the free end? I couldn't find the diameter of the IH ball screws on their site. However, I did see where IH states the x axis gets a support bearing.

http://ihcnc.com/pages/cncoptions.php


Devin

[Runner4404spd]

with a 7/8 ball screw you should be fine without a secondart support. also what your trying to avoid is ball screw whip. if you go to the roton screw catalog in their tech section you can see what your screw does and what its critical speed is based on the support structure. ultimately with a 3000 RPM motor and a 4:1 reduction the screw will turn a max of 700 RPM and thats only during rapid moves. so i think you'll be fine.

[devincox]

Excellent news! Thank you for your reply Runner4404spd.

[LUCKY13]

Interesting with the 7/8th balll screws. If they are the same ones I looked at the specs are kinda odd with the ball nut being a smaller diameter than the 3/4 setup. I thought these would make a good setup giving a stronger screw, but still having more clearance. I had thought about using 1" screws but it seems there would not be enough room for this size setup. I havnt ordered my screw set yet I would be interested in knowing exactly what you have and how it turns out.



Jess

[devincox]

The screws I have were bought from a friend. They are high precision screws from pcb drilling machines which were replaced during maintenance periods. Thus far the screws are perfect. They have preloaded ballscrews and one end is threaded and machined for a pulley. They are perfect for the IH Mill. I had to cut the Y axis but, the X and Z just fit up without cutting. The ball nut is not circular shape like the ones on roton.com, they are rectangular. They have 6 screw holes on the base with which to mount them.
I'll post a pic of the screw/nut after I get home.


Devin

Originally Posted by LUCKY13 Interesting with the 7/8th balll screws. If they are the same ones I looked at the specs are kinda odd with the ball nut being a smaller diameter than the 3/4 setup. I thought these would make a good setup giving a stronger screw, but still having more clearance. I had thought about using 1" screws but it seems there would not be enough room for this size setup. I havnt ordered my screw set yet I would be interested in knowing exactly what you have and how it turns out. Jess

[bohica]

I installed the CNC kit on my IH mill. There was no bearing called for on the free end of the Z axis ball screw. Now that my mill is operational, I can see no negative effects from the lack of a free end bearing.