Need Advice on completed CNC retrofit

[phantomcow2]

Originally Posted by Adobe Machine I just ran a test on Rockford rolled ball screws and their double nuts, using my DRO over 28 inches on the Z axis of my lathe that is being converted to CNC. Just for fun we loaded a 19 inch chuck and a 8 inch kurt vise in the cross slide to possibly duplicate weight and some cutting pressure.Using a simple Z program, back and forth at 51 ipm 22 times, then to home and back to 28 inches, a recorded error ( maxium) of .00087 was noted. It always returned to home at .ooo,(?), the biggest error at the 28 inch stop.The ways and ball screw were well lubricated.Unless you are making a commercial machine that must repeat at .0001- 24 hrs a day, I would say that a well set up system,using rolled ball screws and double nuts, would be fine for your application.Most errors occure due to poor bearing mounts, to include every thing that NC cams has pointed out many times concerning the correct way to engineer the mounts and pre-load.You could spend thousands on ground ball screws, but have horrible errors with out the correct bearing set up. Adobe Machine ( old as dirt)

This is a post I will refer to many times, well done! I think this clears up a lot of misconceptions about this screw, I always believed they were more accurate than the .004" per foot.

[homebrewCNC]

Hey All,

I have decided for the Z axis I will do what Jeff Davis did at homeCNC.info, which is to scrape the rack and pinion and replace the Z axis motion with a ball screw hidden in the head casting. The manual handwheel will be replaced with a 200 ppr encoder to control the up and down motion of the Z axis. If I use an encoder then I will not have to use the jog commands in Mach3 to zero the Z axis, It will also suit my needs for non CNC machining.

I still have not decided which company to go with for the ball screws, they all seem like reputable companies. Since I will be going with rolled ball screws I assume I will have to buy 2 ball nuts for each axis to eliminate backlash?

Should I buy the bearing blocks from one of these companies or should I make them? I have been reading poor bearing blocks will cause unwanted backlash, and I am no aerospace machinist .

Thanks for you time and suggestions. They are welcomed

[dcprecision]

the homeshopcnc.com ball screws are a good buy.

[Adobe Machine]

I would very much advise you to : Use double ball nuts and buy the bearing set for at least the "Fixed end" which should include the pre-assembled housing with fixed angular bearings,the other end is just a simple radial support and you most likley could machine that ( even using 6061 alum.) Go to Rockford Ball screw web site @ www.rockfordballscrew.com.and download their selection chart&service manual ( even tells you how to reload ball screws if you have an "accidental unloading") All the specs are there, with instructions how to set the "preload" on their double nut systems..really pretty neat and readable info.You can use their calcs and formulas to come up with the correct ( and most economical ) size of ball screws.

Adobe Machine (old as dirt)

[phantomcow2]

You should be able to make a nice backlash free setup using a bearing duplex. 15-20 bucks for each set of bearings from vxb.com