*****UPDATE*****
Ball Screws - I got a quote from Nook for some of their rolled screw assemblies with 0.004"/foot accuracy. Cough, Choke, Gasp...They seem pretty proud of their product. They do have a really excellent website and you can get 3D cad files of the screws you spec out. I hunted around on a bit and found a link to Roton on CNCzone. Roton's screws are much cheaper. They don't appear to market their screws for CNC type applications. They are more for non-accurate type mechanical motion applications. They do not have preload ball nut assemblies...so I'm going to try to make my own out of two nuts. I wanted to get screws with a 0.200" lead. They do not have this lead available in a 1" diameter so I got 3/4" These may end up being a little undersized for my setup but I don't plan on running them all that hard so they should be ok. According to the sales rep the screws have an accuracy of 0.003"/foot. The nuts have approximately 0.006" of backlash.
Here is what I orderd from Roton:
I am hoping to build some sort of gizmauchie to hold the type 1 & 5 nuts together is a pre-loaded fashion to eliminate backlash. While I'm waiting for my parts to arrive I started modeling up my design using Alibre. I know it's not Linux software but it is very similar to Pro/Engineer which I use at work. It is magnitudes less expensive then Pro/E and works fine for hobby stuff.
*****UPDATE*****6-NOV-05
Worked on design of bearing/servo mounts:
My ballscrew is a Roton 3/4" with 0.200 inch lead. The root diameter of the threads restricts me to a 15mm ID bearing which seems too small to me. In order to use 20mm bearings I intend to machine the ballscrew end down to 7/16" and shrink fit a 1" OD piece of steel over it that I can machine for the bigger bearings. This provides a surface for the inboard seal and will be easier to machine than the hardened steel of the ballscrew. The other end of the screw will float on a 15mm ID bearing. The smaller bearing is required so that the ball nuts can be installed on the screw. I would appreciate any tips or feedback on my shrink-fit adapter idea.
The bearing I have selected are SKF 7204BEGBP angular contact type. These come in matched sets for mounting in pairs. GB denotes medium preload. I need the preload to eliminate backlash. These bearings are desinged to be semi-idiot proof...If installed as shown in the above pictures the preload will be automatically set (as long as the inner & outer races are compressed together). These bearings go for about $38 each. Matched bearings with no preload are the same price.
On the servo side of the bearings is a spacer and some jam nuts. The spacer provides a surface for the second seal. The adapter diameter then drops to 3/8" and a helical beam type coupling will be used to connect it to the servo motor. Mcmaster sells this coupler for about $25. Standard drive products also has them but charges much more.
The motor mount will pilot into the bearing block and secure the outer races of the bearings. It also will hold a seal. The servo motor will pilot into the motor mount. Access holes in the motor mount will be required so the screws on the coupling can be tigtened. I am hoping to make the motor mount out of some 3/8" plate and some heavy walled tubing.
I would appreciate any feedback on this design especially about the shrink fitting of the adpater. I am toying with welding the adapter to the ballscrew but I'm not too excited about that.