X axis test fit

With the Y axis under control, it is time to turn my attention back to the X axis - by far the most challenging part of the conversion. For reasons that will become clear and for now at least, the ball-nut is being attached to the side of the saddle (as opposed to the horizontal surface where the original lead-nut is located). As a result, its flange (which is hardend and would therefore put up some stiff resistance to modification) will be backwards with respect to the mounting plate. This means that a little finessing is required to hook the nut up to the one-shot oiling system. The plate is cross-drilled and an o-ring fitted where the grease nipple will arrive.

I cut the end off the grease fitting on the lathe (firing the ball bearing and the spring across the shop - never to be found again) leaving a conical section for a good fit against the o-ring. A little 1/8" soft copper tubing fits nicely inside the 1/4" pneumatic tubing that will be used for the plumbing.

Here is the assembly, seen from the free support bearing end. This whole setup is slightly sketchy at best and possibly downright ghetto at worst, but I'm making the best of a difficult situation here. First, the ball-nut has to be where it is because there is no way it will fit between the saddle and the table. The only type of ball-nut that will fit is the flange-less type more typical of U.S. fabricators. However, even that type won't fit in a 1" screw. So I would be forced to use a 3/4" screw which is nigh impossible to find used or surplus on ebay in the required length. Why is this? Because the slenderness ratio i.e. the diameter/length of the screw is inadequate to meet the specifications of the machines from whence these screws come; under compression loading, the screw will have a tendency to buckle. From the research that I have done, the conversion kits that are out there for the RF 45 and clones all have 3/4" screws with a fixed / free bearing support configuration - which is the least robust for buckling and substantially lowers the rpm limit for the screw rotation. Finding a used / surplus, ground (as opposed to rolled), 0.2" pitch, 1" major diameter, C5 accuracy ball-screw with a pre-loaded, G0 (zero backlash) ball-nut (the minimum specification recommended for machining metal) with 39" of travel is entirely possible. Plus, at ten cents on the dollar, It will be significantly cheaper than a new C7 grade, rolled 3/4" screw. I purchased all three screws, one surplus, two used (which came with bearings) for roughly the same as a single new C7 rolled screw without bearings. The risk I am taking is that the used screws may be of somewhat dubious origin. They may have come out of a surplus machine - or they may have been swapped out because they are worn. I have no way to know until they are installed and can be tested under load.

Another ever-so-slightly-less-than-ideal design detail here is the mounting setup for the free support (that is, the bearing that restrains the screw radially but not axially, allowing for heat expansion of the metal in the long axis). In an ideal world, the screw would come right from the fabricator cut to exactly the right length for the table. But it don't and it ain't respectively. I am therefore faced with the choice of either shortening the screw and cutting a new journal, or creating an extension for the table. The former, despite the encouraging words on the subject from the seemingly undeterrable www.5bears.com on his epic cnc-mill-from-scratch write-up, leaves my inner machinist cowering in fear under the lathe. The latter seemed like the better choice for the likes of me-who-will-live-to-fight-again-another-day. Despite the use of mic 6 tooling plate for the mounting plates, the extension will inevitably introduce additional out-of-square error to the surface onto which the bearing is fixed. Imho, however, this kind of error is easier to correct than a home-cut journal that is a few tenths too small for its bearing!

Last and not least: skeuomorph of the day comes from my favorite hardware store, HarSupCo in Montreal: faux-wood patterned cardboard tubes.