Milled Carriage
The sides of the carriage are slightly slanted so during production, the piece can be popped out of the mold. The left side of the carriage required milling so the mounted split-nut would be perpendicular to the lead screw. There is a small ledge that the split-nut subassembly mounting plate's top edge rests against. All milling & drilling was performed using the lathe to assure alignment, especially of the two, lead screw holes (make sure to clear the eccentric for the pinion gear). I borrowed a Taig lathe carriage because, of course, you need two to do the operation. To perform the milling operation, I used a solid carbide, two-flute (for soft materials, use a 4-flute for hard materials) 5/16" finishing end mill. I have also used a fly cutter to mill a carriage. De-burr the dovetail edge where it was milled. Check the entire carriage dovetail for burrs leftover from manufacturing. A dab of kerosene allows a smooth cut on aluminum. This mod was performed before I had either the Taig or the RF-25 mills.
Removed all calibrated dials, glass bead blasted them (sandblasting too aggressive/coarse), then using the lowest lathe rpm, smoothed the scale with 220, 320 then finally 400 grit sandpaper. Do not be too aggressive or you can remove the markings. This method only works for dials that have deep marks to begin with. Indicia will be finer & the knob looks nice when the rough machine marks are removed. Careful, the dials are factory Loctited on & screw off (not pull). I put two small flat sides on the non-threaded area of the lead screws for a very small, open-ended wrench to facilitate disassembly/assembly. Grease (not white lithium) makes these knobs work very smoothly. The two ends of the movable dial scale zero (the ¾ circumference spring clip in the dial bearing block grove) may be rough; remove & grind the ends flat. Go to OEM vise for a close-up photo
Replaced all of the OEM dial brass spinner pegs with a pivoting-type (Wm. Berg) as per MIL-STD-1472. This one change alone greatly enhances the smoothness of operation & is the least expensive modification for the largest increase in machine performance. Remember, that when tapping the steel knob, the tap hole is (larger) for 50% threads not 75% like for softer materials. Always drill the exact recommended tap hole for maximum thread strength. Grease on the stainless steel pivot screw makes it smooth. A small nylon washer, just the size of the pivot screw body, 3/16", (not the thread itself) removes the last of the in-out play of the aluminum spinner knob. I also filed two small flats on the eccentric for the pinion gear, just behind the knob, to accept a miniature 5/16" open-end wrench. This greatly facilitates rack & pinion engagement adjustment.
Lead-screw hole, right side.
Small notches in the pinion help retain the
clip.
To eliminate lead-screw flexing, a bronze oil-impregnated bearing was press fitted & then reamed to 0.25". One corner of the set-screw nut was milled so it would not interfere with the lead-screw. The rack & pinion eccentric bearing set screw area was milled to allow the locking nut to seat evenly. The set-screw end was faced smooth to eliminate the locking ridge which gouged the eccentric housing. Also, note the milled flat area to the right on the X-Axis dial readout mounting block. This is the area where the Z1-Axis dial readout plunger makes contact.