RF-25 Mill DRO Z-axis Scale
Last updated on Monday, March 16, 2020 06:16:04 AM Mountain US Time Zone


Scales, Brackets, Scale, Cable Routing, Analog Readout

Six-inch hardened SS scale (manual) with SPC output & M3-0.5 threads. Trimmed some of the scale
off the top off using a cutoff wheel, followed by a carbide end mill & then diamond wheel grinding.
Radius the two top corners as they are close to the ON/OFF switch.








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Z-axis, 1/8" thick, scale-mounting plate. The four mounting hole locations were accurately
determined using 1/4-20 transfer screws. This bracket configuration allowed me to retain
use of the speed-settings plate. An earlier version used a 1/16" plate, but was too thin.


This vertical-style scale has a good SPC plug receptacle. This type scale was used for the 9x20 lathe scales.
 Not as easy to solder on wires, though, if that is the route one is taking.
All cable plugs are held in place with
a spot of hot glue. Soldered
a 100-mF10v tantalum capacitor across the battery leads of the scale.

The mill's depth-stop function is retained.

Detail of the two, lower brackets.

Installed rubber washers on all scale mounts to allow floating which reduces strain on the transducers.

The RF-25 mill's free-floating Z-axis design works so well that now all of my mill & lathe scales
are attached at only one end while the other end remains captured but loosened to allow floating.
This approach greatly reduces minor out of alignment induced stress on the transducer. This
design also helps to reduce DRO jitter as does a clean, deburred transducer with NR capacitors.

Radius the top scale corners by grinding with a diamond wheel. The scale top end is free floating. Also, the
 zero of the printed in/mm scale is aligned with the bottom edge of the transducer when the quill is fully retracted.
This scale is not a modified digital caliper but a purpose-built vertical scale.
A similar installation was used on the floor drill press Z-axis DRO.

Cable Routing

Cable runs up into the belt guard housing. Button-head bolts look nice.

The black cable is for the Z-axis scale & the gray cable is for the tachometer.
The cables are fastened down about every three-inches along inside right side corner of the belt housing,
then exits behind the DRO's arm mount. The flat sides of all but two cable tie-downs, are set against the housing
inside corner so as to not turn under extended vibration. The arm's base is a triangular bracket
that is mounted under two of the motor hold-down bolts. The arm is made out of 1010 (1" x 1")
 80/20 extruded aluminum. I ran the cables inside the arm's back-side channel & then snapped in
black plastic 80/20 inserts. In retrospect, 1515 (1
-1/2" x 1-1/2") extrusions would have been a little stiffer.
 I like to use a Unibit to make accurate, clean holes in thin materials. I have since removed the quill levers.

Analog Readout

Analog readout for the mill/drill. Two-inch travel range, indicator dial. Use with the extended quill by loosening
black thumb screw, sliding down & relocking. A very low-cost option that gives excellent depth control.





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Scales, Brackets, Scale, Cable Routing, Analog Readout