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9x20 Lathe Spindle Reflective E-O Tachometer & Surface Feet per Minute (SFM)

9x20 Lathe DRO X & Z1 Axes Scales

RF-25 Mill DRO & X Y Z Axes Scales. RF-25 Mill Tachometer & SFM
Taig Mill  Taig Mill DRO & X Y Z Axes Scales.  Taig CNC Mill DRO  Taig Mill Tachometer & SFM  Taig Micro Lathe DRO

Spindle housing shown with the front cover removed. Cleaned the spindle (sandpaper, steel wool & then alcohol) and placed a piece of electrical tape, length-wise. Primed & then painted the spindle flat black. Removed the tape leaving a shinny area. I used a variable 4.7K ohm resistor & two wire leads from the circuit to facilitate adjustment. Before installing, I reproduced the lathe install geometry by placing an aluminum cylinder with a piece of black electrical tape on it into a drill press chuck. Then mounted, instrumented (voltmeter) & pre-tweaked the circuit to get it working reliably. Mounted the reflective tachometer pick-up off one of the bolts. The cable loops over the spindle. Circuit is from the DRO-350 site. The IR sensor is the Fairchild QRB1114.

WARNING: SHOCK HAZARD; FIRST UNPLUG THE LATHE MOTOR FROM THE 110 VAC OUTLET
Power switch housing cover was then removed.
Routed the tachometer cable through a pre-existing hole.
Used spiral cable wrap, a cable tie-down & a grommet to assure
long-term vibration does not abrade the shielded/grounded cable.
I know what the fixed speeds are, though it's easier to look at the
DRO RPM than the chart, but it's the SFM calculator that I find useful.

SFM is only a starting point. When cutting metal, one attends to (among other things): speed, feed,
chip size, chip length, chip coloration, coolant, rigidity, surface finish, sound, smell & vibration.
There are numerous, interacting variables that are unique to any given
machine & setup that simply can not be accounted for by SFM tables.
The rigidity, coolant, and feed in a vertical machining center is a bit better than a hand drill.
 So to say that one SFM value should be the same for both is a stretch.

Lathe Surface Feet per Minute (SFM)

SFM = (RPM· π· DIAMETER)/12          where: π = 3.14159 & the diameter is in inches

Operation is similar to the Mill Tachometer & SFM

For the ShumaTech DRO-350L
AUX ON in setup (Function 0)

Select  "no tool offset" (Function 6, 0)
Move tool bit cutting tip to the part's radius or use the preset function
Zero DRO scales
Define tool offsets (Function 5, #1~9, X part radius, Z1 offset)
Select tool offset (Function 6, #1~9)
Diameter of part should appear on X-Axis scale

Function 7 displays RPM
Function 8 displays SFM

Notes: Scales directions & polarities must be correctly defined in the DRO setup.
SFM changes as the part's diameter (X-Axis) changes during cutting.
Larger diameters have higher SFM than smaller diameters for a given RPM.
Double check initial DRO calculated SFM values by using hand calculations.
SFM is applied equally for either lathe or mill operations.

9x20 Lathe DRO X & Z1 Axes Scales