Taig
Micro Mill Tachometer & SFM
Last updated on
Wednesday, September 15, 2010 07:56:59 PM
Eastern US Time Zone
EO Sensor, Encoded Pulley, Infrared Reflectivity, Surface feet per Minute
This DRO modification has been updated for the CNC conversion but this information has been retained for reference.
Taig Micro Mill
Taig Micro Mill DRO &
X Y
Z Axes Scales.
Taig CNC Mill DRO
CNC
Tachometer
RF-25 Mill
RF-25 Mill DRO
X Y Z Axes
Scales. RF-25 Mill Tachometer & SFM
9x20 Lathe,
9x20 Lathe DRO X
& Z1 Axis Scale.
9x20 Lathe
Tachometer & SFM Taig
Micro Lathe DRO
A
Fairchild QRB1114 E-O sensor
is mounted using a milled
Delrin plastic enclosure so the circuit will not short.
Mounted to the mill head using the two, pre-existing 10-32 tapped holes.
Alignment is easily accomplished
by moving the spindle up or down on the
dovetail mount.
The shielded power/signal cable exits to the left
through a heavily chamfered hole in the aluminum motor support.
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.
For the
DPU-550, a
74LS14 Schmitt Trigger would be needed to make the
tachometer work reliably.
The IC was spliced into the AUX IN to header wires & then shrink-wrapped
Pin 7 is ground, pin 14 is +5VDC, pin 1 is the signal in from the sensor &
pin 2 is the signal
out to the DRO.
Encoded
Pulley
Did not need the black tape. The circuit easily picks up a
pulse from the black set screw,
representing about a 3.5% duty cycle. The sensor is 0.286" from the pulley
surface.
Sensor circuit enclosure with the cover removed. The
two, flat-head screws are 3-48.
A nylon tie serves as cable strain relief & the hot glue keeps it from rotating.
Infrared Reflectivity
A near-infrared (NIR) camera picture, using the
Sony DSC-F717 night shot
mode, showing
the Fairchild NIR emitter glowing at 940 nanometers (nm) which is invisible to the
naked eye.
Objects that appear light or dark to the eye can exhibit either high or low
NIR reflectivity. This characteristic
must be taken into account when selecting materials for use in NIR reflective
tachometer pick-up assemblies.
For example, if the pulley's black set screw had high NIR reflectivity, it
would not have activated the
sensor properly. This principle applies to all materials including: plastic,
metal, paint, tape, etc.
Selecting a material based solely on its visual appearance can lead to a sensing
failure.
Surface feet per Minute
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.
SFM = (RPM· π· DIAMETER)/12 where: π = 3.14159 & the diameter is in inches
Operation is similar to the Lathe Tachometer & SFM
For the ShumaTech DRO-350M, AUX ON in DRO setup (Function 0)
Select
"no tool offset" (Function 6, 0)
Zero DRO scales
Define tool offsets (Function 5, #1~9,
diameter of end mill (or
other) , Z offset)
Select mounted tool offset (Function 6,
#1~9)
Function 7
toggles display between RPM & Z-Axis DRO
Function 8 toggles display between
SFM & Z-Axis DRO
Notes: Scales
directions & polarities must be
correctly defined in the DRO setup.
SFM changes as the
cutter diameter
changes.
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 mill or lathe operations.
Surface Feet/Minute (SFM) Chart 1 SFM 2 SFM 3
Taig Micro Mill DRO & X Y Z Axes Scales
EO Sensor, Encoded Pulley, Infrared Reflectivity, Surface feet per Minute