Stepper Motors & Controller
Last updated on Thursday, October 10, 2019 09:39:20 PM Mountain US Time Zone


Couplers, Cables, Stepper Mounting, 4th Axis, Stepper Controller, Dual Control


Each coupler was modified to include an 8-32 set screw (with a green nylon locking insert) that engages the shaft flat.
The tips were diamond ground flat. The set screw will spread the slit so I tighten the clamping cap-head bolt first.

Stepper motors shown with a Taig NEMA 23 mount & couplers. 305oz-in unipolar rating,
4.2v, 3A, 200 steps/revolution, 3.2mH. Dual 1/4" diameter shafts (with flats) are 7/8" & 5/8" long.

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A Taig NEMA 23 stepper-motor mount screwed onto the lead screw boss.
The ring clamps the split housing to grip the fine threads.


Eight-wire stepper motor leads with 6-pin (crimped & soldered) Molex connected cables.
Black protective sheath removed from one of the stepper motors. Pieces of heat shrink hold the wire bundles.
The stepper-motor connectors can be plugged directly into the controller box without the cables.

Stepper Mounting

Nylon coupling pins.

Coupling pins just engaged.

Note the small gap between the couplers.
Screw the mount in & out to adjust the coupler gap.
Do not over tighten the motor clamping plate & ring.

Mounted X-axis stepper motor.

Mounted Y-axis stepper motor.

Mounted Z-axis stepper motor.

Connector & strain-relief clamp for the Z-axis stepper motor cable.

Mach3 stepper setup for all axes: 200 steps/motor rev x 4 (1/4 step) x 20 TPI lead-screw pitch = 16,000 steps/inch.
305oz-in motors are quite powerful given the scale of the Taig machine. They allow good split-nut clamping pressures &
 fast transition speeds when considering the relatively short distances involved & working in metal on this machine.

4th Axis

CNC rotary table with 305oz-in stepper motor. I see no difference in the amount of backlash between
this & their regular table. Note the addition of a guide plate on the back (or front) edge of the mounting plate.
My stepper setup for Mach3's fourth, A-axis: 200 steps/motor rev x 4 (1/4 stepping) / 5 deg/table rev = 160 steps/ deg

Sherline's super rigid/precise stepper-motor mount.

Indicate the rotary table face by performing adjustments both horizontally & vertically.

Stepper Controller
 Original Controller & Redesigned Panel

Milling the panel on the RF-25 mill. The open-slot area exceeds
the original, 10-hole design area. Original panel layout drawing.
PacTec    Triad    Stepper Motor Basics

The pin out terminal strips pass through & can be directly connected to the PCB inside the case.
Adding the breakout board opto-isolated these connections.

Unpopulated, 4-axes stepper-motor controller PCB.

Populated PCB. 4-40 threads were tapped for the heat-sink screws so no nuts were needed.

Heat-sink compound was thinly applied to the driver chips.




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Note (4) metal tubes were used to increase fan mount rigidity. A green LED was incorporated into
the 2KΩ bleeder-resistor circuit. Molex receptacles are snapped into the enclosure's back panel.
An extra 110VAC cord strain relief clamp was also added. Note the terminal block connections
passing through the rear panel. I leave all J4 jumpers ON so the motors do not idle down. I have
found that the stepper motors can loose some steps after powering-up from the idle-down state.

When powered down, the green LED dims as the current bleeds off. It extinguishes in a few minutes.

 Extra rubber feet were attached directly to the 8-lb. transformer mounts to eliminate any case distortion.
Transformer Triad Magnetics

The horizontal air vents have a nice look.

The table below shows the LPT1 motor outputs for the PCB & the various
Mach3 I/O functions all of which are interfaced through the opto-isolated breakout board.

1 - Output Safety Charge Pump
2 - Output X  Direction
3 - Output X  Step
4 - Output Y  Direction
5 - Output Y  Step
6 - Output Z  Direction
7 - Output Z  Step
8 - Output A  Direction
9 - Output A  Step
10 - Input Limits
11 - Input Mill Tachometer
12 - Input 3D Digitizing Probe
13 - Input E-stops
14 - Output -
15 - Input Spindle Index
16 - Output Spindle Motor
17 - Output Air / Mist / Vacuum 
18 - 25 Ground

These pin out labels were added so they could be seen when the unit is underneath the bench. The PCB
pin-outs (10, 11, 12, 13, 15, have pull-up resistors & 1, 14, 16, 17 do not, plus GND) are connected to the
back-panel terminal blocks (OEM design). The pull-up resistors interfered with the C1 breakout board control
 logic so I removed them from the stepper-motor circuit. These I/O can be used as extension/access to an
enclosed breakout board. Since they are not opto-isolated, I am not using these I/O terminals; removed
in the redesigned panel. Below, note the strain relief clamp (lower right) where the power cord enters.

Dual Control
Redesigned & rewired stepper motor control panel to provide dual, switchable X & Z Axes outputs.

New panel design with switched X & Z stepper outputs to control either the Taig Micro Lathe or Micro Mill.
Drilled & tapped the milled wood base for multiple 10-32, 100 deg, flathead screws, to hold the plastic panel.
The top of the panel aligns against the vise's solid jaw.

For each axis (X & Z) two, 3PDT, 6A switches select the six stepper motor wires between output sockets.
 The center, common switch contacts are connected to the stepper board outputs. The two (left & right)
banks of switched contacts are connected to the Molex socket pins. Switching schematic.

Left & right side switch wires loop over to right & left sockets to keep the front panel toggle positions correct.

Four, switch-lever positions are thrown either left towards the Lathe (ZL & XL) or right towards the Mill (ZM & XM).
Not coincidentally, the lathe is on the left side of the bench & the mill is on the right side of the bench, too.


The lathe uses 3A motors, same as the mill, so all stepper board amperage settings are set at 0.42 VDC.
The new panel design has much tighter tolerances for the snap-in Molex sockets than the first design.

The larger stepper motor is for the carriage & the medium-sized motor is for the cross slide; both are 3A.
The eight motor wires are wired into six-pin, Molex sockets. The cables are 18 gauge.

The Molex pins are both crimped & soldered. The wires were looped to ease installation.








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Couplers, Cables, Stepper Mounting, 4th Axis, Stepper Controller, Dual Control