Stepper Motors & Controller
Last updated on Tuesday, September 19, 2023 04:14:14 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.

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.

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.
Ethernet is now the preferred method of CN control.
The LPT approach is now obsolete & not recommended.

Populated PCB. 4-40 threads were tapped for
the heat-sink screws thus no nuts were needed.
In use, the pull-up resistors were problematic &
were removed from the board. An opto-isolation
breakout board is a far better approach.

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

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 under 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 - Out Safety Charge Pump
2 - Out X  Direction
3 - Out X  Step
4 - Out Y  Direction
5 - Out Y  Step
6 - Out Z  Direction
7 - Out Z  Step
8 - Out A  Direction
9 - Out A  Step
10 - In Limits
11 - In Mill Tachometer
12 - In 3D Digitizing Probe
13 - In E-stops
14 - Out -
15 - In Spindle Index
16 - Out Spindle Motor
17 - Out 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
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.

This switching approach saves having to buy another stepper
board/power supply/enclosure realizing significant savings.



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.

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