Spindle Motor, Mount
& Jackshaft Pulley
Last updated on Friday, March 26, 2021 06:29:10 AM Mountain US Time Zone
Spindle accessories must be wrench
using in forward or reverse to prevent them from spinning off.
The 3-jaw chuck jaws can loosen & fly off the chuck if
spun-up without them being clamped onto a part.
use a motor that is either non-thermally
or has a thermal overload circuit that requires manual reset.
If the motor automatically shuts down due to excessive
heat, it then has the potential (upon cooling) to
unexpectedly start-up again while you are touching/changing
sharp end mills, saw blades, pulleys or other rotating parts.
Sealed, GE H120,
HP, continuous duty,
1725 RPM, split-phase, ball bearing motor,
mounted onto a plate, in-turn held
by a large, galvanized door hinge.
Generally, these hinges are loose so it was drilled
out & a close-fitting bolt with nut was installed.
The motor is
externally cooled by a fan.
Note the height-
adjustable rubber stop. This stop allows belt tension
to be set for optimal performance i.e., good traction,
minimized vibration & compensation for any minor belt
stretching. It uses a 1/4 -20 bolt passing through the
work surface & then screws into a flush nut on a small block
of pressure-treated wood. The hard rubber stop has
washers on both sides to increase rigidity & a star lock
washer is used under the nut. I enlarged the clearance hole &
installed shims on the wooden block. The adjustment
screw is set at an angle perpendicular to the motor mounting
plate bottom. The entire rubber stop face is in contact
with the motor mounting plate. There is a spacer plate
under the hinge. The power cord is protected from abrasion
that could occur from repeatedly pivoting the motor over time.
sealed motor is impervious to metal debris.
1/4-HP is considered by Taig to be the maximum size.
By comparison, this 1/4-HP motor is 50% stronger than
a 1/6 HP motor & 250% stronger than a 1/10 HP motor.
Mounted to the left (CCW rotation) provides additional
work space behind the lathe bed.
high motor weight (~13-lbs.) & low belt
angle give good tension for turning small parts. The motor
is solid mounted, not in a rubber bushing which causes
too much wobble under high torque. This setup also
works well when using the spindle riser block. The ON/OFF
switch is a standard, 20A, wall switch mounted in
an outdoor metal switchbox with a stainless steel cover plate.
I have the switchbox mounted high on the bench
leg making it difficult to bump it ON (switch down) but if I
do accidentally bump it with my knee, it turns the motor
OFF (switch up). Make sure to properly ground the circuit.
For low belt tension, the motor plate rests on its
Higher belt tension places the plate about one or two mm's
above the stop. Vibration against the stop can occur. When
I upgraded the mill motor, I noted the high V-belt traction
due to its locking mounting plate arrangement. This
suggested the addition of the hold down action clamp.
In order to eliminate vibration & increase belt
tension, install a vertical hold down action clamp.
Mount it at the same angle as the motor mounting plate.
It quickly opens & closes using the lever. When closed,
the motor mounting plate is then captured between
the upper & lower adjustable rubber-ended stops.
Belt tension can now be increased when turning larger
pieces. Runs very smoothly & with high V-belt traction.
Motor-reversing switch shown.
Switch is down for normal, CCW rotation & up
for reverse, CW rotation, pointing towards the
direction of rotation. The wiring schematic is on
the motor ID plate. A rubber boot keeps out debris.
Or, use this diagram to wire motor direction switching.
A Double-Pole Double-Throw (DPDT) switch with a center-
detent OFF eliminates a separate ON/OFF switch.
Jackshaft Speed-reduction Pulley
Lathe speed-reduction pulleys are called jackshafts
or countershafts. This design is very sturdy & compact.
Added a 3rd, intermediary pulley, yielding a 10:1
motor to spindle reduction producing a low 178 RPM.
The 3/8" thick arm has vertical height & pivot adjustments
using a 10-32 thumb knob in a machined slot.
It is mounted onto the extended stepper-motor
bracket making an overall strong, rigid arrangement.
The axle is in a precision reamed 1/4" bracket hole &
held in place using a 10-32 nylon-tipped set screw.
Note the rubber bumper (left) that the motor rests
against when pivoted forward to change pulleys/belts.
Two, Taig mill belts (12.5cm flat length) & another
Taig pulley were used in the modification.
The 305 in-oz lead screw stepper motor is tucked
in close & out of the way; everything clears.
This design was also used for the Taig mill
speed-reduction pulley modification.
To return to the original configuration:
the intermediary bracket with its pulley assembly is folded down
(or removed), the motor pulley is removed, flipped 180 deg &
reinstalled, then the longer OEM belt is installed.
The knob has since been replaced with a die-cast
zinc ratcheting locking lever for tighter clamping.
One of the 3rd pulley bearings is exposed by pulling the axle out.
Two, sealed, deep-groove, radial/thrust ball bearings
were used; 1/4" ID & 5/8" OD. The Taig pulley is
made to an interference fit tolerance thereby requiring
it to be first heated before installing the bearings.
Inside, in-between the bearings, on the 1/4" SS axle, there
is a thin metal tube spacer that contacts the hubs.
The steel collar with set screw also has a small
ridge that only contacts the bearing's hub.
Even though the pulley runs on two sealed bearings,
there is a 0.635" unsupported area of axle where the
hole ID narrows from 5/8" to 3/8". Added an oil-impregnated
bronze bearing to lend additional support for the
3/8" pulley hole area. The 0.318" diameter ridge (left)
allows only the edge to contact the inner bearing hub.
A 1/4" collar acts s a spacer &
another (third) thrust bearing.
Before the addition of the bronze bearing, a knocking
sound was present under heavy belt tension & the RPM
readout in Mach3 (with averaging on) use to vary by
one count. Now, the 3rd pulley runs very quietly under
high belt tension & the RPM is rock solid. The bearing
has white lithium grease as an additional lubricant.