Spindle Motor, Mount & Jackshaft Pulley
Last updated on Sunday, September 07, 2014 06:08:41 AM Eastern US Time Zone

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Lathe Motor, Belt Tensioning Animation, Motor Plate Lock, Motor Switches, Jackshaft Speed-reduction Pulley

WARNINGS: Spindle accessories must be wrench tightened before 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.

Lathe Motor

GE motor specs.

Belt Tensioning Animation

Motor belt tensioning animation. Note how the clamp pushes the plate down 2mm. 
Taig Lathe manual.

Caution: Only use a motor that is either non-thermally protected 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 -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.

Motor Plate Lock

The sealed motor is impervious to metal debris. hp is considered by Taig to be the maximum size.
 By comparison, this 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.

The relatively 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 stop. 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 Switches

Under the bench power switch arrangement. Note the (blue) lathe mount reinforcement plate.
(The DC variable-speed motor & controller has been removed)


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.

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 ⅜" 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 " bracket hole & held in place using a 10-32 nylon-tipped setscrew.
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 & reinstalled, then the longer OEM belt is installed.


The knob has since been replaced with a
die-cast zinc ratcheting locking lever to enable a tighter hold.


One of the 3rd pulley bearings is exposed by pulling the axle out.
Two, sealed, deep-groove, radial/thrust ball bearings were used; " ID & ⅝" 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 " SS axle, there is a thin metal tube spacer that contacts the hubs.
The steel collar with setscrew 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 ⅝" to ⅜". Added an oil-impregnated bronze bearing to lend additional support for the
⅜" pulley hole area. The 0.318" diameter ridge (left) allows only the edge to contact the inner bearing hub.



A " 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.

Lathe Motor, Belt Tensioning Animation, Motor Plate Lock, Motor Switches, Jackshaft Speed-reduction Pulley

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