Lead Screw with Split-nut & DC Motor Drives for the Taig Micro Lathe & Mill
Last updated on Tuesday, September 19, 2023 04:46:19 PM Mountain US Time Zone


Split-nut Animation, Exploded View, Nut Subassembly,
Carriage Modification,
Split-Nut Mounted on Carriage,
Bearings & Lead Screw,
Lathe Z1-axis Motor & Clutch,
DC Drive for Taig Mill

This lead screw modification has been removed for the
lathe CNC conversion but the information has been retained for reference.

Split-nut Animation

Split-nut animation.

Exploded View

The aluminum base plate is 1.55" long x 1.15"
wide x 0.1375" thick,
the brass pieces are
1.50" long x 0.3150" wide x 0.3115" thick &
the steel rods are 0.1915" diameter.

Nut Subassembly
The split-nut subassembly opened.

The split-nut subassembly closed.

The split-nut subassembly pushed to the side.

Split-nut back mounting plate.

Carriage Modification

The sides of the carriage are slanted so during
production, the
part can be popped out of the mold.
The left side of the carriage was milled so the mounted
split-nut would be perpendicular to the lead screw.

Replaced all of the OEM dial brass
spinner pegs with a pivoting-type.

To eliminate lead-screw flexing, a bronze oil-impregnated
bearing was press fitted & then reamed to 0.25".

One corner of the set screw nut was milled so
it would not interfere with the lead

Split-Nut Mounted on Carriage

Split-nut subassembly mounted
onto carriage. Nut open.

Nut closed.

Detail of subassembly attachment.
Used 2, 4-40 flat-head screws.

Bottom view.

Bearings & Lead Screw

Two (red) thrust bearings are seen & a
sealed ball bearing is inside the T-bracket.

A (red) thrust bearing is visible & a
sealed ball bearing is inside the T-bracket.

The carriage stop lock screw was moved to the top by
drilling through from the bottom & tapping (10-32).


Split-nut engaged.
To not cross threads I move the lead
screw handle back & forth while engaging the split-nut.

An Acme square-shaped thread might
have helped this potential problem.

Detail of split-nut, engaged. The spilt-nut assembly
is low enough so as to not interfere with
the carriage
stop bar function & also clear the spindle
housing allowing full carriage travel.

Detail of split-nut, disengaged.

Split-nut under spindle housing.

Reamed 1/4" ID bronze bushing
to eliminate lead-screw flexing.

Lathe Z1-axis Motor & Clutch

 A geared DC motor with a sliding coupler-based
clutch was added before the
CNC conversion.
The black rubber outer sleeve slides to the right to
disengage (shown) & to the left to engage the splines.

The clutch allows one to disengage the motor &
then turn the lead screw using the hand crank.

Variable DC Motor Drive for Taig Mill Table

Variable-speed, geared, DC motor
drive for the Taig Mill X-axis table.

This modification was replaced
by the
mill CNC conversion.

The left end of the table is first drilled & tapped
(10-32) to mount the motor bracket.

1/4" to RH 1/2-20 adapter with two, 6-32 set screws.
Note, small aluminum threads can strip.

Adapter threaded onto the lead screw. Clean
the threads with alcohol & use thread locker

(which is a thermoplastic so heat will loosen them).
The set screws need to be flush to clear the table.

Flats were machined onto the adapter to allow
tightening/loosening. A more compact method is to remove

the lead screw, turn the end down to a 1/4" diameter x 1/2"
long stub & then machine a coupler with set screws.

Alternatively, a small zero-backlash coupler could
be affixed to a turned-down lead screw end.

I did this on an earlier modification using a small
coupler & a clutch mechanism (see
lathe above).

End bracket hole is centered on the shaft.

A zero-backlash coupler is attached
to allow for slight misalignment.

A surplus DC motor with gear-reduction
transmission is mounted to its bracket.

Its gear train gives the small motor good torque
which is needed to move an end mill through metal.

Fully assembled table motor drive.

Kit-built variable-speed DC motor speed
controller is used to vary the motor's RPM.

Use this diagram to wire motor direction switching.
It is placed in-between the controller & the motor.

A Double-Pole Double-Throw (DPDT) switch with a center-
detent OFF eliminates a separate ON/OFF switch. 

Power supply for this controller
is 12VDC 1A
; observe polarity.

Split-nut Animation, Exploded View, Nut Subassembly,
Carriage Modification,
Split-Nut Mounted on Carriage,
Bearings & Lead Screw,
Lathe Z1-axis Motor & Clutch,
DC Drive for Taig Mill