Lead Screw with Split-nut & DC Motor Drives for the Taig Micro Lathe & Mill
Last updated on Sunday, September 07, 2014 06:09:40 AM Eastern US Time Zone

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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 setscrew nut was milled so it would not interfere with the lead screw.

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 " 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 was slid right to disengage (shown) & 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.


" to RH -20 adapter with two, 6-32 setscrews. 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 setscrews 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 " diameter x " long stub & then machine a coupler with setscrews.


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 the controller is 12VDC 1A.

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

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