Mill X-Axis Motor Drive & Clutch
This is an archived page. This is an earlier modification that preceded the Taig CNC conversion.
Clutch - exploded view.
This is a 12 Volt DC surplus motor (95 RPM max) with a geared transmission (on the motor's right side) which reduces RPM & increases torque but then can not be freely rotated. A clutch is needed to allow quick engagement to & disengagement from the mill's lead screw. The depicted arrangement allows for both manual & automatic feeds. Most full-sized mills have this arrangement. The motor speed is varied by a simple DC motor controller that utilizes pulse-width modulation. The controller allows high torque at low RPMs. (Employing an in-series variable resistor to reduce speed causes too much torque loss resulting in stalls, especially when making relatively heavy cuts.) The direction of shaft rotation is changed by simply reversing the motor power ± polarity via a double-pole, double-throw switch. One of the splines from the rubber-coupled universal joint is attached (via its only set screw) to the motor output shaft but is located only halfway onto the shaft leaving a hole in the spline. The left end of the brass drive shaft fits into this motor spline hole & is thus allowed to rotate freely while maintaining axial alignment. The other spline goes onto the brass shaft. Its (blue Loctite) set screw rides against the shown milled flat but it is not completely tightened. This 'play' allows the spline to be manually slid left or right while remaining engaged to the shaft during rotation. If positioned very closely, the right spline can be completely locked to the brass shaft & only the rubber coupler slides to the middle to engage both splines. However, sliding then requires more force & the splines are not fully engaged (therefore a somewhat weaker connection). A small ring on the left spline can be installed to act as a coupler stop, so you can just slide it over until it touches. The right end of the brass shaft is attached to a small, zero-backlash universal joint which, in turn, attaches to the mill's x-axis lead screw. Set screws engage milled flats to prevent slippage.
Motor & clutch bracket. Motor mount (exploded view). Left plate holds motor; center plate is a bracket;
right plate attaches to the (left) end of the mill Y-translation table, opposite the hand crank.
The channel milled in the right plate allows Allen wrench (bottom) access to the zero-backlash coupler set screws.
Disengaged clutch. This is the assembled unit with the rubber
coupler & spline slid over to the right.
The motor & lead screw are disengaged.
They are allowed to move freely & independently
while the motor & brass shafts
remain axially aligned. The mill's hand crank can be manually turned.
The two larger
cap-head screws to the right hang the entire assembly on the mill's x-axis bed.
The bed's
end had to be drilled & tapped (10-32) & the lead screw's end was turned down to
accept the zero-backlash coupler. A small coupler (from
Berg), about the diameter of
the ½"
lead screw, was required to clear the confines of the bed ways.
Engaged clutch
Side view showing bracket construction. Coupler & spline slide to the left to engage the motor splines for
transfer of power. The rubber coupler is the only means by which power can be transferred across the two shafts.
To allow easier engagement/disengagement, the squared spline corners were first cut on a lathe to a 45º bevel.
The spline was then mounted onto a rotary table set at a 45º angle & then each rib end was milled on each side.
The resulting 'chiseled' spline ends allow faster, smoother engagements into the rubber coupler.
The same design was used to couple & drive the x-axis of the micro-lathe.
Universal joint - exploded view (left to right) milled spline,
original spline &
rubber coupler
DC motor controller
kit documentation.
Note the white universal joint at shaft/controller union.
Brass speed control knob shaft turns in a ball bearing.
Dedicated controls; speed (left) & x-axis
direction (right).
Center is OFF & left/right positions moves bed left/right.
Black plastic motor housing. Strain relieved,
plastic clad power cable.
Rotary table used to cut chisel points on
spline ends.
Fly cutting using motor feed.
This is an earlier modification that preceded the Taig CNC conversion.