Cross Slide, Compound, Carriage & Feed Gears

Lead Screw & Nut, Bracket, Handles, Compound Upgrade, Tension Bars, Feed Gears

An earlier, simple modification to the cross slide wheel.

Made a ring for the outside of the cross slide hand wheel. Moved the handle out for more leverage.
Used three, M5-.8 set screws (same thread as the handle's shoulder bolt).
 I milled the screw ends flat to remove the sharp ridges so they would not gouge the original knob.
Don't make it too big or it will interfere with your hand on the carriage & compound handles.

Lead Screw & Nut

When I modified the Taig mill for CNC, I had high-quality, precision ground, ½-20 left-hand
lead screw with bearing plate & matching bronze nut assemblies as spare parts.
The Jet OEM lead screw (top) is a flimsy, left-hand ¼-20 with a crude thrust/radial bearing/bracket.

First squared-up the nut on the mill then turned the bronze nut to fit the cross-slide table counter bore (on the bottom).
Drilled & tapped for a 10-32, 100° flat-head cross-point screw that holds the nut in from the top.

Bottom of the cross slide with the bronze lead-screw nut mounted.

Bracket

Machined a solid-aluminum bracket that uses 3, M6-1x75mm cap-head bolts & 6.5mm clearance holes.
Had to tap a 3rd, bottom thread. The steel was about 5mm thick & the drilled hole was 5mm for the M6-1 tap.
Machined bracket from 2.5" round stock 2.87" long. There is a 9/16" clearance hole for the ½" lead screw. This is a super rigid design.

Adapted the threaded Taig mill OEM bearing plate. The lead screw with its bearing, thread into the plate.
The back of the Taig dial has holes for a pin-spanner wrench that I made.

 
Tapped the Taig hand crank end for M5-.8 to accept the Jet OEM handle that rotates on a shoulder bolt.
Super smooth cross-slide control; no flexing or binding. The precision ground ½-20 screw with a quality
bearing & bronze nut are massive when compared to the Jet OEM screw. Retained the black sliding swarf
cover over the lead screw. The dial scale position is resettable though not usually used in lieu of the DRO.

Handles

Made a large, 3.25" cross-slide hand knob for the Jet 9x20. Like the other knobs, there is no knurling;
it would load-up with dirt. The knob is 0.485" thick at the center; same as the Taig OEM crank.
The knob needed a precision-reamed 5/16" hole with a 1/16" keyway. See broach cutting for more information.
Center hole reamed at low RPM on the lathe. For comparison, the rack & pinion carriage hand wheel is 4" OD.

 A small M5-0.8 set screw in the back secures the knob's shoulder bolt in place to hold its adjustment.
The re-zero-type dial scale was retained to preserve the parts spacing. The 0.001" gradations are still correct.

Bottom view showing the cross-slide's massive bracket with the 3rd (added) bolt.
The semi-round bracket has a milled flat on the bottom.

A custom brass bushing was made. It is threaded M5-.8 so it has to be screwed onto the bolt (captured) but
it rotates freely in use. A small collar inserts into the handle base. There is also a shallow, 15/64" diameter
 counter bore (using a 5/32" pilot) that the bolt shank sits in to allow a close but non-binding fit.

Upgraded to chrome-plated steel revolving handles. Drilled out the M5-0.8 thread then drilled & tapped a ¼-20.

Compound Upgarde

Upgraded ball-bearing bracket for the compound.

Tension Bars

Metric (M6-1) die cast zinc ratcheting lever from MSC. 
The brass spacer allows the lever to work smoothly due to the contact of dissimilar metals.
The spacer has been turned down to make the handle as low as possible to reduce compound interference.

Made new, front & back carriage apron tension bars out of thick brass (the original was thin steel, peened to fit).
The cross slide must be removed to access the middle mounting bolt. The front bar is metric tapped for the retaining
bolts and the rear bar is held on by M6-1x17mm bolts to the carriage underside. The rear holes, tapped into the
carriage, required cleaning out with a metric tap. Milled a 0.002" step along the bolting surface to take-up the carriage
play at the bearing surface. Required step size determined using trial & error as it likely varies among machines.
Used a 45° end mill to heavily chamfer the edges. Lubricated it with white lithium grease. Greatly reduced carriage play.
The lathe DRO is mounted off the back of the carriage.

Feed Gears
In order to obtain cross-slide feeds much slower than shown on the chart, use these gear combinations:

At position A of the gear train, use the 28teeth gear
At position C of the gear train, stack the 30t gear on the outside and the 127t gear on the inside
At position B use the 120t gear, secured under a washer, is lined up with the 30t gear of the banjo

Note: Shown below is a Jet BD-920N on its stand which raises the lathe high enough for the big gear to  clear mounting surfaces.
A lathe mounted directly onto a flat surface might require spacers. These gear combinations allow very slow feed rates.
The nine quick-change gears still provide a useful range of different speeds.

Drive timing belts are identified by three parameters & are marked as follows (for the Jet lathe):  170 XL 050 NG

The first number is the belt length (17"). The belt has 85 teeth.
The second number is the pitch (XL=1/5"), e.g., the peak to peak tooth spacing
The third number is the belt width (050= ½")


Belt/gear guard housing notch cut to allow the big gear to clear when the cover is closed.
Gear protruding through the notch. Making a safety guard.

Jet lathe clutch stop, animation. The stop is a ½" diameter, Delrin rod threaded for & held by a 10-32 cap-head screw.

Lead Screw & Nut, Bracket, Handles, Compound Upgrade, Tension Bars, Feed Gears