9x20 Cross Slide, Compound, Carriage & Feed Gears
Last updated on Sunday, September 07, 2014 06:04:50 AM Eastern US Time Zone

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Lead Screw & Nut, Bracket, Handles, Compound Upgrade, Tension Bars, Adjustable Carriage Stops, Feed Gears, Half-nut

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 setscrews (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, -20 left-hand
lead screw with bearing plate & matching bronze nut assemblies as spare parts.
The Jet OEM lead screw (top) is only a left-hand M8-1.25 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
" lead screw.


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
-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. 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 setscrew 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 -20.

Compound Upgrade


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.

jet_saddle_bearing_brass.jpg (66859 bytes)

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 & 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.

Adjustable Carriage Stops

An adjustable carriage stop for the 9x20 lathe. The top piece is aluminum but the bottom piece is mild steel.
The bottom part is stepped to act as a toe-clamp. To preserve a low profile, I did not use a ratchet-style handle.


Low profile; same height as the carriage. The clamp & the fine adjustment use -28 bolts.
Even though I have an integrated lathe DRO, this clamp can be handy for repeated machining operations.


Clamps very tightly. The extra bolt length allows the clamp to be opened wide enough to place on the rail.


A press-on plastic knob is a quick & easy way to make a bolt into a thumbscrew.


Diamond ground the bolt tip for even, consistent carriage contact.


A plain nut with a washer can be used to lock the setting.


Even when mounted on the right-side, it stills clears the tailstock base.


Milled two edges to 45 for safety & esthetics.


A second carriage stop uses a Starrett micrometer head. The micrometer tip is radius.
 The head can be reversed for use on either side of the carriage.


The micrometer head fits into a precision-reamed 0.3760" hole & is held with a 10-32 nylon-tipped setscrew.


Milled three edges to 45 for safety & esthetics.


A second setscrew provides additional strength.

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 (t) gear
At position C of the gear train, stack the 30t gear on the outside & 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.

QUICK-CHANGE GEAR BOX
QC LEVER # INCHES FEED PER
CHUCK
REVOLUTION
1 0.00100
2 0.00089
3 0.00084
4 0.00080
5 0.00073
6 0.00070
7 0.00067
8 0.00062
9 0.00057

    



Jet BD-920N Belt Lathe Pulley Ratios
R
educe belt idler tension & belt breakage by installing an S-link. Using the clutch, slip the Gates V-belt
5M710 (USA) for heavy and/or high RPM loads. The cog belt off the motor, 170XL050 NG, is from Polybelt.
Drive timing belts are identified by 3 parameters & marked as follows: 170 XL 050 NG. The 1st number is the
belt length 17" (85 teeth). The 2nd is the tooth pitch (XL=1/5"). The 3rd is the belt width (050= ").
This drive train has been upgraded to a variable DC motor drive system.


Belt/gear guard housing notch cut to allow the big gear to clear when the cover is closed.
Gear protruding through the notch. Fabricated an aluminum lower safety guard.


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


The detents for the fine feed lever were made with a drill bit & too small. A retaining nut & set screw
on the bottom were first removed. A carbide ball end mill was then used to cut two, better defined
detents for the 4.5mm spring-loaded ball bearing that is held in & adjusted by the top M6-1 set screw.
This lever has a pinion engaging a rack that moves a gear in & out of contact with the transmission.

Half-nut

Replaced the 8 year old worn-out bronze haft-nut. The lead screw ends have to be disconnected by driving out
the aluminum safety shear pin on the left end & unbolting the bracket on the right end. The transmission is held by
two, M8-1.25 top bolts. Shown with the half-nut removed. The diagonal slots of the locking cam simultaneously
move each part open & close by bearing on steel pins that are integral to the bronze sub-assemblies.


Note the integral steel pins & the M5-0.8 left-hand threaded hole for the lower linkage rod.

Reassembled with the steel guides bolted back down. There are two setscrews that adjust the (left) guide
against the nut dovetails. The linkage prevents engaging both the fine & threading feeds at the same time.
The linkage rod is left-hand threaded & screws into the lower bronze nut. Before tightening the main bolts,
make sure the pinion is properly engaging the rack. Then clamp the half-nut onto the lead screw, followed
by tightening the top transmission bolts & the right bracket. This assures good overall alignment & action.

 

Lead Screw & Nut, Bracket, Handles, Compound Upgrade, Tension Bars, Adjustable Carriage Stops, Feed Gears, Half-nut

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