9x20
Lathe Retractable Tool Bit Holder
Last updated on
Saturday, January 05, 2013 06:56:11 AM
Eastern US Time Zone
Retracting Tool Bit Animation,
Exploded Views,
Modular Tool Holder,
Bronze Camshaft with Aluminum
Knob, Assembled & Mounted Holder
An AXA mounted retractable tool bit holder allows me to quickly pull the cutter
back at the end of the
thread, keep the lead screw half-nut engaged, & only advance the compound into
the workpiece. Used
with the updated variable-speed DC
motor drive, single-point threading
is now much easier & precise.
The Hardinge HLV-H has
a built-in tool bit retraction mechanism with the lever on top of the compound.
Exploded views. The holder is based on modified 9x20 compound parts.
Spring-loaded ball bearing detent. The grooved camshaft
is held in using a nylon full dog-point setscrew.
Left to right: Knob with bronze camshaft, modular tool bit
holder, dovetails, gib with setscrews & lock nuts.
Ball-bearing
detent for the levered knob.
Modular Tool Holder
The steel tool
holder is modular so different plates can be designed to hold many different bit
types
including
square-shank & inside threading bars. A solid carbide bit is shown. Two, 10-24
full dog-point
setscrews
hold
the 3/16" (0.1875" or 4.7625mm) tool bit. Five, 8-32 bolts secure the plate to the base.
The two tool bit setscrews are counter bored.
Bronze Camshaft with Aluminum
Knob
An aluminum prototype camshaft was made to evaluate the design.
Cutting the
bronze shaft with a cam on the end. The part was offset 0.1" in the 4-jaw chuck
for a 0.2" range.
The shaft is 0.6300" (16.0mm) diameter.
Making the knob. This large part cutoff was easy now that I
have installed a
variable-speed DC motor drive.
It was quick to determine the detent locations. I assembled
it, moved the knob through its range several
times, then disassembled it, punched the ends of the mark & drilled. Produces a
clean, positive click.
The slot must be the exact same width of the bronze cam &
one
radius distance above
the
centerline for it to properly stop at the two extreme (about a 170 degrees) detent
positions.
If the slot is rotated 180 degrees, the lever will move in the opposite
direction of the cutter.
Having a bronze cam moving against a steel part is smooth & should wear well
over time.
During assembly, the dovetails, cam shaft, & ball detent were lightly lubricated
with grease.
The steel clamping bar is held on using four, 10-32 hex-head bolts.
Note the radius top edge.
The AXA quick-change tool post holder allows accurate height adjustment.
The mounting bar has a radius edge so it fits tightly into the holder's
lower corner.
The mechanism fully retracts 0.2" but pulling it back just 90
degrees gives usable travel.
Note: For thread cutting, the compound was set to 30 degrees using an
angle jig.
¼" diameter stainless steel lever with a ¼-20 threaded, 0.6" brass ball knob.
Retracting Tool Bit Animation,
Exploded Views, Modular Tool Holder,
Bronze Camshaft with Aluminum
Knob, Assembled & Mounted Holder
