9x20
Lathe Retractable Tool Bit Holder
Last updated on
Tuesday, September 19, 2023 04:38:48 PM
Mountain US Time Zone
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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 set screw.
Left to right: Knob with bronze camshaft, modular tool
bit
holder, dovetails, gib with set screws & 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
set screws
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 set screws are counterbored.
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.
Produced 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 radiused top edge.
The AXA
quick-change tool post holder
allows accurate height adjustment.
The mounting bar has a radiused 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
at
about 30 degrees using an
angle jig.
1/4" diameter stainless steel lever with
a 1/4-20 threaded, 0.6" brass ball knob.
Retracting Tool Bit Animation,
Exploded Views,
Modular Tool Holder,
Bronze Camshaft with Aluminum
Knob,
Assembled & Mounted Holder
