9x20 Lathe Retractable Tool Bit Holder
Last updated on
Tuesday, September 19, 2023 04:38:48 PM Mountain 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.

Retracting Tool Bit Animation

Exploded Views

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.

Assembled & Mounted Holder

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