9x20 Lathe Retractable Tool Bit Holder
Last updated on
Sunday, September 07, 2014 06:06:33 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.

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 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.

Assembled & Mounted Holder

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 at about 30 degrees using an
angle jig.

" diameter stainless steel lever with a -20 threaded, 0.6" brass ball knob.

Retracting Tool Bit Animation, Exploded Views, Modular Tool Holder,
Bronze Camshaft with Aluminum Knob, Assembled & Mounted Holder