Had a bunch of dead Harbor Freight 18V cordless drills because the batteries are dead. I upgraded to a Bosch Impact Driver for most of the purposes I used the Drills for. The occasional need for drilling something made me repurpose one of the drills into a keyless chuck for the impact driver. I know I could have bought one, but I think that defeats the purpose of this site and my need to create something.
Step 1: Take Apart a Retired Cordless Drill.
I opened up a retired drill. On the Harbor Freight (HF) drill there was a left handed thread screw locking the chuck to the shaft. Remove that screw.
The HF drill chuck has a 5MM allen socket. Actually, I could not find my metric allen wrenches and I managed to force a 7/32 allen wrench in there, but it was too tight, so I assume it is a metric 5 MM.
To liberate the chuck from from the drill shaft (soon to be an arbor), I clamped the business end of the drill shaft in a vise and used the allen wrench to unscrew the chuck from the shaft. On the HF the threads were right hand thread.
Step 2: Cut the Planetary End Off the Drill Shaft.
I used a cutting wheel to cut the flange off the end of the shaft. At this point I had a shaft that was round, with a threaded end for the chuck.
Step 3: Grind a Hex Pattern on the Shaft
To get a hex shape on the shaft, I winged it.
I put the round shaft in a pair of vise grips and ground two flat spots on the shaft keeping the vise grips perpendicular to the grinding wheel. This allowed me to get two flat grinds opposite each other.
I ground it to about 5/16 across the two flat spots.
I rotated it approximately 60 degrees. I did this by eye.
I repeated the grinding process.
I rotated again for the final grind.
I got out the caliper and continued grinding until I achieved a 1/4 (.2500) measurement on all six sides.
Step 4: Grind a Rounded Grove About 5/16" Up From the End.
After achieving a 1/4" hex pattern, I put the shaft in a cordless drill and ground a rounded groove in the hex shaft about 5/16" from the end. This allows the impact driver to "latch" onto the shaft.
Thats about it.
You might challenge why spending an hour building something that costs about $7 on Amazon is worth it? My answer is because in the end I have a 3/8" keyless chuck drill accessory for my impact driver and I can say I made it...