Fitting a Jacobs chuck to my old post drill

A couple of days ago I posted about a post drill which I've been tripping over since 2012. I bolted it to the middle bent in my timber frame shop the other day, thinking it would be of limited utility to me and my work due to its specialized S&D style chuck which can only fit 1/2" diameter shanks with a flat ground onto them to engage the chuck's set screw.



Then my friend John Johnston showed me a picture of his very similar drill, to which he had fitted a modern Jacobs chuck. His method had been to obtain a chuck with a Morse taper shaft, file a flat on it, and install it into the old drill chuck. I set out to do just that but was unable to find a chuck with the shaft at any of the stores in the area. So I tried something different.

The local Harbor Freight (yes, I know...) had a Jacobs chuck designed to replace worn out chucks on power hand drills. It has a 1/2-20 threaded hole which would normally thread onto the drill's electric motor spindle. Instead, I obtained a 1/2-20 threaded bolt and threaded it into the chuck using Red Loctite (largely superfluous since this fitting actually tightens as the drill spins in the right direction).



 I then measured the chuck's depth to see how long the shaft should be, and cut the head off the bolt. Anytime you do metal work, utilizing new hacksaw blades and files make the work much, much easier.



 I then hand filed the flat onto the new shaft using a new 10" mill bastard file.


 The chuck fit perfectly and works exactly as I had hoped.



It still looks great. I hooked the chuck key to a length of light chain and nailed the chain to the same post so that I can't lose the key. And I'm planning to replace the modern lag screws with old-style square head lags (courtesy of my friend Jim Thommen).



I am not planning a full restoration on this but, now that it will be functional, I may give it a more thorough cleaning. And I still need to find the proper table, of course. 


- Zach Dillinger

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