A new chuck for a Hercus 9″

[Alan GilbieParticipant @alangilbie78933]

The 3 jaw scroll chuck on my Hercus lathe was so badly bell mouthed you could slide a 5 thou feeler gauge between the front of the jaws and a gripped bar. In a word, it was stuffed and could no longer hold bar stock well enough for useful work.

I took the plunge recently, and bought a new 125mm Pratt & Burnerd chuck. The original P&B chuck was made with a threaded back to fit the Hercus lathe spindle nose (1 1/2" diameter and 8TPI) – but these are no longer available. Instead, I had to buy a chuck with a plain back and machine a cast iron mounting plate to suit. This was my first try at machining CI and I was a bit nervous about it.

The mounting plate is bored and tapped to suit the spindle nose and the chuck is located with a 95mm register that I machined for a light press fit. Chuck is bolted to the plate with three M8 Allen bolts that pass through it from the front.
I gather that typical radial run-out for a scroll chuck on a small lathe is around 2-3 thousandths of an inch. However, the result for my new chuck surpassed my most optimistic expectations.
Have a look at this video to see for yourself:
https://www.dropbox.com/s/khy41vth67fxezu/Testing%20runout%20on%20new%20chuck.mp4?dl=0

The dial gauge is showing the run out on a piece of scrap 16mm bar just poked in the chuck.

Gotta be happy with that

[Alan GilbieParticipant @alangilbie78933]

[pgk pgkParticipant @pgkpgk17461]

(Tongue in cheek answer) – I have a dial guage like that.

(Serious answer) – awesome.

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