Jacobs 16N - thread mount?

OK, so mystery solved. Looks like some chucklehead (pun intended) must have bored out the jacobs taper and pressed in a plug, then drilled and tapped 1/2-20. Definately NOT factory.

So...now that I've pressed it out, WTH do I do with this?

Use some locktite, press it back in, and try my luck at boring a jacobs taper? Maybe easier to press in a piece of 3/4" rod, and then turn it down to 5/8 or 1/2" to make it concentric with the body of the chuck?

Any ideas welcome!

Last resort is keep the rest of the chuck as spare parts for my other 16N. (rest of chuck is in REALLY good shape)

Tom
 

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Oh, and if I would have thought it wasn't a #3JT plug pressed in, I would have marked it before I pressed it out. Oh well!
 
If it was pressed in, it probably has a taper. Make a new arbor to the same taper, press it in, take a finish cut after installation, if needed, put it between centers in a lathe and take a truing skim cut.
 
I measured, doesn't appear to be tapered.
 
.958 (measurements taken at top, middle, and bottom), old loctite cleaned out first.

I know my limitations using bore gauges, but I'm usually able to repeat within .001. I took about 10 measurements to make sure I wasn't seeing a taper. (is a taper of .001 over .75" even enough to be considered a taper?)
 
That's over 0.14" bigger than the large end of the #3 jacobs taper they normally have. How much wall thickness is left?
 
Someone made that threaded taper to be able to put that chuck on a cordless or pneumatic drill..... I need to make one of those....
 
what I don't get...why they didn't bore a taper (of some sort). but may be a .002 interference fit with some loctite will be OK for most low-speed drilling operations.
 
Should have read the whole thread before posting.
 
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