Internal Single point threading

[Alittlerusty]

This is my first attempt at single point threading ever, and may as well go big right out the gate. I have 3 chucks for my southbend 16" lathe. 2 of them came with the lathe, a 6"3jaw scroll and a 9" 4 jaw independent. These 2 chucks share a backing plate (spindle is threaded 2 3/8"-6tpi). It is a major pain swapping it back and forth so it's time to make another one. I've decided the new one will be for the 3 jaw. At 2 o'clock on the 6" Chuck and the backing plate on the 9" chuck there are two punch marks and some dykem for orientating the plate on the 6" chuck. I'll post more when I get to the shop.

 

[Alittlerusty]

The previous owner of the 6" chuck drilled and tapped the 4 holes with the Allen screws and the current backing plate registers on the inner circle next to them. This measures about 4", I'll get a better measurement later but I picked up a couple feet of 4.25" round from Craigslist and will use this for the backing plate.

 

[BGHansen]

Sounds like a great project, learn a valuable skill and save yourself some time with future chuck changes. If I was taking on the project, I'd measure the spindle threads via the 3-wire method or a screw pitch micrometer for starters. Then turn an arbor to match the threads. That way you can check your new backing plate threads when you start getting close.

Bruce

 

[Alittlerusty]

I cut a 3 1/2" slug off the round stock (first mistake the spindle is only 1.75" long should have cut it around 2.25" to leave room for facing both sides). Mounted it in the 9" 4 jaw because it has a 3" thruhole and then I can thread all the way thru. I got it running true within a thou and faced the end. Turned the o.d. Down abit to pretty it up. Drilled and bored the center to 2.200". Started boring a relief groove to 2.375"(threads on spindle don't go all the way to spindle register surface) and stopped.

 

[Alittlerusty]

I agree totally BG now lol

 

[Alittlerusty]

 

[GarageGuy]

I learned internal threading from watching this tubalcain video. It takes some practice. I would do a few smaller pieces, then go for it on your backing plate.

 

[Alittlerusty]

I too figured practice was needed so dug around scrap bin and found a candidate to try first. This came from a bulldozer bottom roller assembly

 

[Alittlerusty]

Knocked the split bushing out and mounted in my 12" 4 jaw bored to size

 

[Alittlerusty]

Next I took a 3/4" piece of round and cross drilled then filed the hole square to accept a 5/16" hss tool , drilled and tapped the end for a set screw, now a home made internal threading tool is born.