................Probably 80% of the work I do on my lathe is held in 5C collets. The bulk of work held in chucks is hollowpointing bullet moulds. To go from the 5C setup you have to pull out the collet closer, then knock out the spindle nose adaptor. Then remove the spindle nose protector (it has a L00 spindle nose) and stick the chuck on. Going back to the 5C is the reverse, putting the stuff back.
About a year ago I'd bought a nifty little 4" 4 jaw chuck with a 5C back so it may be used with the collet setup. It's a nice little chuck but if you're going to turn something down several thousandths, and it's not too long a 3 jaw is nice. It's nice because it's fast. It's fast because you don't have to fiddle around with 4 independant jaws.
On the left is the 4" four jaw I bought. On the right is the 5" 3 jaw I adapted. The 3 jaw chuck was from the old *** lathe-mill combo I had first. I say IT was a *** and not all combo machines are but this one was having no power anything and no threading ability, and mainly because everything was loose.
But as it turned out, where ever they sourced this chuck from, they knew what they were doing. It's extremely well machined and finished with it's jaws tightly fitted. The scroll is very smoothly machined, but the kicker is that places that didn't have to be are very well finished. I've wanted to use it for a long time. They don't make a L00 backplate for such a small chuck.
As you can see in both photos, I adapted a 5C blank to use as a backplate. Enco had these on sale and it seemed like a workable solution. This chuck was bolted to a backing plate on the old combo machine's spindle and so it would be to the 5C adaptor. The adaptor was 1"x6" to start with. The chuck requires a locating spigot which is a decimal 4.464" and .217" deep. I turned the 1" thick disk to 1/2" thick then faced it out to leave the spigot 4.465+" for a shrink fit.
Before fitting them together I had to drill the 3 holes in the backing plate. A math wiz I am not. I have a handle on the basics but trying to figure the bolt circle by measuring the chords is way beyond me. I clamped the chuck upside down to a center in the rotary table and with a center in the quill brought it down to center a hole. Naturally the holes were 120* apart so I was now set. I clamped the backplate down against parallels to give the drill bit room for penetration through the plate and drilled the 3 holes.
The backplate went into the chest freezer. The next day the chuck was put into the oven at 400 degrees, with a guide in each hole. Yes, Donna was a work . I turned on the swamp cooler and opened the back door in the kitchen so I had 3600 cfm of airflow through it. I don't find the smell of hot oil and grease offensive, but Donna probably wouldn't enjoy it.
The hydraulic press was all set up with a plastic cuttingboard across the bed. I carried out the chuckbody with hot mitts, and still with the mitts pulled the 5C adaptor out of the freezer (which is like 4' away), set it down over the guides and still holding it ran the ram down and pressed the 2 pieces together.
After removing the guides and bolting them together it went into the lathe and had the adaptor plate turned down to match the chuck body.
It's no big full size chuck but it's size is VERY useable and has allowed me to retain the 5C setup on may occasions. It beats doing that plus humping an 8" 3 jaw chuck up onto the spindle nose.
................Buckshot