[How-To] Indicating a 3 jaw independant chuck

[mksj]

So I do a lot of parts were I am not turning and then cutting off the piece, I also had issues with small diameter work trying to push out between the jaws on my 3J scroll. The 8" Bison combo has narrow jaws and can hold stock down to 0.2" diameter, so even for small work it holds parts much better than my 3J scroll. The Bison combo also repeats to about 0.001" on parts so takes a very small tweak to zero down a part, and I has very low skew when holding parts compared to my other chucks. Typically my 5C is my go to for small work, I may do 8-10 operations on the same piece so it is a lot easier and safer for the hands. I use my 5C about 50%, combo 40% and my 3J PBA scroll maybe 10%. I prefer the holding power of the combo and can work down to surprisingly small diameter materiel, and the flip side with say hot rolled with a rough exterior I can center it up better then a 3J scroll. It all come down to a mater of preference and type of work one does. My forth lathe chuck is the PM 8" 4J independent which I only use for large stock or I am generating a lot of swarf and grit in roughing large stock. The jaws are way too wide and course for most of the work I do. Wouldn't consider a 6J for my type of work.

Combination chuck is a real oddball, but if I just wanted to leave one chuck on the machine as a doall, it would be the 8" Bison combo. I didn't purchase it with that expectation, it was a replacement for the crappy 4J independent that use to come with the lathe and I was not a big fan of removing work from the independent and then having to realign everything with the next op. The lathe also came with crappy 3J scroll (also part of the package) that wasn't even usable. In subsequent years they dropped these chucks for good reason.

Example of a small bronze bushing that needed to be centered and then threaded, also some other machining on the mating part that was not true and so needed to be offset in the chuck to true up. Of note the outer jaws marks on this piece are not from this chuck, it was part of a remnant that was being reused so I could just do a skim cut for the diameter.

 

[mikey]

Looks like the combo is very versatile, Mark. Now I understand why you and Bear like it. Maybe one day one will fall into my lap and I'll get one to form an opinion.

 

[Tim9]

Mark, Bear, I think these chucks are very cool. However, when I first heard of them from Mark, I took a long look at them and decided for myself, they were not worth the cost. I do not own one so my comments are coming from ignorance but it seems to me that a 3 jaw, when used for a first op, would not need adjusting. For a second op, a 4 jaw is faster and should hold more solidly given that the part is held by tension of the screws for each jaw vs a scroll. I can see how putting the part in the chuck would be faster with a scroll but for the rest of it I just don't see the advantage, especially in light of how much they cost.

I can see one if you are trying to avoid having to switch out chucks or if you are dialing the chuck in to make a production run on some nominal stock of the same size but in a hobby shop, these are non-issues.

Again, I am speaking from ignorance. Is my logic off?

It’s heavy. I still need to go to the hardware and get some 7/16”-14/socket bolts. But....damned hurricanes has New Orleans on hold. Maybe tomorrow. But my Rohm chuck is solid steel and incredibly precision. The jaw to body fit is mind bogglingly tight fitting. Like less than 1/2 thousandth in my opinion. Absolutely zero slop anywhere. No comparison to a new Sanoua Chinese chuck.
But yes.....very heavy. It’s an 8” chuck and it’s heavy without the backing plate .

 

[Illinoyance]

Zeroing work with 3 adjusting screws leads to madness. I have 3-jaw adjust true chuck with 3 adjusting screws. I hate having to re-zero it.