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Smallest parts on an ~8" turning center?

jhov

Cast Iron
Joined
Jun 5, 2020
Location
SW Ohio
I'm browsing for an early 90's ~8" turning center (my first, no experience) to turn some shafts 1"D x 14"L, as well as some other parts that fit its envelope. I'm also currently designing a part which will require small custom fine pitch adjustment screws. The screws will be carbon steel and brass and would have a major diameter as small as 0.1" and a length of 0.65", threaded 64 to 80 TPI.

I'm sure the screws are better suited to a swiss style machine, but I can only buy one machine. Could it be made reliably on such a machine with a collet chuck? Would balance turning with opposing turrets help with something this small? Or is the 4000-5000rpm spindles too slow for such small work?
 
I've held down to 1/8" in soft jaws on an 8" chuck.

Not that hard to do, you just have to do some jaw prep,
and then cut them flying, and NEVER EVER close the jaws
without a piece of material in there.

Steel screws, just buy 1/4" or 3/8" stock which is super easy to grab.
The material cost won't kill ya.

Not a big deal. You'll be fine.
 
Are you sure you want an 8" ? I had a South Bend Cyclone with a 6" forkhardt, would do all the work you described and be happy at it. I did run some bigger parts once in a while, took a lot of little cuts but worked okay for onesy-twosies. It was a pretty nice little lathe, actually. 8" is kind of klonky for tiny parts.
 
When I refer to an ~8" turning center, I mean the 15-30hp, 4000-5000rpm machines commonly used with around that size chuck; not limited to only using an 8" chuck on the machine. Sorry if I'm using the wrong terminology, I'm picking things up as I go.

I figure a larger machine is better to a point, as you can work smaller parts in a larger machine but not vis versa. Having no experience, I'm just not sure how small is too small for a larger machine or what special considerations I need to take into account for turning something so small.
 
If you don’t run too many, I’ve chucked a straight shank ER collet holder and used that to hold small dias.
 
The collet chuck is definitely something to look at. Your RPM might have limits depending on what your doing. But much easier to do small work on a bigger machine using that option.
 
I used to run a 120" leadwell cnc with a max turning diameter of 32" It had a 15" chuck.
I also used to turn tiny parts on that very same machine.

Git-R-Done!
 
I bought a 5c collet chuck on ebay for pretty cheap for my qt15 for exactly that reason. It’s very handy for small parts. Easier to get in tight. I also have an s20 pad chuck and a 3 jaw. Sini do lots of small stuff the two collet chucks get the most use.
 








 
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