Second Operation Lathe

Basically, a second operation lathe is used to perform turning operations on a workpiece which has already had some work performed on it in another lathe. Often, the second operation is used to finish the end by which it was held in the first machine.

A second operation lathe will not be likely to have a tailstock, (although it may have a bed turret), and it may not have thread-cutting capabilities.

Before I got my 12x24" Clausing, which could handle the stock through the spindle (and which has both a bed turret and a tailstock, and thread-cutting capabilities), what I used to do to produce one particular part was:

1) Cut workpiece to length from round bar stock (3/4" brass, FWIW) using a bandsaw with a length stop. 2) Mount that in a chuck with soft jaw turned to fit and to provide a depth stop, and face the workpiece, followed by center drilling, through drilling, and tapping. This was done in a Taig, FWIW, for which *all* 3-jaw chuck jaws are soft jaws -- at least from the manufacturer. I simply ordered a few extra sets for special work like this. 3) I then moved the workpiece to a Compact-5/CNC, with a special arbor fitted with a threaded extension to match the thread in the workpiece, and a cam to lock the workpiece firmly against the arbor.

The CNC lathe was programmed to face the now free end, turn the OD down to 5/8" (except for a flange left at the end), thread it at 5/8-27, cut a relief groove att he flange, since threading all the way to the flange was not possible with the existing threading tool.

The Compact-5/CNC was being used as a second-OP lathe, even though it was not designed to be one.

As it worked out, the CNC lathe could turn out its more complex half of the job (without my hands on it) in about the same time that it took me to perform the simpler first operations on the Taig (the bandsawing was done for the whole length of rod before the other work started). Thus, running the two machines at the same time, I was able to complete a lot more parts in a given time.

Normally, a second operator runs the second-OP lathe, and a third (lower-paid) person carries the workpieces from one machine to the other.

As it turns out, I now make that part entirely on the Clausing, using the bed turret. A box tool turns the diameter down. The center-drilling, drilling and tapping are done by other tools held in the turret, and the external threading is done in a single pass with a Geometric style die head, rather than having to be single-pointed with more passes on the little CNC lathe. The only thing that the cross-slide does is cutting a groove to end the threads at the flange, and parting off the finished object.

Also -- the Clausing even has a station free for a knurling head, so the edge of the flange is knurled as well. Next batch, I will be trying out a nice cut-style knurler, which looks kind of like a 3-jaw chuck.

So -- essentially, a second-OP lathe is defined by its use -- but its normal use means that there are some features which are necessary in a toolroom lathe which are not necessary in the second-OP lathe.

I consider having the bed turret as an alternative to the tailstock on the Clausing to be quite useful. I currently don't have room for a second-OP (by design) lathe. The Compact-5, and the Taig are both quite small machines -- a maximum swing of 5" on the Compact-5, and the Taig is a machine which I can run in my lap if I so desire.

If you have production runs which could benefit from having a second-OP machine -- you can get them for a lot better prices than a toolroom lathe.

And it may be worth while just for those occasional things which have to be done while your main lathe is already tied up with another project -- if you can live without a tailstock. If it has a turret, it can use Geometric die heads (or other similar designs) and do threading even without a longitudinal leadscrew. But beware that you know what you *aren't* getting with a second-OP machine. I've never had a chance to get my hands on one designed from the ground up as a second-OP machine, so there are probably features which I don't know about, and hopefully people who have used them will toss in information -- but at the moment, I don't see any other replies yet which have reached my news server.

Enjoy, DoN.

Don,

My sincerest thanks for shedding additional light on the subject. I saved a copy of your response.

Thanks again.