6 tips for improving turning operations

Lathe machinists have always had it tough. There’s the risk of cut fingers that comes with long, stringy chips. Bar feeder-induced noise and vibration—leading to problems with surface finish and premature hearing loss. The endless bending over to change inserts and drills, often in tight quarters, and never mind rooting around in the chip pan for parts that went flying during cutoff. Plus, with the advent of multitask machines, lathe operators must now learn about milling.

Fortunately, there’s plenty of good application advice available from cutting tool specialists and equipment providers. Following are six best-practice tips you might not have heard of yet, ones that will help you improve throughput and reduce costs.

Stay Cool

High-pressure coolant (HPC) isn’t a gimmick. It’s been proven to greatly extend tool life and dramatically boost productivity. That’s because HPC is extremely effective at removing heat from the cutting zone. The result is that cutting parameters can, and should, be increased to generate sufficient heat for the metal-removal process to function properly. On the surface, this may seem counterintuitive—why eliminate heat just to create more? But when you consider that cutting speeds with HPC are often five times that of conventional flood coolant, it’s a no-brainer.

High-pressure coolant is extremely effective at removing heat from the cutting zone.
The Sandvik Coromant CoroTurn 300 (shown) is ported to supply high-pressure cutting fluid directly
above and below the cutting zone. All images courtesy of Sandvik Coromant.

If your shop lacks the funds for an HPC system, don’t despair. Surprising gains are still there for the taking if the cutting fluid—even applied at low pressure—is properly directed. A number of cutting tool providers have recognized this and are producing tool bodies, or holders, with integrated cutting fluid ports. These holders can be ported to supply cutting fluid directly above and below the cutting zone, dramatically reducing heat. Goodbye, plastic hoses and copper lines!

Control the Crib

Cost per edge is important, but it’s not the end game. Choosing the right turning tool for the job is. Yet many metalworking professionals are concerned about out-of-control toolcribs, where the number of insert brands and grades seems to grow with each passing year, with some of those inserts probably dating back to the shop’s first CNC machine. Adding to inventory bloat are enthusiastic sales people who stop by with the latest tool body and pack of inserts and add another handful of part numbers for the crib to manage.

An effective tooling strategy requires working closely with suppliers
in a controlled manner, bringing in new technology to address specific challenges.

Granted, these ad-hoc solutions often bring improvement to tool life or productivity, but an effective tooling strategy requires working closely with suppliers in a controlled manner, bringing in new technology to address specific challenges.

That upcoming order of Inconel shafts, for example, is sure to cause you grief. Rather than applying a general-purpose 80° diamond-shaped insert, because you’re trying to avoid adding to the cutting tool roster, invite your trusted tooling adviser(s) for some test cuts early on—and document the results.

Optimize, Don’t Maximize

Once you’ve found the desired turning tool, don’t run it into the ground. Achievement of maximum tool life is a worthwhile goal, but not at the cost of process stability. If an insert can be pushed to produce 30 pieces before it wears or breaks, change it at 25 pieces, even if the edge still looks like there’s some life left. In addition, if you have a cutting tool that seems to last forever, kick up the feeds and speeds. The most cost-effective lifespan for any tool is 15 minutes when running with the recommended speeds and feeds for a particular workpiece material. So, if tools are lasting hours, you’re losing money.

If possible, change all the tools in the turret
at the same time, at regularly defined intervals.

ne often overlooked bit of fine-tuning is to change all the tools in the turret at the same time, at regularly defined intervals. This minimizes the amount of door opening and, properly implemented, provides predictable lengths of time where an operator can leave a machine unattended to do other work. Of course, this requires careful planning and documentation of anticipated tool life and the cutting parameters that have been tried so far.

Some tools are in the cut much longer than others, and no amount of feed or speed tweaking will get them to wear out at the same time. They can, however, be scheduled for coordinated changeover.

If, for example, the rougher looks ready to fail at 18 minutes, the finisher at 67 and the grooving tool at 39, then:

A) change the roughing tool at 15 minutes;