Give CNC lathes an uptime makeover

I once thought nothing of boring a new set of top jaws. Just remove half a dozen cap screws, take the old jaws out, bolt on fresh jaws, attach a spider or boring ring and crank the hand wheel until the part fits. Setups were long in the 1980s and my boss considered 2 or 3 hours of downtime each day a normal cost of business.

Today, shops might opt for a quick-change chuck. Simply twist a few screws and load a new set of top jaws. And, compared to the hours of lost production in the prehistoric days of paper tape and brazed carbide cutting tools, dropping eight to 10 grand for a quick-change chuck is a no-brainer.

All images courtesy Hainbuch America

Swapping a Centrotex chuck takes under a minute, and is guaranteed to 5µm runout and repeatability, according to Hainbuch America.

Exploded view of Hainbuch’s TOPlus collet system together with a Centrotex masterplate.

But because of different workholding requirements, sometimes even a quick-change chuck can’t cut the mustard. Collet chucks, faceplates and expanding mandrels are just some of the other workholders found in most turning departments, and swapping one out means muscling 20 lbs. or more of an uncooperative steel chuck out of a CNC lathe before mounting whatever workholding device stands at bat next. This is a something that even the speediest setup man needs 20 minutes to accomplish.

“Our industry has worked extremely hard over the last 20 to 30 years to take minutes or even seconds out of cycle time. What we didn’t do is figure out how to take minutes and hours out of changeover time,” said Jeff Estes, director of Partners in THINC Technology Centers for machine tool builder Okuma America Corp., Charlotte, N.C.

Because customers demand products with short lead times and single-digit lot sizes, the time it takes to set up a machine frequently exceeds the time needed to machine the parts. Estes said: “For a lot of our customers, their first part is their only part. They are making extremely difficult, challenging parts. Production output is always going to be based on the weakest link in your system, and that is typically the setup.”

Hainbuch America Corp., Germantown, Wis., addresses this weakest link with its Centrotex quick-change workholder. Guri Singh, Hainbuch’s CNC production manager, said: “Centrotex is a way to quickly change the entire chuck, rather than just the jaws themselves. It works off a pair of male and female tapers separated by precision ball bearings. Similar to the way a Sandvik Coromant Capto system works, everything is manufactured in such a way that the deformation of those three components is very precisely controlled, giving you extremely rigid clamping together with accuracy. It’s a mechanism difficult to manufacture but very simple and robust to use.”