Consider The Humble Chuck

Would you ever think that by changing the way you chuck components in a CNC turning center you could cut operation time by three-quarters? This is a must-see.

Lancashire in England is either associated with a seaside resort on the West coast of the Irish Sea—Blackpool, which may soon be the Las Vegas of England after relaxing the gambling rules—or with the legendary "dark satanic mills" of the mostly dead textile industry.

Those who do not know this county may not associate it with precision turning, but there are a lot of precision screw shops there. One in particular, Luneside Engineering (near the River Lune), had been machining aerospace retaining sleeves from 3 feet 3 inch (1 m) lengths of stainless steel bar.

The following may sound familiar. The sleeve needs to have its OD turned; the ID drilled and bored; the OD and ID rough-threaded; and a slot milled in one end. The sleeve then has to be turned around, back-machined, and mounted on a mandrel for finish-turning the OD thread.

It may be no surprise that the main turning operations were carried out in CNC lathes and the slot was milled in a milling machine. Also, a manual center lathe was used to finish-turn the OD thread.

So the company decided to get a mill-turning center. But it was still not possible to do the job in two operations instead of three. The "Achilles heel" was trying to access the job with turret-mounted tooling when using the more traditional in-spindle collet chuck system. Also, the changeover time from one collet to another was time consuming.

The turning center supplier mentioned the German Hainbuch front-access collet chuck system. The nose of the compact collet chuck holder protrudes more from the front of the machine spindle than in-spindle systems. For Luneside, it meant that the turret tooling could get to the collet face without colliding with the spindle face.

Consequently, all the turning operations and slot milling and end-finishing could be done in the mill-turning center, leaving only a second operation—­the finish-turning of the threads on the mandrel—to be done in a second setup. Collets can be changed quickly.

The result was that the total operational time involving two setups is 10 hours, versus 42 hours before.

On another note, have you ever wished that you could program your lathe chuck? Or do you think I am kidding? Well, a number of Swiss cylindrical grinding machine makers such as Tschudin have offered such a product for holding "difficult" thin-wall shafts. But, the applications are often high value items for the aerospace industry.

Meanwhile, your new operator has deformed that thin-wall component again.

Well, try this. Pratt Burnerd launched its PPC, or programmable powered chuck, at the U.K.'s MACH 2002 machine tool show in Birmingham, U.K., in April. You can program jaw stroke, jaw engagement, backstop, gripping force and speed of movements. Pratt Burnerd has introduced the ability to disengage the spindle drive, under operator command, and re-direct the drive to power the chucking system. In the case where the PPC is offered as an option with a Colchester CNC lathe, the control system integrates directly with the GE Fanuc 21i-t CNC. You do not have to worry about extra controllers, data links or power packs.

The chuck has an extended stroke, so it will grip a wider range of work. The grip is also mechanical, rather than hydraulic, and many machinists prefer the set mechanical grip to relying on a sometimes unpredictable hydraulic one. Also, the pressure can be altered during a cycle—ideal if you start out with a solid billet and will end up with a thin-walled component.