Manual grinding to millionths

Manual grinding to millionths

Precise grinding is a must at Rotech Internationale of Porter, Tex. The company makes premium-grade live centers and live chucks for the metalworking industry. These products require finished tolerances in the millionths. To meet such demanding tolerances

Rotech grinds its live centers and live chucks on Ecotech universal manual grinding machines, holding tolerances to within millionths of an inch.


Precise grinding is a must at Rotech Internationale of Porter, Tex. The company makes premium-grade live centers and live chucks for the metalworking industry. These products require finished tolerances in the millionths. To meet such demanding tolerances and reduce scrap rates to zero, Rotech depends on a pair of low-cost Ecotech manual grinding machines.

The first is an MB1432B with a 12 60-in. work envelope for the shop's smaller jobs, and the second is an M1450B sporting a 20 80-in. envelope for large parts. Rotech does all the grinding for both product lines manually on the Ecotech universals. This includes roughing and finishing, straights and tapers, and I.D.s and O.D.s. Rotech's grinders feature universal workheads, hydrodynamic wheelhead spindles, and hydrostatic way lubrication, all mounted on a heavy, aged cast iron base with hand-scraped ways. Standard machine packages come with leveling plates, 10,000 and 15,000-rpm spindle cartridges, I.D. spindle arbors, coolant systems, wheel-balancing stands and arbors, and peripheral wheel dressers. Key options include variable-speed drives, automatic wheel balancers, digital readouts, behind-the-wheel dressers, and a variety of in-process gaging packages.

The Rotech machines have special built-in fixturing with sine bars in the workholding chucks. This lets company machinists gage part tapers to ASME and DIN standards. They do so while the parts are still in the chuck.

"Gaging in the chuck is important for good process control at tight tolerance levels," says Dale McMillian of Rotech. "It eliminates a principal root cause of system error and saves a lot of setup time. Our guys grind, check, and immediately grind some more if necessary with no time lost in re-chucking, touching off, and offsetting."

Rotech makes its live centers and live chucks in all main taper styles.

But perhaps the toughest one to grind is an HSK on a live chuck. The challenge, according to McMillian, is holding an extremely close tolerance between the part's straight bore and caliper angle. "This dimension is almost impossible to measure without DIN-certified gages," he adds, "and critical to drawing in the tool it holds. If it is not held to one-tenth in either direction, the tool-holder and spindle will experience stress, which can trig-ger a false signal that prevents the machine from starting."

Rotech typically grinds these HSK chucks and most other products in 50-piece lots. They are completed in three chuckings, all on the same Ecotech grinder.

The first step is roughing and finishing all straight O.D.s and faces on all 50 parts. Typical amounts of material removed are 0.002 in. on diameters for roughing and 0.001 in. (+0.0001 in./-0.0000 in.) for finishing O.D.s.

Secondly, machinists reset the wheelhead, switch work-head fixturing, re-chuck, and grind the I.D.s and tapers of the machine end. They then switch workhead fixturing, reset the wheelhead, turn the part around, and grind all I.D.s and tapers of the tool end.

Lastly, to ensure proper mating when the part goes into service, Rotech makes the final grind of the taper in a DIN 69063-certified HSK receiver. Often the amount of material removed is literally too small to measure.

"Such feather-like passes on hardened material are as much a challenge as heavier cuts," explains McMillian. "Unless the grinder's structure is absolutely tight and rigid, it will deflect rather than make the needed feather cut. The Ecotechs handle these light cuts as well as machines costing more."

Since the Ecotech grinders are all manual, Rotech depends on its operators' skill and dedication. As a result of partnering them with the Ecotech grinders, scrap rate is literally zero, says McMillian.

Ecotech Machinery Inc.
Lilburn, Ga.
www.ecotechmachinery.com

Hide comments

Comments

  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.
Publish