To Push or Pull barstock

Feb. 1, 2000
Basing the decision on price alone could be a mistake.

Basing the decision on price alone could be a mistake.

While most pullers work off of springsteel pressure, Royal's Grippex barpuller is coolant-actuated.

A standard barpuller grips barstock using the pressure from springsteel fingers.

As the bar rotates, the cutting tool on Royal's combination-style barpuller feeds in and cuts off the finished part.

Features such as quicker stock-diameter changeovers, lower prices, and less required floorspace make today's barfeeders less dedicated to high-production-run jobs.

Although not as old as dirt, barpullers have been around for awhile. They are simple mechanical devices that grip and pull barstock into a lathe. The barpuller's automated counterpart is a barfeeder, which, instead, pushes barstock. Many shops base the decision on whether to push or pull barstock on price alone. However, as product innovations change the playing field, the capabilities of each take on greater importance.

Barpullers are a simple way to automate a CNC lathe, says Tom Sheridan of Royal Products in Hauppauge, N.Y. There is no electrical tie-in to the lathe's control and no wasted floorspace. They easily move from one machine's turret station to another's, and a single puller grips a wide range of stock diameters.

Royal offers four configurations of barpullers: compact, heavy duty, combination, and coolant-actuated. The first three styles include jaws mounted on springsteel that feed in from the side and pull stock along the Z axis. Users set the gap between the jaws slightly smaller than the bar-stock O.D. That way, the springsteel fingers expand as puller jaws slide over/under the stock. The pressure is enough to grip and pull the material to the next desired length. However, the most advanced models of barpullers are coolant-actuated and combination styles. These two tend to move barpulling towards the production-run arena.

While most pullers work off of springsteel pressure, Royal's Grippex barpullers are coolant-actuated. They are programmable in that a lathe's coolant can be set to turn off and on, thus actuating the puller. Coolant flows through the puller and pushes a piston that closes the fingers around the material. As compared to the other three barpuller styles, the coolant-actuated model does not retain the last piece or remnant of barstock but drops it due to a positive spring release.

A drawback to barpullers is that they occupy valuable tool space in the turret, says Sheridan. For this reason, combination-style barpullers perform both barstock advancement and cutoff. Basically, the barpuller has an attached cutoff tool and occupies the cutoff turret station, which is, for the most part, already a standard tooling location. This configuration also saves cycle time because the machine does not have to index between cutoff and pulling.

Why a puller?
The most common answer given is price. "For less than a $1,000, a shop can automate its CNC lathe," says Sheridan. But besides that, most shops choose a barpuller for short-run, intermittent barstock jobs.

Mound Manufacturing of Miamisburg, Ohio, sees a wide variety of jobs, according to operations manager David Burden. Set-up and tear-down times are important, so the company went with a barpuller for its simplicity. It is on a machine set up for low-volume work from short barstock. Although jobs are short, Mound still wanted bar advancement automated, as did another jobshop, Ritter Machine in Dayton, Ohio.

Many of Ritter's jobs involve thin parts, such as washers. For these, the shop may get between 250 and 300 pieces from a 4-ft bar. Such jobs are perfect for the company's Okuma LCN 8 lathe fitted with a standard Royal spring-steel-model barpuller. "On some jobs, our machines with pullers operate up to a half an hour before needing operator intervention," says Tim Ritter, company owner.

Specialty Manufacturing also barpulls because of the type of parts it runs. The San Leandro, Calif., company produces jet conversions for outboard boat motors, and the process requires making new drive shafts out of mostly stainless steel. Because these shafts are threaded on the ends, Mark Miller, a foreman at Specialty, uses two Royal coolant-actuated barpullers on the shop's Daewoo machines, models 8HC and 200M.

According to Miller, a standard puller could damage the shaft threads, but the coolant-actuated one doesn't because its gripping pressure is adjustable. By bleeding off a certain amount of coolant going to the puller, Miller sets its grip so as not to damage part threads.

Even though Specialty works with 10 and 12-ft bar lengths, it still chose to barpull because drive shaft dimensions change so often. Lengths can vary from 25 to 31 in., and diameters are constantly changing. Lot sizes run anywhere from 10 to 75 pieces, and in Miller's opinion, barfeeders just wouldn't work well for this type of operation.

Often-changing sizes on part diameters are also the reason why Laveen Machine and Engineering of Burnsville, Minn., pulls barstock. According to Bob Jones of Laveen, the company's coolant-actuated barpuller, running on a Mazak lathe, provides a wider range of gripping diameters as compared to a barfeeder. Royal's coolant-actuated puller, for instance, accommodates diameters from 3 /16 to 3 in. Covering such a range with a barfeeder, he adds, would require changing bushings or some such device.

However, barpullers do need a certain amount of stock left sticking out of the collet for gripping. Pullers can grip as close as 0.250 in. away from a lathe's collet or chuck. But Laveen alters the fingers on its puller to go down to 0.100 in. Barfeeders, on the other hand, require no stock for gripping.

The shop runs about 15 different jobs with all different size material through its puller-equipped lathe. "For our limited quantities," says Jones, "pullers are the best choice. We program the puller station once, and with minor adjustments, it's always ready."

Taking the next step
"If a shop is using barpullers, the operation of feeding out the stock is already automated. But improving cycle times even more, means also automating bar loading," says Ray Varady of IEMCA in St. Louis. For this, the next logical step is a short barfeeder, also known as a spindle loader.

These run only spindle-length barstock, as does a barpuller. But shops running barpullers must manually load bars into the lathe headstock, while a barfeeder holds multiple bars for automating both loading and feeding.

But more importantly, says Steven Brown, vice president of operations at SMW in Santa Fe Springs, Calif., today's barfeeders include features that make them less dedicated to just productionrun jobs. These include quicker stock diameter changeovers, lower prices, and less required floorspace. SMW's Spacesaver barfeed model, for instance, needs only a 4 8-ft section of floor, and IEMCA's VIP 70 short loader fits into a 5 5-ft space.

At Ritter Machine, parts per job can run into the thousands, and the company uses a barpuller. Tim Ritter says he might consider a barfeeder if he had more 10,000-piece jobs. But Brown of SMW comments: "Whether a job consumes three or three hundred 4-ft bars of material, the same barfeed investment provides unmanned operation for both."

Barfeeding lets shops run the 5 to 10-part jobs during the day and set up the big production runs for overnight. Because today's barfeeders can compete with pullers when it comes to smaller lot sizes, the smart investment is a barfeeder for when high volume jobs do come along, advises Brown.

A single barfeeder may not handle as wide a stock diameter range as a barpuller, but barfeed changeover times have improved, says Varady of IEMCA. Diameter changeovers, for the most part, take three to five minutes. And, he adds, that is quite comparable to manual-loading times.

For example, the Instrument Development Corp. (IDC) in Mukwonago, Wis., has five Multifeed magazine short bar loaders from Lexair Inc., Lexington, Ky. The systems feature a remote hand-held pendant control for quick and easy setup. IDC gets runs going in as little as two or three minutes. And the Multifeed system's next-bar insert and start time is about 10 sec.

Barfeeders also save a turret station and will not damage potential part surfaces. Mound Manufacturing, for example, works with a lot of exotic and expensive materials for the aerospace industry, so waste is a big concern. The company can't have its spring-steel barpuller scratching part surfaces. For this reason, some jobs run on a machine with a barfeeder.

Running spindle-length barstock means better part support for more accurate machining. But such innovations as FMB Corp.'s process, called TurboCentric, also improve support and accuracy. The process floods the feed channel with oil, and the stock's rotation creates turbo forces that eliminate vibration. This ensures quiet operation, less chuck wear, and better precision.

To run parts at high rpm, IDC uses spindle-length barstock together with a Lexair short barfeeder. The company's solenoid parts were once made from standard 12-ft aluminum bars, but because of increasingly tighter tolerances, says owner and CEO Kevin Sinnett, IDC switched to short bar lengths and a short loader.

"When you try to run a 12-ft bar at 6,000 to 7,000 rpm, the vibration makes it difficult to hold tight tolerances, plus, over time, it can destroy a machine tool," remarks Sinnett. Lexair's Master Spindle Reduction Liner, as an option on its short bar loaders, prevents whip while running a short bar at maximum rpm. This liner, combined with a set of customer-supplied bushings, handles most bar sizes without separate reduction liners.