Bringing Short Run Turning To Bar Machines

Fast job changes on a bar-fed CNC lathe is just wishful thinking if it takes forever to change over the bar feeder. Swiss-Tech Inc., a Delavan, Wisconsin screw machine shop that specializes in Swiss-type parts, was mindful of that fact when it purchased its Star CNC bar machine.

Case Study From: 9/1/1995 Modern Machine Shop

Fast job changes on a bar-fed CNC lathe is just wishful thinking if it takes forever to change over the bar feeder. Swiss-Tech Inc., a Delavan, Wisconsin screw machine shop that specializes in Swiss-type parts, was mindful of that fact when it purchased its Star CNC bar machine.

Swiss-Tech did not want to marry its new CNC bar machine to the same type of hydraulic, replaceable tube-style bar feeders that it was using on its existing CNC bar machines. As its name implies, the replaceable-tube bar feeder has one, replaceable, bar guide tube, and setting it up to run a job involves replacing the guide tube used for the last job with one that closely matches the size of the bar for the next job.

The replaceable-tube bar feeder is economical. For example, if a shop buys a CNC lathe to run one job, it need only buy a replaceable-tube bar feeder with one guide tube, permitting purchase of the bar feeder for the lowest possible cost.

However, most shops use their bar machines for a wide range of jobs, and eventually purchase guide tubes for their replaceable-tube bar feeders in many different sizes. Over time, a shop can make a sizable investment in bar feeder guide tubes.

One disadvantage, however, is that substituting one guide tube for another is time-consuming: the procedure takes about a half-hour and, because the guide tube is 14 feet long, requires two people.

To avoid saddling its new high-performance CNC bar machine with the problems of a replaceable tube-style bar feeder, Swiss-Tech began looking for a better hydraulic bar feeder. The shop concentrated on multiple-tube bar feeder designs.

Following a tip from a business associate, Stewart B. Dobson, manufacturing services manager for Swiss-Tech, visited a firm that was using a Turnamic horizontal, multiple-tube bar feeder made by Spego Inc., Asheville, North Carolina. Unlike the multiple-tube bar feeders Dobson had previously considered, the Turnamic's guide tubes are arranged side by side with their centerlines in the same horizontal plane.

Mr. Dobson liked the direct, uncomplicated operation of the Turnamic; loading a fresh bar into the unit is a one-man job, done in one minute or less, in response to the bar feeder's highly visible end-of-bar strobe light. The operator simply pulls a lever to release a tapered locking pin at the front of the bar feeder, swings the bar feeder out from the back of the lathe, loads a fresh bar and repositions the bar feed.

Mr. Dobson decided that the Turnamic was exactly what he was looking for. When he got back to the plant, he ordered a three-tube Turnamic bar feeder and arranged with the machine tool distributor from whom he had purchased the Star CNC lathe to install it and a Turnamic bar feeder at the same time.

For Swiss-Tech, the most important advantage of the Turnamic is the speed with which it can be set up for another bar size compared to the shop's older, replaceable-tube, bar feeders: "On a replaceable-tube unit, to change from one bar size to another, the operator must unclamp the guide tube and remove it from the bar feeder," Mr. Dobson explained. "It usually takes two workers to handle the 14-foot tube. After the tube is returned to its rack, it must be wiped down because it is usually covered with oil.

"The operator and his helper then install the guide tube for the next job," Mr. Dobson continued. "That involves aligning the hydraulics ports, installing bearing caps and bolting them down, and accurately aligning the tube with the machine tool spindle the procedure usually takes about 30 minutes.

"However, there are times when we can schedule the machine to run a family of parts that are similar except for size," he continued. "The machine can be loaded with all of the tooling required to machine the family of parts, or provision can be made to quickly change the tooling as a unit, so that we can be running the the next job in a minute with the Turnamic instead of waiting a half-hour while the replaceable-tube bar feeder is changed over.

Swiss-Tech's first Turnamic performed so well with the Star Swiss-style CNC lathe that, one month later, the firm purchased a six-tube, Turnamic 126 model bar feeder to serve a newly purchased Hardinge Brothers CHNC I CNC lathe. The Hardinge lathe is not a Swiss-style machine, but Swiss-Tech was so impressed with the ease of loading, rapid changeover and trouble-free operation that the Turnamic brought to the Star bar machine that it decided that it had to have the same performance for the Hardinge.

Swiss-Tech is currently considering the purchase of still another new CNC lathe, and the odds are good that the firm will be purchasing another Spego Turnamic bar feeder. MMS

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