Production Machining

JUN 2018

Production Machining - Your access to the precision machining industrial buyer.

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to permit installing one or more additional lathes and bar feeders than would otherwise be possible. Many companies that buy spindle-length bar feeders do so because they believe they do not have the room for a 12-foot- capacity bar feeder. However, bar feeder suppliers make the point that once prospective buyers calculate the advantages of the 12-foot-capacity bar feeder over the spindle-length bar feeder in terms of productivity gains and increased material utilization, they somehow find the room for the larger unit. Cutting Speeds Historically, shops that operated bar machines have had a problem controlling the whip and vibration that occur in a long bar when it is rotated at high speed. e main causes of the problem have included difficulty of controlling a closely confined bar rotating at speeds of as much as 10,000 rpm and the lack of uniformity in the bar material itself. Ironically, while lathe builders increased the spindle speeds of their machines to improve productivity, shop owners had to cut back on spindle speed to minimize the effects of vibra- tion on such things as accuracy, surface finish and tool life. Today, the situation is much improved. Better bar feeder design plus more widespread use of centerless-ground barstock have made it possible for 12-foot-capacity bar feeders to feed 12-foot bars as much as 2 inches in diameter at or near maximum spindle speeds. Users of such bar feeders no longer must sacrifice spindle speed to get productivity with good material utilization. Minimization of Spindle Downtime e amount of time required to change over the bar feeder to feed a different bar diameter is another important consider- ation. e spindle-length bar feeder has the edge here because of its simpler operation. Typically, the spindle-length bar feeder can be changed over to run a different bar diameter in 5 to 10 minutes, assuming the correctly sized spindle liner is available. Most of that time is taken up in removing the liner from the lathe spindle and replacing it with one that more closely matches the diameter of the barstock for the next job. e fast change-over time of the spindle-length bar feeder is an impor- tant advantage for shops that do a lot of short-run work. e short bar lengths are lighter, less awkward and less fatiguing to handle than 12-foot bars, which also helps speed the change-over. Changing from one bar diameter to another on a 12-foot magazine-style bar feeder can take from 45 minutes on older units to as little as 5 minutes on newer bar feeder designs. Change-over time depends primarily on whether or not the guide channel, which supports and confines the bar as it rotates in the bar feeder, needs to be changed. If the bar size for the next job to be run is similar to that for the job just finishing, the same guide channel may be used, shortening the setup time. If the guide channel must :: Less frequent manual bar loading associated with full- length, magazine-style bar feeders, often aided by overhead cranes and bundle loaders, can create a safer and friendlier environment for employees. 30 PRODUCTION MACHINING :: JUNE 2018 BAR FEEDERS

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