Techspex

FEB 2018

Techspex provides metalworkers free research and analysis tools to help them find the right machine for their job.

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3 techspex.com | The Machine Tool Search Engine techspex.com | The Machine Tool Search Engine to process the particular part. Most lathes come with a 10- or 12-position, drum-type turret capable of using bolt-on- style toolholders. For three- and four-axis lathes, a wide variety of VDI and BMT tool stations are available to accommodate 6,000- to 12,000-rpm rotary tools. This type of tooling is commonly referred to as live tooling. Some stations for live tools have an internal gear train called a doubler to increase the rotational speed of the cutting tool. Static toolholders, driven toolholders and angle heads also can be used in a lathe's tool turret. For additional tool capacity, optional half-index turrets can provide 24 stations (12 for turning and 12 for live rotary tools). Swiss-type machines use smaller toolholders and will accommodate more tools. Some Swiss machines offer tool turrets with as many as 60 stations. Y-axis functionality on a lathe accommodates a greater range of part geometries, and also will enable multiple tools, such as two or three different drills, taps or boring bars, all on the same station. The choice between VDI or BMT tooling is really a matter of preference. Both have advantages and disadvantages. Using VDI tooling is a bit more cumbersome, because it is necessary to indicate the tooling to make sure the cutter is on centerline. However, VDI tooling can be quicker to set up, especially if the tolerances are not close. Some tooling manufacturers offer handy adjustments for VDI tools. More users prefer BMT-style turrets that use a keyway underneath to engage the turret. If the tooling is removed, it's not difficult to replace it and hold repeatability in tool position. VDI or BMT tooling is available in 30-, 45- and 55-mm sizes to match the size of the work being performed. Much like selecting toolholder size on a VMC, the larger the work and the more material being removed, the bigger the lathe tools must be. Note that on a lathe, the turret can accommodate more tools if they are small. Belt-Driven or Direct-Drive Spindles The spindle on a turning center is either belt- driven or direct-drive. Generally, belt-driven spindles represent older technology. They speed up and slow down at a lower rate than direct-drive spindles, which means cycle times can be longer. If you're turning small-diameter parts, the time it takes to ramp the spindle from zero to 6,000 rpm is significant. In fact,

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