Buying a Lathe: Turrets and Live Tooling
When buying a lathe, after considering what sorts of workpieces the machine must be prepared to handle, it’s time to ponder tooling options.
One important consideration when purchasing a turning machine concerns tooling. The number of stations in the tool turret must be adequate for the number of tools needed 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 is 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.
This is part two of a four-part series about buying turning machines.
- Part one: Buying a Lathe: The Basics
Find more insights about acquiring a new machining center by visiting the Techspex Knowledge Center, “Guide to Buying Machine Tools.”
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