Published 04/14/2025

The Value of a Third Turret for Multitasking Machines

A third turret might be the solution to achieve a 50/50 cycle-time balance between a machine’s main and sub-spindles.

Editor-in-Chief, Production Machining magazine

One option for shops seeking to realize high-volume production of feature-rich parts is to use multitasking machines with two spindles and two turrets, which can provide complete part processing in single setups. Perhaps the best scenario when programming those machines is to achieve a 50/50 cycle-time balance between the main and subspindles for optimized throughput.

Unfortunately, depending on part features, establishing that balance is often challenging, if not impossible. However, machines equipped with a third lower turret can help to achieve it.

For example, while the two upper turrets are each dedicated to the main or subspindle, the third lower turret can be in the cut at either. As such, whether the cycle times run longer on the main or subspindles, the lower turret can work together with either to help boost machining speeds. Consider that on a twin-spindle/twin-turret machine, if a part cycle time is 75% on spindle one and 25% on spindle two, a three-turret machine could help reduce that 75% down to 50%.

While twin-spindle/three-turret machines can provide these and other benefits, shops must first consider part volumes and how they’ll process feature-rich parts through the machine. Regardless of the amount of part features, shops must have high enough part volumes to justify setting up a three-turret machine and running it nonstop sometimes for weeks at a stretch.

Once it’s determined that volumes are high enough, shops need to think about part processing. A good starting point is to consider how a part would be run on a two-turret machine, then figure out where (main or subspindle) the third turret could help reduce cycle times. However, programmers must be certain there’s room for two tools to work on the same part simultaneously for performing such operations as pinch turning at one spindle, then pinch milling on the other spindle. Or, having an upper turret and the lower turret drilling multiple holes at the same time and at the same spindle.

When it comes to multitasking machines, such as those with twin-spindles and three-turrets geared toward parts with many features, shops might still be a bit uncertain as to what constitutes a feature-rich part. Basically, these types of parts — which might have multiple surface finish requirements — could have a variety of complex, detailed and intricate features or geometries that require discrete, precision machining operations such as turning, milling, drilling and tapping. Examples include undercuts, threads and holes of various types (blind, tapped and countersunk) and sizes along with slots and radii.

A good starting point for part processing is to consider how a part would be run on a two-turret machine, then figure out where (main or subspindle) the third turret could help reduce cycle times.

Feature-rich parts also require numerous tools and tool changes, and a lower third turret increases a multitasking machine’s tool capacity. In some instances, a machine can have as many as 36 tools at 12 tools per station or 16 tools per station for a total of 48 tools, and all those stations can be live. Plus, with such turrets, tool change times can be faster compared to machines with carousel-type automatic tool changers.

Manipulating lower third turrets for optimum throughput does take some programmer experience and knowhow. To help with programming, some machine controls, like Mazak’s Mazatrol SmoothG3, will display a breakdown of each turret. This enables operators to, offline, see exactly what is happening at each location/turret, switch lower-turret operations between the two spindle locations if necessary, and then perform a simulation to determine if the choices make for optimal throughput.

Other effective control features are wait commands and dwell time functions. Wait commands enable programmers to pause the lower turret or have it wait before carrying out an operation. For instance, the lower turret might wait while an upper turret indexes to a new tool. Then, the two can work together once the upper turret is ready.

Essentially, the dwell time function gives programmers the ability to feed the lower turret at a different rate than the upper turret to optimize part processing before making the first cut. With two turrets working on the same spindle, shops need to determine a happy medium feed rate for both turrets that coincides with the turning spindle speed.

For example, the upper turret is OD turning a part feature that is 4 inches in diameter while the lower is working on a 3-inch-diameter feature simultaneously. In such situations, the dwell time function enables the two turrets to feed at different rates according to the chosen turning spindle speed.

It’s said that 90% of jobs done on twin-spindle/three-turret machines involve producing parts from bar stock, which allows for generating multiple part variations from a single bar size. Usually, the maximum bar stock capacity for those machines is 4 inches in diameter. With this capacity, shops can reduce setup times for part sizes that vary from 3 to 4 inches in diameter, because they eliminate the time spent changing out bar stock sizes, and the workholding on the first turning spindle doesn’t have to change, saving even more time.

In essence, shops can produce entire families of parts with minor variations and do so with zero changeovers. Yes, for the smaller-diameter part versions, the cycle time might be a bit longer because of the additional stock removal. However, the time involved with setup changeovers is eliminated, meaning the machine can run continuously.

An end-of-bar remanent control function activates a machine disposal bucket so that the remanent is ejected from the work envelope, is delivered down a shoot and exits the machine. This eliminates the need to decide exactly what to do with the remanent and keeps production moving smoothly to the next new bar.

Running machines continuously, however, also requires effective chip control. To control chip generation and prevent problems such as bird nesting, Mazak developed what is known as an oscillating cutting function for its twin-spindle/three-turret machines such as the company’s HQR-200 and 250/3 NEO. The function oscillates the cutting tool, which breaks up chips into smaller, more manageable sizes for evacuating them out of the machine as efficiently as possible.

Other helpful features for continuous machine operation are a part unloader and some type of bar stock remanent control. In nonstop production, getting parts out of the machine is critical, so fast unloaders are a must. If they aren’t, the machine has to stop and wait.

In addition, when running bar stock, the goal is to end with the shortest remanent possible. Then, when the machine gets to the end of a bar, the question becomes what needs to be done with the remanent. Shops might choose to cut it into chips or turn it down to a certain diameter, transfer it to the second spindle and unload it. A more effective choice might be to use an end-of-bar remanent control function.

This function activates a machine disposal bucket so that the remanent is ejected from the work envelope, is delivered down a shoot and exits the machine. This eliminates the need to decide exactly what to do with the remanent and keeps production moving smoothly to the next bar.