Shop Doc – When to go Hydromat

Dear Shop Doc,

We are a new job shop looking to add some equipment. We are wondering whether we should invest in used rotary transfer machines like a Hydromat Legacy or stick with multi-spindles. When would we want to use a rotary transfer machine versus the traditional multi-spindle?

When to go Hydromat

Dear When to go Hydromat,

Great question. While rotary transfers and multi-spindles can produce the same parts, a good used Hydromat Legacy will cost from $80,000 to $180,000, while a used multi will cost less than half of that. So it’s important to figure out which machine suits your specific job.

The following are some important factors to consider when choosing which machine is best suited to accomplish the most productive end result. This is not limited to just the Hydromat or multi-spindle. In some cases a CNC Swiss may be a viable alternative.

Quantity of parts: Hydromats are ideal for high volumes. For jobs making less than 20,000 pieces, the multi-spindle is the right choice. This is the case even for complex parts, because with a few exceptions they are easier to retool than a Hydromat Legacy. This is because there is more open space in the machine, which makes the spindles easier to access.

Complexity of parts: For machining complex parts that are hard to hold in collets or chucks yet can be run complete by holding onto the bar in a multi-spindle machine, it makes sense to use a multi-spindle, because there is more holding surface to grip.

But Hydromats are more versatile, because they can have 10, 12 or 16 tool spindles horizontally, or up to eight vertically. For example, machining off-center holes, radial or axial, on center holes, drilling four holes radially and not all the way through, or machining an eccentric dimension on both sides of a shaft, would be easy on a Hydromat. But doing those operations on a multi-spindle would likely be quite difficult and would add significant cost because of high cycle time.

Shape and type of material: The Hydromat is more versatile for machining different material shapes than the multi-spindle because the bar remains stationary rather than rotating. For example, machining hex material on a multi-spindle machine produces an extraordinary level of noise, while on the Hydromat there is very little or no increase in noise. The type of material you are machining should not make a difference when choosing between the multi-spindle and a Hydromat, as long as the material removal is within the limit of the motors on the Hydromat.

Tolerances: In most cases both multi-spindles and Hydromats hold comparably tight tolerances. One big advantage with a Hydromat is that it can turn a part around and machine the other end with a number of features as long as there are free stations. Back-finish on multi spindles with close tolerances is more difficult but usually required on one or more operations after it is partially finished.

However, multi-spindles have an advantage when you need to make a number of recesses (grooves) with a tight concentric requirement. In this case, it is more difficult to hold on the Hydromat, especially when the grooves are larger. It is hard to beat a form and shave tool, if it is in capable hands.

It’s also important to note that a lot of shops have been successful in combining both types of equipment by pre-machining or roughing parts to a semi-finished stage on a multi-spindle and then finishing them on a Hydromat.

Hydromat Rotary Transfer Machine (Photo from

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