Aggregates: The Forgotten Tool
An aggregate or angle head is a device that is attached to the spindle drive of a CNC to allow the user to rout or drill at different angles other than where the spindle is orientated. They are almost always used in conjunction with a tool change format like HSK, ISO or BT.
The use of aggregates on CNC machining centers greatly increases the versatility, capability and the overall value of an already very expensive machine.
CNC spindles in most all cases are always mounted at a right angle to the machine table so there are two distinct reasons to add aggregates to your machine – to change the direction of the spindle (meaning the way the tool is orientated to the workpiece) and to add a new operation to the machine, like mortising, tenoning, sawing or cutting soft materials with a reciprocating knife.
Aggregates and the C Axis – Having a C or a fourth axis on a CNC machine is not necessarily a requirement for the use of aggregates. A three-axis machine could make very good use of a four-way, 90-degree aggregate. This would allow the user to machine in X+ and X-, also Y+ and Y-. However, many aggregates are relatively useless without a C axis.
Take, for instance, a moulder unit. This is an aggregate that can accept profile ground knives to produce curved mouldings such as elliptical or round window casings. This operation absolutely requires an interpolating C axis, allowing you to “steer” the aggregate around the curve of the casing. If a machine does not have a C axis, it will need an aggregate anti-rotation ring or a stop block. This is the device that the torque pin of the aggregate fits into, preventing it from spinning around like a Whirling Dervish on caffeine when you start the spindle motor. If you are not sure if you have the anti-rotation device, call your manufacturer.
But getting back to productivity, let’s take the example of a standard 15-piece stile and rail door. Every operation — raising the panels, doweling or mortising the joints, sizing the assembled door, mortising the lock recess and routing the hinge pockets — can be complete with aggregates on a CNC. What’s required is a horizontal drilling unit for the dowels, a horizontal mortising aggregate for the square holes, a sawing unit for cutting the rails and stiles to length, a 90 degree aggregate for cutting the tenons and a lock recess aggregate for both the deep (lock) cut and the hinge pockets.
If you are using your CNC for nested-base cabinet parts, you have probably not read anything so far to justify the use of an aggregate. But have you ever heard of a floating aggregate? This is a device that, regardless of how your panel might vary in thickness, will always maintain a precise depth of cut on the part. It can be used for precision dovetailing or grooving a tabletop edge to accept a solid wood profile with a tongue. How about compound miter cutting? You can do that, too, with an adjustable-angle sawing aggregate. There is an aggregate available to square up hinge pockets to accept high-end hinges.
A belt-sanding aggregate can sand a door or tabletop edge and an orbital sander aggregate can sand or polish horizontal surfaces, all without moving the part from the CNC. There’s also an aggregate for holding small parts on a vacuum table. Do you see a pattern here?
Heat and aggregate life – Every so often I get asked, “How long can I expect my aggregate to last?” There are two things that will ruin your nice new aggregate — heat and operator error. If you crash it, well, you’re on your own. However, heat, you can control.
Most lubrication will cook off at temps more than 185F, causing the unit to ultimately fail. Heat is a result of excess torque on the gear set, often caused by excessive feed speed, too much chip load or insufficient rpms. While most aggregates use a hybrid grease which liquefies at operating temperature, some will use an oil bath. This works equally as well but has one caveat; oil seals must be tight on the shaft to work, this creates friction which generates heat. As the seals wear, so goes the oil and the result is a failed aggregate.
Oil-mist lubrication is available on some models at a hefty surcharge but you must have an air supply delivered through the “C” axis. That’s the Rolls Royce of lube systems. Almost all aggregates have a temperature strip on the side of the body and it is up to the operator to monitor the unit and make sure it does not overheat. Always partner with a reputable tool supplier to find the optimum tool for your application. They can advise you of the proper feed speeds and chip loads to help your aggregate run within its designed loads.
Noise – Some aggregates can really scream. Those most likely have “Crown Gears” which do a great job at transferring torque at low speeds (<8000rpm) but woodworkers typically run at speeds more than 12,000 rpm. Bevel Gears are the preferred choice here. They run very quiet and have less vibration than their metalworking cousins.
Contact Precision Drive Systems to learn about expanding your shop’s options by adding aggregate heads to your CNC machining center.
Source: Bob Barone has more than 30 years in the woodworking industry as an application specialist. His focus is secondary manufacturing of both panel products and solid woods. Bob is National Sales Manager for Precision Drive Systems of Bessemer City, NC. Contact him at firstname.lastname@example.org. For information also call 704-922-1206 or visit PDSSpindles.com.