Guidelines to help buyers find the best features in CNC machining centers and to prevent damage during use.

The addition of a CNC machining center can mean a large step forward in terms of productivity, consistency and quality. But what functions should a custom woodworker look for when purchasing a CNC machining center? And how can a woodworker avoid damaging such a serious investment? CWB contacted several CNC machining center manufactures to help compute the answer.

Q. What are the most desirable functions that a CNC machining center should be capable of doing, and what are the most useful options beyond that?

A. Michael Cassell, North American CNC product manager, Holz-Her US: The objective of the CNC is to perform as many machining operations as possible in a single setup. Typical machining centers provide routing capability with automatic tool changing, vertical drill and horizontal drilling. Saw blades, either fixed in the X-axis or indexable, can be added, and additional vertical routers, and horizontal routers can be added as well.

A 360-degree C-axis can increase flexibility, and there are a wide range of aggregates as well.

As different applications require different machining operations, it is important to sit with the machine builder and understand the range of options available.

A. Bill Blackmon, Busellato product manager, Delmac Machinery Group Inc.: In today’s market of custom products with short lead times, versatility and ease of use are two essential characteristics of a CNC machine. To that end, any machine should be equipped with a multi-spindle drill head, with horizontal and vertical spindles, an automatic tool changer and multiple machining zones.

From there, the application needs to be classified as mostly panel processing or mostly solid wood machining. In the case of the former, most custom shops today will look to a flat table router for nesting the panel components. The machine should be equipped with a material handling solution for loading and unloading and have effective dust collection. Simple elevation of component parts on pods for horizontal machining or edge profiling is a must.

For the shop that machines mostly solid wood components, a pod and rail machining center provides the fastest table setup and the widest selection of clamping options. These machines should be equipped with a table set-up system to simplify pod and rail placement with the ability to save the setup electronically for quick recall and/or offline setup prior to machining. The option of horizontal routing with an aggregate or direct-drive horizontal router and C-axis capability opens the door to high-end, complex millwork.

Either type of machine needs powerful programming software with a graphical editing environment that can operate in the office and at the machine. In the case of last-minute tooling set-up changes at the machine, the control software must be able to execute previously-created programs without having to re-generate the programs.

A. Sergio Castro, ROUTECH product manager, SCM Group USA: Nowadays, flexibility is the name of the game, and that is mainly what people are looking for. Arched mouldings, horizontal and angle machining, gang drilling, “V” grooving and nesting are some examples of what a flexible machine should be able to accomplish.

Some of the features that a flexible machine should have are: five-axis head, for unlimited tool angle positioning; CNC dust hood, for better dust collection; large tool changer, to accommodate enough tools as well as large cutters; auxiliary multi-spindle drill unit, for line boring and horizontal construction holes; aluminum table, for stability and a multitude of fixturing options; and an HSK electrospindle, for strength and durability.

A. Cesare Magnani, North America product manager, Biesse America: In today’s manufacturing environment, where most of the components come in batches of one or two, the single most important function for a CNC machining center is the ability to set up quickly, possibly not affecting the machine cycle time at all.

The machine units where this function is most important are programming, tooling and the work table.

Machine programming, despite the increased machine technological content, has become extremely user-friendly and yet very powerful. On tooling, the machine’s tool-changing capacity has been increased and in certain models can exceed 100 tools available at any given time.

The most dramatic innovation in recent years, for reduced set-up time, has been the introduction of full CNC set-up tables, pods and rails. The advantage of this technology is the speed of the setup that can happen without interrupting the machine cycle. Additionally, it takes table setup out of the hands of operators, providing error-proof operation.

A. Michelle Young, operations specialist — Weeke, Stiles Machinery Inc.: A CNC machining center should be able to efficiently handle a customer’s workload as well as take into account future production needs of the company.

First, look at part and raw material sizes. In the case of flat table machines, a machining table that accommodates the most common and accessible material size is first and foremost. In the case of pod and rail machines, size the machine to maximize the pendulum capabilities based on your part sizes. Defining the routing functions, such as toe kicks, grommet holes or architectural millwork, is important. A router motor with higher horsepower may be required. Based on the drilling application, the number of vertical and horizontal spindles that is needed is important to be able to optimize the drilling.

Setup can be a time-consuming process. On pod and rail machines, tape measures, laser alignments and LED light systems can be used to align the rails, as well as the pods on the rails. A tool pick-up stand to load tool holders and aggregates into the router and then to the tool changer provides safety to the operator and is an efficient way to load these items.

Q. What are some tips for avoiding accidental damage to the table?

Cassell: Software today can be used to provide protection. Utilize simulation functions to check tool paths and depths. A simple Z-minus search of code also helps identify incorrect depth calculations.

Lasers can be used to position consoles, vacuum pods and to trace or project the part outline. Automatic console and pod positioning system also take away any potential for human error.

Blackmon: The short answer is to provide proper operator training. Table and machine damage can result from several conditions:

1) Tools can work their way out of the collet due to poor collet maintenance or improperly chucked tooling and damage the table or cause bodily injury.



2) Programming errors can drive the tool into the table, so the programming software should have a check for improper Z depths.



3) Placing pods or clamps in the tool path can be avoided with alignment aids or automated placement.



4) Loading the wrong part blank on the machine can damage the machining head or tooling and can be avoided with a labeling and bar-coding program, which can also help with part identification and tracking throughout the shop.

Castro: In order to avoid accidental damage to the table, a CNC machine can be restricted both in its software and mechanically. The problem with that approach is that it will limit the capabilities of the machine. Instead of restricting the machine, there are some other steps that can be taken to minimize table damage. For example:

1) Software simulation with clash detection: CAD-CAM software provides an excellent tool to simulate the machining and incorporates, in the simulation, the machine structure and table. Then, in case of a collision, the software will show and highlight the damage.



2) Properly elevated fixturing: When using vacuum or mechanical fixtures, allow enough clearance between the tool and/or the machining head and the surface of the table.



3) Use of tool presetter offline or built-in the machine: Tool measuring is a critical step. Always keep your devices properly calibrated.



4) Proper operator training and supervision: This is the most important step to take. Always supervise the operator when changing tools or hold-down fixtures.

Magnani: Table damages are the result of mistakes that programmers and/or operators make, and some machines on the market have no device to reduce the impact of such mistakes.

Some of the most useful features that can dramatically reduce such accidents are tool presetters, CNC collision control, machine simulation software, and synch of data between machine software and office software.

Operators always have to pay attention to positioning pods correctly if the machine doesn’t have the ability to set up the table automatically. There are also laser positioning devices that can help operators in setting up correctly. Likewise, tools must be set up correctly, not in just the length, but also in the diameter.

Young: After parts are programmed, there are simulation software options that are available so that you can run a program at the control cabinet to ensure that a table will not be damaged during actual production.

Illustration by Chris Nititham

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