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What to Consider When Buying a Machine Tool

Posted by: 4. August 2016
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In the market for new CNC machine tools, there is a wide variety and selection of machines, offered by scores of machine builders from around the world. Vertical machines, horizontals, lathes, gantries, routers, boring mills, screw machines, grinders—the choices are almost limitless. So where does one start, how does one decide, and what tools are available to assist a buyer through the process of purchasing a new machine?

There are many factors to be considered, and a lot of questions have to be asked and answered prior to selecting the right CNC machine. Answering these questions will help ensure a successful installation once a machine is purchased. There is nothing worse than buying a new machine tool and having it sit in the corner, under-utilized, because it is the wrong machine for the job. Yet, this does happen.

This article is the first in a four-part series on the various considerations for buying a CNC machine. The sole intention of this series is to assist buyers through the seemingly daunting process of selecting the right CNC machine for the job. This article will cover some of the key questions that should be answered.

Start with Why

The first, seemingly simple questions that must be asked are:

  • Why buy the machine in the first place?

  • What is the buyer trying to accomplish in making this purchase?

Before selecting a machine type or specific model, it is necessary to first identify the specific job function or department for which the machine is being purchased. This will give a clear indication as to daily machine usage; lot sizes to be run; and requirements for fixtures and tooling, types of coolant, and tank capacity.

If the machine will be utilized in a job shop environment, the types of parts being machined will be numerous and varied in scope, with lot sizes ranging from one to 50 pieces. Similarly, toolroom or maintenance departments may see a wide variety of machine work but far more limited lot sizes, typically one to five pieces. Machines being purchased for a production environment, however, may be dedicated to machining one specific part or a family of parts. Production lot sizes may range from 100 to 1 million or more parts. Production runs generally have more stringent, dedicated workholding and fixture requirements.

Part-loading considerations are also driven by lot size. Hand loading, pallet shuttles or robot loading are some of the options. Tooling becomes more specific to a production run, whereas a standardized tool assortment works for the job shop. Coolant-tank capacity may need to be increased to handle longer run times for multiple work shifts. Toolrooms and job shops should think about a general-purpose coolant and a flexible delivery system.

Buy with Room to Grow

Once the reason for purchasing the machine has been established, but before machine type or model selection can begin, the technical aspects of the machine come into play, and the most basic but critical questions that must be addressed are:

  • What size are the parts to be machined?

  • Will the machine process tiny parts, large parts or really huge parts?

The answer to these questions will help determine the appropriate size and model of machine.

In a job shop environment where parts of a multitude of sizes and shapes will be machined, and where the requirements might change from day to day, the buyer should consider the largest part that might need to be machined. What size parts will the shop be running tomorrow or next week? Future shop capacity also should be considered in selecting the optimum machine size. Perhaps a shop could secure more business if it had a slightly larger machine. It’s easier to step up to a larger model today, allowing for the possibility of bigger or longer parts to be machined tomorrow, rather than purchase a smaller machine and regret that decision six months later.

The weight of the parts to be machined also should be considered as well as the size and weight of the fixtures to be used. Every vertical or horizontal machining center has a maximum allowable weight that can be placed on the table, but there are other machine tool designs in which the machine base has virtually no weight limit.

Part Shape Shapes Your Choices

Also of utmost importance to selecting the right machine for a particular operation is the geometry and shape of the parts to be machined. Part geometry has everything to do with how the part will be held during the machining process, which will greatly influence the type of holding device or fixtures to be used. Will a simple table chuck do the job, or is a more sophisticated or dedicated fixture, vacuum or hydraulic chuck required? Perhaps the part geometry will require a rotary table for fourth- or fifth-axis machining; and if a rotary table or fixtures are added, the X, Y and Z machine travels must be adequate to hold both the fixtures and the parts combined.

More geometrically complex parts may require a multi-axis machine with full five-axis 3D-machining capabilities, whereby the machine can move in five axes simultaneously, rotating on two additional A and B axes. This enables the cutting tool to approach the part from multiple planes and a variety of directions, reducing the need for multiple operations and additional setups. Part accuracy and repeatability are capabilities that are critical to ensuring the machine’s success.

It’s also important to consider the number of cutting tools required to machine the parts, as well as their length, diameter and weight. The machine’s toolchanger must also have an adequate number of tooling pockets to hold the necessary number of tools.

Need a Meeting of the Minds? Form a Committee

During the machine-buying process, some companies will form committees, especially when numerous departments will be involved in and responsible for the daily operation of the machine. Buying committees allow each department to have input, conveying their requirements and concerns prior to machine selection.

For example, the engineering department may have concerns about the machine’s ability to achieve and maintain the required part specifications and accuracies. The production department will want to ensure that it will be able to meet agreed-upon production requirements and schedules. The maintenance department will undoubtedly have concerns because its members will be forced to live with a poor machine selection. This department may be most interested in the machine’s spare parts; electrical components; electrical and air requirements; grease, air and oil filters; type of machine controller; recommended preventive maintenance procedures and their frequency; and general upkeep once installed. Facility representatives might bring up concerns about factory space, machine footprint and layout, electrical and air drops, and fork truck access. The purchasing department will want to make sure it understands the machine specifications and requirements in order to apply due pressure on the vendors to achieve the best financial deal and follow-up support for the company.

Machine selection by committee is usually done only in larger companies. Even then, if the machine is being purchased to replace an existing machine, and the required machine type and model are already known, a committee may not be necessary.  In a job shop environment, the owner of the company may be the one purchasing the machine and may find the committee method unnecessary and far too time-consuming. Also, in smaller shops, the owner may be the person operating the machine and knows exactly what he or she wants without needing anyone else’s input.

Do Your Research

Inevitably, all machine buyers get to the point in the process of comparing machine types and machine models. Techspex.com, a free research center and analysis tool, can help anyone find the right machine for the job. This handy website database contains more than 500 machine tool brands with more than 8,600 models of every machine type imaginable—all in one place. Techspex maintains the deepest, most up-to-date machine tool information, whether the equipment is a milling, turning, grinding, EDM or coordinate measuring machine (CMM)—it’s all there. Simply enter the basic attributes and specifications that are required, and the system will provide a side-by-side comparison by machine type, model and builder. Every search for a new machine should begin with Techspex.

New users can register for free here.

It can be time-consuming to bring in a multitude of machine vendors with varying skill levels, and the varieties of machine products and options that each machine builder offers can be confusing. Techspex can help sort out some of that information.

Additionally, the 2016 International Manufacturing Technology Show (IMTS), which runs September 12-17, is right around the corner. This is a great opportunity to kick the tires of a machine you have selected through Techspex and shoot for your best deal.

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Barry Rogers recently retired as global director of sales at Haas Automation. Prior positions include director of global sales and marketing for Sunnen Products, and national sales and market manager for Renishaw North America. He also has served as general manager of Cincinnati Milacron’s LK CMM division in Detroit, Michigan. Barry recently started Alpha Strategies, a Chicago-based consulting firm of which he serves as president. 

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