Tips to Consider When Buying a Machine Tool

The ANCA MX7 is a modern CNC Tool and cutter grinder featuring automatic tool loading and a wheel-pack exchanger.
Tool Grinders such as the MX7 can maintain micron tolerances over an extended unmanned production run.
Photograph taken by Prbocchi.

Why? The new machine you purchased could end up in a corner, neglected because it is the wrong one for your job. With plenty of machine manufacturers from all over the world, each with a wide selection and array of machines, the choices for a new CNC machine tool is almost infinite. Horizontal machines? Verticals? Boring mills? Routers? Screw machines? Lathes? Grinders? Gantries? Where do you start, how should you decide, and what can help you through the process of buying a new machine?

There are lots of points to ponder over, and lots of questions raised when selecting your CNC machine. The answers to these questions will help you install the purchased machine successfully. Nothing is worse than leaving a brand new machine tool in the corner, underused, because it’s not the right one for the job. Still, it may happen.

What is your most basic reason for buying the machine? What do you want to accomplish with it? By answering the question, you’ll be able to identify the specific job function that the machine is expected to perform, or which department will be having the machine. This will, in turn, bring up the following questions:

(i) how the machine will be used each day.
(ii) the number of products the machine will manufacture each day.
(iii) fixtures and tooling requirements
(iv) what coolant to use and its tank capacity.

If the machine is to be used in a toolroom or maintenance department, it will be used for a wide variety of work, but it is expected to produce only one to five pieces every time. A job shop will also give the machine a wide variety of work with slightly larger lot sizes, generally one to 50 pieces. Machines that are purchased for a manufacturing environment, however, might be devoted to machining one specific part or even a family of parts. Lot sizes can range from 100 parts to millions.

The lot size will determine the requirements for the machine. How will the machine be loaded – manually, with pallet shuttles, or with robots. Workholding will be much more stringent for a manufacturing run, and dedicated fixtures are expected. Tooling also becomes more specific as the lot size increases. The size of the coolant-tank will have to be increased for longer production hours and more work shifts. Conversely, toolrooms and job shops should consider general-purpose coolants and methods for flexible delivery.

Purchase with Room to Grow

After you find out the reason for purchasing the machine, you should consider the workpiece. What components will the machine make? The answer will raise a few more crucial questions:

What is the expected size and type of workpiece? Will the machine make tiny components, large components, or really huge components? The response to these questions will help determine the right size and model of equipment.

In a job shop where parts of myriad shapes and sizes is expected to be machined, and where requirements will change everyday, the buyer should consider the largest component that needed machining. What will the shop be making tomorrow? Next month? Future capacity should also be considered when choosing the machine size. Would you secure more business with a slightly larger machine. Rather than getting a smaller one and regret that decision six months afterwards, it might be better to buy a larger model today.

The Shape of Your Component Shapes Your Choices

Another priority when choosing your machine for an operation is the geometry and shape of these components. The shape will determine how the component will be held during machining. This, in turn, will determine the type of fixture to use. Will it be enough to use a simple jawed chuck? Or does it require a more complex fixture, such as vacuum or hydraulic chucks? or perhaps the shape requires a rotary table for machining fourth- and fifth-axis? And if a rotary table or fixture is added, is the machine travel on the X, Y, Z axes enough for the combined dimensions of the fixture and the component?

More complex parts will call for a multi-axes machine. By adding rotational axes around X and Y, the cutting tool can approach the workpiece from more planes and angles, reducing the need for additional setups and operations. This will ensure production accuracy and repeatability.

In addition, it is important to consider the number of cutting tools needed, and the length, diameter and weight for each. Make sure that the toolchanger have enough tooling pockets to accommodate them.

Forming a Machine-Tool Buying Committee

Since many factors have to be considered before buying a new machine tool, and lots of questions have to be asked and answered before choosing the CNC machine, it will be helpful to check with all the people and departments concerned with it before buying.

Form a Committee for a Consensus

Throughout the machine-buying process, some companies form committees, especially if numerous departments are involved and accountable for running the machine. Buying committees allow all departments to convey their needs and concerns before machine selection.

Engineering: The engineering department may be anxious about the machine’s ability to make component to specifications and to maintain the accuracy every time.

Production: The production department might bring up concerns about meeting schedules that have been been agreed upon.

Maintenance: The maintenance department will certainly be concerned as its members must be made to live with a poor choice. They will be most interested in the spare parts; the requirements for air and electricity; the filters for grease, oil, and air; the type of controller; the procedure and frequency for maintenance; and general upkeep after installation.

Facility: Facility representatives are going make sure that it can fit into the space allocated for it. And whether the factory’s electrical and air drops can accommodate its footprint and layout. And whether the forklifts can access it.

Purchasing: The buying department is going to ensure it understands enough to press vendors for the best deal and negotiate the right support package after installation.

Machine selection by committee is usually done only at large companies. But if the machine is being bought as a replacement, and the same type and model is to be purchased, a committee may not be needed. For a job shop, its owner may find the committee method too time-consuming. He may also be the one using the machine and does not require a different opinion.

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