Top Considerations for CNC Machining Large Parts

Top Considerations for CNC Machining Large Parts

CNC machines are very versatile for product manufacture and precision machining. Relative to 3D printing, CNC machines can deliver large size parts with amazing accuracy and finish. More often than not, parts to be CNC machined will fall within the capacity of the device. In few instances, the workpiece, may however, be larger than the machine.

For the typical machine shop, it may not be practical to invest in a CNC machine with larger capacity as these jobs may simply be one-off tasks. How then are these parts machined? Well, with through the use of some clever fixturing and some of the tips shared in this article, here are some of our hacks to help you get the most out of your machine and produce large parts.

General Considerations

The general considerations when working with a large workpiece revolves around its size and weight, the availability of tools and the accuracy of the final part. Here’s why:


The size of the workpiece affects the amount of distance that can be covered by the machining tool. If the part is too large, you might need to consider breaking the design down into sections for simpler machining and subsequent assembly. Also, parts that are larger than the worktable might need to be supported by the sides via an external means. This will help to secure the part and ensure balance        


The weight of the workpiece may affect the CNC machine’s balance. The weight of the part must never exceed the machine’s declared limit to prevent accidents and ensure easier manoeuvrability during machining operations.

In order to mitigate other risks that can arise from working with large piece, machinists may opt to use table with outrigger stands and roller stands that can aid movement across the part’s cross section. Finally, ensure that are adequate equipment that will help with the loading and unloading of the part.


The most common machine tools available in the market are suited for the development of small and medium sized parts. With very limited machine tools, there might be a need for many manual touches to finish some crucial parts of the work. Use big fly cutters that extend the reach of the machine and cutting tool. This will help you reach distant edges. Tools like right angle heads can also help you land favourable machining orientation that will reduce the time and effort spent on a section of the workpiece.


There is a risk of losing out on the level of precision and high accuracy that comes with machining a part as a whole. When dealing with large parts, a lot of patience and diligence must be exercised to deliver a final product with the same quality as though it was machined in one go.

Heat dissipation

Large parts would generate more heat during machining than smaller parts. Because of how important it is to ensure that heat is not accumulated during processing, users may need to factor in heat in pre-calculations and ensure that adequate cooling systems are in place when machining the workpiece.

Machining large parts

There are 2 main approaches that may be taken when dealing with parts that are significantly larger than your machine.

First, the machinist must determine an effective strategy to machine the part in multiple setups that fosters integration and synergy in completing the processing of the workpiece into the final part. The second approach is creatively looking at options to fit the part in the machine enclosure for machining at a one go. Whatever approach is feasible in your workshop, here are some key tips to help with machining large parts:

1. Open up the machine

When possible, open up the machine to remove the enclosures and tool changers to gain more room for the part to fit and ease machining.

2. Load the workpiece from different angles

While the default approach to loading workpieces is either straight horizonal or vertical orientation, it is possible to achieve more manoeuvrability by lining up the workpiece diagonally. This way, the machine tools can reach the two corners which is naturally longer than any edge in the part.

3. Weight supports

As earlier noted, bigger parts will be heavy. To ensure that the load capacity of your machine is not exceeded, consider weight supports with outrigger stands. This will help the machine, safety and mobility during machining, especially when the support stands have rollers that aid movement.

4. Spin round workpieces

One advantage of working with round parts is their ability to be spun. This often gives and overlap each time the part is spun. With proper setup, the machine cutting tools can be positioned to take advantage of the overlap and reach unmachined regions.

5. Use Right angle heads

Right angle heads can turn the workpiece around to a favourable orientation that gives the cutting tool an extended reach.

6. Use Big fly cutters

If your part is not significantly larger than the machine’s table, you can use big fly cutters to extend the reach of your machine through the edges of the material.

7. Break parts into small units

Quite simply, break the part up into segments that are within the reach and size of your machine. This can be easily be done via the design process, bringing the part into smaller units. After machining the individual segments, you can then use a versatile method to assemble each part into the final part.

It is important to add that your customer will need to agree to this before you proceed.

FirstPart CNC Machining in China

FirstPart is one of China’s leading manufacturing hub for Additive, CNC and Conventional manufacturing techniques. We boast of excellent in-house capacity, labor force and logistics for dealing with small, medium and large machining parts while delivering exceptional value for money.

Our array of services includes CNC machining, 3D Printing, Rapid Tooling, Die casting, Rapid prototyping,Plastic injection molding, Urethane Casting, Aluminum Extrusion, Post-machining/Finishing services and much more.

As we understand the global challenges that is faced by new businesses in these times of the Coronavirus, we offer product tooling, mass production, bridge tooling and low-volume prototyping/manufacturing with very flexible minimum order quantities. Our services are online, scalable and innovative, with a team of engineers and design experts available to support you through your entire product development cycle.

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