CNC machining – meeting the need for speed

Product developers rightly think of 3D printing as a versatile way to make prototype parts but, in many respects, CNC machining is even more versatile. For a start, almost any solid material can be CNC machined, whereas each different 3D printing technology (and we have five in-house at Prototype Projects) can use only a limited range of materials.

Precision prototype parts

If your prototype requires high-precision components, perhaps for proving a concept or for functional testing, then CNC machining offers a significant advantage over 3D printing. Our general tolerance on CNC machining is ±0.1 mm whereas we quote ±0.5 mm for 3D printing. In reality, our CNC machining centres and lathes usually hold tighter tolerances, depending on factors such as the material and geometry. If a part has a feature with a critical dimension, we can normally achieve the tolerance you require – but talk to us first! With 3D printing, it is much harder to achieve the same level of precision.

Part-to-part consistency is also much better with CNC machining than 3D printing, which matters when you need more than one of a particular part. And a part machined from solid is usually stronger than one built by additive manufacturing, even when the nominal material properties are similar.

A multitude of materials

Depending on what you need a prototype part for, we can machine it in a wide range of plastics, as well as aluminium alloy, stainless steel, mild steel, copper, brass, phosphor bronze, tool steels. If required, we can even work with similar modelling foams and RenShape polyurethane tooling boards.

Given its exceptional versatility, CNC machining should be considered for every stage of a product development project, from concept models through to proof-of-principle functional models, visual models for presentations and marketing, functional testing, handling models, usability trials and testing assembly systems. CNC machining might not be appropriate for every component in a prototype, but it is often used to produce parts that are assembled with others that have been 3D printed and vacuum cast.

Where to go for CNC machining

When you have decided you need a prototype part CNC machined, you will probably need it in a hurry (we know what the world of prototyping is like!). Most product development teams have access to a workshop, and this may even have a manual lathe and mill. Some might even have an in-house 3D printer. However, not many have the luxury of a CNC machining centre, together with the necessary highly skilled programmer and machine operator, programming software and array of tooling needed to get the most out the machine.

CNC machining therefore tends to be subcontracted to specialists. There are numerous one-man-bands who produce very high-quality work, as well as machine shops with multiple CNC machining centres. But if you need something quickly, you will have to phone around to find who has capacity and can hit your deadline.

When speed is of the essence

In response to the growing demand for urgent CNC machining, we invested in plant, people and processes to launch an Express service for CNC machining, with shipping in just three working days. To achieve this rapid turnaround, we have employed more CNC machine operators/setter so we can operate a split shift system and keep the CNC machines working efficiently. We have also streamlined our systems so that, for example, machine setups are paperless. Data processing is simplified because we import customers’ 3D data files into our Mastercam software for generating toolpaths. We don’t need 2D drawings unless there are critical features or tolerances customers need to make us aware of.

Most importantly, we never relax our quality standards to meet the three-day turnaround. However, parts must meet our Express service criteria, covering materials, setups, finishes and so on. For parts that do not meet these criteria, our Standard service is usually suitable, with shipping in seven working days. And for those rare occasions when there is less time pressure, we offer an Economy service with CNC machined parts shipped in 12 working days.

Service levels and finishes

Prototype parts produced with the Express service are supplied ‘as machined’ having been inspected, deburred, cleaned and degreased. However, if your part needs additional finishing for aesthetic or functional reasons, and you can accept a slightly longer lead time, we offer a broad choice of finishes. For example, plastic parts can have EMI/RFI shielding applied (depending on the base material) and we have in-house facilities for wet painting and manual polishing. Other finishes such as anodising and powder coating are subcontracted to local specialists.

Earlier we mentioned that one of the advantages of CNC machining is the tight tolerances that are routinely achieved. Toolpaths are created from the customer’s 3D CAD files, so the machined part should always be right. For the Express service, therefore, we simply inspect the part visually and check the overall dimensions using callipers or a micrometer. For parts supplied through our Standard or Economy service, the extra time allows us to check additional critical dimensions and, if need be, we can do this using our coordinate measuring machine (CMM).

CNC machining is a team game

We are very proud of our state-of-the-art CNC machine tools but we are even more proud of the team that turns customer enquiries into delivered parts. Enquiries are handled by our sales team and, if necessary, customers can have detailed technical discussions about part geometries, tolerances, materials, finishes or any other matters of concern. These discussions can be by telephone, email, or Teams or Zoom video calls. Once an order is placed, the data file (X_T, STEP or IGES) from the customer’s CAD system is checked by one of our programmers, at which point any queries are discussed with the designer. The programmer then imports the file into our Mastercam offline programming tool and uses this software to generate the toolpaths and work instructions for the CNC Machinist.

When the CNC mill or lathe is ready, the machine operator/setter downloads the toolpath, populates the automatic toolchanger with the required tools, and loads the material. After the CNC program has completed, the operator removes the part, then inspects, deburrs, cleans and degreases it ready for packing and dispatch. So, although we use the latest CAM and CNC technologies for producing prototype parts, our team members are crucial to customers getting the right parts at the right time (and with a pack of Haribos).

Talk to us

Do you need CNC machined prototype parts or would you like to discuss what is possible with CNC machining? Talk to us on 01763 249760.