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This finishing option with the shortest turnaround time. Parts have visible tool marks and potentially sharp edges and burrs, which can be removed upon request.
CNC machining produces a part with an “as-machined” or “as-milled” finish as soon as the manufacturing process is completed. The part will have small but visible tool marks and blemishes. The average surface roughness is around 3.2 μm. As-machined parts have the tightest dimensional tolerances and are extremely affordable to produce because post-processing isn’t necessary.
This finish is a good choice for those who are more concerned with dimensional integrity than aesthetics. However, parts with as-machined finishes don’t rank very highly when it comes to protection. Their roughness and lack of protective coating renders them susceptible to nicking, scuffing, and scratching.
| Surface roughness | Applicable materials | Cosmetic availability | Visual appearance |
|---|---|---|---|
| Ra 3.2μm / Ra 126μin | Metals, plastics | Not cosmetic | Machining marks are visible, light surface scratches are visible |
Many times, manufactured parts require additional processing such as surface finishing treatments to get the desired result. Some surface finishing treatments will add a kind of coating to cover the visible lines resulting from cutting the material with a machine tool. Others will remove a very thin layer of material from the surface to make the surface look better. For example, painting is a type of surface finish where a layer of coating is added to the surface, while polishing is a good one of those where material is removed. However, not all the parts require these types of treatments. Sometimes the surface roughness is more important, and the one obtained from machining can be exactly what is needed.
Surface roughness is a feature associated with quality, and it is usually measured as the average surface roughness (Ra).
The average surface roughness or Ra represents the average the profile of the machined part has deviated from the ideal surface.
For parts with “as machined” surface finishes, the standard deviation or standard average surface roughness (Ra) is measured at 3.2 μm (125 μin). However, this could be high for some applications.
Fortunately, the average surface roughness of as machined parts can be reduced to 1.6, 0.8 or 0.4 μm (63, 32 or 16 μin) depending on the requirements of the application. The drawback from doing this is the fact that postprocessing is required to achieve the required reduction, meaning that extra costs and increase lead time will be added to the manufacturing of the part.
A very relevant aspect of the as machined surface finish is the fact that current machine tools technologies, namely CNC machine tools, provide highly accurate machining results.
Therefore, as machine parts can cope with the most demanding tolerance requirements. Applications where tight tolerances are required can benefit from this aspect. However, it is important to highlight that, when improving the aesthetics is required and processes such as polishing are applied, the dimensional tolerances of the part are affected.
Nevertheless, this is not an issue when the parts are used as machined. If your application requires that postprocessing to improve the surface appearance, make sure the extra material removal is considered when calculating the dimensional tolerance.
As-machined services are used in a variety of ways, but typically when a manufacturer needs a custom or unique part for their product. For example, if you need a specific connector for your device that isn’t commercially available, an as-machined service can produce that for you. This is also a common solution for prototypes and one-of-a-kind components.
There are many as-machined services available, so it’s important to do your research and find the best provider for your needs. The quality of the service and the accuracy of the finished product will depend on the capabilities of the machine shop. Make sure to ask about the shop’s capabilities and experience before placing your order.
Here are some things to consider when choosing an as-machined service:
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