Anodizing is an electrochemical process that creates a durable, corrosion-resistant, oxidized coating on a metal surface. It’s a common finishing process for metal parts, especially those made from aluminum. 

Anodizing serves both functional and cosmetic purposes. From a functional perspective, the protective coating enables parts to withstand harsh environments. Aesthetically speaking, standard anodize coatings come in a variety of beautiful colors.  

In some cases, anodizing introduces a level of complexity to the manufacturing process. For example, when anodizing threaded parts, designers, machinists, and anodizers must work together to ensure that this finishing process doesn’t throw the part out of tolerance and negatively impact its functionality.  

Precision Machining Challenge: Protecting Threads from Anodize Buildup

At Arbiser Machine, we’re committed to achieving all specifications and tolerance requirements for the parts we manufacture. Sometimes, we have to think outside the box to accomplish this goal. That’s certainly the case when anodizing parts with small threads. 

Here’s an example: Recently, a customer requested an aluminum part that they needed black anodize to prevent reflectivity. The customer wanted to ensure that there wasn’t any aluminum visible that could reflect the light from the part’s end-use environment. The part design featured tiny tapped holes, each with internal threading to accommodate a screw. 

The anticipated accumulation on the threads was .0006”-.0008” of coating buildup as a result of the anodizing process. The problem is that this amount of coating could be enough to throw a part out of tolerance, making it impossible for the threads to accommodate a screw. 

Arbiser Machine’s Recommendations 

There are a few ways to avoid this issue, depending on the size of your threads and whether or not your threads need to be anodized. 

• For threads smaller than 1/4-20: Because these threads are so tiny, the range of buildup that anodize adds could be greater than the tolerance range for the part itself. The only guaranteed solution for protecting threads of this size from anodize buildup is to mask the holes, which prevents the liquid from coating the threads. In cases where the holes must be anodized, the design will need to be adjusted so the threads are big enough for the tolerance range to accommodate the anodize buildup.
  

• For threads 1/4-20 and larger: If the hole needs to be anodized, we recommend allowing your threads to be machined slightly bigger so that once the anodize has been applied, the part will be in spec. If the hole doesn’t need to be anodized, we can mask the holes the same way we would for smaller threads.  

Customers always have the option of communicating directly with the anodizer to determine the predicted range of anodize buildup and adjust their designs accordingly. But it’s generally easier to let Arbiser Machine manage this process for you. 

We can work directly with the anodizer to determine the proper precision machining specs to produce anodized parts within your required tolerance range. We can also advise you during the design phase on what types of outcomes are achievable so you get the results you’re looking for.

Request a quote today to partner with a precision machine shop that has the engineering experience to navigate your specific part challenges.