Are your finishing requirements adding unexpected time, cost, and hassle to your precision machining orders? 
There are many ways to overengineer a part, and including unnecessarily complex finishing callouts is high on the list. Follow these finishing best practices when designing your next part.

1. Reconsider Hard Anodize for Tight Tolerance Parts 

Hard anodizing a tight tolerance part can be risky because the amount of growth added to the part—anywhere from 0.0005” to 0.003” depending on the specific alloy—may be larger than a feature’s allowable tolerance. 

Complicating matters further is that most of the tight tolerance features on these parts are holes, which must be plated on both sides. If the hard anodize adds 0.003” buildup on both sides of the hole, that hole has a combined total of 0.006” of shrinkage. 

Most precision machine shops don’t want to deal with the risk of receiving parts from the plater that are out of spec, so they’ll typically no-quote these projects. 

At Focused on Machining, we won’t no-quote you. But the only way for us to mitigate risk and ensure that these types of parts are made to spec is to send them to a high-end shop halfway across the country that takes four weeks minimum to process parts.  

Only a highly experienced plating vendor can control the amount of growth that hard anodize adds to a part. We’ll give the vendor a precise range of permissible buildup to ensure the parts are still in spec post-finishing, and they’ll do what it takes to meet our specifications. 

Needless to say, this process can add substantial cost and time to a project, so if you don’t need hard anodize on tight tolerance parts, consider standard anodize instead. 

2. Avoid Intricate Masking Requirements 

Customers commonly request that specific part features be masked to avoid exposing them to the finishing treatment. The problem is that sometimes, their masking requirements are more complicated than they need to be. 

For example, one customer who wanted 60+ parts anodized provided a highly unusual set of instructions: 1) anodize the parts 2) mask multiple features 3) hard anodize just one feature. 

We contacted our trusted plating vendor to see what was possible. We could get into the specifics of the lengthy process they outlined, but let’s just say it involved sending the parts back and forth and performing additional machining operations—and even then, the vendor wasn’t 100% certain the approach would be successful. We explained the situation to our customer and ultimately convinced them that hard anodizing the entire part would save them significant time and money. 

For a different project, a customer provided masking instructions for a side motor plate that would require masking such a large portion of the part and so many intricate features that most platers would simply turn down the job. (It’s important to remember that masking is a manual process and can be very time-consuming.)

The customer had a compelling reason for their requirements: anodize produces an electrically non-conductive coating, and they needed certain features to maintain conductivity. We discussed the project with our customer and recommended a (less expensive) chemfilm coating instead. Our vendor was able to dip the entire part into the tank (no masking required), achieving the desired benefit of corrosion resistance while maintaining electrical conductivity. 

3. Specify Type, Class, and Color of Finish 

When requesting a finish for your part, be as specific as possible. If, for instance, you call out passivation, know that there are three different types of passivation, multiple classes within each type, and several different industry standards.

If you don’t specify the precise type and class of passivation you want, you’re leaving the decision entirely up to the vendor, and your parts might not be passivated to your standards. The same goes for processes like anodizing and chemfilm. 

Color is another essential consideration—and another area where it pays to be specific. You may think that requesting “green” anodize is sufficient, but one person’s concept of green can differ considerably from someone else’s. You’re best off providing a color code so that you get the color you want. 

Keep in mind, too, that when platers attempt to color-match non-standard colors from one lot to the next, inconsistencies can occur. The anodizing process is highly complex, and many variables (e.g., time in the tank, temperature of the tank, cleanliness of the tank) can affect the part's color. If clear anodize is an option, you’ll avoid the headache of dealing with parts that aren’t exactly the right shade.

Why Trust Focused on Machining for Finishing Services? 

At Focused on Machining, we’re committed to helping our customers problem-solve finishing challenges by providing strategic recommendations and working with best-in-class vendors. 

One such vendor is Magnetic Inspection Laboratory (MIL), a Chicago-based company that provides metal finishing, coatings, and non-destructive testing services. Their experienced staff comprises scientists with an expert understanding of complicated chemical finishing processes. 

Before hard anodizing a tight tolerance part, for example, MIL will run tests on a similar size material to dial in their process. They’re one of the only vendors we’ve found who can consistently achieve our specified tolerances for complex orders. 

While many precision machine shops will machine extra parts to send to their finishing vendors to ensure that enough parts come back usable, adding to their customers’ overall costs, we are confident that our trusted vendor can get the job done right the first time. 

Request a quote to work with Focused on Machining and benefit from our well-vetted network of finishing vendors.