Last updated on February 14th, 2025 at 10:30 am
It’s no mystery why powder coating is such a popular choice for precision sheet metal finishing. This process is incredibly durable, provides a consistent and attractive finish, and is available in over 6,500 colors and a variety of textures.
One of the only drawbacks to powder coating is that it adds a slight amount of thickness to a part. For flat parts or parts with standard tolerances, this outcome rarely presents a problem. But if you have features like cutouts and angles, it’s important to adjust your specs ahead of time to ensure that the features are still in tolerance after powder coating has been applied.
Table of Contents
- 1 How Powder Coating Adds Thickness to a Metal Fabricated Part
- 2 Material Considerations for Powder Coating
- 3 Proactive Designs Pave the Way for Optimal Powder Coating Results
- 4 Recommended Default Sheet Metal Tolerances
- 5 Sheet Metal Powder Coating Tolerance FAQ
- 5.0.1 How does powder coating affect the thickness of a metal fabricated part?
- 5.0.2 Why is it important to adjust tolerances for powder coating buildup on metal parts?
- 5.0.3 How can I anticipate and adjust for powder coating thickness when designing metal parts?
- 5.0.4 What should I consider when using textured powder coating on my metal parts?
- 5.0.5 Can Approved Sheet Metal help adjust design dimensions for powder coating, and is there a cost for this service?
How Powder Coating Adds Thickness to a Metal Fabricated Part 
Powder coating involves applying dry powder (usually made out of thermoplastics) electrostatically to create a hard finish on the surface of a part.
Although the powder coats the flat surfaces of a part evenly, overspray of up to 0.002” is virtually unavoidable in features such as cutouts and corners.
This amount of added thickness may seem inconsequential, but when it accrues on two or more edges of a feature, it can quickly become problematic. Even if we mask or plug features before powder coating, some buildup is inevitable.
Adjusting tolerances to account for powder coating buildup
Adjusting your tolerances to account for the thickness powder coating adds is key to guarantee the functionality of your part.
For instance, if a hole needs to fit a peg of a particular size, the buildup from the powder coating could compromise the fit, so you’ll need to loosen the hole’s tolerances to accommodate the anticipated buildup.
It’s especially important to make these adjustments when applying a textured powder coat, which is notably thicker than a smooth powder coat.
Material Considerations for Powder Coating
Selecting the right material for your sheet metal part is crucial to achieving the best powder coating results. Not all metals interact with powder coating the same way, and certain materials may require additional preparation or alternative finishing options. Here are key material considerations to keep in mind:
1. Powder Coating Adherence Varies by Material
- Steel & Aluminum: These are the most common metals for powder coating due to their excellent adhesion properties. However, aluminum requires a pre-treatment (like chromate conversion) to enhance powder adhesion.
- Stainless Steel: While it can be powder coated, its naturally smooth and corrosion-resistant surface can reduce adhesion, making proper surface preparation essential.
- Galvanized Steel: Special care is needed, as some zinc coatings can outgas during curing, leading to imperfections in the finish. A primer or pre-treatment may be required.
2. Surface Preparation Is Essential
- The metal surface must be clean and free of oils, oxides, or contaminants to ensure even coating and strong adhesion.
- Blasting or chemical etching may be needed for certain materials to improve adhesion.
3. Heat Sensitivity of Certain Alloys
- Powder coating requires curing at high temperatures (typically 300–400°F). Some alloys, especially thin-gauge aluminum or heat-treated metals, may experience slight distortion or loss of temper during curing.
4. Conductivity and Electrostatic Application
- Since powder coating is applied electrostatically, materials with poor conductivity (such as certain aluminum alloys or anodized surfaces) may require special grounding or pre-treatments for an even coating.
By selecting the right material and ensuring proper preparation, you can maximize the durability, appearance, and adhesion of your powder-coated parts. If you're unsure about the best material for your application, our team at Approved Sheet Metal is happy to help!
Proactive Designs Pave the Way for Optimal Powder Coating Results
At Approved Sheet Metal, we often receive designs that include the note “all dimensions after finishing.” This instruction indicates that our team will need to adjust design dimensions to accommodate a particular finishing method, a service that our metal fabricated part shop is pleased to provide to our customers free of charge.
That said, no one knows your part as well as you do. When we loosen tolerances without understanding the full context of your part and its application, we run the risk of hindering the part’s intended function.
We’ll always make every effort to get the information we need to produce the best results. However, anticipating the need for adjustments up front and modifying your design before placing an order alleviates the risk of important details getting lost in translation.
Ready to work with a sheet metal shop that is always thinking one step ahead? Request a quote today.
Recommended Default Sheet Metal Tolerances
| DIM | Tolerance (MM) | Tolerance (Inches) | Description |
| A | ± 0.13 | ± 0.005 | Sheared Edge to Hole |
| B | ± 0.13 | ± 0.005 | 2 Holes on One Surface |
| C | ± 0.25 | ± 0.010 | Formed Edge to Hole |
| D* | ± 0.76 | ± 0.030 | Holes Across 2 Bends |
| E* | ± 0.76 | ± 0.030 | Holes Across 4 Bends |
| F | ± 0.25 | ± 0.010 | Sheared Edge to Bend |
| G | ± 0.38 | ± 0.015 | Across 2 Bends |
| H* | ± 0.76 | ± 0.030 | Formed Part |
Noted dimensions are to be taken while the part is in a restrained condition. Noted dimensions are for parts within a 12” envelope.
* Dimensions D, E and H are not recommended forms of dimensioning
These tolerances are recommended and best practices. We can obtain tighter tolerances (depending on part geometry/ construction), contact us for more information
