Why Sheet Metal Design Clearances are Important

When creating a product, your first priority is for it to function properly. After all, something that doesn’t work is as good as it not existing at all. When it comes to designing sheet metal enclosures and parts, it is crucial to account for manufacturing constraints. Imagine spending time and effort to design what you think will be the perfect enclosure, but during assembly, the parts don’t fit together. That’s a recipe for disaster!

In this blog post, we will discuss sheet metal design clearances. By heeding these tips, you can account for every manufacturing constraint as you design, and your parts will have a better chance of fitting together.

Why clearances are important in sheet metal manufacturing

Clearances refer to the amount of space required for the proper functioning of mating parts, fasteners, and other components within the design. These spaces have to be accurately calculated. If not, assembling and disassembling parts in the future will be a troublesome procedure. There could also be production delays and damage caused to your parts if clearances are not on the mark.

At Protocase, there are a few different types of clearances within the manufacturing process for custom sheet-metal enclosures and parts.

Cutting Tolerance

We cut most of our parts using fiber lasers. An extremely hot laser beam is created from a computer numerically controlled machine, which is then used to cut through the sheet metal. This machine has a +/-.005” tolerance when cutting flat profiles. Say, for instance, you have a piece of metal that you want cut at 1” x 1”. The possible ranges for the final size of this part could be anywhere from .995” to 1.005”.

It’s important to remember to allow for component tolerance when cutting parts with cutouts to fit components such as power supplies or printed circuit boards (PCB). If you have a circular component such as an optical cable, you should look at doubling the tolerance. Make the cutout 0.10” larger as there is tolerance around the entire perimeter.

Bend Tolerances

After sheet metals are cut on our fiber lasers, most of them are then deburred. This is to ensure that the edges are smooth. Unless your design is a flat panel, your parts will go through the bending operation next. Our bending machines all have a possible bend tolerance of +/-.01”, which means if you are bending a 1” flange, it could be anywhere from .990” to 1.010”. This is probably our largest tolerance that needs to be accounted for. It is also the main reason why we typically design all of our assemblies with a minimum gap of .010” between all mating surfaces.

With bend tolerances, an important thing to keep in mind is that stacked or consecutive bends come with increased bend tolerances. It’s important to account for fluctuation in bend sizes to accommodate a mating part. Simply put, if there are more bends, there should be larger gaps between parts.

Powdercoat Coverage

Powdercoat typically adds anywhere between .003”-.005” of thickness to your parts. This can particularly be tricky when designing cutouts for components. You want to ensure that, after we powdercoat your part, the component still fits within the cut out. Again, if you are trying to accommodate a circular component, you need to make sure the clearance is doubled by the .003”-.005” value.

If you opt to have your parts powdercoated and a clear coat applied on top, you should account for both thicknesses.

Screw Clearances

In sheet metal, it’s common to mount your parts together using self-clinching fasteners on one part, and machine screws on the other.

Each size screw has a tight, normal, and loose fit. For example, a #6 screw could have a mounting hole that ranges from Ø.144 to Ø.170. We typically mount our hardware at Protocase with a fairly loose fit. This is to ensure that after parts are cut and bent, the screws will still mount correctly. If you have a large stack up of bends on a part that need to mount to another, these screw clearances should be a loose fit. We also recommend slotting your mounting holes in the direction of your bends.

Conclusion

Design clearances can play a crucial role in ensuring that manufacturing constraints are accounted for. By paying attention to our recommended sheet-metal clearances for the laser cutting, bending, fastening and powdercoat processes, you can greatly increase your chances that your assembly will fit together on the first try.