What are tolerances?
Tolerances are the permissible limits of variation to enable a product or its parts to work properly, aesthetically, and safely. Tolerances span a variety of measurable physical properties, including:
- Physical dimensions (height, width, etc.)
- Color, shape, texture, and other physical qualities
- Electrical Resistance
Note that tolerances are almost always expressed in a range. Imagine you need adhesive to connect two parts together. The adhesive may have many tolerances, including:
- How thick or long the adhesive can be (e.g.,1” in length with a tolerance of .1” of variation)
- How much heat the adhesive can endure (e.g., up to 500°F)
- Where the adhesive can be placed in XYZ dimensions on the part (e.g., 3” up from the leftmost corner with a tolerance of .3”)
Your contract manufacturer will need detailed notes on tolerances. Complexity varies widely—a simple child’s toy may have dozens of tolerances, while a car will have thousands. Each component of a finished product will have its own tolerances for any number of holes, fasteners, materials, and other parts.
These tolerances add up quickly—and your manufacturer needs to know about all of them.
The importance of tolerances in manufacturing
Tolerances are essential to the manufacturing process; they provide manufacturers with key data on how to build your product (or parts for your product). There are a number of reasons why you should provide a list of tolerances to your manufacturer:
- You’ll save money. By providing tolerances upfront, manufacturers won’t have to guess at measurements; they’ll also have a much better idea of what materials meet your tolerances. You’ll also give manufacturers a window of how precise they need to be, which can lead to substantial savings—we’ll discuss this point more in the next section.
- Your product will be more aesthetically pleasing. Tolerances can include a range of colors, shapes, and textures to keep your product in line with branding and marketing goals. You’ll also be able to eliminate visible gaps between the surface of your product and the layers beneath—or just about anything else you want to make your product more pleasing to the end user.
- Your parts or product will be more functional. This is perhaps the most important reason to define tolerances. Parts can become completely useless if they fall outside the window of tolerance needed to integrate them into a particular product. Products can fail to meet the end user’s needs if they can’t operate in the environments typical to their usage. Tolerances are key to functional products.
- You’ll improve your time-to-market. Guesswork and manufacturing don’t mix. By giving your manufacturer a precise framework to manufacture your part or product within, they’ll be able to more quickly develop a process to create it. The sooner your manufacturer develops the process, the sooner they can start actually producing your part or product—and the sooner you’ll get to market.
- You’ll be happier with the whole process (and your manufacturer will be, too). Tolerances give your manufacturer more flexibility in how they produce your product—that leads to cost and time savings. The detailed information you provide will also make their lives easier. You’ll be happier with the end results, for all the reasons we listed above—and communications with your manufacturer will be much easier.
With all of the advantages to providing tolerances, it’s easy to understand why they’re so important. But which tolerances should your part or product have?
Tight and loose tolerances: The advantages of each
Here’s something important to keep in mind: Tolerances provide a range—limits on the physical properties of each component of a part or product.
Imagine your product needs a hole for a fastener. You might tell your manufacturer that the hole can be placed anywhere and can be any size. Conversely, you might tell them that the hole must be placed within 1” of the leftmost corner of your product with a .001” tolerance, and that the hole must be 1” in diameter with a .01” tolerance.
These are examples of loose and tight tolerances, respectively. Tolerances exist on a spectrum of loose to tight, and there are advantages to being on any point in that spectrum.
The advantages of tight tolerances
Tight tolerances offer only a small window of variation—at times, they offer no variance at all. In circumstances where tolerances are tight, manufacturers have to expend time and energy to ensure that the materials and processes used meet highly precise demands.
The advantage of these tolerances is, of course, that you’ll know exactly what the end part or product will be, with almost no variance at all. Tight tolerances are required when manufacturing a number of parts and products, including those for:
- Medical devices
- Military applications
- Products designed for children
- And many more
When safety and functionality are of utmost concern, tight tolerances are essential. You may have parts that must have almost no friction with other parts, all while fitting seamlessly together—you’ll need very tight dimensional and radial tolerances. You may know that your part will be exposed to extremely high heat, water, or other significant environmental hazards. You’ll need tight temperature tolerances or a tight tolerance for ingress protection.
In short, the advantage of tight tolerance is precision. Tight tolerances are imperative when there are safety concerns around a part or product.
The advantages of loose tolerances
Where tight tolerances give precision, loose tolerances give flexibility. Imagine your part or product has incredibly broad tolerances—the manufacturer could then use almost any materials or processes to build it!
This level of flexibility usually means you’ll save both time and money. Achieving tight tolerances can be incredibly challenging and time-consuming. In circumstances where the aesthetics or functionality of a particular component can take a backseat, it’s often best to opt for looser tolerances.
Which tolerances should I choose?
Generally, parts and products will have components with a wide mix of different tolerances. Talk to your engineers to determine which tolerances might be appropriate for each component. You should have the same conversation with your manufacturer—one of the reasons we recommend onboarding your manufacturer early in product development is to ensure each component has the proper tolerances.
How to discuss tolerances with your manufacturer
- Ask about the tools they have available. Parts created by hand are less precise than parts created by a CNC machine. The equipment your manufacturer has available will dictate how tight your tolerances can be.
- Talk about each step of the process. Adding an adhesive to a surface will change its thickness, which can affect tolerances. When one part is fitted into another part, you need tolerances for both parts—you may then need tolerances for the whole once it’s fitted together.
- Discuss the end product. What industry are you building parts or products for? What environment will the final product be used in? Are there particular points on the part or product that are more likely to be exposed to stressors? Knowing everything you can about the end product will help you understand which tolerances are important to discuss and how tight they need to be.
- Go over every measurement you may think will be important. You might want your final product to weigh less to reduce shipping costs. You might need it to be within a certain range of colors to meet branding goals. Talk about any important physical quality with your manufacturer.
- Discuss cost. Your manufacturer wants to make the process as simple as possible—it will save both you and them time and money. Discuss a range of costs per unit with your manufacturer; that will help them establish how tight tolerances can be and what materials can be used.
- Ask about their prior experience. An experienced manufacturer will have a better idea of which tolerances are important in your industry. They’ll also have better tools and techniques to lower the cost of production, even with tighter tolerances.
General Label has decades of experience offering manufacturing and custom converting solutions. We know how to make designs with tight tolerances come to life quickly, all while helping you lower manufacturing costs. Contact us today!