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Tolerances and margins in precision engineering: How strict are they?

Understanding tolerances and margins in precision engineering are crucial to the overall success of a component. You can’t just cross your fingers and hope for the best, the component will either conform or it won’t. So, it is important the engineering firm you work with understand the importance of tolerances and aid you with your design decisions to ensure the right results. 

In this article, we will be detailing why tolerances and margins are so important along with how we meet strict brief specifications. Utilising our vast knowledge base, experience and specialised machinery, we are adept to undertake the most difficult of projects. Our team are proud to have been serving a variety of different industries and meeting a range of different component briefs for the last 30 years. 

What are tolerances and margins in precision engineering?

Measure twice, cut once comes to mind when we think about these two things. They are a set of measurements that allow a final component to be functional and aesthetically pleasing. They can be slim, and simply put, if they aren’t met the component will not fulfil its purpose. Inconsistency leads to major faults, which is why many companies choose to subcontract our services as we are able to meet specific briefs with our specialist machinery. 

CNC machining costs can increase by more than double between a rough tolerance of +0.030 and a standard tolerance of +0.005? And if you are looking for a +0.001 tolerance, the cost can increase by up to four times. Whilst the cost can be higher for tight margins, if you need to meet a certain standard, it’s certainly worth the additional cost as you’ll ensure the component will function as required. 

Every designer should know the tolerance is ultimately the most important factor in the journey from original sketch to final product. 

Epal’s measures – Getting it right the first time

You can avoid major faults by choosing an established firm to work with that understands the importance of tolerances and margins in precision engineering. Our customers utilise our skills time and again as we’re able to provide the right component, the first time. How do we achieve this? You need a combination of:

  • High-quality machines
  • High-quality software
  • Engineering expertise to make the parts
  • Inspection to ensure you get what you asked for

If you receive a component that exactly meets your original brief, you can rest assured that it will conform – fulfilling your needs and often exceeding your expectations. Your dedicated engineer should be in contact with you over the process to update you on any issues prior to the final component. Ultimately, meeting tolerances and margins the first time, will reduce costs.

Why accuracy and precision are crucial during prototype development

There will likely be a manageable tolerance with any component produced – perhaps a micron or millimetre will allow the piece to still function correctly. However, deviation from these guidelines can impact a prototype hugely. 

If you are trying to understand how a design will function in the real world, after having only seen it on a computer previously, you need a precise finish. Otherwise, you may move forward to mass production only to then realise the fault when it is too late. Not only does this slow down the process and see you incur additional costs, but it may also damage your client reputation if you present a non-conforming prototype.

Prototypes reveal issues ahead of time and so, working with a precision engineering firm that has specialist, high-quality machinery and expertise to guide you through the process, can guarantee success. 

Tolerances and margins in precision engineering

Factors affecting tolerances and margins in precision engineering

Tolerance needs to be understood in terms of thickness, straightness, twist and mass of a component part. Then there is the tolerance that recognises the effects of temperature and humidity on a product – designers have a lot to consider. 

Generally, there are three main factors we look at:

  1. Additional coatings: Machined parts may also have a powder coating, anodising, polishing, electroplating, galvanising and heat-treating processes. These may not seem like they’d have a major impact, but each adds a microlayer which increases exterior measurements. 
  2. Thermal expansion: Soft and composite metals have a tendency to change their volume in response to temperature alterations. Depending on the function of your component, this may be yet another consideration you need to make. 
  3. Welding process: Welding involves high temperatures and again, this can have an effect on the material. CNC machine services can eliminate this factor as it provides a far more precise finish. However, the temperature at which the material is put under should still be discussed with your precision engineer.

Choose an established precision engineer that has experience delivering projects with strict specifications. Tolerances and margins in precision engineering should not be overlooked. Rather, your design should be discussed in the initial stages to ensure there is a full understanding of what result is required. It is also important to talk through factors that may affect the final outcome. If you have considered all possible issues, the team will be more equipped to mitigate or fix them should they arise.

How tolerances link to quality

How do tolerance measures link to quality? You may think the two are not closely linked. However, this is far from the case. In fact, the two go hand in hand. As we’ve mentioned, if the tolerance deviates widely – it won’t function correctly and so, this is a measure of quality.

Also, if you are making a component that works in tandem with another, any slight changes or imperfections to the tolerances will greatly reduce the compatibility of the two components. Functionality is one of the most key aspects of measuring quality.

Aesthetics are always going to be important when assessing the quality of a product. If you want certain parts to be flush against each other – both tolerances and margins play an important role. So by taking care of measurements and carefully planning, the overall look will be much more successful.

At Epal Engineering, we pride ourselves on providing the right service, first time, every time. 

How to avoid common changes

It is always possible to over or underestimate margins in engineering. However, knowing where this stems from can help you avoid them in the future. While these mistakes may seem obvious – many often get overlooked.


What can happen during the design or manufacturing processes is that old tolerance is carried over as they are assumed to be correct. This could be due to a lack of experience in this area, or simple laziness. When a professional is not approached to oversee or carry out these important factors – you can be way off the mark. Accurate calculations are determined by many factors that should be checked and checked again. Even if they have worked in the past.

Missing calculations

Although it may seem like common sense, many people forget that to have a successful end product, you need the margins and tolerances for ALL components that work together. Otherwise, you will fail to define one piece and it will have a knock-on effect on every other part of the process. Just one incorrect or missing calculation could set you back time and money.

How can Epal Engineering assist you? 

We have discussed what tolerances and margins in precision engineering are and common errors people make when calculating them. It just goes to show that even being a millimetre off on your measurements can render a product useless. This will see a considerable loss in funds and time to go back and fix it. However, if they are carefully thought out and recorded correctly from the design, right through manufacturing – you are more likely to hit targets and keep yourself on track to exceed expectations. 

Our team of engineers are equipped with all of the skills to take on jobs both large and small. We’re comfortable working with the toughest metals down to the most delicate materials. So, no matter what sort of project you’re looking for, we can help every step of the way, from initial ideas all the way through to finishing and quality checks. 

This even includes design services and precision calculations. We always strive to get things right the first time, so we do not skimp on measuring twice and cutting once. With plenty of industry knowledge and experience, you can rest assured we won’t make any of those common mistakes. To learn more about us and how we can help you, please visit our website by clicking here, or why not give us a call on 01903 74435?

If you would like to learn more about Epal or what we do, why not give these a read?

CAD/CAM software: How it aids precision engineering

Prototyping Parts – Costs and Things to Consider

The Ins and Outs of Precision Wire Erosion and EDM Machining

Epal Engineering

Here at Epal Engineering we are really proud of what we do. We are passionate about doing the best job for all of our clients and working to an extremely high standard to make sure they get exactly want they require.

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