Fastener Technology

Ultimate Guide on Tolerances for Fasteners & Assemblies

Tolerances for Fasteners and Assemblies

One of the keys to understanding the metric system is the understanding of its tolerance system. There is simply no manufacturing method that enables production to perform to exact dimensions. In the inch system, tolerance is mainly done by giving minimums and maximums.

The ISO tolerance system was created by the International Standard Organization in 1948. Originally it was developed for fits and is still mainly used in this manner. It is based on IT Grades which are base tolerances from which all the individual tolerances are derived.

The system is composed of a letter and number base.

The letter indicates the location of the tolerance (whether plus or minus, how much plus, how much minus).

The number indicates the tolerance range. The bigger the number, the bigger the spread between the minimum and the maximum, and therefore the larger the tolerance range.

Download the Bossard Technical section for basic tolerances and tolerance fields, or email ProvenProductivity@bossard.com with any questions regarding tolerances.

 

Joe Stephan
Application Engineer

November 17, 2017
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Why Should You Use Standard Metric Fasteners?

Standard Metric Fasteners

What is meant by the term “standard fasteners”? Generally, it refers to fasteners that are stocked on the shelf rather than made to order, which translates into shorter lead times. Often, looking at a catalog will give you a pretty good idea of what is available, but below are some general guidelines and a few exceptions to note.

Standard fasteners lengths follow a pattern. For short fasteners, typically lengths under 20mm are available in 8, 10, 12, 16 and 20mm. Lengths from 20mm to 70mm are available in 5mm increments, while lengths over 70mm skip to 10mm increments. For example, you can get an M10 x 65 or M10 x 70, but the next available length is M10 x 80.

Width Across Flats (WAF) for hex products can be a bit confusing. DIN standard hex head parts are generally stocked more than ISO standard hex heads. This can be significant in diameters M8, M10 and M12. DIN parts are 1mm larger WAF for these sizes, requiring a larger wrench to drive them. Other diameters share the same WAF for both standards. Many distributors consider DIN and ISO hex heads as equivalent even though the heads may be a slightly different size.

Metric socket head products are not readily available in all property classes. Socket head cap screws are offered in 8.8 and 12.9, but not in 10.9. Flat socket head cap screws and button socket head cap screws are available in 10.9, but not in 8.8 or 12.9. Exceptions can be made with special orders, but these are not considered standard.

Contact us through ProvenProductivity@bossard.com to learn more about standard, readily available fasteners.

 

Doug Jones
Applications Engineer
djones@bossard.com

November 10, 2017
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How to Match Nuts, Bolts, AND Washers

When selecting fasteners that are to be assembled together, it is important to consider their strength compatibility. The nut should always be stronger than the bolt, so when using higher strength bolts, such as metric class 10.9, make sure to use the correct, corresponding nut. In this case, a class 10 nut would be correct. Stronger nuts may be used with lower strength bolts without any problems.

Strength of washers should also be considered, but are often overlooked. Using non-heat treated washers with heat treated hex head cap screws can cause joint settling as the relatively small bearing surface of the cap screw can embed itself into the soft washer over time, causing a loss of clamp load.

Standard metric flat washers have class designations that can be paired with heat treated bolts. Below is a compatibility chart that will help you make the right choice.

Matching Nuts Chart

Check out the “Technical Resources” section at www.bossard.com for more information on selecting the proper fasteners, or reach out to us at ProvenProductivity@bossard.com with any questions.

 

Doug Jones
Applications Engineer
djones@bossard.com

November 03, 2017
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Why Process Control is Important for Fasteners

How Important is Process Control for Fasteners

Many fastener manufacturers are faced with several different customer requirements or international standards. This leads manufacturers to create sampling plans to detect nonconforming product during mass production or final inspection. There are also several different AQL (Acceptance Quality Limit) levels according to batch or lot sizes. Do you think relying on final inspection sampling is the best idea? Even if they choose various samples from multiple bins of the same batch?

Fastener manufacturers are no different than any other industry. Speed, delivery, and quality are key, and most companies have been driving lean methodologies and efficiency tools into manufacturing processes. But does this have a negative impact on quality? Maybe, but most fastener manufacturers do still maintain minimum sampling plans that are fairly aligned with some international standards for mass production.

So what is a good detection method to minimize nonconforming product during the manufacturing process? Contact us through ProvenProductivity@bossard.com, and see what quality processes we encourage Bossard manufacturers to use to ensure quality fasteners for our customers.

 

Tony Peters
Quality Manager

October 27, 2017
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The Importance of Friction in Your Bolted Joint: Part 2

When doing research for your bolted joint it is important to understand the coefficient of friction of the finish of the fastener. There are many different options for coatings that will give you different ranges in values. Typically, those values are tested to a certain specification. Whether it’s an OEM specification, or per the ISO 16047 standard, each one can have minor differences (if you have questions on standards reach out to a Bossard engineer). So what do those values actually mean and how are they relevant to your joint?

Most of the testing that is done to validate the values of the coating is done on M10 surrogate bolts with a standard hex head cap screw. They are tested in lab conditions with either a plain finish washer or nut that is cleaned and degreased or with different variations done in a lab setting. The cause for concern is using those values in your joint. The values can change depending on your bearing surface and your mating threads (material, surface condition, lubrication, bearing surface area, etc.). As stated in previous Proven Productivity blog posts, it’s important to understand the relationship so you prevent costly errors down the road.

That is why we at Bossard always recommend doing bolted joint testing. We have the capability to perform joint testing so we can help you better understand the coefficient of friction and the torque tension relationship in your joints. We can perform testing onsite at your facility or you can visit one of our engineering design centers.

Contact us at ProvenProductivity@bossard.com for more information.

 

Jon Dabney
Application Engineer
Jdabney@bossard.com

October 13, 2017
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Why You Should Respect Your Fasteners

Take a minute to think of some of the most amazing mechanical marvels we have today: electric vehicles, exo-skeletons, cell phones, wind turbines, and many more. What do most of them have in common? They are all held together with some type of fasteners.

Now think about your product. What happens if the fasteners fail during use? At best, the customer is not happy and may look at other brands for their next purchase. At worst, damage to property or personal injury could result.

So, why are fasteners always the last thing we think about in our design? It’s true that assembly is the last step in the product design process, but fastener selection should be carefully considered in the early product design stages to ensure the best and safest product. Early fastener selection is also associated with time and cost savings making your process more lean and efficient.

Not sure what is the best choice? Have questions about what’s readily available or what’s new in fastener technology? Contact your fastening solutions provider to help you select the best hardware for your project. Don’t wait until two weeks before production starts!

Contact ProvenProductivity@bossard.com for information about the latest and greatest hardware innovations, and get help with your next project!

Doug Jones
Applications Engineer
djones@bossard.com

October 06, 2017
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Why Quality Fasteners are Worth It

You’ve spent months on your design doing careful analysis and selecting the right materials. You are finally getting close to production – but wait, you haven’t selected a fastener supplier yet. You need mostly standard fasteners, except for those few specialty print parts. It’s just fasteners; how hard can it be?

The next step is to turn over your fastener list to the buyer and have them find the cheapest hardware they can negotiate to save a few pennies on the product. After all, it doesn’t matter where they come from. All fasteners are the same, right?

This scenario may be a bit harsh, but is all too often true. If manufacturers are making standard fasteners, they should be using the same fastener standards. Unfortunately, some manufacturers take short cuts to keep costs down in this highly competitive market. Some low-cost providers may make perfectly good fasteners 90% of the time, but is 90% good enough for your design? Assembly issues, failures in the field, warranty claims costs, and poor customer satisfaction when a new widget breaks or doesn’t perform as advertised can be very expensive and time consuming.

My advice is this: know where your fasteners are coming from. Here are some questions you can ask yourself before selecting a supplier:

  • Does the manufacturer have good process controls?
  • Are they tracking reject rates both internally and externally?
  • Are they subcontracting fastener finishes or heat treatment?
  • Do the subcontractors have good process controls?

Contact us through ProvenProductivity@bossard.com and see what steps we take to ensure good quality fasteners.

Doug Jones
Applications Engineer
djones@bossard.com

 

September 22, 2017
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Length of Engaged Thread

Length of Engaged Thread

Length of engagement is important to understand. The required minimum length of engagement changes for different materials and hardness of said materials. This is something that needs to be determined during the design process.

When screws need to be fully loaded in tensile, it is important to note the strength of the material that the ‘nut’, or female threaded component, is made of. The minimum length of the engaged thread will depend on it. Ultimately, it is important to achieve the required minimum length to give the joint the durability it needs.

Below are some examples of recommended minimum lengths of engaged thread in internal threads based on the material of the nut component for heat-treated steel bolts. These have been determined from practical trials:

Recommended minimum lengths of engaged thread in internal threads.

Make sure the toolbox of information needed to determine the proper length of engagement is readily available. Reach out to us at ProvenProductivity@bossard.com if there is any questions regarding this!

June 02, 2017
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Fatigue Resistance in Fasteners

Fatigue Resistance in Fasteners

Simply put, you want your fasteners to hold up under many situations including conditions of changing load. However, some fasteners cannot hold up to the challenge. One of the most common forms of fastener failure is fatigue. That is why fatigue resistance and strength is something to look for in your fasteners.

A fastener can experience fatigue for a variety of reasons including assembly parameters, fastener material, geometry, and stress on the fastener. Fatigue often occurs in the first load-bearing part of the thread, and it can be detrimental to your project. This means your design must allow for screws to increase its fatigue strength. However, the fatigue strength of fine threads decreases with increased rigidity and fineness of thread, so there are some things to keep in mind with fatigue strength in your fasteners.

There are ways to increase the fatigue strength of your screws. These would include measures that reduce the effective peak stresses or prevent combined loading.

Check out some options for increasing your fatigue strength:

  • Use longer screws rather than shorter screws
  • Use screws with waisted shanks
  • Use pins or fitted shoulder screws to absorb lateral forces
  • Adequate and controlled pre-stressing of the screws

Reach out to us at ProvenProductivity@bossard.com to learn more about fatigue resistance and to find the fastener with the perfect fatigue strength for you.

May 26, 2017
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bigHead® for Wind Turbines

bigHead® for Wind Turbines

Solving your fastening problems is what bigHead does. Whether it is a difficult project or an extreme environment, we can come up with fastening solutions tailored to your needs. That is what bigHead did for offshore wind turbine maintenance hatches.

Siemens nacelle suppliers approached bigHead with a fastening problem. They recently came up with a composite hatch to replace a steel panel for covering a maintenance hatch. The only problem with the composite hatch was fastening it with traditional bolt fixings. This was a challenge because two people were required to perform the operation—one inside and one outside the nacelle. That made the operation not only less safe, but more challenging and time consuming to perform.

However, bigHead and Siemens came up with a solution through prototyping and extreme testing to make sure the fastening solution could hold up under the harsh conditions that the offshore wind turbines endured.

The solution for these offshore wind turbines was surface bonding the 316 marine grade stainless steel bigHead to the outer skin of the nacelle and passing the threaded stud section through its composite structure. This means the panel can easily be secured or removed by one person from the interior of the structure. The bigHead’s large perforated head allows a generous flow of adhesive to firmly secure it in position and its outer surface includes an over-moulded insulation layer that safeguards the nacelle against lightning strikes.

bigHead and Siemens worked together to create the perfect fastening solution for a tough problem. bigHead has been manufacturing its distinctive and leading brand of discrete bonding fasteners for over 50 years and has extensive experience across a wide range of industries where formed and molded composite products require discrete and completely secure fixing. Applications range from carbon fiber panel fixing in specialist and luxury car production to building and construction, railway carriage construction, marine and boat building, and more.

Do you have a tough problem that needs a fastening solution? Reach out to us at ProvenProductivity@bossard.com and we can find your perfect solution or even develop one for you.

May 19, 2017
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