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Clamping Down on Holding Capacity Standards

Robotic Industries Association

Recently, you may have referenced materials for the purchase of clamps, including viewing the product specifications.  You found that the data for clamps varied company to company.  So, you ask, when is a 1000-lb. holding capacity clamp really a 1000 lb. holding capacity clamp?  And, how is holding capacity defined?  What clamp gives me the real holding capacity and reliability I require to meet my application needs safely and achieve my productivity improvement and cost-reduction goals?  The answer:  It all depends on how one determines and defines holding capacity.

There are numerous variables that can affect the final holding capacity that are reported by different manufacturers.  These include the design of the clamp itself, the thickness of the clamp material, the relative hardness of the material, the quality of the rivets, the riveting methodology, the quality of the material, the quality of the stamping (cleaner holes mean rivets/bushings fit better and provide a smoother action), and structural rigidity of the assembled product.  Any of these could affect the actual holding capacity.  In turn, the individual testing procedures will yield variances in the definition of holding capacity. Here are some considerations you need to know before pushing a clamp to its published upper limit.

One of the first issues to consider is the positioning of the spindle in relation to the pivot point of the clamping bar during the testing of holding capacity. The further out the spindle is placed on the clamping bar the lower the holding capacity.  Depending on the clamp, the position of the spindle can affect the determined holding capacity by as much as 50 percent.

A second point to consider is that many companies in the industry sacrifice their own innovation and reverse engineer what others have done.  The problem with many reverse engineered designs is that there is often no testing to go along with the product.  Since the product design was copied, so is the data from the original design.

Third, and very important to understand, is the definition of holding capacity.  Each company typically (not always) publishes their defined holding capacity in its product catalog.  But, read the individual definitions carefully . . . some clearly indicate the holding capacity is the clamping load the clamp can withstand before there is no permanent deformation of the clamp components, providing safe and repeatable toggle action.  But, others indicate that the holding capacity is the clamping load at which there is distortion of the clamp resulting in failure (unlocking).

At DE-STA-CO Industries, we have set the industry standard to provide you with clear definition and testing criteria that furnish you with reliable data regarding the specifications of our products.  We define deflection as the amount of distortion the clamp undergoes when subjected to a clamping load.  Meaning, when the clamping load is removed, the clamp will not return to its original shape, at which point the clamp integrity has been compromised.   Additionally, permanent deflection is defined as the amount of permanent set the clamp takes when subjected to a clamping load.  

Taking holding capacity testing a step further, DE-STA-CO Industries includes a safety factor in its clamp capacity rating.  To rate the clamp we take it to the point where the clamp begins to yield and then we use a percentage of that value as our catalog holding capacity.  Using our in-house test lab DE-STA-CO Industries has proven that the holding capacity of its clamps are typically greater than those of competitive products.  Through years of testing competitively rated products, we consistently find that many other clamps on the market begin taking a permanent set well below their rated capacity.  This is a serious concern to us, and we took strong interest in wanting to ensure customers such as you were informed, and that our customers receive tried and true DE-STA-CO Industries products that translate to an improvement in your manufacturing application and environment.

The lack of communication on standards has brought us to you…. to ensure that you understand what questions to ask, the individual testing that has occurred, and of course knowing the answer that best meets your goals.   In the case where you think you are going to push the upper limits of a clamp’s stated capacity, make sure you understand how the capacity was determined.  Is the capacity based upon where the clamp begins to yield or where you actually have failure?  If it’s the latter, pushing a clamp to its limit could have severe consequences to your workforce, to the integrity of the product, to your manufacturing output, and to your costs.

With the standards we use comes confidence.  With confidence comes the reassurance of having the true holding capacity you need for your application.  THIS is what helps support quality and lean manufacturing!  THIS is what brings you productivity improvement and cost-reduction. 

In an era when lean manufacturing and diligence to quality compliance are critical for the livelihood of the manufacturing industry, DE-STA-CO Industries, once again, has taken the industry to new heights by setting the standard for determining clamp holding capacity that goes beyond ordinary claims in the industry.  Yes – we are clamping down on holding-capacity standards … with your interests at heart.

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