Tower Hardware

Antenna Systems has the hardware for your towers and other communication system assets. If you need something and you don't see it listed on the website, please contact us (or by phone 847-584-1000) and we'll get you what you need in the shortest time possible.

Do you get torqued up over loose bolts? You think a bolt might be loose, so you "torque it down." But you tightened the one next to it only a few months ago, and now you can actually see it's loose. Ah, the solution is obvious. Set the torque wrench and tighten it up. But just as you get close to the torque spec, that bolt snaps.

If this sounds familiar, you need to know more about torque and its role in making threaded fasteners secure. Otherwise, your installations are each a collection of fastener failures waiting to happen.

A bolt or any other threaded fastener becomes tight when you place it under the correct amount of tension. So what is correct? The answer is not what most people think it is.

You've probably seen a standard torque chart. It shows how much torque to apply to a bolt of a given size and hardness. But in the fine print, if you're lucky, the chart says this is for "typical" bolts. Ah, an undefined term strikes again. What does this note mean?

First, understand that the "typical" value in the chart can be way off from the value you actually need. Just how close that chart value comes to what you need depends on several factors. For example, you use a different torque value for a lubricated bolt than a dry one. The material of the bolt is another factor. And what if it has "moly" (molybdenum) in the threads? And what if it's a used bolt?

The answer to that last question is "Replace the bolt." To understand why, we must understand why that torque value exists in the first place. This understanding will also help answer those other questions, though your proper approach should be to use the recommendations of the fastener manufacturer (should be on the hardware package) or equipment manufacturer. A generic chart just gets you close; relying on that value can result in reduced clamping power in the fastener.

Another problem with torque charts is the values usually account for only a bolt and nut. The locking hardware is also a factor, and it usually gets left out of the chart. So the value is inherently wrong. In manufacturer instructions for assembling with locking hardware, the manufacturer develops the torque value for the fastening system through calculations and testing. If you decide to leave out that locknut for whatever reason, you'll then have the wrong torque values. Assemble per the instructions, to ensure a safe and reliable installation

What's torque?

In mechanial physics, "torque" refers to rotational force. In our case, it's force applied to a fastener. As you tighten something by hand, you suddenly need much more force to turn it any more. Why? Because you are now starting to stretch the bolt. While the bolt is in a stretched state, it tries to shorten to its normal length. The resultant force is what gives the fasteners their clamping power.

If you keep turning, you'll exceed the memory of the metal. The point at which you do this is its "elastic limit." Just before you hit this, you get maximum clamping power. If you exceed it, clamping power permanently and precipitously drops. The bolt assumes a longer length permanently, and the elasticity changes. So does the torque needed to tighten it. It now acts like a different bolt, because it actually is a different bolt. You have deformed it.

The loss in clamping power for any fastener that you use once and then try to use again is typically 50%. Retightening is a form of re-use. For non-critical applications, it's OK to re-use fasteners. But if it matters to you whether the connection holds up, always use new fasteners. That means once you torque it down, don't go back and tighten it. You will actually weaken the connection by doing that.

A wrenching problem

This brings us to another problem. How do you know what torque you're putting on that bolt? Getting an accurate torque wrench reading starts with selection, care, and storage; errors in these areas can easily make your wrench wrong.

Powered torque wrenches require a higher degree of care than their non-powered counterparts and cost more. Manual torque wrenches come in beam, solid-handle, and breakaway styles. The beam wrench is the simplest and least expensive. But it is also the most prone to inaccuracy and requires excess “elbow room” to use. Avoid this version.

Solid handle wrenches come in analog "clock face" gage and digital variations, typically with high resolution. Use this style only if the wrench has a max torque indicator (on the analog, this is usually a resettable red needle). Otherwise, you may find yourself trying to make measurements where getting into position to view the gage is impossible. Neither this style nor the beam style will stop you from over-torqueing.

For towers and similar installations, use a breakaway wrench (or "click wrench"). It comes in vernier or digital display variations. You pre-set it to the desired torque value, and the handle "breaks away" when you reach that value.

You lose accuracy when your measurement is less than 20% or more than 80% of the range of the wrench. Before torqueing a fastener, ensure the threads are clean. Lubricate if required, but leave dry if the torque spec is for dry threads. Put the torque wrench to the rotating part (e.g., the nut), not the bolt.

Be sure you understand and correctly apply the torquing pattern for the particular assembly in which you're installing fasteners. If you don't know what that is, ask. Never tighten related fasteners one at a time; that's how you warp metal plates and cause other mechanical deficiencies.

Storage and calibration

A torque wrench that has a mechanical setting is compressing against a spring. That spring slowly loses calibration while it's compressed. If you store a torque wrench with the setting at anything other than zero, you lose accuracy for the next use.

When you take the torque wrench out, exercise it before first use. Also exercise between uses. To do this, run the torque setting up to your desired torque and then down to zero, then to the desired torque. If you get the wrench out only to see someone else (couldn't have been you) left it set at anything other than zero, exercise it five times and then leave it at zero. Set the wrench aside for an hour, then exercise it twice more before using it.

Your torque wrenches have a recommended calibration frequency. Observe this schedule, and plan ahead so the calibration can be done at at time when you don't need the wrench on a project. If someone drops a torque wrench, don't use it; send it out for calibration.

Siting and specifying a communications tower is a challenge. We are here to help. Feel free to contact us (or by phone 847-584-1000) for more information.

Drawings with the appropriate Professional Engineer state seals are always available to meet your local zoning ordinances.

Antenna Systems & Solutions, Inc. is proud to be a leading provider of communication towers, MET towers, radar towers, and monopole towers.

Our extensive inventory of guyed towers, monopole towers, self supporting towers, and radar towers allows us to ship immediately following a natural disaster.

We stock ROHN 25G, ROHN 45G, ROHN 55G, ROHN 65G, ROHN 80G, ROHN 90G, ROHN SSV Self Supporting Towers, ROHN SCL Self Supporting Towers, ROHN RSL Self Supporting Towers, and Monopoles.

Please take some time to read our Tower Safety page. This very informative resource may save your life.

It covers such areas as:

• Electrocution hazards.
• Fall hazards.
• Mixing of products.
• Qualified installers.
• OSHA.

The National Electrical Code, NFPA 70, provides communications system installation requirements in Chapter 8. Other NEC Articles may also apply, especially those in Chapter 5. The IEEE provides many communications-related standards. If you go to the IEEE Website's Standards library and select "Communications" you will see these. It's a huge list, but only certain ones will apply to your specific application.

Some state and local authorities have additional state requirements. Check with the Authority Having Jurisdiction to determine which, if any, state and local requirements apply.