Featured this issue:

Torque Reaction and Compensation
Product Spotlight – Lightweight Graphite Arms
Ask the Expert – Electricity Bills and Compressors

Torque Reaction and Compensation

Do you have critical joints where the type of tool you use produces reaction torque? Do you deal with repetitive strain injuries? Bolt cross threads? Alignment issues? Or are swing bar tools considered unsafe at your facility? These are all good questions and daily issues that can lead to expensive quality issues, or worse, workman’s compensation claims or work stoppage.

A simple and relatively cost effective way to deal with reaction “kick” (shock or twist of a power tool which is absorbed by the operator’s arm or body when the power tool reaches final torque) and alignment issues is the use of torque arms, torque tubes or reaction arms. Whatever you call them, and in whatever configuration, they can solve many of these problems.

As a guideline, 35 in.lb should not be exceeded when using straight (in-line) screwdrivers. Pistol grip tools can be used at less than 45 in.lb, and angle tools up to 26 ft.lb can be used without an arm.

If it is a DC electric tool which has programable ramp adjustability (accelerates or decelerates the tool until right before it shuts off at the desired torque to control “kick” experienced by the assembly team member) you can use the same configurations at higher torque.

DC Pistol grip or “gun” style tools can be used at higher torques without an arm up to 8 Nm and angle tools up to 45 Nm. Very soft joints typically produce more reaction forces, so the values listed are guides only. (Demonstrations at actual tool torques are always recommended.)

There is a case for the use of different types of tools. Example, pulse tools produce no “kick”, but they are, for the purpose of this discussion; not an option due to joint design. When exceeding these torques, torque arms in the multiple configurations can be used:

Physical dimensions based on the working range and torque capacity of the tool (not the torque specified for the joint) determines arm configurations. I.e. The tool has a capacity of 10-55 Nm but the job requires 30 Nm, therefore the capacity of the arm must be at least 55 Nm, not 30! Remember the idea is to protect the workers, and failure to do so will cause WSIB to challenge the decisions of not just the company, but of the supervisor as well. It’s not worth the fines – don’t let cost be the driving factor after making a good decision to move forward with an arm.

There are standard “off the shelf” arms (see fig. 2 to 4) as well as custom arms (fig. 5) for specific applications. Other applications include using arms to eliminate cross threads as well as tapping threads. Here, the perpendicularity of the arm to the work piece is critical and high strength arms are the key to success.

Torque Arms

Torque arms vary widely in range from micro size of less than 1 ft.lb to over 3,000 ft.lbs. If there is a tool, an arm can be engineered to support it and it’s specified capacity of weight and torque. Generally, tools over 500 ft.lbs tend to be put on torque tubes (see fig. 4) versus 3-D arms (fig. 2) due to space requirements, but don’t count any idea out.

Ultra light, high strength carbon fibre arms (fig. 6 – Product Spotlight) add a lot of mobility to the job. Torque arms tend to be very rigid and you must follow the movement of the arm, not the movement of the part. As long as everybody understands the restrictions, you can usually work around them and implement the arm with total success. The concept is critical. The carbon fibre arms (fig. 6) have gained a lot of notoriety lately as the costs have come down dramatically. They typically can’t exceed 30 Nm torque capacity and a balancer is almost always required, but mobility is greatly enhanced over that of a typical arm.

If you want to go to the next step when tool position or bolt patterns are required to properly seat or eliminate production issues – encoder or “smart arms” not only take the torque but also tell you where you are located within a space of defined area. Feedback mechanisms to the assembly line ensure all criteria is met before the part is allowed to move to the next bolt position and consequently, the next station. This type of arm is typically used with DC electric tools on critical applications such as differential carriers or cylinder heads in lower volume production. We will go into smart arms and positioning systems next month so please check back with us. It’s a very interesting article.

One other caution is to ensure your parts are secured firmly in place as the torque reaction of the tool not only goes through the arm but also through the parts. If the part is not fixed in place and able to withstand the capacity of the tool, it’s going to move at the speed of the tool. A moving part at 300 rpm makes for an ambulance trip and a visit from the labour board. You always need expertise during quoting and implementation, and as always, that can be found at Core Tool Technologies!

Ask the Expert – Electricity Bills and Compressors

Our electric bills are rising with lower production – “Why is my air compressor running when production is down?” Ideas? Please help!

Well, without seeing your plant, I am assuming your compressor has had it’s preventive maintenance done, filters cleaned or changed, etc. I would suggest that you should walk through the plant when production is not running; a Saturday morning?

Air leakage might be occurring. Typically, you can hear the “hiss” at each station. it could be as simple as a broken hose or poor air couplers.

Here’s something to consider: EVERY 1/4″ air leak costs approximately $11,000 per year in electricity costs. Although we like to think so: Compressed air is not free – It will be time well spent. Let us know!

Product Spotlight: Light Weight Graphite Arms

The ERGO-12 and ERGO-30 Telescopic Reaction Arms are used to absorb and transfer the reaction force generated at the screwdriver during fastening, without having a significant effect on freedom of movement, thereby reducing operator fatigue. Through the use of carbon-fibre tubes, the arm is extremely tough while being light at the same time. With the universal mounting adapter, the ERGO-12 is capable of being mounted problem-free in most work areas.

• Solidly constructed rotation and swivel joints. The universal adapter allows for easy mounting in most work environments.
• Telescopic carbon-fiber arm. The tubes have been polished for a precision fit and are guided in low wear polymer bushings.