

| Subject: | Some Comments on the Torque Wrench Discussion |
| From: | Frank Grunthaner |
| Date: | Mon, 14 Oct 2002 22:51:44 EDT |
The debate over the merits of clicker vs beam torque wrenches moves me to a few comments. In my experience, I have used 4 different types of torque wrenches: the trusty beam, the widely available adjustable clicker, the dial (actually a beam and gear mechanism as has been pointed out) and the fixed calibrated clicker. To begin, I've been wrenching bolts for more than 44 years, the last 43.8 using a torque wrench. Most of that twisting has been done on automobiles ranging from American iron, through German alloys, through French mystery metals and on to Italian aluminum. My laboratory is often described as a stainless steel palace. The UHV hardware ranges in value from about $75,000 to $1,500,000. The proper tightening of flanges is critical to avoid leaks which can trash the experiments. Our typical operating pressures are below 10(-10) torr. To achieve these pressures, the systems are baked for extended periods to peak temperatures of 235 C to 450 C. These thermal cycles are particularly stressful for bolt preloads on copper sealing systems. Bolt torque specs range from 14 foot pounds to 125 foot pounds. All bolts are silver plated for thread lubrication. Noone works in that lab with using a torque wrench on every bolt. Over the years, I've fired a few for just such a transgression. My advice is, however educated your hand or butt is, use the torque wrench. Cheap insurance. Remember, no single time job is nearly as expensive as the second or third redo to get it right. Now as to the torque wrench issue. As far as I'm concerned, the key problem here is calibration. Now the trusty beam and the disguised beam (dial) both rely on the basic material properties of the beam. Anybody anywhere can reestablish zero (bend the pointer or rotate the bezel). The adjustable clicker can lose its calibration all too readily. Heavy over torque beyond the click point. Sharp drop to concrete. Massive ingestion of oil, dust and dirt. The real problem is with the adjustability. With adjustment comes the need to calibrate often and well. Now, the best wrench I use (used the same type for more than 30 years) is the fixed calibration clicker. This wrench is available in a wide range of torque values. One wrench, one value. For the lab, we use about 6 different bolt sizes, so we maintain 3 sets of 6 different wrenches. Now these wrenches are not ratchet drives, but rather use a replaceable box, open, Allen or torx head. Used like a regular open or box end wrench. I have had these recalibrated and never had one go out of specification. For automotive wrenching, however, I use an adjustable clicker and a beam wrench. The beam is usually a PITA to get just where I need it, so I never (well almost) use it on an engine. Nope. I use it to calibrate the clicker. I have a 1/2 inch drive beam and a 3/8 inch dial. I have appropriate box square sockets to drive them with the 1/2, 3/8 or 1/4 inch drive adjustable clicker. Just before use, I set up the clicker to the torque I need, then on to the job. As part of this drill, I always clean the threads of any reused bolt by chasing it with a die. I always use a MoS2 thread lubricant on anything except exhaust manifold bolts. There I use a WS2 lubricant because of the temperatures. All the hardware I'm talking about are available from Craftsman, Mac, Snap-On or from McMaster-Carr. Just a comment, Frank Grunthaner
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