- Joined
- Jun 29, 2014
- Messages
- 4,060
O.k., I'll try to concisely summarize this problem...I'm looking for some insight and expertise on how torque wrenches work and maintain their accuracy:
Case in point: Adjustable, manual, ratcheting torque wrench - typically used at the 20 in-lb setting. The claimed accuracy of the torque wrench is +/-10%, so one could reasonably expect a range of 18-22 in-lb in practice. The torque wrench is stored in a tool drawer and is on a calibration schedule in an ISO 9001:2015 manufacturing facility. In other words, assume no extreme abuse or misuse of the instrument.
Problem/Headscratcher: We torque a series of bolts to 20 in-lbs while the torque wrench is oriented in the vertical plane. The operator normally starts the wrench handle in the "down" position, or pointing towards the floor and swings the handle up to torque the bolt to the setting of 20 in-lbs. Here is the headscratcher: the operator was interrupted after reaching torque on a bolt. When returning to the work, she placed the wrench on the bolt with the handle in the "up" position, or pointing up towards the ceiling. Without remembering that she had already torqued the bolt, she then commenced work and torqued the bolt to 20 in-lbs, suggesting that it hadn't been torqued previously.
This accident was observed by the manufacturing engineer and was curious about how this could happen. He tool the wrench to the QC lab where we have a calibrated torque meter on the wall. Sure enough, the wrench behavior was replicated on the meter. This time however, the wrench was under torquing by 5 in-lbs when starting in the "down" position and over torquing when starting in the "up" position - both outside of the claimed instrument tolerance. A calibration of the torque wrench put us back on track...
Questions:
Case in point: Adjustable, manual, ratcheting torque wrench - typically used at the 20 in-lb setting. The claimed accuracy of the torque wrench is +/-10%, so one could reasonably expect a range of 18-22 in-lb in practice. The torque wrench is stored in a tool drawer and is on a calibration schedule in an ISO 9001:2015 manufacturing facility. In other words, assume no extreme abuse or misuse of the instrument.
Problem/Headscratcher: We torque a series of bolts to 20 in-lbs while the torque wrench is oriented in the vertical plane. The operator normally starts the wrench handle in the "down" position, or pointing towards the floor and swings the handle up to torque the bolt to the setting of 20 in-lbs. Here is the headscratcher: the operator was interrupted after reaching torque on a bolt. When returning to the work, she placed the wrench on the bolt with the handle in the "up" position, or pointing up towards the ceiling. Without remembering that she had already torqued the bolt, she then commenced work and torqued the bolt to 20 in-lbs, suggesting that it hadn't been torqued previously.
This accident was observed by the manufacturing engineer and was curious about how this could happen. He tool the wrench to the QC lab where we have a calibrated torque meter on the wall. Sure enough, the wrench behavior was replicated on the meter. This time however, the wrench was under torquing by 5 in-lbs when starting in the "down" position and over torquing when starting in the "up" position - both outside of the claimed instrument tolerance. A calibration of the torque wrench put us back on track...
Questions:
- The uninformed assumption here is that torque wrenches should work consistently in any orientation? Is this a sound assumption?
- Assuming that it is not a sound assumption, how would orientation affect the torque setting and knock it out of calibration?