The effects of process faults and misalignments on the cutting force system and hole quality in reaming

A chip thickness and cutting force model that considers the deflection of the tool and the regenerative effect resulting from the presence of process faults and misalignments has been developed for the reaming process. Through a series of experiments, the model has been calibrated and validated. The model predicts tool displacement, torque, thrust, X and Y forces, and the average radius of the reamed hole. The developed model is also shown to be capable of being used as a basis for the on-line detection of process faults present in the system.     

Los Angeles City Hall

This paper describes the Los Angeles City Hall building and a unique seismic strengthening program. Four hundred and sixteen high damping rubber bearings, 90 flat sliding bearings and 64 viscous dampers have been installed as part of the seismic rehabilitation. The building is a 460 feet tall steel frame with unreinforced masonry infill. The rehabilitation consists of installing high damping rubber bearings at its base supplemented with nonlinear viscous dampers. This paper describes various aspects of the project including the development of seismic performance goals, identification of inherent seismic deficiencies of the existing building, evaluation of alternative strengthening schemes, the final design process and construction issues. Copyright © 2000 John Wiley & Sons, Ltd.     

Mechanistic model for the reaming process with emphasis on process faults

A mechanistic model is developed to predict the cutting forces for an arbitrary reamer geometry. Inputs to the model include: tool geometry, feed, speed, initial hole geometry, and process faults including parallel offset runout, spindle tilt, their respective locating angles, and tool/hole axis misalignment. Given these input parameters, the model predicts torque, thrust, and radial forces. The cutting edges of the reamer are divided into elements and the elemental forces are determined from a fundamental oblique cutting model. The model is calibrated over a range of feed, speed, and varying tool geometry. Model validation tests were conducted and model predictions match experimental data well. The effects of process faults on cutting forces are examined through model-based studies. It was found that parallel offset runout, spindle tilt, spindle tilt locating angle, and tool/hole axis misalignment have significant effects on the radial forces. These radial forces are shown to be correlated to hole quality.     

Minimally invasive disc surgery. Nucleotomy versus fragmentectomy

There is continued debate as to the optimum surgical management of a herniated disc with sciatica. There are proponents of conventional microdiscectomy as well as those who advocate minimally invasive approaches, including central disc decompression or nucleotomy as well as arthroscopic lumbar microdiscectomy and fragmentectomy. In this controversy (I), Dr. Gary Onik takes the position that central disc decompression is both safe and efficacious and may be the procedure of choice for recurrent disc herniations (II). Dr. Parvis Kambin takes the opposing position and advocates arthroscopically assisted fragmentectomy as the procedure of choice.