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Materials and Manufacturing Considerations in Product Design
Published in Joseph Datsko, Materials Selection for Design and Manufacturing, 2020
Consider also the plight of the machinist who has to make the specimen. Again, it has been the author’s personal observation that the typical skilled machinist produces the gage section in the following manner. He first paints the “blank” specimen with a very rapidly drying paint called “layout blue.” He then goes through the exact procedure with a “scriber” and scale to draw the gage section on the blank that a draftsman does in making the original drawing. The machinist then clamps the blank in a vise on a milling machine with a very light force. He moves the blank in the vise until the scribed line representing the gage section is parallel to the top of the vise jaws. He does this visually. He then proceeds to advance the milling cutter through the blank until the machined surface appears to coincide with the scribed line. The same procedure is followed for the second side. Consequently, neither the maker nor the user of the specimen actually “measures” the gage section. In summary, the specimen shown in Figure 1–2 is designed as a good project for a draftsman to draw but a poor project for a machinist to fabricate.
Applying Strain and Stress in Multiple Dimensions
Published in Jenn Stroud Rossmann, Clive L. Dym, Lori Bassman, Introduction to Engineering Mechanics, 2015
Jenn Stroud Rossmann, Clive L. Dym, Lori Bassman
In the previous chapters, we have discussed primarily axial loading conditions and how to determine stresses and deformations under these conditions. We now turn our attention to bodies subjected to a twisting action caused by a torque or a twisting moment. As before, we will be looking at the isolated effects of this one type of loading; we will later be able to combine multiple loading configurations to address more realistic, real-world problems. One example of a twisting external load is in the tightening of a vise grip: the user applies a torque to the threaded screw of the vise, turning it, which in turn causes the jaws to tighten. In practice, rods for transmitting torque, such as motor shafts, are generally circular or tubular in cross section. Most of our examples and applications, therefore, will involve circular sections.
Fluid Conductors and Connectors
Published in Anton H. Hehn, Fluid Power Troubleshooting, 1995
To assemble screw-type couplings, place the socket in a vise and turn the hose into the socket until it bottoms. Then back it off a quarter- to half-turn. Next, lubricate the nipple and the inside of the hose with heavy oil. Then thread the nipple into the socket, leaving a small gap. Always make certain the lubricating oil is compatible with the tube. Some couplings require a mandrel for assembly. It is threaded to the nipple and prevents the end of the nipple from damaging the inner tube during assembly. Some couplings are designed to bite directly into the wire reinforcement. For these, the cover must be skived or peeled off. The notch or knurl on the coupling can be used as a guide for the skiving length. To skive a hose, first mark the length, then place it in a vise and cut through the cover with a knife, or with a hacksaw using backstrokes. Make a diagonal cut and peel the cover off with pliers. Be sure not to damage the reinforcement.
Individualized prediction of pedicle screw fixation strength with a finite element model
Published in Computer Methods in Biomechanics and Biomedical Engineering, 2020
Jonas Widmer, Marie-Rosa Fasser, Eleonora Croci, José Spirig, Jess G. Snedeker, Mazda Farshad
Computed tomography (CT) images (Philips, Brilliance 64, 0.5 mm resolution) allowed assessment of vertebral bone integrity prior to screw insertion. In each vertebra a pedicle screw was inserted in either the left or right pedicle under guidance of an experienced surgeon, using a free-hand technique. The screw entry point was carefully chosen, and the screws were inserted parallel to the superior endplate and they followed pedicle direction (Zhang et al. 2006; Le Cann et al. 2015). Six different polyaxial pedicle screws (5 mm × 35mm, 6 mm × 30mm, 6 mm × 40mm, 6 mm × 45mm, 6 mm × 50mm, 6 mm × 55mm) from the MUST Pedicle Screw System (Medacta International SA, Castel San Pietro, Switzerland) were used. For each specimen, the length and the diameter of the inserted screw depended on the size of the vertebral body and the pedicle, respectively (Weinstein et al. 1992; Suk 2011). The anterior parts of the vertebrae were potted into appropriate boxes using Polymethyl methacrylate (PMMA; SCS-Beracryl D 28 Powder and SCS-Beracryl D 28 Liquid, Suter Kunststoffe AG, Fraubrunnen, Switzerland). For the purpose of being CT transparent, the boxes were manufactured from Polyethylene terephthalate (PET). Postoperative CT scans were performed, and screw alignment was assessed using an iterative closest point algorithm, which matched the box and screw geometry to the CT image (Besl and McKay 1992). For further stabilization during testing, a metal plate was placed through the vertebral foramina and fixed on both sides to the boxes before testing. The boxes containing the specimens were mounted on a universal 3-way tilting vise, positioned on a X-Y-table free to move in the plane perpendicular to the direction of screw extraction, and angles in all planes were adjusted to achieve axial screw alignment as computed. Uniaxial tensile load was applied to the screw head with a universal testing machine (Zwick-Roell, Zwick GmbH, Ulm, Germany) (Figure 1). We used the Xforce HP 10 kN load cell with a measurement accuracy of ±0.5% for force measurements above 100 N and manufactured by the same supplier as the testing machine. Conforming to ASTM standard, the velocity of screw extraction was set to 5 mm/min (Tolunay et al. 2015; ASTM F543-17 2017; Aycan et al. 2017). In addition, a preload of 5 N was applied for improved alignment and to get rid of the initial slack (Schmid et al. 2017).