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These are some more renderings and drawings of the James Machine.
This is the complete assembly of the machine showing details on the floating arm design.
This is a rendering of the arm assembly.
This is a rendering showing the arm assembly at its end of travel position and illustrating the arm catch mechanism.
This is a rendering with the tower and table cover removed.
This is a sample drawing of the test shoe.
Below is a report I wrote to help explain the James machine and its math to sales and engineering personnel.
Understanding the James Machine and Its Math Calculating COF The James Machine measures static coefficient of friction. (1) Static coefficient of friction is the ratio of the horizontal component of force applied to a body that just overcomes the friction to slipping to the vertical component of the weight of the object applied to it. (2)The coefficient of friction is generally denoted by the Greek letter m as shown in figure 1, "F" is the horizontal component of force and "N" is the verticle component of force.
figure 1 This simple formula is used by push or pull type friction testers. Although the James Machine pushes the test shoe, it does so through a ten inch articulated arm. Verticle force is applied to the arm during the test and as the table moves the angle of the arm decreases. This changing angle divides the verticle force over the shoe to horizontal force pushing the shoe until horizontal force is sufficient to overcome friction and the shoe slips. Coefficient of friction is determined by calculating the angle of the articulated arm at the instant that the shoe overcomes friction and slips. The angle of the arm is denoted by the greek letter q or the letter "A". (1)Thus the formula used by the James Machine is shown figure 2.
figure 2 This formula is used on inclined plane model testers. (7)The only other force involved is the mass of the shoe. When the weight of the shoe is less than a pound, its effects are considered negligible otherwise you must factor out the weight of the shoe for accurate test results as shown in figure 3 .
figure 3 The James Machine records COF data on a chart that does not factor out the weight of the shoe. Therefore the weight of the shoe must not be greater than a pound. Calibration The procedures used for calibration of the James Machine verify the operation of the machine and its components. (3)First, Borco, a material used on drafting boards, is used to as a reference surface to test the validity of the shoe leather and second (4)the frictionless shoe procedure is used to test the machines operation. The procedure calls for fixing a frictionless shoe to the arm and a counterweight pulling on the frictionless shoe. This provides a known horizontal force pulling on the shoe and the weights over the shoe provides a known verticle force. The simple formula, shown in figure 1 and figure 4, can be used to predict the point of equilibrium.
figure 4 In this formula m represents the tangent of the angle that the arm must achieve for equilibrium between the counterweight and the horizontal force imposed by the arm.The procedure of using a frictionless shoe for calibration will mask some mechanical problems. The frictionless shoe will mask nonorthogonal travel of the table to the plane of strut or arm. Nonorthogonal travel causes low COF readings and has been the most predominant obstacle that has hindered the development of the Michelman James Machine and may be a significant issue in older machines. The counterweight pulling on a frictionless shoe may also mask vibration present in the machine. Excessive vibration will cause low COF numbers, but may not add or subtract from the force applied by the counterweights. Reporting Results (5)The test procedure requires reporting the twelve readings, an arithmetic average, temperature and humidity at the time of the test. (6)On many test performed by R.D. Jablonsky also included sample standard deviation [ sn-1], sum of squares of values [Sx2] and number of data. Although not required there is an apparent benefit to this information and the Michelman James Machine could easily incorporate this data in its printed report.
(1)ASTM standard test method, D 2047-93 3.1.3 (2)Machinest handbook, Friction (3)ASTM subcommittee ballot D21.06, using a Borco/standard leather reference surface. (4)ASTM calibration procedure F-489 (5)ASTM standard test method, D 2047-93 9.1 & 9.2. (6)Comparative analysis of official vinyl asbestos tile (OVAT) substrate with proposed official vinyl composition tile (POVCT) substrate (7)Significance of test results, Effects of varying loads
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