1 M XXXXXXXXXXWinter Semester Final Design Project By Dr Hany Gomaa and Dr John Cheung 31/March/2020. Part A – 25 Marks 1. Describe the different methods of tolerancing for the location of holes....

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1 M313-2020 Winter Semester Final Design Project By Dr Hany Gomaa and Dr John Cheung 31/March/2020. Part A – 25 Marks 1. Describe the different methods of tolerancing for the location of holes. Provide a sketch to support your answer. 2. Explain what is meant by the virtual condition and how does it change for external and internal features using the different modifiers (MMC, LMC and RFS). 3. What is the distance between the two-extreme permissible centre positions of the hole as shown in Figure? 4. Give reason(s) for using multiple start (lead) threading in fasteners. 5. Explain the general function(s) of a bearing and the purpose of adding seals to it. 6. Explain the relationship between surface finish and lubrication. 7. Select and explain the type of ball bearing that is best suited to meet both of the two following design considerations: To withstand both radial and thrust loads and having the thrust load higher than the radial load. 8. You are required to choose the best power transmission method suited for the machinery layouts shown in the figure. You need to choose either gears, chains or belts to meet the design specifications. Give a brief summary of your choice for the power transmission method which must be supported with calculations. 2 9. The component has been produced according to the specifications shown in Figure (a). Then each part has been measured as illustrated in the Table. Which part would be acceptable or rejected? State your reasons. Show your calculations. Change the design specifications to Figure (b), which part would be acceptable or rejected? State your reasons. Show your calculations. 3 10. Draw the necessary views to represent the caster frame as shown in the figure below. Using the table given, add all the required welding symbols. Identify each part of the welded assembly and add a part list on the drawing. The welded joint has been designed using the weld size having 33 percent of full-strength. Use scale 1:1 for your drawing. 4 Part B – Gear Box Design - 75 Marks A light-weight reduction gearbox needs to be designed using as many standard parts as possible with minimal oil leakage. The gear drive system is housed inside a rectangular casing which is split horizontally into two halves, see sketch for the split line. The two casing are fastened together using a number of M6 screws, hence a screw joint arrangement. (The top half can come off completely from the bottom half after undoing all the screws.) Hint, screw joint between a flange and a casing. The input shaft of 22mm in diameter rotates at 3000rpm. It is to be supported by two plain bearings subjected to a cyclic radial load. The are lubricated by oil. The plain bearing in the open-end of the shaft must be protected using a removable cover plate together with an appropriate seal and gasket. For the closed end of the casing, no cover plate is needed. The output shaft is 28mm in diameter and rotates at 1000rpm. It is to be supported by two rolling element bearings which are subjected to a reversal radial load. They are also lubricated by oil. The rolling element bearing in the open-end of the casing must be protected using a removable cover plate together with an appropriate seal and gasket. This bearing is also considered to be at the hot end of the shaft, where the outer race of the bearing must be allowed to slide axially. The rolling element bearing at the closed end of the casing is considered to be supporting the cold end of the shaft. The casing closed end also does not require a cover plate. The centre distance between the two shafts is 76.2mm. The pinion gear with a module of 3.18mm is to be fixed to the input shaft using appropriate fasteners permitting quick assemble and dissemble process. It is positioned at the mid-span of the two plain bearing supports. The mating gear is also mounted at the mid-span of the output shaft using appropriate fasteners for quick assembly and disassembly. It is again located at the mid-span of the two rolling element bearing supports. The design constraints of this reduction gearbox used are: • Maximum gearbox size – 210mm x 140mm x 175mm. • Light weight. • Use standard steel spur gears with 20º degree pressure angle. • Use standard fasteners. Scope of work: 1. Determine a pair of spur gears having 20º pressure angle and 3.18mm module for the above design specifications. 2. Draw or sketch the design of the following important areas only: a. How the shaft is being supported by the bearings which is in turn being supported by the housing and casing. 5 b. How the gear is being fastened to the shaft. c. How the cover plate together with the seal in the open end of the shaft is being fixed to the casing. 3. Draw an optimum assembly sectional view across the horizontal split line showing as many components as possible used in the design of the reduction gearbox. a. Provide a detail part list for the assembly drawing. 4. Choose the appropriate class of fit and determine the corresponding limits of size for the following areas: a. Input Shaft: i. Between the input shaft diameter and the plain bearing inner diameter. ii. Between the housing bore diameter of the casing and the plain bearing outer diameter. iii. Between the pinion hole and the shaft diameter. b. Output shaft: i. Between the output shaft diameter and the rolling element bearing inner diameter. ii. Between the housing bore diameter of the casing and the rolling element outer race diameter. iii. Between the gear hole and the shaft diameter. 5. Determine the geometrical tolerance for the holes in the cover plate used in the open-end of the output shaft: i. Assuming the M5 screw joint having H11/c11 fit has been chosen. Fine the maximum allowable positional tolerance allowed. 6. Make a separate drawing of the output shaft and dimension it. The dimensions must also include the limits of size, geometrical tolerances and surface finish for the following three key areas. a. The two bearing surfaces being machined by grinding. The geometrical tolerance can be assumed to be 0.05mm. b. The shaft portion where the gear is being supported. It will be machined by turning. The geometrical tolerance with reference to the two bearing surfaces is assumed to be 0.1mm. 7. Make a separate drawing of the gear located in the output shaft using a conventional representation and dimension it. The limit for the keyway is assumed to be +/- 0.25mm and the geometrical tolerance is 0.1mm with reference to the bore of the gear. Sketch the gear tooth profile. Use the outer diameter and pitch diameter and root diameter to dimension the gear teeth. 8. Make a separate drawing of a partial sectional view of the screw joint assembly for a portion of the gearbox showing the top and bottom of the casing including an appropriate sealing between the two mating faces. In the sectional view, you need to dimension the length of the M6 screw (LG), the tapped threaded length, the drill hole depth, the drill hole diameter and the top casing cover thickness. 9. Make a separate drawing of the cover plate used in the open-end of the output shaft using a conventional representation and then dimension it. a. The mating surface is finished by grinding. It has a geometrical tolerance of 0.02mm. b. The holes in the cover plate of Ø5 with H11/c11 fit has a geometrical tolerance calculated in Part 5 with reference to the mating surface. c. On the mating surface, design three datum target points for inspection purposes. 6 10. Write a brief report on the design having the following heading: Summary, Introduction, Design, Calculations, Drawings, Conclusions and Recommendations. Maximum of 5 pages of main text not including sketches and drawings. Notes: • All drawings and sketches must be manually drawn. • Using an optimum dimensioning method to achieve the least accumulation of tolerance. • Dimensions in mm. • Third angle of projection. 7 M313-2020W- Final Project 175