METU – Mechanical Engineering Department
ME 308 Machine Elements II
Spring 2009 ‐ Term Project
“Gearbox and Bearing Design”
Salih ALAN B‐175 5256 firstname.lastname@example.org
Ali Murat KAYIRAN A‐209 5266 email@example.com
Gökhan ÖZTÜRK G‐156 5246 firstname.lastname@example.org
Due Date: 29.05.2009 10:00 (to B‐175)
A design team is given the task of developing a new multipurpose gearbox. Fig. 1 shows the general layout of the gear box and
the two stage transmission unit is shown schematically in Figure 2. The first stage is built up with helical gears. The second stage
is constructed as a bevel gear set. Bearings are located on the shafts as shown in Figure 2.
Table 1: Gearbox specifications
Input shaft speed(rpm) 750
Input power (kW) 10
Number of load cycles for helical pinion 5.108
Reliability (%) 99
Velocity ratio of the helical gear set 2.15‐2.20
Velocity ratio of the bevel gear set 1.55‐1.60
Factor of safety 1.20
Efficiency for helical gear set 0.97
Efficiency for bevel gear set 0.96
Quality number 10
Diameter of Shafts 1‐2‐3 (mm) 28‐32‐42
Working temperature (oC) 50
Oil type SAE 30
Required service life (hours) 40000
Reliability of the bearings (%) 90
Figure 1: General layout of the gearbox.
ME 308 Spring 2009 Term project
The material of the helical gears are through hardened and tempered steel with a hardness of 360 BHN (grade 1) and the
material for bevel gears are carburized and case hardened steel with hardness of 55 HRC (grade 1). The gears are cut using the
cutter in Figures 14‐7 and 14‐8 (Shigley 8th Ed.) and have 20° normal pressure angle with FDI (full depth involute). Helix angle is
15° for helical gears; choose the minimum number of teeth to avoid interference and undercutting. The bevel gears are straight
bevel gears with 20° pressure angle. Design all the gears for the minimum standard normal module. Choose recommended
modules, from the table in “Notes to Be Used in Examination”. After finding the appropriate module, design the face widths for
the specified factor of safety. Find the tooth and face contact ratio of helical gear sets. For each gear, provide a manufacturing
table containing all the necessary gear parameters (Table 2). After you have designed all the gears, determine the lengths
shown in Figure 2 and fill Table 3. Take the clearance between the wall and gear surface at least 50 mm. Select all the bearings in
the gearbox. For the bearings which support shaft 1, use deep groove ball bearings. Note that, the bearing at B is the floating
bearing. For those on shaft 2, use angular contact ball bearings. Tapered roller bearings will be used on shaft 3. The shaft
diameters are determined at most 3 mm larger than the minimum bearing bore diameter.
Figure 2: Schematic view of the gearbox
• Make the detailed design of all the gears, select the bearings, and make a geometric design of the casing excluding
strength considerations in detail.
• All dimensions and tolerances should be shown.
• Show all the design details in order to locate the bearings.
• Explain the construction of the casing.
• In your detailed design, consider the assembly steps. You may prepare an animation video file to show the assembly.
Also, consider the maintenance of the gearbox (lubrication, disassembly, etc.).
• Prepare a user manual showing technical properties (maximum velocity, maximum temperature, lubrication period,
lubrication level, etc.) and maintenance procedure of the gearbox designed.
• Prepare an animation of the working gearbox.
Table 2: Gear manufacturing table
Part name / Index
Normal pressure angle, φn
Normal module, mn
Helix angle, ψ
Addendum of the cutter, a
Dedendum of the cutter, b
Face width, F
Table 3: Geometric parameters* [mm]
L1 L2 L3 L4 L5 L6 L7
*Distance between load application points.
ME 308 Spring 2009 Term project