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BOSTON UNIVERSITY
ME 359 Final Project Report
Group #5 Alex Patow, ME 2015
John Griese, ME 2015
Michael Gonzalez, ME 2014
Abby Dutke, ME 2015
12/1/2013
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ME359 Final Project Report
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Description
The objective of this project is to design a manufacturable prototype gear box. The gear box is
required to have a ratio of 1/240, and a minimum life of 25,000 hours. The input and output shafts are
orthogonal and a maximum of 1.5 inches past the outer surface of the gearbox. The output shaft and its
bearing must support an eccentric load of 50lbf, and have a maximum input shaft rotation speed of
240rpm.
Alex Patow – Spec Parts, CAD, CAD Drawings, Presentation and Report
Michael Gonzalez – Spec Parts, CAD Drawings, Tolerancing, Presentation and Report
John Griese – CAD, CAD Drawings, Tolerancing, Life Analysis, Presentation and Report
Abby Dutke – Spec Parts, CAD Drawings, Presentation and Report
Design Review
The final design of the project includes a 10 tooth spur gear, a 100 tooth spur gear, a 1 start
worm, and a 24 tooth worm gear. The input shaft houses the worm, which is paired with the worm gear.The 10 tooth gear shares the same shaft as the worm gear and is paired with the 100 tooth spur gear.
This gives us a gear ratio of 1/240 and the orientation of the worm and gears makes the input and
output shafts perpendicular. The input and output shafts both protrude 1 inch (nominally) from the
surface of the box. All bearings were specified to support a 50lbf eccentric load with a maximum speed
of 240rpm with a lifetime of 25,000 hours under these most strenuous conditions.
Our gear box housing is made out of 304-Stainless Steel sheet metal which is 0.060” thick. There
are two parts to the housing. One fits into the other and they are connected by self-clinching nuts. The
holes will be drilled into the flat sheet metal pieces, which will then be bent in a set of presses to
achieve the desired shapes.
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ME359 Final Project Report
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Gear Trains without Shared Axles
[
]
Gear Trains with Shared Axles
Tolerance Analyses
We encountered significant problems with SDP-SI’s catalog, which led to discrepancies in
tolerancing. When we measured some of the downloaded parts with Smart Dimension in SolidWorks
they were different, about twice as large in certain cases, than the size stated on the website. The most
intensive analysis was for the input shaft because it drives the dimensions in spacing the rest of the
features. For the input shaft (shown below) we performed a detailed circuit analysis. This was not
necessary for the rest of the components for which we did basic tolerance analysis.
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Input Shaft
Calculate distance from outer face to 2nd Shaft hole (J), J = - F.W. - O.S. + W.H + P.D.P
Measurement Nominal (in) Upper + (in) Lower - (in) MA X MIN
Flange Width (F.W.) 0.045 0.000 0.002 0.025 0.021
Outer Shaft (O.S.) 1.000 0.005 0.005 1.005 0.995Worm Hole (W.H.) 1.730 0.005 0.005 1.735 1.725
Pitch Diameter Center(P.D.C.) 0.438 0.000 0.000 0.438 0.438
2nd Shaft Hole (J) 1.123 0.010 0.012 1.133 1.111
First Groove (G1) O.S + B.W. = G1
Measurement Nominal (in) Upper + (in) Lower - (in) MA X MIN
Outer Shaft (O.S.) 1.000 0.005 0.005 1.005 0.995
Bearing Width (B.W.) 0.188 0 0.005 0.188 0.183
First Groove (G1) 1.188 0.005 0.01 1.193 1.178
*The greyed cell indicated the critical dimension, i.e. the dimension which, the actual part cannot be
greater or less that without a chance that the part will not fit.
Second Groove (G2) - B.L. + F.W. + O.B.L. + F.W. -B.L. = G2
Measurement Nominal (in) Upper + (in) Lower - (in) MAX MIN
Flange Width (F.W.) 0.045 0.000 0.002 0.025 0.021
Outer Box Lenth(O.B.L) 5.811 0.005 0.005 5.816 5.806
Bearing Width (B.W.) 0.188 0 0.005 0.188 0.183
Second Groove (G2) 5.525 0.005 0.019 5.530 5.506
Bearings (from SDP-SI)Measurement Nominal (in) Upper + (in) Lower - (in) MAX MIN
Bore Diameter 0.25 0 0.002 0.25 0.248
Outer Diameter 0.5 0 0.003 0.5 0.497
Bearing Width (B.W.) 0.188 0 0.005 0.188 0.183
Flange Width (F.W.) 0.045 0 0.002 0.025 0.021
Worm (from SDP-SI)
Measurement Nominal (in) Upper + (in) Lower - (in) MAX (in) MIN (in)
Groove Diameter 0.21 0.003 0 0.213 0.21
Groove Width 0.029 0.003 0 0.032 0.029
Retaining Rings (from McMaster-Carr)
Measurement Nominal (in) Upper + (in) Lower - (in) MAX (in) MIN (in)
Bore Diameter 0.25 0.0008 0 0.2508 0.25
Face Width 0.625
Overall Width 0.875
Outside Diameter 0.583
Hub Diameter 0.375
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ME359 Final Project Report
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P.D. 0.5
Second Shaft
Bearings (from SDP-SI)
Measurement Nominal (in) Upper + (in) Lower - (in) MAX MIN
Bore 0.1875 0.0000 0.0020 0.1875 0.1855
Outer Diameter 0.3125 0.0000 0.0030 0.3125 0.3095
Bearing Width (B.W.) 0.125 0.000 0.005 0.125 0.120
Flange Width (F.W.) 0.023 0.000 0.002 0.023 0.021
Retaining Rings (from McMaster-Carr)
Measurement Nominal (in) Upper + (in) Lower - (in) MAX (in) MIN (in)
Groove Diameter 0.147 0.002 0.000 0.149 0.147
Groove Width 0.029 0.003 0.000 0.032 0.029
Worm Gear (from SDP-SI)
Measurement Nominal (in) Upper + (in) Lower - (in) MAX (in) MIN (in)
Bore Diameter 0.1869 0.0010 0.0000 0.1879 0.1869
Hub Diamter 0.625
Hub Projection 0.3125Length 0.5625
P.D. 1.000
10 Tooth Gear (from SDP-SI)
Measurement Nominal (in) Upper + (in) Lower - (in) MAX (in) MIN (in)
Bore Diameter 0.1873 0.0005 0.0000 0.1878 0.1873
P.D. 0.4167
O.D. 0.5
Output Shaft
Calculate Total Length B.W. + I.W. + B.W. + O.L
Measurement Nominal (in) Upper + (in) Lower - (in) MAX MIN
Bearing Width (B.W.) 0.281 0.000 0.005 0.281 0.276
Interior Width (I.W.) 2.000 0.000 0.010 2.000 1.990
Output Length (O.L.) 1.000 0.005 0.005 1.005 0.995
Calculate Total Length B.W. + I.W. + B.W.
Measurement Nominal (in) Upper + (in) Lower - (in) MAX MIN
Bearing Width (B.W.) 0.281 0.000 0.005 0.281 0.276
Interior Width (I.W.) 2.000 0.000 0.010 2.000 1.990
Total Length 2.562 0.000 0.020 2.562 2.542
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ME359 Final Project Report
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Total Length 3.562 0.005 0.025 3.567 3.537
Bearings (from SDP-SI)
Measurement Nominal (in) Upper + (in) Lower - (in) MAX MIN
Bore 0.375 0.000 0.002 0.375 0.373
Outer Diameter 0.875 0.000 0.003 0.875 0.872Bearing Width (B.W.) 0.281 0.000 0.005 0.281 0.276
Flange Width (F.W.) 0.062 0.000 0.002 0.062 0.060
Retaining Rings (from McMaster-Carr)
Measurement Nominal (in) Upper + (in) Lower - (in) MAX (in) MIN (in)
Groove Diameter 0.303 0.003 0.000 0.306 0.303
Groove Width 0.039 0.003 0.000 0.042 0.039
100 Tooth Gear (from SDP-SI)
Measurement Nominal (in) Upper + (in) Lower - (in) MAX (in) MIN (in)
Bore Diameter 0.3747 0.0005 0.0000 0.3752 0.3747
P.D. 4.1667 4.1667 4.1667
Length 0.787 0.787 0.787
Bearing Fits
Shaft Tolerance
Conditions:
Normal Load
Rotating in Direction of Load
All Shafts are <.71”
Tolerance Classification: J5
For All Shafts: Tolerance is +.0002, -.0001
Housing Tolerance:
Conditions:
Outer Ring Stationary
Housing Not Split Axially
Tolerance Classification: H6
For All Shafts: Tolerance is +0, -.0005
Component Life AnalysesRequirements
50lbf over hung load at output shaft
Output shaft is 1.5” max
Max speed of 240 rpm
Life of 25,000 hours
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Assumptions
Assume no axial load, all load radially
Wear on the gears should be negligible compared to wear on the bearings
Weight of the shaft and shaft components is negligible compared to the 50lbf eccentric load
Force Analysis
Where:
P = dynamic load; x = .6 (from tables); Fr = 50lbf
Lifetime Analysis
Where:
m=3 (ball bearings); P=dynamic load; C=dynamic load rating; L10=life in millions of hours
Input shaft:
√ ()
√ ()
All Gears with 0.375” Bore
All bearings are rated for well over 50lbf static load and also well over the 30lbf dynamic load,
including a 1.5x safety factor. Even adding that 50lbf load, the static load rating (273lbf) exceeds
the minimum requirements for both the input and output shafts.
We specified our bearings to the input rotational velocity. Any section between input and
output will be rotating slower than the input velocity.
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Actual Work Estimate
Part/Assy Description Responsible Engineer
Completion Time
Estimate
[min]
Spec/Find Parts- \\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\Worm & Worm Gear Alex & Mike 60
Spur Gears Alex & Mike 60
Bearings Alex & Abby 20
Retaining Rings Alex & Abby 15
Self-Clinching Nuts Alex 5
CAD- \\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\
Box Alex 60
Input Shaft Alex & John 45
Output Shaft Alex & John 45
Assembly Alex 60
Modify Downloaded CAD Models Alex 45CAD Drawings- \\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\
Worm Alex & Abby 30
Worm Gear Alex & Abby 30
10 Tooth Spur Gear Alex 20
100 Tooth Spur Gear Alex 20
Box Pt 1 Mike 30
Box Pt 2 Mike 30
Input Shaft Alex & John 40
Output Shaft Alex & John 40
Assembly Alex 45
Written- \\\\\\\\\\\\\\\\\\\\\\\ \\\\\\\\\\\\\\\\\\\\\\\Tolerancing John & Mike 480
Life Analysis John & Abby 150
Project Report Abby & Mike & John &
Alex
300
Project Presentation Abby & Mike & John &
Alex
210
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ME359 Final Project Report
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Bill of materials
Drawings
(Attached)
ITEM NO.PART
NUMBERDESCRIPTION VENDOR
MANUFACTURING
PROCESSESQTY.
1 102 24 TOOTH WORM SDP-SI P/N: A 1B 6-N24024 DRILL 1
2 101 1 FLUTE START SDP-SI P/N: A 1C55-N24 1
3 103 10 TOOTH SPUR SDP-SI P/N: S1084Z-024A010 1
4 104 100 TOOTH SPUR SDP-SI P/N: S1VS24-100F1524 MILLING 1
5 602 SECOND SHAFT SDP-SI P/N: A 7Y55-FS3118G 2
6 603 OUTPUT SHAFT SDP-SI P/N: A 7Y55-FS8737G 2
7 601 INPUT SHAFT SDP-SI P/N: A 7Y55-FS5025G 2
8 201 INPUT SHAFT MCMASTER-CARR P/N: 8984K823 TURNING/DRILL 1
9 202 SECOND SHAFT MCMASTER-CARR P/N: 8984K823 TURNING/MILLING 1
10 203 OUTPUT SHAFT MCMASTER-CARR P/N: 8984K823 TURNING/MILLING 1
11 301 BOX PT. 1 MCMASTER-CARR P/N: 8983K62 SHEET METAL 1
12 302 BOX PT. 2 MCMASTER-CARR P/N: 8983K62 SHEET METAL 1
13 704 PEM NUT PEM P/N: S-632-0 ZI--N 8
14 703 6-32 MACHINE MCMASTER-CARR P/N: 91735A142 8
15 502 SIDE-MOUNT MCMASTER-CARR P/N: 97431A280 2
16 501 SIDE-MOUNT MCMASTER-CARR P/N:97431A300 2
17 503 SIDE-MOUNT MCMASTER-CARR P/N:97431A320 2
18 702 SHAFT PIN MCMASTER-CARR P/N: 92373A106 2
19 701 KEY MCMASTER-CARR P/N: 98535A130 MILLING 1