Final Project Report

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

ME359 Final Project Report

Page 1 of 10

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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Ninput = # input teeth

τinput = input torque

ωinput = input rotation speed

Noutput = # output teeth

τoutput = output torque

ωoutput = output rotation speed

GR = gear ratio

Gear Speed Relation

v = velocity at gear tooth contact

R = radius of gear

ω = rotation speed

DP= diametral pitch

F = force at gear tooth contact

PD = pitch diameters

N= number of teeth

(

)

(

) (

)

Gear Torque Relation

(

)


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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) MAX 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 0.995

Worm 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) MAX 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)


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)


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 P.D. 0.5


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Second Shaft



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



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)


Bore Diameter 0.1869 0.0010 0.0000 0.1879 0.1869

Hub Diamter 0.625 Hub Projection 0.3125 Length 0.5625 P.D. 1.000

10 Tooth Gear (from SDP-SI)


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


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

Total Length 3.562 0.005 0.025 3.567 3.537

Calculate Total Length B.W. + I.W. + B.W.


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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Bore 0.375 0.000 0.002 0.375 0.373

Outer Diameter 0.875 0.000 0.003 0.875 0.872

Bearing 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



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)


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

Housing

2nd Shaft Hole

Calculate Total Length (parallel to input saft) B.W. + I.W. + B.W.


Worm 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

Output Length (O.L.) 1.000 0.005 0.005 1.005 0.995

Total Length 1.168 0.015 0.015 1.183 1.153

Calculate Total Height(perpendicular to input saft) I.H. + (P.D.(worm) + P.D.(10))/2


Input Shaft Hole (I.H.) 1.500 0.005 0.005 1.505 1.495

P.D.(worm) 0.500 0.005 0.005 0.505 0.495

P.D.(10) 0.417 0.001 0.001 0.417 0.416

Total Length 1.958 0.008 0.008 1.966 1.951

Output Shaft Hole

Calculate Total Length (parallel to input saft) 1/2*P.D.(10) + 1/2/*P.D.(100)


P.D.(10) 0.4167 0.0005 0.0005 0.4172 0.4162

P.D.(100) 4.1667 0.0005 0.0005 4.1672 4.1662

Total Length 2.2917 0.0005 0.0005 2.2922 2.2912


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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 Analyses Requirements

50lbf over hung load at output shaft

Output shaft is 1.5” max

Max speed of 240 rpm

Life of 25,000 hours

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:


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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.

Work Estimate and Actual Preliminary Work Estimate:

Part/Assy Description Responsible Engineer Model Time

Completion Estimate [min]

Drawing Time Completion Estimate

[min]

Sprocket Alex Patow 45 30

Shaft Mike Gonzalez 45 30

Body John Griese 30 30

Assembly Abby Dutke 60 30

Arm 1 Alex Patow 30 30

Arm 2 Mike Gonzalez 30 30

Arm Assembly 1 John Griese 45 30

Arm Assembly 2 Abby Dutke 45 30


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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 45

CAD 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


Page 10 of 10

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

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