L8_Bearings and More Gears

8/3/2019 L8_Bearings and More Gears

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Revisions List

Names, description (Table Vise Re-Design), etc.

Isometric

Cross-sectionView

Individual views of parts that

have changes

One sheet for each

design solution.


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Bearings


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Bearings

Plain Bearings

Rolling Elements Bearings

Ball, cylindrical roller, needle, tapered roller, and

spherical roller

Fluid Bearings

Magnetic Bearings

A device that allows constrained relative motion between

two or more parts.


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Plain Bearings

Consists of a bearing surface and no rolling elements

Least expensive, compact, high load carrying capacity

Relatively high friction

Can be used with or without lubrication

Bushing Two-Piece Spherical

Plain Bearing


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Plain BearingsBearing Materials

Standard Handbook of Machine Design- Available online through UB Libraries


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Plain BearingsBearing Materials

Optimization process can be used to select appropriate material.


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Rolling Element Bearings

Spherical balls are used to maintainthe separation between the bearing

races.

Large reduction in rotational frictioncompared to plain bearings.

Capable of supporting both radial and

axial loads.

Can tolerate some misalignment of

the inner and outer races.

Ball Bearings


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Use cylinders (with slightly longer

length than diameter) as rolling

elements.

Higher radial load capacities than ball

bearings due to increased surface

area.

Lower capacity and higher frictionwhen subjected to axial loads.

Cylindrical Roller Bearings


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Use long, thin cylinders as rolling

elements.

More compact and require less

clearance.

Extremely high radial loading possible

due to the large number of rolling

elements.

Needle Bearings


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Use conical rollers that run on conical

races.

Whereas most rolling bearings are

suitable for only radial or axial

loading, tapered roller bearings are

suitable for both.

Due to manufacturing complexitiesthey are usually more expensive than

ball bearings.

Tapered Roller Bearings


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Use rollers that are thicker in the

middle and thinner at the ends, with

matching profile on races.

Adjust to support misaligned loads.

Difficult to produce (expensive) and

have higher friction than a

comparable ball bearing.

Commonly used in vehicle

suspensions.

Spherical Roller Bearings


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Fluid Bearings

Support loads solely on a thin layer of

gas or liquid.

Hydrostatic: externally pressurized

fluid bearings. Usually oil, water, or

air that is pressurized by a pump.

Hydrodynamic: rely on the speed of

the journal self-pressurizing the fluid

in a wedge between the surfaces.

Frequently used in high load, high speed, or high precision

applications where ball bearings have shorter life or higher

noise and vibration.


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Magnetic Bearings

Supports a load using magnetic

levitation.

Very low friction and no

mechanical wear.

Can support the highest speeds of any bearing, no known

maximum relative speed.

Usually require constant power and complex control systems.

Can run without lubrication and in a vacuum- used turbo

molecular pumps due to low contamination.


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Methods of Bearing Retention

From Pg. 2225 of Machinerys Handbook.


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Gear Geometry


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Spur GearsExternal

Cylindrical gears withstraight teeth cut parallel

to the axes.

Tooth loads produce no

axial thrust.

Shafts rotate in oppositedirections.


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Spur Gears: from Machinerys Handbook


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Helical Gears

Cylindrical gears with teeth cutat an angle to the axes.

Provides drive between shafts

rotating in opposite directions.

Superior load carrying capacity

and quieter than spur gears

Due to a more gradual tooth

engagement.


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Helical Gears

Beginning on Pg. 2100 in

Machinerys Handbook


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Helical Gears

Chapter 10 in Standard

Handbook of Machine

Design.


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Bevel GearsStraight Bevel Gears

Straight teeth are radial

towards the apex and are of

conical form.

Used to connect two shafts

on intersecting axes.

End thrust developed underload acts to separate the

gears.


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Straight Bevel Gears: Machinerys Handbook

All dimension formulas given on pages 2088-2089.


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Final Project Expectations


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40% of

Final Grade


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Problem Identification & Product Description

Hand Sketches

Detailed hand sketches clearly showing the intended product and how it works.

You will get no credit if you show a picture- this has to be a handsketch.

Identify the product you are designing and describe the need for that product.

Emphasis should be placed on how your product is different than what iscurrently available.

Pro-Engineer Solid Modeling

Entire project must be accuratelymodeled in Pro-Engineer (time-consuming

but easy 10 points).


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Working Drawings showing full detail

I should be able to go to the machine shop and produce your final product

based on what you specify in this section.

Working Drawings Parts

Should include adequate dimensioning of all parts (10-12 required).

All drawings should include a template with the following information:

Your name

Product name

Part name

Part material

When applicable, proper tolerances should be given.

You will loose a lot of points here for sloppiness.


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Working Drawings Assembly Drawings

Both assembled views and exploded views are required.

Should include all the information required for assembly.

All parts should be properly labeled.

Bill of Materials (BOM)

A list of all required (custom and off-the-shelf) parts. Quantity and part

names are required (another easy 10 points here).


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Materials Selection & Manufacturing Processes

Identify materials being used and why that material was chosen.

Aluminum due to lightweight

Teflon due to low friction

Stainless steel due to low corrosion

Identify manufacturing processes to be used and why.

Casting or forging due to irregular shapes.

Raw material processed on milling machine or

lathe.

Purchased part (give vendor and part number)

Reaming or grinding required for special

tolerances.

Include each part regardless of complexity.


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Design Analysis

Comparison of your product with what already exists.

Why you chose your design over alternate designs.Give some advantages and disadvantages.

Finite Element Analysis (FEA)

Every project is required to have some aspect of the design analyzed using

Pro-Engineer FEA.

Due to the wide variation of products it is up to you to decide what the critical

parts of your design are and how you want to analyze them.

If you are unclear on how you should approach this with your project then it is

your responsibility to ask someone.


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Cost AnalysisHow much will your product sell for?

Price breakdown for each part.

How does this cost compare with competitive products?

Is this a reasonable price for someone to pay?

For price breakdown there are several sources

For purchased items and raw materials (list your source):

McMaster Carr

Fastenal

MSC Industrial Supply

It is fine to use bulk quantities and determine per unit price

For machined parts I would recommend talking to the Machine Shop

Staff to determine a time estimate for machining.

Machine shop rates vary but use $35-50 per hour.

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L8_Bearings and More Gears

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