Week 5:

Components and Assemblies

Mechanical Training Roadmap

01 �Introduction to �Design Principles

02 �CAD Basics

03 �Manufacturability

And Materials

04 �CAD Topics Pt. 2

05 �Components and

Assemblies

06 �Drawings and

Special Topics

Week 5 Agenda

• Building an Assembly in Inventor

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• Types and Use Cases for Fasteners

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• Alternative Joining Methods

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Assemblies in Inventor

How do we bring multiple parts together in Inventor?

Defining an “Assembly”

• An assembly is a composition of parts/modules to create a more sophisticated machine or product.

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• Subassemblies compose a single mechanism within a larger assembly.
• Ex. Body of an airplane or engine of an airplane

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• Both are .iam files.

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Note: assembly and subassembly distinction only for organizational purposes

Assembly Constraints

• Like with sketches, Inventor doesn’t know how parts fit together, unless you tell it
• Constraining an assembly: using part geometries to define the location of parts with respect to each other
• “These two cylinders are concentric”
• “These two faces are flush with each other”
• “This face is attached to that face”

Mate Constraint

“Glues” a part face onto another, or makes them flush with each other.

Mate Constraint (Axes)

Selecting cylindrical surfaces instead of flat ones aligns their center axes.

Angle Constraint

Sets two faces at an angle to each other.

Tangent Constraint

Makes a curved face touch another flat or curved face.

Insert Constraint

Aligns two cylindrical features together. Used mainly for screws.

Symmetry Constraint

Positioning two parts symmetrically according to a plane or planar face.

Motion Constraints

Makes different parts move/rotate together. Used for gears and gear racks.

Direction

Whether the two parts move in the same or opposite direction.

Ratio/Distance

The gear ratio; how much one part moves compared to the other part.

Constraint Status Icons

• [○]: part is under-constrained
• [●]: part is fully constrained
• [–]: constraint status is unknown
• If you see this, you need to rebuild the assembly

How to Make a Good Assembly

1. Place your first part
2. Constrain it fully with respect to the origin
3. Place your second part
4. Constrain it fully with respect to the other parts
5. Repeat steps 3 - 4 until you have all your parts

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Tip: Keep the number of types of fasteners to a minimum!

How your part tree should look (all [●])

Fasteners

How do we correctly source and utilize fasteners?

Fasteners and Holes in CAD

• Model fasteners can be found from vendors like McMaster!

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• Designate hole locations using sketch points!

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• The hole type can be simple ( ), clearance ( ), threaded ( ), or taper tapped ( ).

(Always use this for threaded holes instead of CADing threads from scratch!)

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• If you would like to add a countersink ( ), spotface ( ), or counterbore ( ), select the proper seat.�(Make sure you select the appropriate fastener to match!)

Types of Fasteners

Nut - Fastens to threaded components, esp. bolts

Washer - Helps distribute loads on nuts/bolts

Threaded Inserts - Adds pre-tapped threads to holes

Bolt - Inserted to holes and constrained by a nut

Pin - Used as aligners, pivots, and first points of failure

Set Screws - Interfaces a shaft with the parts rotating around it

Bolt Types & Naming

Imperial

8-32

Thread Gauge

(0-12, corresponds to a bolt diameter, >¼” uses the actual diameter)

8 → 0.164 in

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Threads per Inch

(reciprocal of thread pitch)

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32 threads per in

Flat Head

Socket Head

Button Head

Hex Head

Phillips Head

Shoulder Bolt

Bolts

• Come in coarse and fine thread
• Coarse (few) - More availability, easy to make
• Fine (many) - Stronger, more difficult

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• Length of a bolt is measured by the threaded and unthreaded length
• Always ensure at least there is at least a radius’ distance from the bolt shaft to the wall
• Ensure at least three full threads are engaged, though more provides better support

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Washers and Nuts

• Washers help distribute loads
• Good to use to prevent fasteners from loosening
• Also includes spacers to provide extra contraint

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• Nuts interface with threaded components
• Locknuts are more vibration-resistant than standard nuts
• Thumb nuts are easy to tighten by hand, but stick out
• Coupling nuts provide extra length and can couple two threaded components together

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Pins and Rivets

• Pins easily align and secure parts, or join moving components
• Best utilized as a first point of failure OR as a temporary locking mechanism

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• Rivets are used to create permanent attachments for parts
• Works well for parts that are too fragile to join with bolts or screw
• Generally not used within RJ, but we have the capabilities to utilize rivets

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Set Screws and Threaded Inserts

• Set screws interface a shaft with components that rotate around it
• These are pre-threaded and come with some manner of housing (i.e.- shaft collar)

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• Threaded inserts allow you to add threads to parts without tapping
• Heat-set or press fit inserts are very helpful for 3D printed and plastic parts

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Alternative Joining Methods

What other options exist for constraining parts?

Shaft Assemblies

• Shaft Collars
• Holds and positions shafts, or limits movement

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• Bearings
• Allows freedom of movement around a shaft, load bearing

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• Retaining Rings
• Holds components onto a shaft

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• Spacers
• Provides lightweight spacing between parts, limits movement along a shaft

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Adhesives and Zip Ties

• Adhesives include glues, epoxies, and tapes
• Always check for the compatibility and warning labels

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• Zip Ties can be very useful for organization, though not ideal for other applications
• Keep these in mind when it comes to wire/cable management!

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Design for Assembly (DfA)

• When adding fasteners to your design, you need to think about how you will install them and how long it will take!
• Ex. bolt holes need to be accessible for assembly and disassembly

Summary

What did we learn? What’s next?

Summary

In this week we…

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• Introduced the key tools for creating an assembly in Autodesk

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• Overviewed the types, identifiers, and use cases for fasteners

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• Discussed hardware and non-hardware methods for joining and constraining parts in real assemblies

Training Feedback

Bonus Slides

Additional Tips on Assemblies and Fasteners

Constraining to Work Planes

• Totally possible (after all, they’re flat faces too)
• Useful for centering parts
• Good practice to constrain first part in assembly to the 3 reference planes
• Keeps part in place
• Keeps the reference planes in convenient places for future assembly

Bolts vs. Screws (Dawn of Justice)

• Require a nut/threaded hole to make the joint lock
• Have a constant diameter
• Require a hole to be inserted

Bolts

• Always used without a nut
• Has a non-uniform cross section (many times comes to a point)
• Can be inserted without a hole (but best practice to have pilot)

Screws

Welding

MIG Welding -

cannot use on Aluminum

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TIG Welding -

can be used on Aluminum