1. Fasteners and Welding
Lecture 22
Autumn Quarter

2. What’s Coming Up? Today Fasteners & Welding Tuesday
Working Drawing Set
Wednesday
Measurements Lab
Thursday
Quiz on Fasteners and Welding
Introduction to AutoDesk Inventor
Instructor:
Fasteners and Welding are the last items needed before studying working drawings. Working drawings have an assembly, parts list, and details of each part. The assembly shows how the parts fit together and the information on fasteners and welding is needed.
Autumn Quarter

3. Fasteners and Welding Objectives:
Understand importance of fasteners, learn how to specify threaded fasteners and represent them in drawings and learn about other fastening methods.
Understand basics of welding symbols
Instructor:
We find fasteners of all kinds in daily life – buttons, zippers, velcro, wood screws, nuts and bolts, clips, etc. In this session we are going to deal primarily with threaded fasteners. We will follow fasteners with the discussion of weldng symbols.
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4. Topics For Today Importance of fastening Threaded fasteners
Non-threaded fasteners
Other machine elements
Adhesives
Welding
Instructor:
There are non threaded fasteners such as clips and rivets. We will talk only briefly about adhesives but they play a large role in assemblies.
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5. Importance of Fastening
50% of production time for the average item is spent on assembly/fastening.
Fasteners are critical to product performance and reliability
Choosing the proper fasteners is an important part of product design
Instructor:
The first bullet talks about how manufacturing time is spent on fasteners and assembly. Toyota saved time and money a few years ago when the changed the rear bumper sub assembly from 7 parts to 3 parts.
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6. Three Methods Commonly Used in Fastening
Mechanical Fastening
Bolts, screws, rivets, keys, pins
Paper clips, zippers, “Velcro”
Bonding
Welding, soldering, brazing, gluing
Forming
Sheet metal, plastic snaps parts
Instructor:
This slide shows one way to categorize fastening.
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7. Threaded Fasteners – Terminology
Instructor:
If possible, find some large nuts and bolts or any nuts and bolts to pass around the class when you start this discussion of threaded fasteners. Remind the students that this knowledge about threaded fasteners will help them when they have to go the hardware store for parts.
External Threads
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8. Threaded Fasteners – Terminology
Internal threads
Threads inside a hole
Made by drill & tap:
drill smooth hole
make threads with a tap
Instructor:
If possible, purchase a tap or borrow one from the machine shop to pass around. Oil is used many times to help cutting the threads and keep the tap cool.
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9. Threaded Fasteners – Terminology
Bolt - head on one end, threads on other end, used with a nut
Stud - rod threaded at both ends
Cap screw - head on one end, threads on other end, NOT used with a nut
Machine screw - similar to cap screw but smaller
Set screw - used to prevent 2 rotating parts from moving separately
Instructor:
Again, it is a good idea to have real examples of these parts to pass around. It is even better if you can find an assembly that has these fasteners included.
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10. Threaded Fasteners – Specification
Example of a typical thread specification (in inches)
UNC - 3 B
.5 - major diameter of .5 inches
threads per inch
UN - form Unified (i.e. shape of the thread)*
C - series (C means coarse), F (fine), EF (extra fine)
Instructor:
In the hardware store, they probably have boxes that just say ½ - 28 and the length of the bolt.
* There are several thread forms. UN is common.
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11. Threaded Fasteners – Specification
Continuation of example of a typical thread specification (in inches)
UNC - 3 B
3 - class of fit (3 is precise, 2 is normal, 1 is loose fit)
B - internal thread (A is for external)
Instructor:
Let the students know that they will have to know this information to solve the working drawing problem that is coming later this week. This material will also be on the midterm exam or the final exam.
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12. Threaded Fasteners – Specification
Example of a typical metric thread specification
M6 x 1 - 4H5H
M - indicates thread form is metric
6 - major diameter in millimeters
1 - pitch in millimeters
4H5H - tolerance (capital letters for internal thread, lower case for external thread)
Instructor:
This is an example of a metric thead note. Today, in the US many car parts are metric rather than inch. Note that the metric thread notes start with M. Note also that in the inch based thread note, the number of threads per inch is given while in the metric threads it is the pitch or distance between threads. Number of threads per inch = 1/pitch. The tolerance shown here is the equivalent of the class of fit in the inch-based notes.
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13. Representing External Threads
Options for representing external threads in a drawing
Schematic 2. 1.
End View
Detailed
Instructor:
The detailed threads took so long to draw by hand that the schematic and simplified representations were developed. However, with CAD systems it does not take long to create the detailed thread symbols once and use them over and over. Note in the schematic representation that the thin lines represent the crests of the threads and the shorter, thicker lines represent the root. Where possible the spacing between the thin lines should be the pitch on the actual thread. For small fasteners with fine threads this convention is relaxed.
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14. Representing Internal Threads
Options for representing internal threads
Schematic (in section)
Detailed (in section)
Unsectioned
End View
Instructor:
Note that in the end view of the drilled and tapped hole the visible circle is the diameter of the drill bit that was used to create (drill) the hole and the hidden circle represents the diameter of the cutting edges of the tap.
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15. Non-Threaded Fasteners
Rivets
Pins
Keys
Retaining rings
Locking washers
Instructor:
Again, bring in rivets, pins, keys, retaining rings and washers of various kinds. If you cannot find the actual fasteners, show pictures from the book or from catalogs. Tell the students that there are Appendices that have tables for all kinds of fasteners. An example of a retaining ring is the clip that is used to hold on a door handle or window crank in a car. Lock washers can be found on the bicycle axles to keep the nuts from loosening. If there are fenders on the bicycle they are probably fastened by rivets.
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16. Other Machine Elements
Springs
Bushings
Bearings
(See references for more details)
Instructor:
Here are more items that you should bring for the class to see. The springs were discussed in one of the labs earlier in the term. Bushings are typically softer metal (bronze) used to protect the harder parts (steel or cast iron). They are typically force fit into the hole and have a clearance fit with the shaft. Bearings are usually ball or roller bearings where the balls or rollers are held in place by inner and outer retaining rings.
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17. Adhesives Used to join thin or dissimilar materials
Seal a joint as well as bond it
Can be used to coat threads and prevent loosening
Instructor:
It is difficult to find guidelines as to how to write specifications for adhesives. If your students are going to build robots, the third bullet is important if they are using nuts and bolts to do the assembly. They should purchase something like Loctite™ for this purpose or they can use cheap fingernail polish.
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18. Thermal Fastening
Soldering - solder (filler) melts but parts to be joined remain at low temperature
Brazing - filler is melted, and parts to be joined are heated but do not melt. Can be used to join dissimilar metals
Welding - parts to be joined and filler (if any) are melted, pressed together and then cool. (See Section 9.8 in BTG)
Instructor:
Soldering and brazing use metal alloys that melt at lower temperatures than the parts that they are joining. When welding the filler metal is the same as the parts that are being joined and the filler and portions of the parts to be joined all melt. In these three processes, the temperature and the strength of the bond both increase from soldering to welding.
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19. Welding Symbol Reference Line Leader and arrow
Basic weld symbol (location & depth of weld)
Finish symbol
Weld symbol
Dimensions
Supplementary symbols
Tail and specifications
Instructor:
Welding symbols can quickly become complicated. Have the students look at the examples in the text and in the appendix that deals with weld symbols.
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20. Welding Symbol
Leader
Reference Line
Tail
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21. Welding Symbol – Example
Fillet Weld
Weld around
Arrow side
Opposite side
Instructor:
There are many different types of welds and associated weld symbols. Again refer them to the Appendix to see all of the possibilities.
Specification Result
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22. Welding Symbol
Below reference line describes the ARROW side of the weld
Above the line describes the OTHER side
Joint described by symbol (fillet, square)
Numbers by symbol indicate size
Circle at joint specifies weld around
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23. References Threaded and Other Fasteners
BTG Chapter 9, Appendices A24 – A42
Welding
BTG Appendix B.25
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24. Assignments Dwg 43 – FB-1D – Fasteners
Answer questions about fasteners using the tables in the book.
Due Today
Dwg 44 – FD-3B – Welding Symbology
Add notes to the Welding Symbols as needed to make them match the schematic
Due Tuesday
Dwg 45 – Working Drawing Set
A Handout will be provided in class
Instructor:
The students will do only one page on fasteners and one page on welding before they start to work on the working drawing set. The working drawing set should give them more experience in this area. Most CAD packages have dimensioning and note capabilities so that thread notes and weld symbols can be added to drawings.
Autumn Quarter