>> This is a lecture on working drawings, which consist
of a complete set
of standardized drawings specifying the manufacture
and assembly of a product based on its design.
So we're going to be putting everything that we've talked
about so far in terms of grading parts,
into this complete set called "Working Drawings."
The set should completely describe the parts,
both visually and dimensionally --
always think about whoever is going to manufacture
or implement your design; should show think the parts
and the assembly, how the different parts fit together;
and identify all the parts needed,
as well as standard parts.
Standard parts are parts that you did not design or parts
that are commonly available in stores,
as opposed to nonstandard parts.
The main parts of the complete set
of working drawings include detail drawings
of each nonstandard part.
So any part of your design that is not going
to be bought needs detail drawings.
You also need an assembly or some assembly drawing,
showing all the standard and nonstandard parts
in a single drawing, how they fit together,
and a bill of materials, as well
as a title block describing information needed
for a drawing.
Going in detail to the detail drawing,
it's a dimension multi-view drawing of a single part,
describing the part's shape, size, material,
and finish in sufficient detail for the part
to be manufactured based on the drawing alone.
So this is where you're going to first create a 3D model,
and then turn it into multi-views, and add dimensions
and any additional descriptions needed in order
to manufacture the part.
So it should show all the necessary dimension views,
indicate the materials and tolerances,
indicate any finish treatments, plating, et cetera,
and requirements for surface finish roughness.
Standard parts are not included in detail drawings
because they are parts that are normally purchased
and not manufactured.
It is often preferred to show just one part per sheet in order
to be less confusing,
unless it's a really fairly simple part,
or a group of simple parts you can have them more
than one in one sheet.
When more than one detail is placed on a sheet,
the spacing between details is carefully planned
so that it's really clear which parts of the drawing are
for which part of the model.
An assembly drawing shows how each part
of a design is put together, both --
you need to show both the standard and nonstandard parts.
If the design depicted is only part of a total assembly,
it is referred to as "subassembly."
If your entire assembly is complicated, you might want
to divide it into subassemblies.
You usually do not include dimensions
in the assembly drawing,
unless those dimensions are critical during assembly.
Hidden lines are usually needed.
The main purpose of the assembly drawing is
to really show only how the different parts fit together.
And there are different types of assemblies,
depending on your needs.
An outline assembly gives a general graphic description the
exterior shape.
And this is usually used for simple assemblies.
We have sectioned assemblies
that give general graphic description
of the interior shape by passing a cutting plane
through all the parts.
So if you have complicated assemblies that have a lot
of interior parts, sectioned assembly might be useful
to show how these interior parts fit together.
A pictorial assembly gives a general graphic description
of each part, standard and nonstandard,
and uses center lines to show how the parts are assembled.
For our lab, you're going to use this pictorial assembly.
Now, here's an example of a pictorial assembly,
and it shows the different parts.
Center lines here indicate how the different parts fit
connected [phonetic] to each other.
And here's an assembled drawing of the parts.
Here's an example of a sectioned assembly,
showing different hatch patterns
for different parts in the assembly.
The material for the part can be identified
by different hatch patterns, of course according
to the standard symbols for the hatch patterns.
Or you can also use different angles for the different parts
of the assembly to distinguish them.
Now, for very thin parts, such as this indicated here,
instead of using section lines, you can just fill it
in in black; parts like gaskets shown above too small to hatch
and are filled in solid black.
The parts list, also known as the bill of materials,
includes for each part a part name, item number, material,
and the quantity that's for the assembly.
For standard parts, include a catalog number and the company
or a store where you can buy them.
Parts lists may be on a separate document,
especially if you have a fairly complicated assembly.
You can identify each part on the drawing
by using leader lines
and balloons assigning each part a detail number
in sequential order and keyed to the list
of parts in the parts list.
Or if there's space you can place the part number directly
on the drawings face.
An example of the parts list of bill of materials,
it lists chronologically each item and the number you need
for each name and description as well.
And here's the leaders with numbers
and balloons corresponding to each
of the parts in the parts list.
The title blocks, we've talked about it previously.
It's used to record all the important information necessary
for the working drawings.
The title block is normally located
in the lower right-hand corner.
Almost all engineering firms have their standard
or default elements that are included
in the engineering drawings.
But some of the information should include name,
and address of the company, or design activity,
title of a drawing, drawing number, names and dates
of drafters, et cetera, predominant drawing scale,
a drawing sheet size letter designation,
actual or estimated weight of the item, sheet number
if there are multiple sheets.
With respect to scales there are different ways of calling
out scales that's typical for mechanical engineering,
and most other engineering.
The scale is in the form one is to something.
So length of the drawing, one, corresponded
to the length in real world.
So for instance, if you get a map and the map says a scale
of one -- one is to 2,000, a length of 20 millimeters
on the map corresponds to 20 millimeters times 2,000 is equal
to 40 kilometers in the real world.
Sometimes an architecture --
sometimes often civil engineering,
instead of using one is to something, as the callout,
here you give the size on the drawing
that equals the size in the real world.
An example is two inches equals five feet, meaning a distance
of two inches in the drawing corresponds
to five feet in real life.
Now, we've talked about first and third angle projections.
You have to be careful; in North America we use the third
angle projections.
And in Europe they used mostly first angle projections.
And you need to specify this in your drawing,
in the title block.
Third angle projections are used in the US
when the front view is below the top, and to the left
of the right-side view.
So the top is below the front, and the right is
to the right of the front.
The first angle projection is --
we are initially [phonetic] especially if you are used
to third angle projection.
Instead -- if you remember our glass box model,
instead of projecting the features of an object,
the frontal plane, to get the front view,
in the first angle projection you actually project it
to the back.
So you project it to the shadow of an object behind it.
So as a result the top is typically below the front view,
and the right side view is to the left of the front view.
As I said, this is confusing
since we've been using third angle projection.
But I just want you to be aware
that other systems are also used.
The projection used in the drawing should be indicated
in the title block, so nothing should confuse the audience.
And here's the symbol for the first angle projection.
As I said, the front view is above the top view,
and the right side view is to the left of the front.
As I said, it looks weird.
We always use this convention here.
There's the symbol for the first angle project.
And if you look at the symbol, it would look weird to you
that the smaller circle is visible,
because if you're looking from the right of this object here,
it should be -- and this is a consequence
of the first angle projection.
The third angle projection is what we will be using,
and this is the one that you should be really familiar with.
The top view is above the front, and the right-side view is
to the right of the front view.
And this assemble here, the two circles here,
the two concentric circles to the left
for this trapezoid here, seems correct to us,
because if you are looking at this trapezoid here,
which is to be the object from the left,
you should see the smaller circles visible
because it's closer to you.
As I said, for us this looks weird because according
to our third angle projection,
the smaller of the two circles should be in because
from our third angle projection it's actually further away
from us.
And the first thing you need to do is, you know,
if you're not sure is to check whether the drawing is using the
first angle projection, you would see the symbol;
or if third angle projection, you would see the symbol,
the concentric circle to the left of that trapezoid.
A little bit on threaded fasteners; because we talked
about assemblies we need fasteners to connect
or join parts together.
Okay; so fastening is a method of connecting or joining two
or more parts together using processes or devices.
Threaded fasteners are cylindrical surfaces
with mating helical cuts.
And helical threads have three main applications,
number one to hold the parts together; it can also be used
to adjust the position of the parts connected to each other
by rotating the helical threads;
it can also be used to transmit power.
Some terminology for threads, okay, the depth --
the highest part of the thread here,
this is for an external thread, is called the crest,
and the lowest part is the root.
And the depth is the difference between the crest and the root.
And this is of course the axis of the thread.
This is the minor axis.
Minor diameter is the diameter measured to the root,
and the major diameter is measured to the crest.
Now, the pitch is the distance
between either two successive crests, or two successive roots.
For an internal thread, here's the corresponding definitions.
The crest is -- that's the lowest part,
and the root is the highest part for an internal thread.
There are many different forms
of commonly used forms of threads.
We have sharp V, American national, different types,
depending on the profile of the threads that you use.
We're going to talk a little bit
about the unified USA thread series; and after 1948
by US, Canada, and UK.
To make sure -- these were designed in order
to make the fasteners interchangeable.
The UN designation specification has two main elements, the major
or outside diameter of the thread,
which is specified either by a size number running from zero
to 12, corresponding to point zero six
to point two one six inches.
That's the type number.
The major diameter can also be specified in fractions
of inches, and then the inverse pitch,
which is threads per inch.
So instead of giving the distance between the crest,
or the distance between the roots, you take one divided
by the distance between the crest will give you the inverse
pitch, which is the number of threads per inch.
Here's the UN thread series, the Coarse series, or UNC,
used for rapid assembly, generally used.
They are a Coarse and are easy to engage and start using.
We have the FINE series, UNF,
for applications requiring greater strength,
or where the length of engagement is limited;
used extensively for aircraft
and automobile manufacturing requiring more accuracy.
Extra fine series for highly stressed parts,
as parts that are supporting a lot of loads.
We also have the 8N series, which is a substitute
for the coarse thread series
for larger diameters, larger than one inch.
And all diameters have eight threads per inch,
often used as bolts for high-pressure pipe applications.
We have the number five, which is the 12N series.
It's a continuation of the fine thread series
for larger diameters.
And the 16N series, continuation
of the extra fine thread series for large diameters.
There is an illustration of the callout.
We have here the diameter, three-fourths,
the threads per inch, NC, national, the coarse series,
the class of 5th -- the 7 class of 5ths [phonetic],
LH for left-handed, and thread depth.
Some of the default values may not be part of the callout.
So, for instance, it's needed to be implied, because it's based
on the diameter and the threads per inch.
The class default is 2A or 2B.
And if there's no designation for the handedness,
the default is right-handed.
There are two types of classes, as mentioned earlier;
refers to external threads and internal threads.
Class descriptions provide liberal allowance for ease
of assembly when threads are dirty
or slightly damaged -- not commonly used.
And we have class two for commercially produced bolts,
screws, which are far more common; and class three used
in precision assemblies.
As opposed to the unified thread series, the UN,
we also have the metric thread specifications.
And the form is slightly different.
And for metric here's the callout.
And it gives you the major diameter of the thread,
and here instead of giving the inverse pitch,
it actually gives you the pitch which is the distance
between either the crest or the root.
So the pitch is stated explicitly
in the metric specification,
as opposed to the UN wherein you give the inverse pitch;
so inverse pitch for the unified specification.
There are different ways of specifying thread details
in drawings, depending on your needs.
We have the detailed thread representation.
As you can see, the detail it shows the individual crest
and root lines.
It's used when the diameter of the thread is one inch or larger
on plotted or hand drawings.
Use only when it's important to show the function of the thread.
If the main function of the thread is
to simply put the pieces together, you don't need to go
through the detailed representation.
It's not typical for hand drawings,
because it's very tedious.
On the other hand, we also have the simplified
or schematic forms.
So a simplified is right here.
And here's the schematic.
So for the simplified, we imply the depth of the threads
with hidden lines for the simplified representation.
So they actually look like cylinders.
And as a result, it can be confusing.
On the other hand, for the schematic we use alternating
long, thin, and short thick lines, like here, long, thin,
and short, thick lines to represent roots and crests lines
in schematic representation.
Spacing schematic does not necessarily need
to match the actual pitch.
So this is simplified.
This schematic is somewhere between the tedious detail
and the oversimplified
and sometimes confusing simplified representation.
So comparing the two representations detail is very
tedious to construct, and hence not commonly used.
Simplified is fast, but potentially confusing,
because the hidden lines can be mistaken
at cylinders corresponding to all features.
A schematic is best overall.
It's balanced.
It's fairly easy to construct,
and yet you could really close the threads even though
that those are not accurately shown.