DrawingBasics

As you work to develop CAD fluency,

which means to be able to do your CAD work quickly and accurately,

it helps to have a good CAD process.

Now, a good CAD process always starts with understanding

the purpose for the CAD work.

In other words,

understanding the job that needs to be done.

Now in the product development process,

we have a variety of ways that we understand the job that needs to be done.

For example,

we might

read

a design brief or have a discussion with a client or anything like that.

But in the process of learning CAD and being given exercises and

activities the way we're doing in this course,

one of the important ways for you to understand the job that needs to be done

is

to be able to read

and interpret correctly an engineering drawing.

Usually,

in this course, for the purpose of reproducing the geometry

found

in those engineering drawings.

So, in this video,

I'll take the time to describe to you part drawings

and assembly drawings.

And I will simply

attempt

to demystify what otherwise may appear

like a complicated set of documents.

But as soon as you sort of break them down and see what's in them,

you'll be able to begin the process of reading and interpreting them correctly.

So, I'm gonna jump right now into a set of graphics.

We're gonna take a look at these graphics now, and we can see

there is a product here.

It is a turbocharger.

This particular turbocharger for the discussion

that we're gonna have right now has two pages

of a drawing.

So, the drawing is shown right here.

We're gonna look at sheet 1

of this drawing set,

and we're just gonna start

breaking down its pieces,

and then we'll look at sheet 2, and then we're gonna

spend a little bit of time looking at an assembly drawing.

OK.

For sheet 1,

we need to understand that the overall graphic that's

around the edge is called the sheet format.

In fact,

we can

just sort of take out all the geometry and specific

geometric information and what's left is called the sheet format.

All right.

The sheet format has zone markers.

These zone markers are used for to facilitate communication

on design teams or across a large geographic distances.

We can say,

hey,

something's going on in C2, area C2, of the drawing.

Let's take a look and see what that is.

Also, in

the

drawing we have the thing that is called the revision block.

The revision block describes the latest change at

least that has been made to the drawing.

In this case,

it's a revision A,

meaning it's just the initial release.

The revision block only appears on sheet 1.

We also have the thing on the drawing that's called the title block.

The title block

has a lot of very important information.

And within the title block, we find things that

are critical for being able to reproduce the geometry

that's in

the drawing. And so, we're gonna take a deeper look now at the title block,

and we're gonna look at three separate parts of the title block.

First, we're gonna take a look at this part here, which, of course, has like the title,

also has a thing called

the size, and, by the way, we are looking at B size drawings.

These are 11 by 17

inches.

That's how big those drawings are.

Now, a couple of key things to pay attention to here.

Item number 1 is you should always have a sense

for what revision of the drawing you're looking at.

This is important because occasionally you'll

be working with a colleague or another

entity,

maybe a supplier or something like this,

and you want to make sure that you're on the same page. And the

way we do that is you make sure you're looking at the same revision

of the drawing.

Speaking of pages,

which is not what I meant just a minute ago,

there

are

multiple sheets in this drawing set,

and there's always a list of how many sheets there are.

That's important to know because if there's additional information on

sheet 2 or 3 or 4 or 5 or 6,

we want to go and get them.

Also, we have

information that is

related to the overall

mass properties of the object represented in the drawing. In this case, the weight

is shown, and then also here to pay attention to is the scale.

The scale is important to understand in the sense that if the scale was 1 to 1,

then the object in the drawing would be printed

on the drawing at the same size as the actual object.

When the scale is 1 to 5,

in this case,

every 1 inch that's printed on the drawing represents 5 inches

in

reality.

All right.

The next part of the title block that we're gonna take a look at captures authorship.

And also, thedrawing has been checked, and frankly, you should

always have your drawings checked. And you should not

trust drawings that have not yet been checked.

Also, in this part of the drawing, we find the units

for

how the drawing was created.

In this case, this drawing is in the units of millimeters.

We also find the important

area that is describing the material of the object represented in the drawing.

In this case,

the turbocharger in the drawing is of titanium grade 5.

Also, in the drawing, we can find

finish if there is one specified and if there's

not one specified, it will simply say that.

And then,

also, here there's a section for comments. And in this course,

this is where we actually put our color specifications.

This

is not a color specification for the turbocharger.

This would have meant the turbocharger was

perfectly red.

But

I have just put that in there as a quick sample just

to show you that those will often show up in our comments.

We also then have this other part of the title block,

which is the sheet tolerances.

Now, what's going on with sheet tolerances?

First of all,

we have to know that this part represents

important information relative to the dimensions in the drawing.

So, we're going to go look at one of the dimensions right now.

From the

top edge of this object to the center of this hole

is supposed to be 23.00 millimeters.

Now, we can understand from this part of the drawing and from the sheet tolerances

that what this means

is that because our

has two

bits of information beyond the decimal point,

then we will be referring to

this portion in the general

tolerances,

the sheet tolerances,

which mean that the 23

is plus or minus 0.15 millimeters.

Now,

if our drawing would have instead just had one

bit of information beyond the decimal spot,

we would have been looking at plus or minus 0.25 millimeters.

Now, this is important because all of those tolerances are essential,

but we don't want to put them,

every single one of them on the drawing itself

because it will

clutter up the drawings.

So, they go into the sheet

definition, so into the sheet tolerances.

That's what that means.

OK.

Well, those were the main things that we wanted to look at in the

title block. We have finished our sort of deep dive on the title block.

And then, I'll just go through a few other things here and say that

drawings always have

a set of general drawing notes.

These drawing notes apply to the entire drawing

set,

sometimes just the entire page,

but sometimes it can apply to all the sheets.

But then we also have specific notes that can apply to just a specific

part located or a specific portion of a part located on the drawing,

and there's always a leader line

that is connected to where that note matters.

All right.

Now, we have to look at the geometry

of the drawing. Here, we have what's called the orthographic projections,

the orthographic projection views we could call them.

OK.

And then,

we also have

within those orthographic projection views, a special kind of line that we don't

see anywhere else and that is a dashed line and that dashed line

is called a hidden line. And a hidden line is

like an X-ray view we basically can see into the object

and what all the dashed line

are representing internal geometry

that we can't see from outside but we

can see through in an X-ray sort of form.

Now, there is another image

on here, another view, it's called the isometric view it's the one at the top

right of the drawing, and the top right drawing

view the isometric view never has hidden lines.

This

is a standard for drawing so we can always see the isometric view

and we can have a sense for what the object is that's to help us with that,

but it's not gonna show us hidden lines.

Now, it's worth spending

just

a little bit of time trying

to understand what is this orthographic projection.

If you understand the thing that I'm going to describe in the next moment,

then orthographic projections will become meaningful to you,

will become useful,

and you'll be able to understand engineering drawings

of

this form indefinitely into the future.

So, I'm gonna show you the same orthographic projections

shown

in just a little bit larger here,

and what we want to do is take a look at the front view for a second.

When we're looking at the front view,

what

we are really looking at

is

a

projection

of the object directly onto its front face.

Now,

if you can see the red box that's on the right-hand side here,

the front view is exactly the front view direction.

Now,

if I were to

take a line

and draw it on the paper between the top view and the front view

and then fold it right there at 90 degrees,

I would create the edge of a cube.

And the edge of that cube would be such that when I

look down from the top of the cube, I see the top view,

and when I look at the front of the cube, I see the front view.

Now, likewise,

if I were to fold between the front view and

the right view and leave the paper at 90 degrees,

I'd form another

edge of a cube.

And when I look at the right side of that cube, I would

see the right view, and when I look at the front view,

I would see the front view, and if I look at the top view,

I'd see the top view.

And this is how an orthographic projection works.

It's simple

when someone has described it to you,

but is otherwise,

for some people,

not super obvious. So, hopefully, you will walk

away with a little bit of information there

on how to interpret

these

orthographic projections.

So, now, you should be able to look at an engineering drawing like this

and not get super overwhelmed by it because

you know that all the information around the edge

is the sheet format.

You know that down in the bottom right corner, we

have our title block with a bunch of essential information.

We have our revision block at the top right.

Then, we have two kinds of views here.

We have the orthographic projections, which have the front,

right,

and top view, and then we have the isometric view,

which is shown without hidden lines in the top right portion of the drawing

and helps us get

even a better sense for what the object is all about.

OK.

That was what sheet 1 looked like.

Now,

in sheet 1,

we saw those orthographic projections;

we saw the isometric view.

And in sheet 2,

we see what is called auxiliary views.

Now,

auxiliary views are not limited to

being on page 2,

they could be on page 1.

But in this case,

in this particular drawing,

our auxiliary views happen to be on sheet 2.

They could have been on sheet 3, 4, 5, 6,

or 1.

OK.

Now in order to understand the auxiliary views,

we need to

zoom in just a bit

on this portion of sheet 1

and see what's going on here.

Within this set portion,

when we're looking at the front view from sheet 1,

we see this dashed line with the two arrows on it.

This is called a section marker,

and what a section marker means is that we are going to slice the part

right where the dashed line is, and then we're going

to look in the directions of the arrows labeled AA.

And what are we gonna see if we do that?

We're gonna see

this box that's now

highlighted on sheet 2.

How do we know that that's the box we're gonna see?

Well,

primarily, we know it's the box we're gonna see because

it's labeled.

It's called section AA, and that's exactly what we were looking at

in sheet 1 was a marker showing what section AA would be.

And now on sheet 2,

we're looking at that.

So, we're going to

go take a look even deeper now at sheet 2.

Now that we know that we're looking at 2

section views,

section views are auxiliary views.

Alright,

now a few things to point out on this sheet.

We have

the name of the auxiliary view with its scale,

if it has been scaled, and this one has been scaled.

We also see that

there's a new kind of line that's appearing on the drawing,

and this is the crosshatch.

Whenever there's a crosshatch,

this means that we have sliced through material

and we're actually looking at material and not void space.

So, for example,

if we look at the holes that are on the same view,

those holes are not crosshatched, that means

they're void space. It means there's nothing there,

but the crosshatch means there is something there and that's material.

All right.

What is the next piece we're gonna look at?

We're gonna notice here that there are center lines and center marks.

These pieces of

sort of invisible geometry,

maybe we can call them,

are important for dimensioning too

or understanding symmetries in some cases.

All right.

We also have in this sheet 2 dimensions,

such as this dimension,

which means that the overall length of this object is 268 millimeters.

We also see some other dimensions,

some that appear a little bit more complicated.

And what this dimension means,

the dimension that says

4X R20.00

means

that there are four arcs on this part that have a radius

of 20 millimeters.

And then, likewise,

there is a dimension here that says

there are four circles on this part that have a diameter

of 20 millimeters. So, when there's an R,

this is a dimension that goes on an arc

or an incomplete circle when there is the diameter symbol or the letters DIA.

This means that this is a diameter and we do that for full circles.

The 4X that precedes it in this case simply means that

there are four

identical geometries on this part

that have that same

dimension.

Now, of course, on this drawing, there are many dimensions. That is the purpose

of the drawing is actually to convey geometric information.

And don't forget the rectangular red box there in the title block

the drawing is also designed to convey

material information.

All right.

So, we have just taken a look at

part drawings.

In this case,

a multi-sheet part drawing for this turbocharger.

And hopefully,

we have,

as I mentioned before,

demystified it a little bit

and shown

that it is full of

orthographic projection views,

isometric views,

and some auxiliary views,

and then those allow dimensions to be put onto

the object that help us understand more and more about it.

OK.

It is now time for us to stop thinking about part drawings,

and we're going to talk about

assembly drawings. And in this case, I'm showing you a five

sheet assembly drawing for the NES game controller by Nintendo.

Now, it's five sheets because we need to know

this thing in the top left corner

is just an isometric

screenshot

just to let you know the object that we're working on.

It's not part of the actual drawing set.

All right,

so within this drawing set,

however,

there are five sheets. And we're going to take a look at just three of those sheets—

sheet 1,

sheet 2,

and sheet 3.

The other sheets are valuable,

but they're not going to teach us anything new about how to interpret

an assembly drawing,

which is what we're gonna do right now.

All right,

take a look at this first sheet

of the

Nintendo NES game controller, and let's notice first of all

the things that are similar from the part drawing,

part drawings that we looked at.

Sheet formats the same exact concept; zone marker,

same concept; revision block, the same; title block, same concept;

general notes, same concept. We have orthographic projection views here.

We also have isometric views, and we also have dimensions.

So, what's new then?

Well,

there are some new things here.

We have assembly dimensions.

These are dimensions that don't exist on any part drawing.

This is one of the main purposes of assembly drawings is to help convey

dimensions that are essential,

but don't exist on part drawings.

For example,

this is

measuring from one edge

of a part to another edge of another part.

That 17.20.

All right.

We also can notice here in the title block

that material and finish

don't make a lot of sense

in an assembly drawing because the assembly is

made up of various parts that all have potentially

different materials and different finishes.

And therefore, it is traditional

and expected

that those bits of information

don't exist on the assembly drawing,

but that the reader of the assembly drawing is

encouraged or directed

to the actual art drawings.

All right,

let's

take

a look at,

oh,

that's the part that I just talked about right now.

OK.

Now on to sheet 2.

All right.

For sheet 2,

it's essential to realize that there is a new kind of auxiliary

view that we're looking at now and it's called an exploded view.

And the beauty of the exploded view

is that it's broken up the part into all of its

pieces so we can take a deeper look at them.

Now,

each of the parts has a callout balloon on it.

And the callout balloon has a corresponding line in this table which

is called the bill of materials or sometimes called the part list,

but we will call it the bill of materials.

Now, all of the objects

in

this particular assembly

have a callout balloon and have a location in the bill of materials.

Also, in the assembly drawing, we can notice the thing that's called the explode line.

The explode line helps to understand that, for example,

the bottom left the screw goes through that bottom cover

through the circuit board

through

the membrane and up into the top cover,

and it is an indication

of how these

parts line up with each other.

OK.

We're now going to take a look at step, excuse me,

sheet 3.

And in sheet 3,

we're going to see

that a number of things are the same as they were in part drawings.

For example,

the section markers,

the section views,

the general nodes,

the specific notes.

But we now have a new thing

that could have existed in a part drawing but it

didn't exist in our part drawing for the turbocharger.

It exists in this one,

so I thought I'd take a second to talk about it

and that is called the detail view.

And a detail view is another auxiliary view

and what it is is it's a zoomed in portion

of

the stuff that's inside the detail view marker.

The detail view marker is that circular

line that has two arrows on it pointing to a D, in this case,

and that line is dashed.

And that tells us

that we're gonna zoom in on that area, and it's going to appear

somewhere else on the drawing, and it's going to tell us something that is

otherwise hard to look at at the size

that it exists normally in the drawing.

OK.

So, that's what you need to know about assembly drawings

and

what you need to know about part drawings.

So,

before we leave this whole topic,

I think it's worth saying

a few things.

And item number 1 here is

I hope

that when you look at the engineering drawings, they won't look

as daunting as they did before we had this small discussion.

But what I hope mostly

is that you'll actually look at the engineering drawings.

You need to spend some time with the engineering drawings.

OK.

I want to spend 5 to 10 minutes with each of the drawings.

OK.

We want to examine

each

engineering drawing starting with the title block,

then with the notes

on page one.

Then, we want to look at the views,

try to understand what the views can tell us and why they're there.

We want to try to envision the geometry.

We want to do the same then for all those pages.

And we wanna look for details

such as specific dimensions or specific details that maybe

in a detail view or in a section view.

OK.

Just as a final recap on here,

we're after

getting good at CAD fluency.

CAD fluency starts by having a good understanding of why you need to create a model.

That model understanding can come from a variety of places,

including talking to a client

or

following a product development process for a given company.

In this case, in this course, we're gonna

have a number of exercises at the beginning here

where you create geometry that's conveyed to you in an engineering drawing. So,

you need to learn how to read those engineering drawings. And this video

demystified them

just a little bit

hopefully making them less daunting,

something you're willing to engage with and to actually read.