>> This lecture is about adding text
and dimensions to our drawings.
Starting with adding text, some basic rules are,
we want it to be as simple as possible.
In order to do that we use the TXT font style.
And all drying notes are added in capital letters.
So nothing fancy; easier and simpler is better.
The minimum text height should be .125 inches
or three millimeters in the final print out.
And the text height in the drawing notes
and the text height
of all dimensions should be equal to each other.
Notes and dimensions should be placed outside
of the part geometry so that it doesn't interfere
in the drawing itself and confuse your audience.
Now, some dimensioning terminology:
a dimension is a numerical value that defines either the size
or position or geometric characteristics
of a feature in a drawing.
One type of dimension is term basic dimension.
It's one in which it is given a theoretical exact size
of the feature.
Of course that's only-- that's an idealization.
The basic dimension is indicated by a box around it.
Here's an example of a dimension.
It's showing the width of this feature here.
Here's an example of a basic dimension.
It's showing this height here but we indicate that it's basic
by putting a box around the number itself.
A dimension line is the thin line--
thin, solid line which shows the extent
and direction of a dimension.
Dimension lines are broken for insertion
of dimension numbers right in the middle.
So there's an example here.
Here's the dimension line and here's the dimensions.
There's two numbers here because it indicates tolerance.
So an extension line also known
as a witness line is a thin solid line perpendicular
to a dimension line used to indicate
which feature is associated with a given dimension.
And there should be a visible gap between the feature
that you're to mention and the end
of the extension or witness line.
So the audience doesn't get confused
between what are object lines in the drawing
and what are extension lines.
So here's an example of a long extension line, okay.
It's pointing to this feature here being dimensioned,
and notice that there is a visible gap in all of--
here's another dimension line; there's a visible gap.
Leader line is a thin solid line used to indicate the feature
with which a dimension, note, or symbol is associated.
Sometimes instead of using a dimension line we use a
leader line.
Here's an example here of a leader line.
It's a dimension for the diameter
of this small circle here
and this arrow here is called a leader line.
The phi, the Greek letter phi,
in front of the dimension itself indicates that it's a diameter.
Other terminologies: arrows, of course we use arrows
that are placed at the ends of the dimensions
to show the limits of the part we're dimensioning.
The arrow should be uniform in size and of the same style.
You notice that all dimensions here have arrows pointing
towards the dimension line.
Tolerance is the amount a particular dimension is allowed
to vary.
So as opposed to a basic dimension
which is theoretically exact, okay,
sometimes we indicate tolerance, meaning that it can vary
within certain limits.
Here's an example of a tolerance here.
So it's saying here that the dimension here is acceptable
as long as it's between a minimum of 2.490
and a maximum of 2.510.
That's an example of a tolerance.
And that's an example of what's called a limit
of size tolerance.
You indicate the largest and the smallest acceptable size
of that feature as opposed to a plus and minus dimensioning,
another method of indicating tolerance.
Okay, and you give a positive allowable
and a negative allowable variance
from a target specified dimension.
Here's an example of a plus and minus dimensioning.
The target is 1.250, and the positive error is .032
and a negative error is .01.
What that means is that this part here, this dimension here,
which to the location of the center
of the circle here is acceptable as long
as it's not smaller then what's that,
1.24 and not bigger then 1.283.
I'm just adding and subtracting this positive
and negative errors.
The datum is a theoretically exact point used
as a reference for dimensioning.
A technical datum dimensioning or baseline dimensioning is one
in which all the dimensions
and positions are calculated relative
to an origin point defined by datum.
Here is an example of datum or baseline dimensioning.
Here's the origin, so here's one datum here
for vertical dimensions here's another datum here
for horizontal dimensions.
And take note all dimensions are referred to these two datum's.
Some illustrations regarding the height of dimensions,
it should be at least .125 inches if you're going to do it
by hand, make sure that it's--
you can use horizontal guidelines for hand drawings.
There's not enough room for both the dimension line
and the dimension itself, I can put the arrows outside,
or you can put the arrows inside and the dimension outside
or if it's really really small, both the arrows--
both the dimension lines and the dimensions could be outside.
Similarly for millimeters,
looks like the minimum height is three millimeters
in the final print out drawing.
Size and location dimensions are used to describe the size
of parts and locations of features within the parts.
So of course the dimensions we're talking
about are the depth, the width and the height.
And location would be locating say, centers of--
center lines for circles.
Staggering the dimension text illustrated here,
these are dimensions-- diameter dimensions.
Very important-- okay you want
to put the dimensions outside the part geometry.
Look at all these dimension lines inside the boundary
of the drawing.
Okay, you don't want that because the arrows here,
the dimensions, will interfere with the drawing itself,
so you indicate that the dimensions outside the part
geometry and notice again, the extension lines
or the witness lines that indicate the locations
that you are trying to dimension,
and notice the visible gaps as well.
For repeated dimensions, such as this,
instead of dimensioning all four of the small circles,
you can use the X. 4X; diameter .375,
that means that the diameter of appears in these for circles.
Regarding detailed dimensioning, some rules.
Diameter is specified for holes and blind holes.
A blind hole is one that does not go through, okay,
if you don't specify the depth, okay,
the assumption is it's a true hole; the hole goes all the way.
So if it's not-- if it's a blind hole,
you have to specify the depth of the hole by using the depth.
Drilling operations, okay, pertain to counterbores
and countersinks and spotface as well.
A counterbore symbol is placed before the diameter callout,
and the depth of the counterbore is added with a depth symbol.
So these are two examples of holes that are not true holes.
Okay, if the depth's stated, it's a counterbore.
If it's not, it's a spot face.
Okay, so if you look at the way to dimension a counterbore,
it should show the diameter of the true hole followed
by the diameter of the counterbore and then
to that of the counterbore.
Here's an illustration for the counterbore.
Here's the counterbore symbol, and here's an example
of a counterbore, and here's the front view of the counterbore.
So basically, it's too circles in the top view, right,
the outer circle is the counterbore,
and then you have a smaller circle that is a true hole.
Instead of dimensioning the depths here, or the heights here
in the front view, it indicates the depth of the counterbore,
we collect all of the pieces
of information regarding the geometry
of this counterbore by using three parts.
With a leader, okay, pointing to the counterbore,
the first line here is the diameter of the true hole,
which is the smaller one, counterbore symbol, okay,
than the diameter of the outer circle, the bigger circle,
and then the depth symbol.
So this is the depth symbol here.
All right, and I will show you how--
where you can find these symbols--
the counterbore and the depth as well
as the countersing symbol in AutoCAD.
On the other hand, for the countersink,
here is the cross-section of a countersink.
They look similar from the top, but they're really not.
So for the countersink, you use the countersink symbol
to indicate the diameter followed
by the angle specifications.
You don't give the depth because the depth will be determined
by the outer diameter and the angle of the countersink,
so here's an illustration here.
You have two circles here, the diameter here is
for the smaller diameter is for the middle two holes,
so that's 10, and here's the countersink symbol.
And the second diameter symbol is for the outer circle,
the countersink, and then instead
of indicating the steps here, down here,
we indicate the angle, and that's the angle
between in the front view you just line here and this line.
So the depth here will turn out to be what it is based
on the given diameters and the angle of the countersink.
So if you think about drilling operations, this angle here
of 90 will determine how deep this countersink is
from this elevation here to this elevation.
So no need to indicate the depth.
The spotface is very similar to a counterbore.
So instead of having to capture all the little details here
in the front, regarding the size and configuration
of these two drills here, we capture them
in one counterbore symbol here and countersink symbol here.
Here is an illustration of another blind hole.
That means this hole here doesn't go all the way through.
If it doesn't go all the way through,
you have to indicate the depth here.
That's the depth.
Otherwise, if you indicate this depth here, it would be assumed
that this hole is a true hole; it goes all the way through.
These are the diameters of all of these concentric circles,
okay, and we tried to stagger the X of the dimensions.
Avoid over dimensioning okay,
because an over-dimensioned part might confuse
whoever is trying to manufacture this part.
And so here's an example here.
You indicate this with A, and indicate the width,
B. You don't need to indicate the difference between the A
and B here which is this dimension here,
because chances are both A and B are going
to be slightly in error.
Which means that B minus A is not going
to be exactly what this is.
If you remember, manufacturing operations are subject to error.
So say if I indicate the exact value of A here, and the value
of B here, and also indicate C, that's going to be
over determined, and if A and B are in error,
A plus B is not necessarily going to be equal to C. Okay.
Also, when deciding where to show a dimension,
you select the view that is most descriptive.
So we're trying to indicate here in this example in the height
of this part of the L. Okay, and it's preferred to mention it
in this view, right, because you can clearly see that this is
for the lower part of the L rather this one here.
So this one is technically not wrong,
but putting the dimension here is preferred.
Some-- I'll summarize some fundamental rules
of dimensioning.
You will need size and dimensions
to indicate length width, height, or with depth
and height, as we called them before, as well as diameters
of circles and radii of arcs.
So if it's a whole circle, at the diameter.
If it's just an arc or part
of the circle, it would be a radius.
You also need to add the position dimensions
to locate all centerlines of all circles as well
as other key features.
The size and position
of its feature must only be defined once
to avoid over dimensioning.
So if you already indicated the height of, say, the centerline
in the front of you, you don't you don't need to do
that in the right side view.
Remember, the height dimensions are--
can be shown both in the front and in the right side view.
The depth can be shown both in the south
and right side view while the width can be shown
in the front or the top view.
You only need to show it once.
And as we said earlier, you of dimensioning.
The view where it's-- showing the most characteristic
or descriptive shape of the object.
All English parts or dimensioned into decimals and not fractions.
So architects like 1/16, 1834.
We use decimals.
Even for inches.
For metric parts, we use millimeters also in decimals.
And we do not need to indicate the units.
Because it will be very apparent from the--
and understood from the drawing itself whether it's in metric
or Imperial, whether it's in millimeters or inches.
We always need to leave enough spaces between the object
and the first row of dimensions.
You don't want the dimensions to be too close to the object.
Successive rows of dimensions should also have
at least .25 inch or six millimeter spaces between them.
Very important place dimensions outside of the views, okay,
because you don't want to dimensions
in the dimension lines interfere with the drawing itself.
Except for very, very large circles.
If I have a very large circle,
I can put the dimensions inside the circle.
One very important thing here is illustrated here
for rule number 10.
You need to place longer dimensions outside
of shorter ones.
Here's illustration here.
We're trying to-- notice the dimensions 1.10 for the height
of the centerline here, and 1.70 for the height of this age here.
This is the correct way to do it
because the 1.70 is a longer dimension compared to the 1.10
so you put 1.70 outside.
If you do it the other way, like this,
the smaller dimension being outside the longer dimension,
what happens is the witness line here
for the 1.0 will cross the dimension line.
You don't want witness lines crossing dimension lines
or dimension lines crossing each other.
Place the dimension text between the dimension lines
so there should be a break in the dimension lines
and the inserted text in between.
Use the arrow heads as shown here.
Same era size for all the dimensions.
Inch drawings do not--
okay, here's one way
to distinguish whether the dimensions are
in inches or millimeters.
Four inches, the preceding zero is not included.
So for instance, for half of an inch, one half inch, we use .50.
The fact that there's no zero in front of the point we know;
we're implying that it's in inches.
On the other hand, for metric dimensions,
you include the preceding zero.
So one half of a millimeter is shown as .0 .50
with a zero in front of it.
Okay before you submit your lab on dimensioning's, okay,
what I want you to do is go
through the dimensioning checklist to make sure
that you satisfy all the requirements
and you are following all the rules.
You're not violating any of the dimensioning rules.
Number one overall dimensions of the objects should be shown.
Front, the width, the height, and the depth.
Dimensions are not duplicated in two views.
If you are he showed in the front,
for the height you're not show it on the right side view.
And vice versa.
No dimension is included, it's not needed
to produce the object. Remember that the reason why you're putting the
dimensions is because you're trying to make sure
that whoever looks at your drawing will be able
to create whatever parts you design.
So if a particular dimension is not needed to proceed to produce
that object you don't need included.
There's no need to calculate scale or assume any dimension
to define or check features.
So it has to be completely defined okay and also you want
to minimize errors on the part of whoever's manufacturing it
by requiring them to make calculations.
They don't need to do any calculations
or make any assumptions to create it.
The dimensions are related to the view
that best describes or shows the feature.
We are he talked about that.
Okay, whenever possible, you try to place dimensions okay
in between the two views for which they are applicable.
So height dimensions, heights are shared
within the front and the right views.
So you put it whenever possible in between the front
and the right side views.
The other hand width dimensions are shared
within the top and the front.
So whenever possible, put width dimensions in between.
Multiple dimensions should be uniformly spaced
and there should be a minimum space in between them
in the final print out.
We Artie talked about this longer dimensions are placed
outside shorter ones because we don't want witness lines
crossing dimension lines.
All strings of dimensions are lined up so if you have a series
of dimensions along a single line they should be perfectly
lined up.
So one way to do that is you can either you can rely
on your Osnaps or maybe even your snap
when you're doing it in AutoCAD.
Whenever possible when dimensions are not given,
okay so this is kind of emphasizing we said earlier.
You want to choose the view where it's most descriptive.
And usually when it's a hidden line it's not easy
to describe or visualize.
So whenever possible avoid dimensioning hidden lines.
Of course, sometimes it's not possible because may be
that feature only appears as hidden in order to get the view.
Dimensions do not cross other dimension lines
or witness lines.
Okay, again, so dimension lines cannot cross each other witness
lines cannot cross dimensions lines, however,
witness lines can cross each other.
See this is a witness line this is a witness line.
And they cross each other perfectly fine.
Okay. Centerlines of all arcs and circles are located
with respect to the important features of the object.
So when you ever you have a circle or any arc,
you need to make sure that number one,
the centerline symbols are indicated in the drawing.
Number two, that the locations
of the centerlines are indicated by dimensions.
The radius of all arcs and fillets and diameters
of all circles have been specified.
Again, if it's a whole circle,
you use the diameter symbol indicate the diameter
of the circle.
It's only part of a circle, such as an arc,
or a fillet, use radius.
A little bit more about tolerances.
Two different ways of indicating tolerance again tolerance means
that were allowing that particular dimension
to deviate slightly from the ideal value.
So in the limit tolerance you indicate the highest
and the lowest possible limits of the object.
Example, you indicate 12.0 to 12.5 saying
that that dimension is acceptable as long as it's
at least 2.0 and at most 12.5.
On the other hand, the plus
and plus minus tolerance gives a targets or nominal value okay
and then you get a plus error and then a minus error.
Plus or minus okay.
That's followed by a plus minus expression of tolerance.
So example is 12.5 plus or minus .25.
So this plus minus severance expression is equivalent
to this.
Okay were saying that here the target is 12.25.
It could be smaller by up to -.25 or bigger by up
to .25 giving exact limit tolerance.
This is an example of plus minus tolerance
but it's bilateral and equal.
So here's some illustrations in terms
of representing tolerance values.
So this is limits minimum here in maximum
and here's plus minus.
Here's the target value, nominal value,
and the plus minus, and this is the error.
Now, for the plus minus, you have something called
by lateral tolerance which means that you are allowed
or you can have an error both in the plus or the minus direction.
If they are equal, meeting the error in the positive is as big
or can be as big as the error in the negative,
it's called equal bilateral.
On the other hand, it's an equal bilateral if the variation
in the positive is not the same as the variation--
allowable variation in the negative.
Okay sometimes you for plus
or minus tolerance you can only have a unilateral tolerance.
Meeting you only allow it to be--
to vary, or be an error in one direction.
And no error in the other direction.
So for example if you look at a bolt and a nut, okay,
you want to make sure that the nut,
the bolt will go inside the nut which means
that the bolt can be slightly smaller but not bigger
because otherwise it will not go into the bolt.
On the other hand, the knot can be slightly bigger
but not smaller than the target area otherwise it will not be
big enough to accommodate the diameter.