Dimensions and tolerance

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Blueprint, reading, dimensions and intolerance.

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After completing this video, you'll be able to

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identify dimension types and interpret dimensional tolerances

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for this video.

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We want to begin with the supplied data set

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precision machine and caliper dash inch drawing dot PDF.

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We're gonna be taking a look at this PDF drawing of the

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caliper which is going to be the focus of our courses.

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Now, on the left hand side of this PDF note that we have several different sheets,

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we've got a main page, an exploded view caliber front, rear and piston.

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Now on the main page,

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we have information about the general design that we're working on the name of the

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project per potentially the revision of the project

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and part number weight and so on.

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As we move through the different sheets,

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we're gonna get additional information on the second sheet.

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We have an exploded view of the assembly.

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This highlights the three different machine components that we'll be making.

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The caliper front, which is item number one, the caliper rear,

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which is item number two and the piston which is item three.

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We can see in the parts list that we have two of the piston so quantity two

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and then we have one of the front caliber and one of the rear caliper parts.

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As we move through to individual detailed drawings of the specific parts,

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we get more information.

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We now have an idea of the projection type of the drawing

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information about tolerances located in the title block at the bottom,

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right,

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more information about the specific part number or drawing number,

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the approval and the material and so on.

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When we have a detailed drawing,

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it's important that we identify a handful of areas and make

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sure that we understand the data that we're looking at.

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The first thing that we want to identify is

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that we have several different views of the part.

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We have a front view, a top view,

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potentially different side views and section views.

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Each of these are in the drawing to represent

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specific information that's critical for manufacture or for inspection.

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Now, when we take a look at these,

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you can see that the main view does list several different dimension types.

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There is a dimension for the diameter of this hole 0.255 plus or minus 0.4.

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There's a diameter of this hole 0.313 plus or minus 0.5.

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Some dimensions will not have additional tolerance values on it.

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For example, the depth of the bore where the piston goes is 0.65.

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For that information,

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we need to take a look in the bottom section of our title

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block and note any specified tolerances based on the number of decimal places.

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So if we zoom in a little bit and we go down to the bottom section of our title block,

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we can see here that any of the dimensions that aren't otherwise specified

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as a tolerance value with two decimal places is plus or minus 20.5.

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That means the depth of the bore, the distance between the bolt holes,

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the heights that are listed here,

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those are all plus or minus 0.5.

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Anything else that has additional tolerance values is

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likely going to be using a tighter tolerance.

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For example, the piston bore at 1.6 diameter

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can be up to 1.65 or down to 1.55.

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And this is critical to understand because these are the ranges of

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acceptable values that we can have when we machine the parts.

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Some of these dimensions will also have

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additional balloons or bubbles around them.

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Uh Typically these are critical dimensions, things that must be inspected,

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but generally when you are machining apart,

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any dimension that is listed on a drawing is something that you're going to inspect.

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Let's go ahead and zoom back out a little bit

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and take a look at a couple of other dimensions.

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You can see here that this dimension starts off with two X,

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the diameter symbol and 20.255 plus or minus.

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When we have a dimension listed like this,

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it's important to note that the two X generally represents that

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there are two instances of that specific hole on the caliper.

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This is a symmetric part we can see on the other side,

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there looks to be another identical hole.

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Sometimes you'll see the letters T Y P for typical listed on specific features,

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things like a file radius value.

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Now, if that same radius value is used across the entire design,

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a lot of times you'll see a single dimension and

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T Y P listed for that as the typical value.

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That way anything else that isn't specifically called out as

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a different value will be that typical measured value.

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When we have symbols like this,

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we can see that we're listing a diameter which is

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the hole or the passing hole that we have here.

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And then we have a counter bore, that counter bore is a diameter of 0.38.

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There's no additional tolerance listed.

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So it's plus or minus 0.5 as specified in the title block.

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Now, you'll note that we don't have a distance or a depth of that hole.

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And we have to look at another view

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here. We can see 0.44 is listing the depth of that

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if we move on to the caliper rear, this is a very similar drawing.

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We have section views.

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We have information about specific holes and features,

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but we also have a new type of dimension listed.

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Now, this is two X.

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Again, there are two instances of this hole,

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but this time it is a quarter dash 20 UN C or a course thread with a two B fit.

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Now,

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this tells us all we need to know about how that hole needs to be drilled and tapped.

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It gives us the information knowing that it is a quarter

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we can see in the section view E E

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which is represented here going through the caliper,

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this is a blind hole.

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So more information is needed when we're talking about

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gathering some of these dimensions from a 3D model.

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But a lot of the information is critical is listed here on the detailed drawing

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as we move over to the last sheet. This is the piston.

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Now, it is important to note that just because you have a detailed drawing

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doesn't necessarily mean that it is 100% accurate or correct

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if there's anything that stands out on a detailed drawing,

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for example, the 1000.1 and 0.2 champers listed here,

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those values in respect to the rest of the model seem to be a little bit large

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because we only have the detailed drawing at this point.

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We don't necessarily know if they're wrong or not.

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But sometimes looking at a detailed drawing,

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you can pick out information that may or may not be accurate.

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It's important that you always question anything that doesn't

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appear to be accurate in a detailed drawing.

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The detailed drawing is going to be a conversation between

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the designer and the person who is manufacturing the part.

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You'll also note that in the title block,

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there is no name or stamp for approval on this specific sheet.

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If we go back to the caliper rear and caliper front,

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we can see that the front has an approval but the rear and the piston does not.

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While this may be a simple oversight, these are all things that should be identified

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as you should never make or produce a

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part that hasn't already been reviewed and approved

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at this stage.

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Go ahead and look back through each sheet of the detailed drawing and

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identify specific dimensions and information before moving on to the next step.