MEC322 - Engineering GD&T and Metrology Lecture #2

Geometric Tolerancing

This is a method to specify the shape, form, or function of a particular part.

Purpose of size geometric tolerancing?

Is that size tolerancing doesn’t cover the full picture about the possible ways that the material can come in terms of quality even if the sizing it correct.

How is a GT&D defining?

It is defined using a control frame which is a box that specifies the smaller nuances that need to be fulfilled by the manufacturing company to ensure your parts fit.

How is a GT&D Box defined

Left Side - GT&D type that is being specified
Center - Represents the geometric dimension while displaying the relative amount of material that might be required.
Right Side - These will indicate the lettering of the datums for the system within itself

Location Tolerancing

These consist of two GT&D - Position and Concentricity. Most important when locating positions

CMM Machine

These is probe based machine that interacts with the geometry of the part making contact with the part to indicate the geometry of complex part

Form Tolerancing

The possible form tolerances are straightness, roundness, cylinderical & flatness.

Orientation Tolerancing

• Parallelism

• Prependicularity

• Angularity

Runout Tolerancing

Tolerancing used to measure the rotational length of a part.is used

Rule #1

If a geometric sizing is the only thing present on a particular part defects are still allowed. Considered as curve, angled parts, ect.

Rule #2

For material amounts the RFS “Regardless of feature size” is the default GT unless mentioned to be MMC “Maximum material Condition” or LMC “Least material condition”

MMC

Maximum material Condition is defined as having the most material for that particular tolerancing present.
Hole - Smallest Sized Hole
Shaft - Largest Sized Shaft

*ALL THAT FIT WITHIN ITS TOLERANCING*

MMC Rules #1 and #2

#1 → This indicates that if a MMC is being using the roundness, straightness and other properties should also be included or chance of part fitting greatly reduces

#2 → Most engineers are more inclined to have MMC automatically reference on the dimensioning sheet as they feel it protects them from the possibilities of too small and not connectable parts

Surface Profile Tolerancing

Outline of the surface has a reference for how high or low that specific parts can be in elevation to one another.

Cannon Ball Measuring Caliper

This was a caliper invented to indicate if a cannon ball was the correct size to be inserted into a cannon so that it doesn’t blow up everyone

Side Calipers

Accurate to 1/1000’’ and uses the vernier scale to be more accurate. Used by closing the area you want to measure and then finding the geometry.

Micrometer

Accurate to 1/10000’’ and uses the vernier scale to be even higher in accuracy regarding these system. Used by closing the area you want to measure then finding the value it relates to.

Reading a Vernier

#1 → Start by lining up the zero value with the part

#2 → See which value on the vernier scale in perfectly in line with it’s regular rulers part and that will be the indication of the meausrement

Gauge Blocks

These are block of square or rectangular shape that are used a reference height where it’s perfect to the height listed up to 1 millionth of a inch. Comes in various packages according to the number of blocks required.

Gage Plugs

These are screw based checkers defined into two parts

Go: Smaller tolerance sizing → defined where if the screw has easy screwing without loose or challenging it is consider viable.

No Go: Larger tolerance sizing → defined where you want to ensure that diameter isn’t going to over screw itself and as a result not get stuck meaning it can only be rotated 1-1.5 times.

Snap Gague

These are gauge that consist of a go and no-go component, where the go it the smaller length having the part enter, and then the no go is a larger length to ensure that the part itself isn’t too small.

Dial Indicator

These are used to indicate length of a mechanic part by measuring by rotating a pin around having values of 0.001in or 0.01mm, depending on the equipment

Pneumatic Gage Principal

These work by connecting to the surface of a part, or the inside of a part, to see the flatness of it by shooting the part and tracking the amount of air released.

Electronic Amplification Gague

This is a gauge that collects the bending, compressing or stretch forces for a particular part and keeping track with electrical signal that when connecting will decode itself give readable measurements to the manufacturer.

Optical Comparators

These is a super zoomed in measuring device that has two different colors for one have the material and the other about the free space and with it you can identify certain aspects such as angles and ect.

Toolmakers microscope

Includes a crosshair for measurements of very tiny parts that are very challenging to measure without tools.

Optical Flats

These are glass lens that can tell us the different surface levels for a particular material in terms of how it’s outlined.

curve → Indicates a elevation change

flat line → Indicate flat surface

bended edges → Edges worn

Surface Finish

These occur as small deactivations in production might be unavoidable.

Important surface finishes

→ Friction

→ Assembly (Glue)

→ Mechanical Properties Impacted

→ Coatings

Comparison of surfaces

There are three test that can be used to check surface finish.

• Comparison with standard surface parts

• Optical instruments

• Stylus instruments

TIP: Fingernail see up to 0.001’’ of a material difference

Stylus Instruments

A common example is an instrument that electronically measures the difference that occurs in the heights of the material. A common example is a Talysurf

Optical Instruments

Optical Instruments uses light interference of returning beams to indicate how well aligned the surface was or if interferences would occur.

4 Elements of surface finish

• Waviness - Widely space due to machinery

• Lays - Created by cutter

• Flaws - Cracks, holes

  • Roughness - Fine irregularities from the grinder or cutter

Ra vs Rz

Ra - Takes the average of the heights over the entirety of the material to compute a average result

Rz - Takes 5 different sections (Rt) and find the average of each of those parts and then gets the average of those sections

*Usually Rz is greater than Ra

What are the 3 styles of CMM

Gantry Style CMM - Provides the most accurate and stable measurements, and it is most commonly used within the industry.

Horizontal Arm CMM - These are less accurate but are smaller and place onto side areas that make it easier for acessing the purpose it provides.

Articular Arm CMM - This is the least accurate type of CMM as it is controled by the user themselves and they might not apply the necessary force of percious that the measurement needs to be as accurate as possible. controlled

CMM Touch Probe

There are 3 types of touch probes

#1 → Fixed

• These are probes made of solid material that must be taken care of so that the accuracy of the measurement can be continued

#2 → Touch Triggered

• These are probes that electrical components in them send signals into softwares about the specific information that they can find about the geometry of the part.

#3 → Optical

• Usally a laser that measure the distances between the different surfaces but they are the least accurate probe style

Setting up a CMM machine

1. Calibrate the probe by taking calibration sphere measurements.

2. Define the parts of the datum (x,y,z axes)

3. Measure the part