DML Final 2

What rotates on a lathe?

The chuck and the workpiece

What is turning?

Metal cutting process used for the generation of cylindrical surfaces

What are the 3 common holding methods on a lathe?

1. Chuck

2. Between Centers

3. Collet

Where should the tool bit be positioned when operating a lathe?

Directly on the spindle centerline

What rotates on a milling machine?

The cutting tool and the spindle

What are the 2 common types of milling machines?

1. Knee and column mills

2. Bed mills

What is the most common work holding method on a mill?

Vise

What is milling?

Metal cutting process used for the generation of rectangular surfaces

What is the difference between relay and proportional control?

Relay control can be either on or off: can be -12V, 0V, or 12V, but no in between. Proportional control allows the robot to speed up proportional to how far you push the joystick

What are 5 benefits to using 80/20?

1. Easy to take apart

2. Easy to attach to each other

3. Available

4. Strong

5. Light

When is it acceptable to leave a machine running?

When touching off on the workpiece

What is the maximum allowable material which can be removed in a single pass on the mill or lathe?

One hundred thousandths of an inch (0.100")

When should the speed range on the mill or lathe be set?

BEFORE the machine is turned on

When should the chuck key be removed from the spindle?

After clamping the workpiece

Which way should the spindle be rotating on the lathe?

CCW

When changing the spindle speed (not ranges) on the milling machine, should the spindle be running?

Yes

What are the 4 steps of the design process?

1. Recognize the need

2. Define the problem

3. Gather info/background research

4. Concept generation

What is the purpose of tolerances and when should they be used?

Tolerances note the allowable margin of error for each dimension. They should always be used on final part drawings because manufacturing dimensions without tolerances are useless. Tolerances are not necessary in conceptual sketches.

List 10 items a proper detail drawing should contain

1. Dimensions needed to locate every part feature

2. Tolerances for every dimension on drawing

3. Unit specifications (inches, mm...)

4. Material specification (aluminum, steel...)

5. Quantity of parts to be made

6. Surface finish specifications for every surface

7. Appropriate hole and thread notes for every hole

8. Unique part name and number

9. Designer/Drawer's names

10. Additional info about breaking sharp corners

What is the definition of horsepower?

1 hp = 550 lb-ft/s

What is the shape of a torque vs. speed curve for electric motors?

Linear

Gearing can be used to increase motor torque at the expense of what?

Output speed

Given a motor shaft speed of 150 rpm, a 6" diameter wheel, and 75% efficiency, what is the linear loaded velocity of the robot [ft/sec]?

v=(pi)(d)(rpm)

v=(pi)(6in)(150rpm)(75/100)(1/60)*(1/12)

v=2.95 ft/sec

What are fasteners primarily designed to do?

Clamp parts together

What keeps a bolted joint tight?

Adequate torquing/stretching of the bolt

Properly torqued fasteners can withstand how many more force application cycles before failure?

~1000 times

The equation for calculating the required fastener tightening torque depends on what 2 variables?

1. Desired preload

2. Fastener diameter

What is the thread pitch for a 10-32 fastener?

0.0313" (1/32)

How much radial clearance does a close fit hole for a 1/4" bolt leave?

(major diameter) - (close fit decimal equivalent) = total

radial clearance = 1/2*(total)

radial clearance = 0.0035"

What is the appropriate tap drill size for tapping a

(1/4)-28 thread in steel?

0.228" (#1)

What qualifies as an industry-standard clearance hole size for a 3/8" fastener?

Close fit: 0.386"

Free fit: 0.397"

When should fasteners be loaded in shear?

Never

List 3 considerations when designing motor hubs

1. Dimensions

2. Clearance

3. Finished surfaces

List 4 common ways to transmit torque through a hub from strongest to weakest

1. Gears

2. Screws

3. Length

4. Material

What is an advantage of press fits (interference fits)?

Self-tightening

When transferring torque using set-screws, it is important to use "D" shaped shafts with small flats cut into them. What is this called?

Mechanical engagement

List 2 advantages of keyways and/or pin joints

1. Stronger

2. Long lasting

What are 4 advantages of splines?

1. Provide positive mechanical engagement

2. Easy removal without damaging components

3. Can be designed to slip at a predetermined amount of torque transmission

4. Simple to fabricate

What are 4 things that should be present in assembly BOM's?

1. Part numbers

2. Part quantities

3. Part descriptions

4. Unique item numbers matching balloon numbers on assembly drawing

What 3 pieces of information are required to properly denote fasteners in assembly BOM's?

1. Fastener thread specification

2. Fastener head type

3. Overall fastener length

Define sheetmetal

Workpiece with a high ratio of surface area to thickness

Define sheets vs. plates

Sheets: <= 1/4" thickness

Plates: > 1/4" thickness

What are the 3 most common sheetmetal operations?

1. Shearing

2. Bending

3. Stretching

What 3 sheetmetal capabilities does the lab have?

1. Shear

2. Brake (bending machine)

3. Punch press for creating round holes

What is the structural benefit of bending sheetmetal edges/flanges?

Increases rigidity

List 4 key elements to decision matrices

1. Clearly defined and weighted objectives

2. Justified magnitude assignments with traceable supporting data

3. Use linear score assignments

4. Highest scoring concept wins

Why are separate decision matrices created for separate functional subunits of a design?

Certain components of one design may be better than another design, but the entire design might not be better overall

What are 3 things that can cause calipers to measure inaccurately?

1. Not zeroed

2. Dirty

3. Not perpendicular to part surface

LOOK OVER DFM QUESTIONS

QUIZ 7

Define the electric arc welding process

Using an electric arc to heat separate pieces of similar material to be joined to a temp high enough to cause melting and coalescing