Final Review
The equation for calculating the required fastener tightening torque depends on which two variables:
Desired preload and fastener diameter
Q.When operating a lathe the tool bit should typically be positioned:
Directly on the spindle centerline
Q.Which of the following is not a common component of an engine lathe: A. headstock B. cross slide C. tool post D. tailstock E. ram
E. ram
It is acceptable to temporarily leave dial calipers and parallels out of their storage boxes while working on equipment (T/F)
FALSE
What is the equation used to calculate required fastener torque
T = .2F x D where F is the desired preload and D is the nominal bolt diameter
When changing spindle SPEED (not range) on the milling machine the spindle must be running
TRUE
decision matrixes are used to unbiasedly evaluate different ideas based on a weighted set of objectives the design team decides are important for solving the problem
TRUE
once the spindle COMPLETELY stops, it is still dangerous to remove chips by hand (T/F)
TRUE
fit
The general term used to describe the range of tightness designed into parts which assemble one into another
How are threads on quality fasteners made and why
They are rolled, because rolled threads produce superior surface finish which lowers stress risers
What is the purpose of tolerances and when should they be used?
Tolerances note the allowable margin of error for each dimensions. They should always be used on final part drawings (not concept sketches)
After creating a decision matrix, the concept with the highest overall value should always be selected for use in the final design
True
The speed (HI/LOW) on the mill or lathes should be set BEFORE the machine is turned on (T/F)
True
Accuracy
how close the results of a measurement conforms to the correct value or standard
What is the structural benefit of bending sheetmetal edges / flanges
increases structural regidity
What happens as pitch increases to the required tightening torque
it decreases (but more threads per inch = higher torque)
What happens to the required tightening torque as grade increases
it increases
Q.The common types of milling machines are:
knee and column & bed mills
To reduce part cost use larger/smaller feature tolerances
larger
To reduce part cost design to use larger/smaller cutting tools
larger less likely to break
Torque vs speed for electric motors are
linear, as speed increases torque decreases
Give an example of a qualitative assessment
maneuverability, ease of manufacturing, how pretty it looks
To reduce part cost design parts for min/max material removal
min less time
To reduce part cost use arbitrary/nominal dimension
nominal
Why are decision matrixes weighted
not all objectives are equally important
The maximum allowable material which be removed in a single pass on the mill or lathe is:
one hundred thousandths of an inch (0.100")
Gearing can be used to increase motor torque at expense to:
output speed
What keeps a bolted joint tight
adequate torquing/stretching of the bolt
When should the lathe key be removed from the spindle:
after clamping the workpiece before turning on the lathe
avoid/use mirror images (versus identical) parts
avoid identical is significantly easier to make
Precision
refinement in a measurement, specially as represented by the number of digits given. (how close together measurements are)
To reduce part cost design parts to be smaller/larger
smaller less material used
To reduce part cost design around custom/standard cutter sizes
standard
Use a(n) ____________________ (of size __________ ) to finish drill the hole to final size for threading
tap drill (of size #[decimal eq.])
tolerance
the allowable variation for any given size in order to achieve a proper function. Tolerance equals the difference between the upper and lower limit ex. 1.500 +/- 0.25 in
Q.What rotates on a lathe:
the chuck and the material/workpiece
Q.What rotates on a milling machine:
the cutting tool and the spindle
pitch is:
the distance between crests or root
thread length is
the distance that is threaded
Use a(n) ____________________ to accurately locate and begin drilling the hole
center drill
Fasteners are primarily designed to do what?
clamp parts together (NOT act as pivots/axles or locate parts with relation to each other)
To reduce part cost use cone-bottomed/flat-bottomed holes
cone-bottomed thats just how drills do things
what are the two varieties of fastener threads available
course and fine
To reduce part cost use coarser/finer surface finishes
courser
grip length is
the length of the shank
What is a nominal size
the size used for general description e.x 3/4-inch shaft
basic size
the size used when the nominal size is converted to a pure decimal and from which deviations are made to produce limit dimensions e.x 0.75-inch shaft
To reduce part cost design parts with/without lots of fillets and chamfers
without
Disadvantages of splines:
difficult to fabricate cannot be designed to slip at a predetermined torque
When operating a lathe the tool bit should always be positioned:
directly on the centerline
List two advantages of keyways and/or pin joints
easy to disassemble, will not likely slip
Find part zeros using a(n) ____ and DRO
edge finder
To reduce part cost use fewer/more finished surfaces
fewer
To reduce part cost use more/fewer dimension datums
fewer less zeroing = less time spent and time = $$$
Parts of a fastener
head, bearing surface, shank thread crest, thread root, thread point
Components of the of the engine lathe
headstock, spindle, ways, tool post, bed, cross slide, carriage, tailstock.
bilateral tolerance
A way to express tolerance by using both plus and minus variation from a given size 1.00 +/- 0.002 in
Which statements are true about installing/removing tools on the milling machine: A. always perform tool changing above the plastic covers on the table B.always raise the spindle to the uppermost position using the quill handle C.always secure the quill/spindle in the upper-most position using the spring loaded lock D.always place the spindle in neutral before changing tools
A, B, & C in that order
which of the following rules apply when turning on the milling machine: A. check speed range before turning on B. check tool clearance before turning on C. check tool direction when turning on D. check your e-mail before turning on
A, B, C
The following personal items are dangerous to wear when operating powered equipment: A. shorts or open-toed shoes B. long hair which is not securely tied back C. jewelry on your hands or wrists D. loose fitting clothing
All the above
The following rules apply when using the lathe: A. always make sure the spindle is rotating CCW (looking towards the spindle) B. always turn spindle off before measuring or inspecting the workpiece C. allow the machine to stop completely before switching spindle directions D. ramp gently into contact with the workpiece E. always file left handed so your wrist is never close to the rotating chuck jaws
All the above
The following rules apply when using the milling machine: A. never bring anything within 6" of the cutting zone while the spindle is running B. always remove parallels after clamping the workpiece in the vise C. always lock the quill int the uppermost position before changing tools D. always adjust the spindle speed while the spindle is running E. always ramp gently into contact with the workpiece
All the above
allowance
An alternative term for tightest possible fit, that is, minimum clearance or maximum interference
Fasteners should never be loaded in _____
"shear"
What is the appropriate tap drill size for tapping a 1/4 - 28 thread in steel:
#1 (0.228)
What is the thread pitch for a 10-32 fasterner
0.0323 (the inverse of the threads per inch, in essence 'inches per thread')
What are the following qualifies as an industry-standard clearance hole size for a 3/8th fastener?
0.386" (close fit) 0.397"(free fit)
List three considerations when designing motor hub:
1. How the hub will be attached to the motor 2. How the hub will be attached to the wheel 3. How power will be transmitted
List the four common ways to transmit torque through a hub from STRONGEST to WEAKEST
1. Splines 2. keyway and pin joints 3. set screws 4. press fit
List at least 10 items a proper drawing should contain
1. dimensions to locate part features 2. tolerances for every dimension 3. units specifications 4. material specification 5. quantity of parts to be made 6. surface finish specification for each feature 7. hole & thread notes for every hole 8. unique part name and/or number 9. designer/drawer name 10. additional info about breaking sharp corners, etc.
What are three things that can cause calipers to measure inaccurately
1. not deburring parts 2. not zero 3. damaging the calipers 4. not help correctly
List the first four steps of the design process:
1. recognize the need 2. define the problem 3. gather informations (background research) 4. concept generation
List the three most important items to bring to lab
1. safety sheet 2. long pants 4. proper shoes
unilateral tolerance example
1.00 + 0.002 in and 1.00 - 0.002 in
List five benefits to using 80/20:
1.Easier to assemble 2.Can be reused 3.Low density 4.Relatively strong 5.premade attachment (6.)Easy to cut
Properly torqued fasteners can withstand how many more force application cycles before failure?
1000 times more
1 HP = ? lb-ft/s
550
limit dimension/tolerance example
9.998 in - 1.002 in
What is the functional difference between a between a bolt and a screw?
A bolt is always paired with a nut while and screw is threaded into the material it will hold
Q. Which of the following is the most common work holding method on a mill: A. holding in a chuck B. holding between centers C. holding in a vise D. holding in a collet E. holding in your hands
C. holding in a vise
Q.Which of the following is NOT a common work holding method on a lathe: A.holding in a chuck B.between centers C.in the tailstock D. in a collet
C. holding in the tailstock
It is acceptable to leave a machine running: A. when changing tools B. when clamping the workpiece C. when measuring the workpiece D. when touching off on the workpiece
D. when touching off on the workpiece
Q.Turning is a metal cutting process used mainly for the generation of rectangular surfaces (T/F)
False, cylindrical
Manufacturing tim is an example of qualitative assessment (T/F)
False, it is quantitative
Q.Milling is a metal cutting process used primarily for the generation of cylindrical surfaces (T/F)
False; rectangular
When transferring torque using set-screws, why is it important to use "D" shaped shafts with small flat cuts into them (and what is it called)
Less likely to slip (positive mechanical engagement)
It is ok to leave the cutting tool or workpiece rotating when making measurements under what circumstances:
NONE always make sure the spindle comes to a complete stop before measuring
Advantages of splines:
Provide positive mechanical engagement easy to remove without damaging components
Explain the difference between relay and proportional control
Relay is on or off but proportional is variable.
What is the advantage of press fits?
Simple to fabricate
For female threads is the UNC or UNF stronger
UNC The smaller minor diameter means there is more area engaged by the threads
For male threads is UNC or UNF stronger
UNF The larger minor diameter gives a greater cross-sectional area of the weakest part of the fastener
Given a motor shaft speed of 150 rpm, a 6" diameter wheel and 75% efficiency, what is the linear (loaded) velocity
V = .75 x 150 rev/min x 6/12 π ft/rev x 1/60 min/s remember: π d n e
Axis of motions of lathe
X & Z
Why should fastener threads never be placed in shear?
the threaded portion of the fastener is slightly smaller than the unthreaded shank allowing it to quickly loosen the threaded length offers much less bearing area which reduces the load carrying capacity the motion causes the thread to file material from the inside of the hole
To reduce part cost use thru/blind holes
thru
To reduce part cost use tapped/thru-bolted holes
thru-bolted
What is the sole purpose of a fastener
to clamp parts together
How should engineers prevent relative sliding of parts fastened to each other
use dowel pins
To reduce part cost use stronger/weaker material
weaker always use weakest material that gets the job done
