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Lesson (Week) #15

EGR-110-40, Burgener, Monday, December 6th, 1999

Administrative notes and announcements:

Don't forget to check your grades, the grades page of this website was updated Sunday Dec 5th. Don't delay !! Check it so I don't have to hold up the entire class grades to inspect and correct your grade/s. Be aware that I changed a couple, thinking they were typos.

Remember the free AutoCAD 2000 30-day evaluation copies mentioned in the web page for Week #9 (or was it #10?). Well, I just heard of a student receiving his CD, after 4 weeks. He was totally honest that we was simp[ly a student and had no plans to make the purchase. Order your if you haven't already, and have it in time for your Winter engineering classes.

Textbook Significant Facts:

p437, Oblique views. "Cavalier Oblique" is drawn full scale in all directions (looking unusually long), "Cabinet Oblique" is drawn 1/2 scale in the "axis of projection".
p464 SAE stands for the Society of Automotive Engineers,
p464 AISI stands for the American Iron and Steel Institute, who publishes the books for I-beams and other standard steel shapes. p269 ACME threads are much heavier (wider) than Unified National Screw threads. Acme threads are often seen in vices or c-clamps where they withstand a a high thrust load while turning.
P270, Right hand threads are by far the most common, where you turn the bolt clockwise to "tighten" it, or to move it "away" from you. Some rare cases warrant Left head threads, such as old gas fuel tank connections (old propane, maybe acetelene still), older car lug bolts on wheels, special "reverse seating vlaves", bicycle peddles, and of course turnbuckles (as shown on pa 295).
p271 UNC is Unified National Course threads that have a low number of threads per inch.
p271 UNF is Unified National Fine thread series of threaded fasteners that have more threads per inch. p271- Class 1, 2, and 3 threaded fasters. Class 1 are generally "loose" and can rattle a bit until they're tightened. Cheap swing sets or toys may use theese and are easily assembled by hand, until time to apply torque with wrenches. Class 3 threads have very low allowance, resulting in a snug fit.
"A" stands for an external thread, such as on a screw or a stud. "B" stands for an internal thread such as inside a nut or threaded hole. Try to remember "A into B".
p 279, Carriage bolt has a rounded head, but a square shape directly underneath. The square shape avoids the need for a wrench to hold the bolt, so long as the material the bolt holds is soft, such as wood. These carriage bolts are often seen in wooden picnic tables. When used for steel (such as in children's wagons), a square hole is stamped to hold the bolt from turning.
p279. Be familiar with screw heads: Torx (6 rounded points, often used on car trim and seat belts), Phillips (simple cross shaped hole), Hex (or Allen or socket headed cap) has a hexagonal hole for an "allen key". The Allen company was famous for these fasteners, thus the trade name "Allen".
P279, Grades 0 through 8. The higher the Grade number the stronger the steel is in the fastener. For grades 5, 7, and 8, the bolt head has radial lines 2 less in quantity, than the grade. That is, 3 radial lines on a hex bolt head mean Grade 5 steel, 5 radial lines means Grade 7 steel.
p286- Set screws are sometimes used to hol pulleys or fan blades to rotating shafts. Usually set screws are contained within the "collar" so that nothing protrudes to catch on sleeves, or to throw the assembly off balance. An exception is the square head. Old garden or farm equipment may have square headed set screws (I'd guess most often slow turning, though). Sometimes there may be two set screws in the same threaded hole, to ensure the "lower" one doesn't vibrate loose. Also see set screw on page 303, holding the "spider gear" to the shaft.
p304, Woodruff keys. In general a woodruff key looks like a nickel cut in half. A semi-circle groove is cut into a shaft for the round side of the key to fit. The flat side fits in a groove in the pully or fan blade that connects to the shaft.
p307, Cotter Pin- often used to ensure axle ("castle" or slotted) nuts don't loosen on cars, usually on the front axles. These "hair pin" wire things stick through a hole in the shaft, then bend to hold their position. Lawnmower wheels and wheels for toys may be held with cotter pins.
page 348, recognise an explode view wheel described or shown. Exploded views make assemble easy, but are very expensive to draw. Modern Solid modeling software such as Autodesk's Mechanical Desktop MIGHT make these drawings cheaply. We may be seeing them more often in the future. Sears had a good reputation for exploded views for their lawnmowers and other machinery. Tricycles or ready to assemble furniture may come with exploded views int he assembly instructions (is you're lucky).


Handouts:

None


Returned Papers:

I returned the CAD portion of the Quiz 2, graded.

I also returned the students' ENCODER assignment, with blocks for the electrical components.


Collected during class:

Students turned in the magnitudes and directions (tension or compression) for the four 2D vector problems assigned and passed out last week. Handwritten on a sheet of scrap paper is acceptable, but CAD should have been used to get at least 2 significant digits accuracy.

Answers:
A=153 lbs Tension
B=106 Compression
C=83 C
D=298 C
E=273 T
F=186 C
G=797 T
H=772 C

Students were given one last chance to turn in late homework. I collected a couple AutoCAD files.


Due next class:

Major CRAM for the Final Exam ! Study all your Quizes, Midterm and Home Work assignments. Be prepared to see several problems or questions you've seen before, reworded a bit. Check this website for Week 15 and for the Final Exam pages for warnings. Also check your grades.


Heads Up:

Major CRAM for the Final Exam ! Study all your Quizes, Midterm and Home Work assignments. Be prepared to see several problems or questions you've seen before, reworded a bit.

The Final exam will be the usual time we have class, but on the "16th" week, next Monday, Dec 13. Expect a vector problem similar to those assigned in Week #14. Angles and the loads may of course be different. Also expect some multiple choice or true/false questions on material covered today. I promise I'll actually do the AutoCAD assignment ahead of time, this time.

Also, in the past I've been burned for taking too long to turn in the final grades, If there are any questions about loose ends or missed assignments, PLEASE get with me soon, so I don't have to delay the final grades to make the resolution.

Home Phone: 596-7573 email: Burgener@Bigfoot.com