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Lesson (Week) #13

EGR-110-40, Burgener, Monday, November 20, 2000

Administrative notes and announcements:

Don't forget to check your grades.

WARNING: The campus academic computer lab will be closed for a few days over the Thanksgiving weekend.

Textbook Significant Facts:
Later. None
Below was added on Friday, November 24th:
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 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 these 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 hold pulleys, gears, 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.
p246 BOM stands for Bill of Materials. Notice "Material List" is another name. Advanced AutoCAD training (and additional software, such as Excel) can teach you how to develop BOMs automatically by assigning "attributes" to blocks of all the parts of your drawing.
page 348, recognise an "exploded view" when described or shown. Exploded views make assemble easy, but are very expensive to draw. Modern Solid modeling software such as Autodesk's Mechanical Desktop 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 in the assembly instructions (if you're lucky).

Later- I passed out the ENCODER electrical schematic.
Added on Friday Nov 24th:
The students are to make blocks for 4 components (on layer zero), and insert them into the diagram ENCODER shown below, on the respective layer. The conductors (wires) are to be .01 wide polylines.

Use the STRETCH command to convert the ASIZE titleblock and border drawing to BSIZE. That is, STRETCH the right side of the ASIZE 6 inches to the right to make it as wide as the BSIZE border. Be sure the title block is included within the crossing window of the STRETCH operation. The upper right cornber of the BSIZE border should be 16,10, instead of 10,7.5 as was for the ASIZE border. Suggest change the LIMITS to suit the new border for BSIZE, too.

Suggest follow the GRID and SNAP advice on the below screen capture. DON"T USE DONUTS for the terminals of the compnents. DONUTS take a long time to generate on the display.

Collected during class:
Later. I think you owe me The Dimensioning/Paper Space assignment.

Due next class:
ENCODER homework assignment, involving repeditive symbols (BLOCKS), similar to last year's version, shown below.

See advice above.
encoder.gif, Encoder, using BLOCKs

Heads Up:
Next week we'll study vectors. Expect one homework assignment, and possibly one vector problem on the final.

We also need to cover some fasteners I think you should be able to recognize, and some other standard view-styles (similar to isometric) before we finish the course.

Oh, and we MAY have a simple assignment with GD&T symbols and more traditional tolerances.