Administrative notes and announcements:
Don't forget to check your grades.
Who's going to deliver the course evaluations? They need to go to Diggs Hall, Room 122, by one of the students, and must be returned together. As I recall, there'll be a box in the hall to drop the envelope in.
Returned homework: The Viewport Auxiliary view assignment, page 416 lower left, FIG. 12-3-C.
Collected this class: Nothing.
Due NEXT week: The Dimensioning/Paper Space assignment, page 158, 217, 41, 159, etc.
Textbook Significant Facts:
P193, know what a datum is. Itís the "edge" in which the dimensions are measured. Some parts can have three datums (primary, secondary and tertiary).
p193, chain (or continuing) dimensions can result in high (bad) tolerance "stack up".
p193, center left, notice the GD&T symbols.
p763, various GD&T symbols.
P194, right bottom, Basic size is the "nominal dimension", the "ball-park" dimension.
P194, rb, limits are the most and the least the dimension can be and still be acceptable.
P194, rb, tolerance, is the difference between the most and the least of the limits. Also see the table on p 195
P194, rb, Maximum material size, is the condition in which the object weights the most. The holes are all the smallest they can be. The overall dimensions are at the largest they can be.
P195, lr, Limit dimensioning. Like mentioned above, this style of dimensioning, provides the inspector with the most and the least the dimension can be, and still be acceptable.
P196, lr, Equal Bilateral tolerancing has the same value above and below the "basic" dimension. AutoCAD uses the term "Symmetric" for this.
P196, lr, Unequal Bilateral tolerancing is where the tolerance above and below the basic dimension are NOT equal. AutoCAD calls this style "Deviation".
p197, lr, %%P is the "jury rig" to place +/- into DTEXT or MTEXT.
P198, Tolerance Accumulation is where the worst case of each dimensions can add up to a significant amount. Also know as Tolerance "stackup". Chain (or Continue) dimensioning (see page 199) allows for high tolerance stackup.
P199, ll, thereís that ANSI Y 14.5 again.
P199, Clearance fit (always have clearance)
P199, Interference fit (always interfere)
p199, Transition fit (sometimes a gap, sometimes requires a "press").
p208 to 212. Surface finishes. Be sure to recognize the symbol (check mark) as requiring special polishing or other "smoothing" operation. The lower the number on the symbol, the smoother the surface, and the more time (more expense) is required to produce the required smoothness. Flame cuts result in extremly high surface number, meaning the surface is very rough.
(stay tuned for more)
New AutoCAD Concepts:
Tolerancing, setting the dimension style for it.
Geometric Dimensioning and Tolerancing (GD&T) symbols (Tolerance icon on Dimensioning Toolbar)
Repeditive symbols (BLOCK command). For this class, draw your symbol on layer Zero, with color and linetype Bylayer. This allows the color and linetype to be controlled by the layer on which it's later INSERTed. Furniture is often created using blocks, in architectural drawings.
MEASURE, This command can place a symbol (BLOCK) every so many units along a polyline. This was the OLD way for drawing fence lines and railroad tracks.
DIVIDE, This command is siliar to MEASURE but instead of the distance between symbols (BLOCKS), you specify the number of segments you want the polyline to be devided into, with a BLOCK at each "break". It's not used very often.
Quiz NEXT week ?? Do we need one?
Be prepared for a Tolerancing assignment where you need to create dimension styles for Symetrical, Deviation, and/or Limits styles of tolerancing. We'll also likely learn the GD&T symbols and how to place them, but we won't go into WHEN to use them as far as we could (should) go.