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Lesson (Week) #10,

EGR-110-40, Burgener, Monday October 30th, 2000

Administrative notes and announcements:
Don't forget to check the grades page for your current grade record. I calculated the "acumulative" for each student, too, as if the class HAD to end right now. Please check the math works out correctly. I still have a few stray papers to grade, though.

Textbook Significant Facts:
I went over several areas of the textbook, highlighting pages, some of which might have already been covered earlier. Oh, please check this list again, in a few days. I'll update it for what was really covered in class, which might be more or less.

P171, bottom, parts of dimensions
p172, ll, usually show the dimensions in the view that shows the shape. An exception is "plug" type "lathed" objects.
P172, last line, remember to stagger dimensions to make them readable.
P173, ur, donít cross dimension lines. Place the small dimensions nearest the object. Keep dimensions off the object. Avoid using visible (object) lines, centerlines (?), or hidden lines for dimensioning. Add extension lines.
P174 DIMSCALE magifies the size of all the dimension features, but doesnít change the "wording" of the text.
P174 bottom, donít cross dimension lines, especially the text or arrows.
P175 left, always leave DIMASO turned ON. Always preserve the "Standard" Dimension style. You may need to return to it as a "baseline".
P174 ur, leaders should be drawn parallel. Diameter and radii dimensions "leaders" should point directly to the center of the circle or arc. When possible, draw all the leaders at 45 degrees.
P176, ll, to "force the diameter symbol, type the characters "%%c" before the brackets (<>) of the dimension text. Use the properties icon to fix dimension text this way AFTER placing the dimension.
P177 top left, the Fractional system of dimensioning is out of style. You may need to use it for revising old drawings, though.
P177, left, architectural units (feet and inches) can be set in the dimension style.
P177, bottom left, metric (millimeter) dimensions usually have a zero to the left of the decimal point, when the dimension is less than one millimeter (0.2 mm). But inches are usually shown WITHOUT the zero (.25 inches).
P178, left bottom, again, keep DIMASO turned on. This allows easier update of all the dimensions that use the same dimension style, AND it allows the dimensions to update when the object is scaled or stretched to a new size.
p179 ll, place dimensions between views when possible (although I could swear other books say the opposite).
P179 lr, on very large drawings, dimensions might be placed on the object, only to avoid really long extension lines.
P181, right side, again, use "%%C" to force the diameter symbol into dimensions.
P182, ur, although I donít recommend it this early, you can place centerlines in circles if you have the proper setting for the DIMCEN dimension variable. As I recall, a value of negative 1/3 the radius of the circle is ideal. This also places the centerlines when dimensioning arc radii, too, which isnít usually wanted.
P185-6, machining features: counterbore, spotface. Donít forget countersink, boss, round, chamfer, fillet,
p187, ur, ANSI Y14.5 is the gospel of modern dimensioning standards. The country (if not the world) is very slowly moving toward it.
p187 ur, for repeditive features, use "4X" or whatever, BEFORE the dimension.


New AutoCAD Demonstration:
I'll assign 5 drawings from the textbook for dimensioning, next week (see below). Each will have different dimension "settings", and should involve a different "dimension style". One style will have ticks instead of arrowheads, another will have feet and inches intead of inches alone, etc.

All drawings will be bordered by ASIZE, much like you did for the auxiliary view assignment, which is due next class. Each of the 5 dimensioned drawings is to be seen in a separate paper space viewport. 1 of the 5 is already completed. You can simply INSERT it into your new drawing, and them add the dimensions to it, on a layer named Dimensions. Each of the 5 is to have it's respective dimension style, with all dimensions updated to that dimension style.

This assignment brings up two new concepts I was unfamiliar with before preparing for this lesson, back in '99. I've learned that AutoCAD has the capability to control LTSCALE and DIMSCALE (the size of arrowheads, gaps, text, etc) as a function of the Zoom value of the paper space viewports.

After drawing and dimensioning all the drawings in Model space (don't adjust LTSCALE nor DIMSCALE), toggle to Paper Space (Layout tab), and make a viewport for each drawing, so that each of the 5 can be seen in it's own viewport. Make each viewport active, and in turn, Zoom in or out on each drawing, until each drawing will print out about the same size.

The default value of PSLTSCALE (1), allows the apparent Paper Space zoom scale (remember Zoom XP?) of each drawing to control the lines breaks, NOT the "real" size, as created in Model space. The breaks in the centerlines (or hidden lines) SHOULD appear reasonable, in all viewports.

The next step is to set DIMSCALE to Zero in each Dimstyle, and REGENALL. This SHOULD adjust the DIMSCALE setting for each viewport to be controlled by the viewports Zoom scale. This way, the tiny drawing will have arrowheads and text ligible, and similar to to the biggest drawing. However, I had difficulty making this work. I tried REGEN in each viewport and REGENALL. The only sure way to make the dimensions appear right was to select all the dimensions of a certain dimstyle, change them a different dimstyle, then change them back again to the respective (correct) dimstyle. Only after "re-assigning" them to the proper dimstyle, did they shrink or grow to the correct geometry size.

Those of you with a new AutoCAD LT at home, should have no problem using it for this dimensioning assignment.

The problems will be:
Page 158, FIG. 6-2-C,
page 217, FIG. 7-2-E,
page 41, FIG. 2-6-K,
page 159, FIG. 6-2-E,
and one other not yet chosen.

Check the website shortly before next class for more guidance.


Collected during class:
Nothing


Due next class:
The Viewport Auxiliary view assignment, page 416 lower left, FIG. 12-3-C.


Heads Up:
Next class we'll continue into dimensioning. I'll show how to set different types of tolerances, and how to draw the symbols used for Geometric Dimensioning and Tolerancing. I'll also assign the 5 problems for the dimensioning assignment described above. Not sure right now whether to make it a one-week or two-week assignment.