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Lesson (Week) #9,

EGR-110-40, Burgener, Monday October 25th, 1999

Administrative notes and announcements:
To find your current grade, look on the "home page" of the class, below the link for the Final.

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Show and tell:
I showed an AutoCAD drawing we received from the Port of Anchorage, that includes a rotated UCS, an inserted title block into paper space, and 3 floating viewports.

Returned and Reviewed Midterm:
I returned the midterms, and asked if anyone had questions. One student had a perfect midterm score.

Show and tell (again):
I showed the class the old sample drawing "solar.dwg" and demonstrated how widespread the range of views is with AutoCAD. We zoomed in so far we could see single words on the lunar lander plaque. Then we zoomed out so far that the entire solar system appeared to be a small dot.

Textbook Significant Facts:
I went over several areas of the textbook, highlighting pages, some of which should have already been covered when we did the section view work. Other pages cover machine part features, or dimensioning. In the table below, the letters "ul", "lr", "c", mean "upper left", "lower right", and "center", etc.

P64, lr, no gap should exist between a centerline and the connecting extension line. Other books say the exact opposite. Just be consistent one way or the other.
P67, ul, Centerlines shouldnít terminate at object lines
p106, ul, same as p64 above.
P153, breaks in long simple parts, tubular shapes, "general" break lines
p154, ur, "lie" a little to simplify section views.
P185, c, counterbore, spotface
p186 and p285, countersink
p187, ur, repetitive features and dimensions, "2XÖ" "(TYP)"
p209-211, surface finish marks. High number means rough surface, low number means smooth, and expensive.
P233, section views
p235, top show centerlines, but not hidden lines
p235, ll, "full section" looks like Ĺ is removed
p235, lr, patterns for general pupose or cast iron (ANSI31), and steel (ANSI32)
p236, ll, crosshatching lines should be neither parallel nor perpendicular to edges
p237, ll, thin items, such as gaskets can be drawn solid, and probably should be for economy.
P238, "half section" looks like ľ of the object is removed.
P240, cr, nuts, bolts, pins, rivets, shafts, etc are not crosshatched in section views
p240, gaskets shown as solid
p241, offset section view. Donít show where section line "bends"
p242, ribs arenít crosshatched (typically)
p242, "lie" a bit for section views of symmetric items. Show as if itís got even number of holes, even iif itís really an odd number. Rely on the "front" view to show the truth.
P244, "revolved" sections for long parts or "ring" parts easily show the shape.
P246, ur, "broken out" sections show sectioning just for area of importance
Someplace I also covered the machining terms "chamfer", "fillet" (concave), "round" (convex), and "boss" (elevated island-looking area).

Intro to Dimensioning:
I showed a typical dimension on the board, and pointed out several parts, such as "extension line", "dimension line", "dimension text", "terminator" (arrow head), "leader", gaps here and there, and "extension". I pointed out that old AutoCAD (Release 9 or 10?) required knowledge of "dimension variables", which controlled all these features, and their sizes. The operator had to type or select (off menus) the 6 to 8 character "dimvars", and enter the desired settings. Nearly all dimvars begin with "DIM". The only one (or maybe the first one) worth memorizing is "DIMSCALE" which scales up the SIZE of everything. The text still is honest, but is enlarged or reduced depending on the DIMSCALE value. All the gaps, extensions, and terminators also change size. Since R11 or so, AutoCAD has had dialog boxes to alter the dimvars indirectly. Itís still a good idea, however, to learn the 6 to 8 character dimvars, though, in case you ever continue into programming or "script" file (macro) writing.

AutoCAD Dimensioning Demo:
I quickly sketched a plate in AutoCAD and began demonstrating the dimensioning icons. I showed how to alter the number of decimals from the default 4 to only 2 (Annotation>Units>Precision). I showed how to force the text to go between the extension lines, for small values (Format>Fit>text only), I showed how to truncate the leading zero, for dimensions under 1.00 (Annotation>Units>Supress leading zero). I showed how to allow the operator to control placing the text for diameter dimensions (Format>User Defined) (I think). What else? Oh, I showed how to enlarge the size of all the dimension geometry with Geometry>Overall scale, and warned about the danger of using "Linear scale" (cheating factor) on the Annotation dialog box. I briefly showed how to change the terminators from arrow heads to dots or architectural ticks (on Geometry dialog box). I demonstrated for the class the icons: Linear, Aligned, Radial, Diameter, Angular, Dim Styles, and Dim Update. I advised the class to turn on a running osnap, starting with ENDpoint.

Advice for the UCS and Viewport Homework:
I demonstrated to the class (again): UCS control, starting paper space (by double clicking on "Model" at the bottom of the screen), inserting a title block drawing (asize.dwg), and creating, moving, and stretching floating viewports. Using a studentís completed solid model, I showed the steps to complete the UCS and viewports project (page 416 FIG 12-3-B, Connecting Bar), which is due next class. Each viewport can get the same "zoom scale" with Z(enter) .025xp (enter). Aligning the views can be easily done by moving the viewports, using construction lines and osnaps.

I also made available an optional magazine article explaining paper space and floating viewports. It walks the students through a paper space tutorial, but doesn't teach UCSes.

Just the optional paperspace article mentioned above.

Due next class:
The UCS and viewports project (page 416 FIG 12-3-B, Connecting Bar), discussed above.

Heads Up:
Next class we'll continue into dimensioning. I'll show you how to save the dimvar settings (once you've got them all adjusted) as "Dimensioni Styles". We'll have another CAD assignment where at least two separate Dim Styles are required. Maybe it'll be a tiny object requiring fractions for the dimensions, and another huge part requiring dots for the terminators, and 2 decimals. You'd then need a dim style for each, and show them both in separate floating viewports, with asize.dwg surrounding them. Maybe.

Either next week or the week after, we'll get into various types of tolerances. You might care to read (skim) ahead Chapter 7, beginning on page 171, and chapter 26, beginning on page 529. We'll likley learn "limits", "deviation", and geometric tolerances with AutoCAD. Be aware we'll only have a day or two of tolerancing. We really can't cover it well in such little time.