Chapter 8/9 Dimensioning/Tolerancing

Agenda Chapter 8: Dimensioning – Terminology and Conventions – Linear Dimensions – Dimension Styles, Scale, Units – Aligned – Radius and Diameter – Angular – Ordinate, Continue, Quick Leader – Holes – Applications to Sectional and Orthographic views

Linear Dimensioning Methods 1.Select linear dimension, start, end, move, click 2.For vertical same, except may need type V 3.Select linear dimension, R-click, select object

Change Text

Change Text in Dimension (fig 8-7) Start Dimension, after selecting 2 nd extension line, type t, then 5 x 1.5 (7.50) You may also type m for Mtext and use dialogue To edit an existing dimension, use dimension text edit tool – change style or justification To edit dimension text, choose the A dimension symbol

Dimension Styles We’ve used this to change center marks to lines Also can change the scale of measurements for drawings not-to-scale – Primary units tab – Dimensions must always reflect true size – Does the preview reflect change in scale? Also can change text size & placement – Text tab, modify height, alignment, placement

Different Format Requirements for Millimeter and Inches drawings

Units All dimension values are given default tolerances for manufacturing, for example: Therefore a dimension of 5.50 means less tolerance than – Again, go to Dimension Styles>Primary Units – Experiment with leading zero suppression (needed for inches drawings) – Experiment with precision, and format

Aligned Dimensions Can be by selecting extension lines  and by selecting object – Hit return after starting, select line, and location – You may type M, T for text options, A for angle of text

Radius and Diameters

Rule: arcs use radius, circles use diameter – Any arc > 180 degrees  use diameter Radius: select arc, position dimension – leader line is neither horizontal nor vertical – Modify text by typing M, type “– 4 Places” – Can remove center pt mark: syms&arrows/none Circles: need diameter value + center pt info – Change center pt to center line – Tweak the scale factor so line crosses edge – Add horizontal and vertical dimensions to circle – Then add diameter dimension…angle leader line

Do NOT over-dimension Angle Dimension

Rule: arcs use radius, circles use diameter – Any arc > 180 degrees  use diameter Radius: select arc, position dimension – leader line is neither horizontal nor vertical – Modify text by typing M, type “– 4 Places” – Can remove center pt mark: syms&arrows/none Circles: need diameter value + center pt info – Change center pt to center line – Tweak the scale factor so line crosses edge – Add horizontal and vertical dimensions to circle – Then add diameter dimension…angle leader line

ORDINATE DIMENSIONS

Ordinate Dimensions Based on X-Y coordinate system. No extensions, arrows, etc Useful when there are lots of circles – to place center points

Ordinate Dimensions First, relocate the origin – Tools>New UCS>Origin Click on lower left corner Turn on ORTHO button Select Ordinate Dimension Tool – Select lower endpoint of circle centerline – Select point on X-axis directly below centerline – Right-click to repeat on other features – Extend centerlines as needed – Add diameter dimension for holes

BASELINE DIMENSIONS

Baseline Dimensions Used to show a series of dimensions originating from a baseline – Eliminate tolerance buildup associated with chain type dimensions – Only use after an initial dimension drawn Linear Dimension first (nearest object) Select baseline tool – Continue to select extension lines for remaining objects

CONTINUE DIMENSIONS

Continue Dimension Chain dimensions based on initial linear/angular/ordinate dimension Place first linear dimension Choose Continue dimension Continue placing new dimensions along edge of object

QUICK DIMENSION TOOL

Quick Dimension Inserts many dimensions at once Lets you select a number of extension lines, – Then c for continue OR o for ordinate

QUICK LEADER TOOL

Quick Leader Leader—slanted lines that extend from notes or dimensions to a specific feature on the drawing Usually end with an arrowhead or dot Same as Radius and Diameter but used when no circle present Click Leader tool – start point (arrowhead), end point (of slant) – End point (of horizontal line) then text – Curved line possible if type s after clicking on tool

HOW TO DIMENSION HOLES

HOLES IN SECTION VIEWS

HOLE PATTERNS

FILLETS AND ROUNDS Are usually the same size…can use a note:

PLACEMENT OF DIMENSIONS

SECTIONAL VIEWS may need to adjust section angle for dimension line visibility

ORTHOGRAPHIC VIEWS Do not double-dimension 30 This would doubly define the 30 !! Holes dimension in circle view GOAL—Minimum Dimensions needed to completely define all features

Agenda Chapter 9—Tolerancing – Direct tolerance – Tolerances in Inches and Millimeters – Plus and minus tolerances – Limit tolerances – Angular Tolerances – Chain vs Baseline Dimensioning : effect on tolerance

MILLIMETER STYLE

INCHES STYLE

ACCEPTABLE OBJECTS, Millimeters +/- Tolerances

ACCEPTABLE OBJECTS, INCHES STYLE +/- Tolerances

AutoCAD Plus/Minus Tolerances 1.Text option – Linear dim, t, type text “5.00%p.02” for +/- 2.Mtext option – Linear dim, m, click to right of value, %p, etc. – dimension style/primary units to set precision 3.Using Dtext – Type dtext, place start, define ht/angle, type dim 5.00%p.02, then enter 4.Dimension Styles – sets for all future dim’s – Modify/tolerances/ method/symm, value – (or deviation, 2 values)

LIMIT Tolerances Same meaning, easier to read

LIMIT Tolerances with dimension style toolbar

LIMIT Tolerances with dimension edit toolbar (When only a few need limit dimensions)

ANGULAR Tolerances with dimension style toolbar Same as for linear, use Mtext or text option

CAUTION!!! Double Dimensions

CHAIN vs BASELINE and tolerances