$2\mathrm{.}16$ ARCS AND CIRCLES

When an arc is less than a complete circle, it is dimensioned by is radius, abbreviated $R.$ A radius may have a definite location, such as the R $1\mathrm{.}00$ & R$4\mathrm{.}50$ in drawing $11$ A$004$ or it may be a "float ing radius" that runs tangent with other ares or lines, as with the R$\mathrm{.}75.$ A radial dimension is not normally used for circles or diameters, because it would double the tolerance. For example, a $1\mathrm{.}00$ diameter with a print tolerance of $+-\mathrm{.}01$ would permit dimensions between $\mathrm{.}99$ and $1\mathrm{.}01,$ but a $\mathrm{.}50$ radius $+-\mathrm{.}01$ would permit diametric dimensions between $\mathrm{.}98$ and $1\mathrm{.}02.$

INSTRUCTIONS: Refer to drawing $11$A$004$ to answer the following questions

Interpret the abbreviation CRS used in the title block.

Is the print drawn to $($a$)$ half$-$size or $($b$)$ twice$-$size?

What is the thickness of the spacer?

Is the spacer symmetrical about the vertical or the horizontal center line?

How many holes does the spacer contain?

What is the tolerance on the center hole diameter?

What is the tolerance on the bolt circles?

What tolerance is assigned to the angular spacing of the drilled holes?

What is the angular dimension between each large hole?

What is the angular dimension between each small hole?

What is the overall dimension along the vertical CL $?$

What is the overall dimension along the horizontal CL $?$

What is the MMC of the center hole?

What is the MMC of the $\frac{O}{.}688$ holes?

What is the tolerance on the drilled holes?

INSTRUCTIONS: Calculate the dimensions for the following letters found in drawing $11$ A$004.$

Optional Math Exercises:

Using the trigonometry tables from the Math Appendix, calculate the Cartesian coordinates $(x$&$Y)$ for the $\frac{O}{.}688$ and the $\frac{O}{.}938$ holes.

Using the formula from the Math Appendix, determine the distance over pins of adjacent holes for both the $\frac{O}{.}688$ and the $\frac{O}{.}938$ holes.

Unit $2$

$45$