Measuring and Layout Tools flashcards

$1\text{ in}=25.4\text{ mm}$ exactly. Multiply inches by 25.4 to get mm; divide mm by 25.4 to get inches. 1/2 in = 12.7 mm and 1/4 in = 6.35 mm (not 0.25 mm).

Accuracy: closeness to the accepted reference value. Precision: repeatability among repeated readings. Resolution: smallest displayed increment. More display digits do not make a tool accurate.

Spindle moves 0.5 mm per turn and the thimble has 50 divisions, so each is 0.01 mm. Reading = sleeve + thimble $\times$ 0.01: sleeve 7.5 mm, thimble 23 gives 7.73 mm. Do not miss the half-mm line.

Take the main-scale value just before the vernier zero, then add the aligned vernier line times the increment: $12.00+7\times 0.02=12.14$ mm. Check the instrument's own increment.

Upper limit = nominal + plus deviation; lower limit = nominal - minus deviation. For $25.00_{-0.05}^{+0.10}$ mm the band is 24.95 to 25.10 mm, so 24.94 mm fails.

Diametral $C=D_{\text{hole}}-D_{\text{shaft}}$; centered radial clearance is half that. 15.20 mm and 15.05 mm give 0.15 mm diametral, 0.075 mm radial. A negative result suggests interference.

Subtract the start reading from the end reading. A part from the 1-inch line to 1 11/16 inches is 11/16 inch long; from 2 to 7 3/8 inches is 5 3/8 inches. Do not report the endpoint as the length.

Legs of 3 and 4 units give a diagonal of 5 when square: $\sqrt{300^2+400^2}=500$ mm. Multiples like 6-8-10 also work; measure both legs and the diagonal.