Hi,
I've been looking into Squares, Combination Squares, Rules and Straight
edges. Trying to determine price versus performance trade offs. I just
got an email from Starrett with a their technical specs in a few MS
Word documents so I thought I'd post some info as people see interested
about this stuff. [prices are from ww.msc-direct]
SQUARES
Part No
13 Squareness: .0015"
14 Squareness .0005"
20 Squareness: .0001" per foot
21 Outside and Inside Squareness .002"
55 Squareness: .0001" per foot
61 Squareness: .0005"
453 Squareness: .0001"
457 Squareness: .004" per inch
COMBINATION SQUARES
Square Heads - Squareness of head to blade (90 degrees)
2 1/2" (+/- .0005")
4", 6" (+/- .001")
12" (+/- .002")
18" (+/- .003")
24" (+/- .004")
150mm (+/- .02mm)
300mm (+/- .05mm)
600mm (+/- .1mm)
Lateral squareness - 1/2 width of blade maximum.
Miter (45 degrees) - +/- .004" per foot (12")
Center Heads -
Working edge shall bisect 90 degree angle within +/- .005" (+/- 3
minutes)
Protractor Heads -
Base to blade inspection within .004"
90 and 180 degree inspection within (15 minutes)
Base concavity tolerance .002" maximum
RULES AND COMBINATION SQUARE BLADES
Scale Accuracy: End grind to the first / last inch line, 1" (+/-.0025")
>From the Zero "0" end of the scale to graduations located in the range
of:
first 6" (+.004"/-.0035")
6"-12" (+.005"/-.0035")
12"-18" (+.006"/-.0035")
18"-36" (+.007"/-.0035")
36"-48" (+.010"/-.0035")
48"-60" (+.011"/-.0060")
60"-72" (+.012"/-.0070")
72"-96" (+.014"/-.0090")
96"-120" (+.016"/-.0110")
120"-144" (+.018"/-.0130")
Over All Length:
6" +.004"/-.0020"
12" +.005"/-.0035"
18" +.006"/-.0035"
24"-36" +.007"/-.004"
48" +.010"/-.005"
60" +.011"/-.006"
72" +.012"/-.007"
96" +.014"/-.009"
120" +.016"/-.011"
144" +.018"/-.013"
Straightness: .001"/Foot from Mean Plane
Parallelism : .002"/24"
Squareness : 5 Minutes or .0015"/Inch
STRAIGHT EDGES
Edge straightness: .0002" per foot from a mean true plane. Total
variation, from high spot to low spot, can be .0004"
per foot at any point along its edge.
Flatness: No curvatures perceptible to the naked eye.
Parallelism: within .0004" per foot.