Using Angle Gage Blocks
Webber Angle Gage Blocks permit fast, simple, and accurate measurement of angles.  A set of
only 16 blocks will combine to make 356,000 different angles from 0° to 99° in steps of 1 second
to an accuracy of less than 1/1,000,000th of a circle.  

Their versatility derives from being able to use the blocks in combinations in either "plus" or 
"minus" positions.   For instance, to obtain an angle of 33°, take the 30° angle and add the 3°
angle, making sure that both the "plus" ends are together.

To make a 27° angle, you use the same two blocks but wring them together so that the "minus"
end of the 3° block is over the "plus end of the 30° block.  This will subtract 3° from 30°, giving
the desired 27° angle.
Webber Angle Gage blocks are more accurate and easier to use than a sine bar.   Setting an angle
with a sine bar is more difficult to set because of the trigonometric formula that must be used. 

For example, setting a simple 27° angle with a 5-inch sine bar:

 1)    Find sine of 27° =                       .453990499 
 2)    Multiply by length of sine bar =  2.269952495    
 3)    Round to closest .0001"            2.2700         (Closest combination with average set of blocks)
 4)    Calculate Size Error                 -0.000475 or -47.5µin. (Difference between Step 2 and Step 3.)
 5)    Calculate the Residual Angle Error:  ≈ 2 arc seconds
        Residual Angle Error = Calculated Size Error / 4.85 x Length of Bar

1 arc second = 4.85 microinches per inch.  For a 5-inch sine bar:  1 second error = 24.25µin/in.
For the above example, the residual error would be 47.5µin / 24.25µin. or about 2 arc seconds.

Using a sine bar, a combination of 2.2700 inches must be built.  For most sets, this would be a
combination of 3 blocks:  2-inch, .120", and .150"

With an Angle Gage Block set, only 2 blocks are required:  30° and 3° Subtracting the angles as
shown above.   And, there is no residual error.
Error of Measurement Using a Sine Bar
©2018, Webber Gage Division, The L. S. Starrett Co, Westlake, Ohio , 44145