ENGINEER SQUARES
 |
 |
 |
 |
 |
CLICK HERE FOR THE LATEST PRECISION MEASURING INSTRUMENT RANGE.
CLICK HERE FOR THE LATEST PRECISION MEASURING INSTRUMENT RANGE.
CLICK HERE FOR THE LATEST PRECISION MEASURING INSTRUMENT RANGE.
CLICK HERE TO VIEW OUR "Rules & Tapes" PAGE
A
machinist square or engineer's square is the metalworkers' equivalent
of a try square. The engineers square consists of a steel blade inserted
and either welded or pinned into a heavier body at an angle of 90°.
Usually a small notch is present at the inside corner of the engineers
square. This prevents small particles from accumulating at the juncture
and affecting the engineers square's reading.
|
|
|
|
In use, the
engineers squares’ body is aligned against the one edge of the object
and the blade of the engineers square is presented to the end or body of
the object. If the end is being checked, then a strong light source
behind the engineers square will show any mismatch between the blade of
the engineers square and the end of the object. The purpose of this
action is to check for squareness or to mark out the body of the
workpiece.
Machinist squares (engineers square) can have a linear
error of no greater than 0.0002 in/in. Engineers squares must be
occasionally checked for accuracy. The four disk method is one way to
verify overall squareness. However, it cannot detect bent blades.
There
are several different International or National standards that
Engineer's Squares are manufactures to, two main ones being: - BS 939.
(British Standards). - DIN 875-1 (German/Euro standards).
Under
both these standards there are basic dimensions set out for engineers
square’s blade/body length ratio, and cross sections of both, as well as
different types of engineers square such as those with a solid body and
an inserted blade, or those with a single piece blade and body being
precision ground with another plate attached to the base of this to
provide a engineers square 'butt' to reference to.
Also
under these standards there are different grades of accuracy that a
engineers square can be made and sold to. It usually relates to a
deviation of 'X' amount of blade lean Vs height of measurement usually
done at the top of the blade. This also assumes that the blade and body
widths are both perfectly parallel making for a true reading along the
blade length and inside and outside the square.
|
|
 |
 |
Typically
there are A or B grade engineers squares made and sold. B grade being
perfectly serviceable for most general use where accuracy is required in
a workshop situation. The better A grade squares are typically used in
applications where a higher grade of accuracy is required, in a toolroom
for example, or for checking other squares for square, or for making
jigs and fixtures where supreme accuracy is needed.
The
simplest method of checking a low grade engineers square for accuracy
is to draw a line across a board with a flat face and straight edge.
Then flip the engineers square over 180 degrees and check if the blade
aligns with the line just drawn. Any error is multiplied by two and
appears as a wedge or taper.
The
ultimate method of mechanically calibrating a engineers square or
similar is with a cylindrical master square sitting on a granite or cast
iron surface plate that is flat. By nature of their construction a
cylindrical master square cannot help but sit at a perfect 90 degree
angle to the flat surface. An engineers square to be tested can be
presented to the master and feeler gauges used with a source of light
behind the gap to get a reading of deviation. If done cleanly, correctly
and accurately this method can find errors down to 10 µm, which is the
limit of practical accuracy since thermal expansion from contact with
the fingers will distort the blade by approximately that much.
Other
methods of calibration of an engineers square are available. This can
involve modern technology by using a CMM (Coordinate Measuring Machine)
for example, or a vertical machining centre with a dial indicator in it.
Many
variety of engineers squares are available from Miller’s Tooling. Eg;
bevel edged die squares, adjustable squares, combination square sets,
etc.
