
D-60
D
■ General Notes on Use of Height Gauges
1. Potential causes of error
Like the caliper, the error factors involved include parallax effects, error caused
by excessive measuring force due to the fact that a height gauge does not
conform to Abbe's Principle, and differential thermal expansion due to a
temperature difference between the height gauge and workpiece.
There are also other error factors caused by the structure of the height gauge.
In particular, the error factors related to a warped guide face and scriber
installation described below should be studied before use.
2. Guide face (column) warping and scriber installation
Like the caliper, and as shown in the following figure, measurement errors
result when using the height gauge if the reference column, which guides the
slider, becomes warped. This error can be represented by the same calculation
formula for errors caused by nonconformance to Abbe's Principle.
Installing the scriber (or a lever-type dial indicator) requires careful
consideration because it affects the size of any error due to a warped
reference column by increasing dimension h in the above formula. In other
words, if a long scriber or lever-type dial indicator is used, the measurement
error becomes larger.
■ Notes on Using the Height Gauge
1. Keep the column, which guides the slider, clean. If dust or dirt accumulates
on it, sliding becomes difficult, leading to errors in setting and measuring.
2. When scribing, securely lock the slider in position using the clamping
arrangements provided. It is advisable to confirm the setting after clamping
because the act of clamping on some height gauges can alter the setting
slightly. If this is so, allowance must be made when setting to allow for this
effect.
3. Parallelism between the scriber measuring face and the base reference
surface should be 0.01 mm or better.
Remove any dust or burrs on the mounting surface when installing the
scriber or lever-type dial indicator before measurement. Keep the scriber
and other parts securely fixed in place during measurement.
4. If the main scale of the height gauge can be moved, move it as required to
set the zero point, and securely tighten the fixing nuts.
5. Errors due to parallax error are not negligible. When reading a value, always
look straight at the graduations.
6. Handling after use: Completely wipe away any water and oil. Lightly apply a
thin coating of anti-corrosion oil and let dry before storage.
7. Notes on storage:
Avoid direct sunlight, high temperatures, low temperatures, and high
humidity during storage.
If a digital height gauge will not be used for more than three months,
remove the battery before storage.
If a protective cover is provided, use the cover during storage to prevent
dust from adhering to the column.
Example: Effect of measuring point position
When h is 150 mm, the error is 1.5 times larger than
when h is 100 mm.
4. Error due to inclination of the main scale (column)
According to JIS standards, the perpendicularity of the column reference edge
to the base reference surface should be better than:
This is not a very onerous specification. For example, the perpendicularity limit
allowable is 0.61 mm when L is 600 mm. This is because this error factor has
a small influence and does not change the inclination of the slider, unlike a
warped column.
5. Relationship between accuracy and temperature
Height gauges are made of several materials. Note that some combinations
of workpiece material, room temperature, and workpiece temperature may
affect measuring accuracy if this effect is not allowed for by performing a
correction calculation.
6. The tip of a height gauge scriber is very sharp and must be handled
carefully if personal injury is to be avoided.
7. Do not damage a digital height gauge scale by engraving an identification
number or other information on it with an electric marker pen.
8. Carefully handle a height gauge so as not to drop it or bump it against
anything.
3. Lifting of the base from the reference surface
When setting the scriber height from a gauge block stack,
or from a workpiece feature, the base may lift from the
surface plate if excessive downwards force is used on the
slider, and this results in measurement error. For accurate
setting, move the slider slowly downwards while moving
the scriber tip to and fro over the gauge block surface (or
feature). The correct setting is when the scriber is just felt
to lightly touch as it moves over the edge of the surface.
It is also necessary to make sure that the surface plate and
height gauge base reference surface are free of dust or
burrs before use.
f = h = h
a
0.01
+
1000
L
( )
mm
L indicates the measuring length (unit: mm)
l
f
h
a
h
h
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