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Quick Guide to Precision Micrometer Heads
Measuring Instruments
Key Factors in Selection
Key factors in selecting a micrometer head are the measuring range, spindle face material and shape, accuracy, stem type, graduation style and thimble diameter.
Stem Stem locknut type Constant-Force Device
Plain stem A micrometer head fitted with a constant-force device (ratchet or friction
thimble) is recommended for measurement applications.
B
If using a micrometer head as a stop, or where saving space is a priority, a
head without a ratchet is probably the best choice.
The stem used to mount a micrometer head is classified as a plain or Micrometer head with Micrometer head without constant-
locknut type as illustrated above. The stem diameter is manufactured to a constant-force device force device (no ratchet)
nominal Metric or Imperial size with an h6 tolerance.
Spindle Lock
The clamp nut stem allows fast and secure clamping of the micrometer
head. The plain stem has the advantage of wider application and slight If a micrometer head is used as a stop it is desirable to use a head fitted
positional adjustment in the axial direction on final installation, although it with a spindle lock so that the setting will not change even under repeated
does requires a split-fixture clamping arrangement or adhesive fixing. shock loading.
General-purpose mounting fixtures are available as optional accessories.
Measuring Face
Flat face Spherical face Anti-rotation device
A flat measuring face is often specified where a micrometer head is used in Measuring Range (Stroke)
measurement applications.
When choosing a measuring range for a micrometer head, allow an
When a micrometer head is used as a feed device, a spherical face can adequate margin in consideration of the expected measurement stroke. Six
minimize errors due to misalignment (Figure A). Alternatively, a flat face on stroke ranges, 5 to 50 mm, are available for standard micrometer heads.
the spindle can bear against a sphere, such as a carbide ball (Figure B).
Even if an expected stroke is small, such as 2 mm to 3 mm, it will be cost
A non-rotating spindle type micrometer head or one fitted with an anti- effective to choose a 25 mm-stroke model as long as there is enough space
rotation device on the spindle (Figure C) can be used if a twisting action on for installation.
the workpiece must be avoided.
If a long stroke of over 50 mm is required, the concurrent use of a gauge
If a micrometer head is used as a stop then a flat face both on the spindle block can extend the effective measuring range. (Figure D)
and the object it contacts provides durability.
Figure D
Figure A Figure C
Gauge block
Figure B
Non-Rotating Spindle Head’s stroke
Obtained stroke
A non-rotating spindle type head does not exert a twisting action on a
workpiece, which may be an important factor in some applications. In this guide, the range (or stroke end) of the thimble is indicated by
a dashed line. For stroke ends, consider the thimble as moving to the
position indicated by the line when designing the jig.
Spindle Thread Pitch Ultra-Fine Feed Applications
The standard type head has 0.5 mm pitch. Dedicated micrometer heads are available for manipulator applications,
1 mm-pitch type: quicker to set than standard type and avoids the etc., which require ultra-fine feed or adjustment of spindle.
possibility of a 0.5 mm reading error. Excellent load-bearing characteristics
due to larger screw thread.
0.25 mm or 0.1 mm-pitch type
This type is the best for fine-feed or fine-positioning applications.
B-99
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