The Engineer's Notebook
Each issue of The Misumi Voice will feature tutorials and case studies on designing
your automation equipment using components available from the Misumi catalog. In
this very first issue, we start with the basics for linear motion implementation.
Precision Shafts
Due to their simple structure allowing high dimensional accuracy in machining, shafts
are used for high precision linear guides. Misumi shafts feature:
- Fit tolerance g6 (for requirement of precision motion with fine linear accuracy)
or f8 (for use with grease or oil-lubricated bearings).
- High surface hardness with employment of induction hardening and hard chromium plating.
- Excellent circular tolerance and straightness plus concentricity and perpedicularity
of finish ends.
- A wide choice of end finishes.
Typical linear mechanism using two parallel shafts (see Figure 1 and Photo 1)
- Using two shafts eliminates displacement, achieving high-precision linear motion
capability and high load capacity. (See Photo 1)
- Two types of bushings are available: linear bushings and oil-free bushings. Typically,
linear bushings are used.
- Oil-free bushings have high load capacity (compared to linear bushings) and are
recommended for mechanisms subject to shock. Oil-free bushings, however, have larger
friction resistance compared to linear bushings (which contain linear ball bearings),
and should not be used for mechanisms subject to long continuous operations.
Photo 1 and Figure 1:
1. Shaft Holder 2. Shaft 3. Stopper 4. Linear
bush
Linear mechanism using a single shaft (see Figure 2 and Photo 2)
- With a linear mechanism using a single shaft, the shaft can serve as a motion guide
involving linear and rotaty motions or as a linear guide by restraining rotation.
Figure 2 shows the latter case.
- The linear mechanism prevents rotation because the cylinder piston is acting as
a second shaft. Therefore this configuration is not suitable for applications that
require high load capacity. Photo 2 shows an example of using a linear shaft and
air cylinder.
- For a single-shaft mechanism, either long linear bushings (double-type or long-type)
or oil-free bushings (for intermittent motions) should be selected to obtain linear
stability and high load capability.
Photo 2 and Figure 2:
1. Air Cylinder 2. Shaft 3. Oilless bush
Note: With this mechanism, rotation is restrained by the shaft and air cylinder,
thus not recommended for extreme load.