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Low Cost Automation Tutorial

#002 Precision Shafts

Category : Linear Motion Components
July14, 2009

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.

Examples of linear motion applications using shaft(s)
a) Typical linear mechanism using two parallel shafts (see Figure 1 and Photo 1)
1. Using two shafts eliminates displacement, achieving high-precision linear motion capability and high load capacity. (See Photo 1)
2. Two types of bushings are available: linear bushings and oil-free bushings. Typically, linear bushings are used.
3. 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.


b)Linear mechanism using a single shaft (see Figure 2 and Photo 2)
1. 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.
2. 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.
3. 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.