Bases of fits

Basic size

Limits And Fits Bs4500

Fig. 19.11 Bilateral limits

Minimum limit Maximum limit

Fig. 19.11 Bilateral limits

The two bases of a system of limits and fits are

(b) the shaft basis.

Hole basis (Fig. 19.12) In this system, the basic diameter of the hole is constant while the shaft size varies according to the type of fit. This system leads to greater economy of production, as a single drill or reamer size can be used to produce a variety of fits by merely altering the shaft limits. The shaft can be accurately produced to size by turning and grinding. Generally it is usual to recommend hole-base fits, except where temperature may have a detrimental effect on large sizes.

Hole Shaft Basis System

Shaft basis (Fig. 19.13) Here the hole size is varied to produce the required class of fit with a basic-size shaft. A series of drills and reamers is required for this system, therefore it tends to be costly. It may, however, be necessary to use it where different fits are required along a long shaft. This BSI data sheet 4500A gives a selection of ISO fits on the hole basis, and data sheet 4500B gives a selection of shaft-basis fits extracted from BS 45000, the current standard on limits and fits.

The ISO system contained in BS 4500 gives an extensive selection of hole and shaft tolerances to cover a wide range of applications. It has been found, however, that in the manufacture of many standard engineering components a limited selection of tolerances is adequate. These are provided on the data sheets referred to above. Obviously, by using only a selected range of fits, economic advantages are obtained from the reduced tooling and gauging facilities involved.

Engineering Symbol For Hole And Shaft

Was this article helpful?

0 -1
Pencil Drawing Beginners Guide

Pencil Drawing Beginners Guide

Easy Step-By-Step Lessons How Would You Like To Teach Yourself Some Of The Powerful Basic Techniques Of Pencil Drawing With Our Step-by-Step Tutorial. Learn the ABC of Pencil Drawing From the Experts.

Get My Free Ebook

Post a comment