Computer Aided Design (CAD) Week 10 :: Limits, Fits and Tolerances

Limits and Fits Example Application Clearance Fit Interference Fit

Limits and Fits - Terminology

CLEARANCE FITS INTERFERENCE FITS TRANSITION FITS

Limits and Fits – Background to BS ‘Selected Fits’ NEGATIVE POSITIVE SELECTED FITS

Limits and Fits – Background to BS ‘Selected Fits’ SELECTED FITS

H11-c11 – Extra loose running fit Provides a large clearance. Gives easy assembly. H9-d10 – Loose running fit Used where ease of assembly is required (e.g. pulleys) H9-e9 – Easy running fit Suitable for smaller parts, e.g. camshafts etc. H8-f7 – Normal running fit Good quality fit which can be easily produced. H7-g6 Close running or Location fit Expensive to produce. H7-h6 Precision slide or Location fit Precision Slides with good lubrication under constant Temp. Limits and Fits – Classification

H7-k6 – Push or easy keyring fit Location of parts which are not dismantled often. H7-n6 – Tight keyring fit Tight assembly of long parts where H7-k6 isn’t sufficient. H7-p6 – Light drive fit Used to secure steel parts. Dismantel & renewal required. H7-s6 – Heavy drive fit Permanent assembly of ferrous parts. Shrunk-fit required. Limits and Fits – Classification

Consider a Drive pulley and shaft assembly (shaft = Ø40). The keyway provides positive drive rotation. The required fit is H7-h6. Calculate: the Maximum and Minimum Limits for the size of Hole & Shaft. Limits and Fits - Question

Limits and Fits - Solution Ø40 H7 = +25 upper 0 lower I.E.: Max Limit of Size of Hole: = Min Limit of Size of Hole: 40 – 0 = Ø40 h6 = -16 upper 0 lower I.E.: Max Limit of Size of Shaft: = Min Limit of Size of Shaft: 40 – 0 =

Limits and Fits - AutoCAD

Machining and Surface Texture Surface Roughness of 3.2 µm (Machining Optional) Machining of Surface is Required 3.2 Machining of Surface (removal of material) is Prohibited! 3.2

Machining and Surface Texture All surfaces are to be machined. A value can be added as necessary. Typical Drawing with Surface Roughness