Computer Aided Design CAD Week 10 Limits Fits

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

Limits and Fits Example Application Clearance Fit Interference Fit

Limits and Fits - Terminology

Limits and Fits - Terminology CLEARANCE FITS INTERFERENCE FITS TRANSITION FITS

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

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

Limits and Fits – Classification n H 11 -c 11 – Extra loose running fit Provides a large clearance. Gives easy assembly. n H 9 -d 10 – Loose running fit Used where ease of assembly is required (e. g. pulleys) n H 9 -e 9 – Easy running fit Suitable for smaller parts, e. g. camshafts etc. n H 8 -f 7 – Normal running fit Good quality fit which can be easily produced. n H 7 -g 6 Close running or Location fit Expensive to produce. n H 7 -h 6 Precision slide or Location fit Precision Slides with good lubrication under constant Temp.

Limits and Fits – Classification n H 7 -k 6 – Push or easy keyring fit Location of parts which are not dismantled often. n H 7 -n 6 – Tight keyring fit Tight assembly of long parts where H 7 -k 6 isn’t sufficient. n H 7 -p 6 – Light drive fit Used to secure steel parts. Dismantel & renewal required. n H 7 -s 6 – Heavy drive fit Permanent assembly of ferrous parts. Shrunk-fit required.

Limits and Fits - Question n Consider a Drive pulley and shaft assembly (shaft = Ø 40). The keyway provides positive drive rotation. The required fit is H 7 -h 6. Calculate: the Maximum and Minimum Limits for the size of Hole & Shaft.

Limits and Fits - Solution nØ 40 H 7 = +25 upper 0 lower I. E. : Max Limit of Size of Hole: 40 +. 025 = 40. 025 Min Limit of Size of Hole: 40 – 0 = 40. 000 nØ 40 h 6 = -16 upper 0 lower I. E. : Max Limit of Size of Shaft: 40 -. 016 = 39. 984 Min Limit of Size of Shaft: 40 – 0 = 40. 000

Limits and Fits - Auto. CAD

Machining and Surface Texture 3. 2 Surface Roughness of 3. 2 µm (Machining Optional) 3. 2 Machining of Surface is Required Machining of Surface (removal of material) is Prohibited!

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