DESIGN/CADCAM 3DIMENSI: TOLERANCE ZONE

ISO Tolerances are indicated by letters an numbers.

There are 20 tolerance quqlities,which are indicated by number : 01,0,1,2,3,4......,18 (the bigger number the wider the tolerance-zone).

In each grade,the tolerance zone in creases with the basic size.

The letters give the position of the tolerance zone in relation to the 0-line ( zero-line ).

Capital letters are use for holes.
Small letters are used for shafts.
H,h- Tolerance touch the 0-line ( zero-line ).

FIT COMBINATIONS

A. Hole Basic System

All the Hole-Tolerances have zone H
Hole Tolerance : H
Matched with shaft Tolerance
Clearance Fits ; a,b,c,d,e,f,g,h.
Transition Fits : i,k,m.
Interference Fits : p,r,s,t,v,x,y,z,za,zb,zc.
Application ; Tool machines,Engines,Contruction for Vehicles etc.

B. Shaft Basic System

All the shaft Tolerances have zone h.
Shaft Tolerance : h
Matched with Hole Tolerance
Clearen Fits : A,B,C,D,E,F,G,H.
Transition Fits : I,K,M,N.
Interference Fits : P,R,S,T,V,X,Y,Z,ZA,ZB,ZC.
Applications ; textile machines,agricultural machines etc.

C. Comparison of the 2 Systems

Advantage of Hole Basic System : Production an control of shaft tolerances is not as difficult as those of holes.
Only a few toola as e.g reamer are necesary.
Advantage of Shaft Basic System : Usually shafts have not be machined,bright material can used.

EXAMPLEs of DIFFERENT ISO-Fits

CLEARANCE Fits

Description ; run with rel,much clearance
ISO Fit Basic Hole : H7/f6
ISO Fit Basic Shaft : h6/F7
Applications : crankshaft,piston,valves etc.
Description : run with rel,little clearance
ISO Fit Basic Hole : H7/g6
ISO Fit Basic Shaft : h6/G7
Applications : dividing heads,spindle bearings of machine tools etc.
Description : just sliding.
ISO Fit Basic Hole : H7/h6
ISO Fit Basic Shaft : h6/H7
Applications : tailstock,spindle sleeves etc.

TRANSITION Fits

Description : can be moved with little force.
ISO Fit Basic Hole : H7/j6
ISO Fit Basic Shaft : h6/I7
Applications : ball bearing fits,position pin etc.
Description : can be moved with middle force.
ISO Fit Basic Hole : H7/k6
ISO Fit Basic Shaft : h6/K7
Application : ball bearing fits,position pins etc.
Description : can be move with middle force
ISO Fit Basic Hole : H7/m6

ISO Fit Basic Shaft : h6/M7

Applications : levers on shafts,bearing bushes etc.

INTERFERENCE Fits

Description : can be moved with high force.

ISO Fit Basic Hole : H7/p6

ISO Fit Basic Shaft : h6/P7

Applications : levers on shaft,bearing bushes etc.(as above)

Description : not possible to move,shrink fit.

ISO Fit Basic Hole : H7/s6

ISO Fit Basic Shaft : h6/S7

Applications ; wheel rings,seat ring etc.

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CAD CAPABILITY

Regardless of the type of work shops do, most find it necessary to have CAD capabilities as well as CAM. Even if a shop receives all its work electronically as CAD files, the programmer often needs to clean up the geometry in order to create the tool paths properly.

Basic functions such as point, line, arc, fillet, spline, chamfer and rectangle creation are essential for creating or modifying any type of geometry. More advanced CAD capabilities, such as surface creation and manipulation, allow you to create complex models from scratch, or to modify existing models to make them machinable. In addition to geometry creation, a good CAD provides features to speed part modeling, such as multiple viewports and construction planes.

Addition CAD features such as surface shading help depict the geometry in a way that is clear and easy to understand.

Many shops prefer a package tha includes both CAD andCAM. Using a tighly integrated CAD/CAM system eliminate the need to translate files between separate CAD and CAMpackages. Since an integrated CAD/CAM system uses a cammon database for both the CAD/CAM information, complete data compatibility is maintained at all times. In addition, this type of CADCAM system shares a common interface, avoiding the problem of having to train programmers on two separate systems.

TOOL PATH EDITING

A good CAM system gives you final control over the tool path so you are not forced to use a tool path you do not want, or use a parameter that the system includes by default. Many systems give you the ability to graphically edit the tool path after it has been generated. This not only gives you final say over exactly what the tool path does, but also gives you the ability to cut, paste, reverse or reorder sections without taking the time to recreate the entire tool path. This also applies to machining parameters such as feeds and speeds. It is important that you are able to change these settings without recreating your entire tool path.

Computer Aided Engineering Tools

Engineering analysis is concerned with analysis and evaluation of engineering product designs. For this purpose, a number of computer-based techniques are used to calculate the product's operational, functional, and manufacturing parameters. Finite element analysis (FEA) is one of the most frequently used engineering analysis techniques. Besides FEA, tolerance analysis, design optimisation, mechanism analysis, and mass property analysis are some of the computer aided techniques available to engineers for the purposes of analysis and evaluation of the engineering product designs.

TOLERANCE ZONE

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