Chapter 25
Tolerance Fit Calculator ISO 286, Edition 2010

    25.1   Selection of Fits
    25.2   Calculation of Possible Fits
    25.3   Example for Cylindrical Fits
    25.4   Further Possibilities

This calculation module enables you to determine the deviations of different tolerance fits for a given nominal diameter very easily and fast. Here all IT classes and tolerance fields according to the standard ISO 286 are available. The program determines only interferences or expects a user input.

A clearance specifies a negative interference.

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Figure 25.1: General overview

25.1 Selection of Fits

The upper part, the ‘selection of fits’, calculates the minimum and maximum interference by the determined deviations (UK = ei-ES and Ug = es-EI). Positive values indicate an interference, negative values indicate a

clearance. The upper part of the fit calculation allows you to select the tolerance field for the shaft and the hub very easily from the listbox. The fit calculator provides the tolerance system according to DIN ISO 286 including all IT classes. The upper part of the fit calculator allows to choose the tolerance field for the hub and the shaft.

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Figure 25.2: Tolerance field

The program determines the lowest and highest interference or the clearance of the selected fit. Thereby, the calculator displays the type of fit:

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Figure 25.3: Deviation for the selected fit

The deviations of shaft and hub can be entered manually. In order to do so, please enable the option ‘Activate the input of user defined tolerances’.

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Figure 25.4: User-defined tolerances

25.2 Calculation of Possible Fits

For the calculation of possible fits, the desired interferences must be entered by the user. The clearance is also specified as a negative interference.

Examples:

Tolerance fits can be searched on the basis of default settings. For the dimensioning of a fit you have different possiblities.

First Option

You can specify the lowest and highest interference for the calculation.

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Figure 25.5: Lowest and highest interference

The button ‘Search fits’ shows you all possible fits.

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Figure 25.6: Search fits

The option ‘Show only preferred fits’ is enabled by default. The list of fits is limited. Disable this option and click the button ‘Search fits’. The number of fits increases. The message ‘More than 500 fits were found. Only preferred fits are shown’ may occur. If you confirm this message with ‘OK’, the option ‘Show only preferred fits’ is automatically enabled. Then you can choose a fit from the listbox.

Second Option

Enable the following options and easily take over the tolerances from the upper fit calculation. Click the button ‘Search fits’ and the appropriate fits will be displayed.

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Figure 25.7: Specified tolerance field

For the calculation of possible fits, the IT scope can be selected. The following IT scopes are available:

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Figure 25.8: IT scope

25.3 Example for Cylindrical Fits

The following section gives some guidance on selecting fits according to E. & K. Felber. There are features that can be expected in general during the assembly. The assembly rules specify the character of the fit and all features correspond to the mean value of fits.

The list contains fits that are used frequently. Almost all fits can be formed in quality (e.g., from H8/f8 to H8/f7 to H6/f6). In general, the standard fits (e.g., H8/f7) can be used. According to the function, you have to select fine qualities (e.g., H6/f6) for larger requirements (requirements for accuracy and uniformity).

The following examples are taken from the mechanical engineering and cannot to be considered as complete in any detail.

25.3.1 Examples for Interference Fits

Interference Fit: H8/u8; U8/h7; H8/s7; S7/h6; H7/r6; R7/h6

Feature, Assembly: The parts are assembled and tightened and have a strong interference. The parts are pressed together or assembled into position while hot and cooled. In general, a safety device against torsion or shifting in lengthwise direction is not necessary.
Examples: Spur gears that are mounted tightly on a shaft, couplings, collar rings, press rings, wheel rims, bearing bushings in housings, bushings in gear hubs, tight pivots, bushings made of synthetic resin pressed material, parts which cannot be loosened by large forces.

25.3.2 Examples for Transition Fits

Transition Fit: H7/n6; N7/h6

Feature, Assembly: The parts are mounted against each other. High pressure is necessary to join and separate the parts. Due to clearance, the parts have to be secured against torsion.
Examples: Bearing bushings at machine tools, wheel rims on wheel bodies, levers and cranks on shafts, impact-loaded parts, bushings in basic bodies, gears and couplings on shafts.

Transition Fit: H7/m6; M7/h6

Feature, Assembly: Parts sit tightly on top of each other. Joining and separating cases require large expenditure of energy by using a hammer, parts have to be secured against torsion and shifting.
Examples: Pulleys, gears, bushings, lever on shafts, cranks for lower forces, piston pins in pistons, coupling pins, fixing pins

Transition Fit: H7/k6; K7/h6

Feature, Assembly: Parts stick together and can be joined and separated by using some hammer blows without enormous expenditure of energy. Parts have to be secured against torsion and shifting.
Examples: Coupling parts, pulleys, flywheels, handwheels, hand levers on shafts, gears on machine tool spindles, bearing bushings in wheels and in basic bodies, fixing pins, pins, bolts, centralisations, coupling halves and gears on shaft ends of electric motors over Ø 50 mm.

Transition Fit: H7/j6; J7/h6

Feature, Assembly: Easy to join by hammer blows, often movable by hand, not intended for functional shifting, applicable for parts which have to be disassembled very often, a securing against torsion and shifting is possibly necessary.
Examples Change gears, gears, pulleys, adjusting rings, bushings, bearing bushings and handwheels which have to be removed very often, centralisations, coupling halves and gears on shaft ends on electric motors up to Ø 50 mm.

25.3.3 Examples for Clearance Fits

Clearance Fit: H7/h6

Feature, Assembly: Parts can be moved manually by using lubricants. Still usable for a slow shifting.
Examples: Centralisations, change gears, adjusting rings, coupling parts wedged on shafts, tools on arbors (e.g., milling cutters on milling-machine arbor), idler bushings, handwheels on spindles, spacer sleeves, sealing rings, all kind of guides, tailstock sleeve, plain bearings with very small clearance, chain wheels, large gears.

Clearance Fit: H8/h9

Feature, Assembly: Parts fit easily into each other and are easy to move.
Examples: Less important centralisations, adjusting rings, crank handles, gears, couplings, pulleys which have to be moved over shafts, idler bushings, use of cold finished round steel (round steel, finish polishing made of tool steel, cold work steel, high-speed steel).

Clearance Fit: H11/h9; H11/h11

Feature, Assembly: Parts can be easily stuck together. Clearance as low as possible with relatively large manufacturing tolerances.
Examples: Less important centralisations, parts which are to be stuck together, soldered or welded, parts that are pinned, bolted or clamped on shafts, spacer sleeves, hinge and snap pins, extensive use of cold drawn steel bar (e.g., round steel, uncoated according to ISO tolerance field h9/h11).

Clearance Fit: H7/g6; G7/h6

Feature, Assembly: Parts are easily movable and twistable but without noticeable clearance.
Examples: Bearings for high requirements, change gears, movable coupling parts, indexing pin, valve lever, cluster gears in gearboxes.

Clearance Fit: H7/h7

Feature, Assembly: Parts have noticeable clearance and are movable into each other.
Examples: Main bearing on machine tools, gear shafts, main bearing for shafts that run in two bearings, cardan shafts, camshafts, crankshafts, bearing bushes, sleeves and floating sleeves on shafts, timing shafts, slide blocks in guides, snap rings.

Clearance Fit: F8/h9

Feature, Assembly: Parts are movable, run easily and have large clearance.
Examples: Shafts with multi-bearing system, bearing shells, bearings where viscous lubricants have to be used, bearings that are exposed to contamination (e.g., bearings on brackets), bearings of lead screws in slides, chain sprockets run loosely, rope sheaves, axle boxes, use of cold drawn round steel, bearing of shafts of dynamos, fans, centrifugal pumps.

Clearance Fit: H8/e9; E8/h9

Feature, Assembly: Parts are movable into each other and have a small to large clearance.
Examples: Main bearings for crankshafts, guide crossheads, guide for piston rods, pistons in cylinder, bearings for gear wheel pumps, rope sheaves, bearings in internal combustion engines.

Clearance Fit: D10/h9

Feature, Assembly: Parts are very easily movable into each other and have a very large clearance.
Examples: Transmission shafts and countershafts, plain bearings for rough and adverse conditions, secondary bearings for agricultural machinery, loose pulley, common bearings for locomotives, stuffing boxes, bearings in centrifuges, axle boxes for conveyances, general centralisations, spindles for textile machinery.

Clearance Fit: H11/d9, H11/d11; D11/h11

Feature, Assembly: Parts have large clearance and large manufacturing tolerances.
Examples: Guides and plain bearings of secondary importance, heat-treated plain gearings (e.g., by liquids and gases), hinge pins and forked bolts, rivet pins, rivet joints, removable levers and cranks, socket wrenches, bad lubrication of parts, shafts for turbogenerators and continuous-flow machines, high-speed spindles for textile machinery, holes H11 (producible by using a twist drill that is guided in sleeves), use of cold finished round steel h11.

Clearance Fit: C11/h11; H11/c11

Feature, Assembly: Parts with larger clearance and large manufacturing tolerances.
Examples: Secondary bearings for agricultural machinery and household appliances, pivot pins.

Clearance Fit: H11/a11; A11/h11; H12/b12; B12/h12; H11/b11; B11/h11

Feature, Assembly: Parts with very large clearance and large manufacturing tolerances.
Examples: Secondary bearings in locomotive and railway carriage construction, hinges, bearings for agricultural and construction machinery, door hinges, pivot pins, bearings that are exposed outside to elements.

25.4 Further Possibilities

Clicking the link ‘More calculation modules’ leads you to our web site. Here you can register for a free test account in order to use all eAssistant calculation modules (e.g., shafts, cylindrical gears, bevel gears, springs). Find more information in section 2 ‘Registration’).

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Figure 25.9: Link to our web site

Please Note: If you registrate for the first time, you will receive a password in order to login. The project management helps you to start the calculation modules. The list on the left side shows all calculation modules including the free modules. If you use these modules, then no time will be deducted from your account.

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