PASS TOLERANCES

The tolerance of the dimensions that allow the two mechanical elements to work together determines the conditions in which these two elements will work together. These situations range from very loose to very tight.

The exact position without spaces is indicated by an upper or lower case "H".
Capital or lowercase letters "A" to "G" for spaced inserts,
Capital and lowercase letters "J" to "Z" are used for tight fit.
(Note: I, L, O, Q capital or lowercase letters are not used in tolerance display)

Each fit has a degree of tolerance. These degrees range from 5 to 11 in practice. (1,2,3,4 degrees are used in the manufacture of measuring instruments that require very high precision). The smaller this degree, the greater the precision of that tolerance.
Example: While Ø120 H7 dimension can be maximum Ø120.04 mm, Ø120 H11 dimension can rise up to Ø120.25 mm. The high degree of sensitivity of the given tolerances is an issue that directly affects the cost. In other words, the cost of machining a bushing in the tolerance of "H7" is more than the cost of machining in the tolerance of "H11".

As can be seen from the graphic on the right, as the tolerance decreases, the cost of surface treatment increases too much. Example: If the tolerance of the surface to be machined is +/- 0.7 mm and the cost of this processing is 1 unit, if this tolerance is reduced to +/- 0.1, the unit cost increases 10 times, and if it is reduced to +/- 0.01, it increases 30 times.

MEASUREMENT VALUES OF SPECIFIED TOLERANCES

Stated tolerances vary with diameter or width. Tables for these values ​​have been produced and almost every manufacturer has these tables. These tolerance tables are also available on the internet. TOLERANCE TABLE

UNIT HOLE, UNIT MILE TOLERANCES

One of the elements that will work interlocked will definitely be inside and outside. Internal dimension tolerances (such as bush and shaft) are specified with capital letters (such as H7, K6), and external dimension tolerances are specified with lowercase letters (such as m6, h8). The tolerance of one of these two elements is always specified in the tolerance of "H" or "h", which is the non-backlash tolerance, while the other element is specified with one of the gap or tight fit tolerances.

UNIT HOLE TOLERANCE: If the inner dimension (hole, gap, etc.) is given with "H" tolerance and the size of the material to be inserted is specified with one of the tight or hollow tolerances, this tolerance is called unit hole tolerance. Example H7-k6.

UNIT SHAFT TOLERANCE: If the material to be inserted (shaft etc.) is given with "h" tolerance and the outer dimension (hole, etc.) is specified with one of the tight or hollow tolerances, this tolerance is called the unit shaft tolerance. Example h7- K6.
WHEN UNIT HOLE, WHEN UNIT MILE TOLERANCE IS USED.

When to use a unit hole and when to use a unit shaft tolerance may be a preference of the designer, but at times determined by requirements. For example, if the fitting surfaces of a purchased ready-made material are provided with a certain tolerance, the tolerance suitable for that material is used. Example; A unit shaft tolerance is used to mount a material with an inner diameter of "H" tolerance to the shaft, and a unit shaft tolerance is used to mount a material whose outer diameter is provided with a tolerance of "h" to the hole diameter.
Example: Since a purchased bearing will be provided with an outer diameter of h, the tolerance that must be used is the shaft tolerance. This is a requirement for other ready-made components such as bearings provided with certain tolerances.

TOLERANCE PAIRS

Materials that will work with each other always take double tolerance values. These tolerance pairs have been reduced to some standards as a result of experience. These tolerance pairs to be used according to the places of use are usually matched as follows. (Note below are not guidelines, but advanced uses in practice.)

SPACED PASSING TOLERANCE PAIRS

H7-h6: Used for elements whose surfaces are lubricated. Example: Pulley hubs, retaining rings, clutches, moving bench parts that need to be replaced frequently.

H7-g6: Don't get stuck. Example: Gears that need to shift axially, couplings, connecting rod bearings, pistons

H8-h9: Don't be comfortable. Example: Transmission shafts fixing rings, belt pulleys, gears, clutches, etc.

H7-f7: Animated fit. Sample ; Machine tools main bearings, crank shafts,

H7-e8: Spaced inserts. Crossings that must maintain mobility in sample heat

H7-d9: Multi-cavity inserts.

TIGHT PASS TOLERANCE PAIRS

H7- j6: Click and click: They are easy tight joints made by hitting the tree with a hammer. Example: belt pulleys, gears, hand wheels, bearing bushes etc.

H7-k6: Comfortable clamping with hammer: Example; pulleys, bearing inner rings, hand wheels etc.

H8-n6: Difficult hammering: Example; pulleys, clutches, couplings etc.

H7-n6: Pressing: Example; Pulleys that will not be removed again, rotors placed on the motor shaft, gears to be placed on the trunnion, bushings inside the hubs, etc.

PRESS PASSES

Do not allow the press or slot to expand by heating.

These are the passages made by crying and will not be removed again.

H7-r6: Inserts that will not play under the effect of moderate constant force. For example, steel ring fitting on cast iron core, bushings pressed into bearing in connecting rods, etc.

H8-u8: Inserts that will not play under great constant force