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Application of Interference Fits:
levers and cranks on shafts, toothed gears and pulley on shafts, bushes in bases (housings).
Figure 4 Interference fits
1 lever on shaft, 2 pulleys on shafts, 3 bushes in bases (housings)
Application of Clearance Fits:
slide bearings, guides, movable coupling elements, cluster gears in transmissions, pistons in cylinders of engines.
Figure 5 Clearance fits
1 flat guide, 2 dovetail guide, 3 flat guide with dovetail, 4 inverted guide, 5 cylindrical guide
Fits appear on surfaces where assembled parts are in contact with each other or on which parts movable against one another can come into contact.
We distinguish between the following fits according to the form of the surfaces:
- cylindrical fits fit between cylindrical mating surfaces
- flat fits fit between plane surfaces
Fitting works are marked by different methods applied in the individual and series production.
Individual production
In the field of crafts and in case of repair work fits are being manufactured by hand.
First one part is produced, and then the matching piece is fabricated by testing and reworking. One part is adjusted to the other until the desired type of joint is reached.
Example:
During the repair of a machine a damage in material was discovered at a guide top, and this element can no longer be used. It is not possible to get a spare part from the producer of the machine, and there is no engineering drawing.
With the help of the lower part of the guide the new guide top has to be manufactured as matching piece and adjusted.
Series production
In the industrial production the various component parts of machines and plants are produced independently of each other by using different methods and in different production fields.
The necessary dimensional accuracy of the component parts is specified by fit directions in the working drawings. The component parts are worked until the dimensions correspond to the fit directions. Manual reworking will only be necessary, if the component part shows defects caused by electrodeposits, formations of buns, corrosion or transport (defects due to blows, local upsetting deformations) and which prevent an assembling.
Example:
A shaft has broken in the transmission of a machine. Spare shafts for this transmission are offered by the producer, the broken shaft is dismantled, the spare shaft is inserted - it fits since the shafts for this transmission have been fabricated with fixed measures, they are exchangeable.
Manufacturing Condition:
If component parts which belong together due to their function are to be assembled, they have to be “exchangeable”!The fabrication of well fitting and easily exchangeable elements is the precondition for time-saving and economic assembly.
What is the purpose of
fitting?
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Which types of fits are
distinguished?
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Which methods can be applied in fitting
works?
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Which manufacturing condition is good for an economic
assembly?
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