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Module 7: Maintenance Practices (B1) > 7.6: Fits and Clearances > Flashcards

7.6: Fits and Clearances Flashcards

1
Q
A

is not possible to maintain constantly

i.e A one inch shaft - nominal size. Not possible to manufacture exactly 1.00000’’ so a tolerance must be used, and also integrated with fits and clearances

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2
Q
A

The total permitted variation above or below the nominal size

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3
Q
A

A bi-lateral tolerance

Bilateral tolerance is the amount of variation above or below the design size Example 3.75 +/- 0.05

Unilateral tolerance is the amount of variation in one direction either above or below the design size Example 3.75 +0.05/-0.00

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4
Q
A

May require force to assemble parts

Clearance Fit - a clearance fit is one having limits of size defined such that a clearance always results when mating parts are assembled.

Interference fit - an interference fit is one having limits of size so prescribed that an interference always results when mating parts are assembled.

Transition fit - a transition fit is one having limits of size so prescribed that either a clearance or an interference may result when mating parts are assembled

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5
Q
A

Go/ No Go gauge

Ovality

This usually occurs as a result of the surface wearing, through friction or linear movement. Ovality can apply equally to holes and shafts.

Holes may be tested for ovality, using such instruments as Go/No-Go gauges, internal micrometers, or callipers, as were previously discussed in the tools module.

Testing roundness of a shaft may be achieved by placing the shaft to be tested on a V-block and rotating under a scribing block or a dial test indicator (this same method may be used to checking shafts for bow)

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6
Q
A

Yes by means of a strain gauge

'’Solid or tubular shafts that must be checked for twist will possibly have witness marks or lines engraved or etched at each end of the shaft. The shafts can be checkedm by mounting the shaft in V blocks and, then, locating these marks in the horizontal position.

It is possible to measure the amount of twist, to which a shaft is subjected, whilst in operation of rotationm using strain gauges. These emit varying amounts of electric current when under strain, giving an indication (on a calibrated instrument) of the load being applied.’’

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7
Q
A

Holes can be drilled and reamed using standard size drill reamers

If the shaft is constant and the hole varies in size, then the system is said to be ‘shaft-based’.

If the hole is constand and the shaft varies in size, then the system is ‘hole based’.

The hole based system is the one in more general use

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8
Q
A

Allow for interchangeablility between parts

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9
Q
A

1 in 600

'’In general, a maximum bow of 1 in 600 is normally acceptable unless otherwise stated in the Repair Manual’’

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10
Q

What is it not possible to do with a Nominal size component?

A

Nominal size of a component is not possible to maintain constantly

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11
Q

Will a Transition fit require force to assemble?

A

Transition fit, may require force to assemble

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12
Q

How can Ovality of a hole be checked?

A

Ovality in a hole can be checked with a Go / No Go gauge

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13
Q

Max bow in a shaft is?

A

Max bow in a shaft is 1 in 600

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14
Q

Where is the Hole base system of fits and clearances more common and why?

A

Hole based system of fits and clearances is more common in Europe because holes can be drilled and reamed using standard size drills and reamers

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15
Q
A

Option C: Dimensional and geometric

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16
Q
A

Option C: 1:600

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17
Q
A

Option A: a DTI and ‘V’ blocks

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18
Q
A

Option C: 1 in 600

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19
Q
A

Option B: 0.748 inch

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20
Q
A

Option B: Tolerance

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21
Q
A

Option C: 2 inches +- 0.002

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22
Q
A

Option B: a permitted variation on a dimension to allow for inaccuracy of equipment

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23
Q
A

Option C: the same size as the hole

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24
Q
A

Option B: 20 times its depth

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25
Q
A

Option B: a clearance fit

26
Q
A

Option B: no less than twenty times the depth

27
Q
A

Option A: some sort of driving force

A press fit is a small interference only.

28
Q
A

Option C: One gauge depth and 0.75 inch diameter

29
Q
A

Option B: 0.0015 inches

30
Q

Module 7 . 6 . 1
Q 16 When you inspect a component to see if it is within limits you would use: -

(a) An Internal Micrometer
(b) A go and no go guage
(c) A six inch rule

A

(b) A go and no go guage

31
Q

Module 7 . 6 . 1
Q 17 The acronym NAS stands for: -

(a) Normal Aeronautical Standard.
(b) National Aerospace Standard.
(c) Naval Aviation Standard.

A

(b) National Aerospace Standard.

32
Q
A

the same size as the hole

33
Q
A

Clearance Fit

34
Q
A

BS EN 20286

35
Q
A

an interference fit

36
Q
A

specification of material with the hole and specification of fastener

37
Q
A

quoted with reference to the basic size

38
Q
A

0.0015 inches

39
Q
A

Tolerance

40
Q
A

hole is bigger than shaft with shaft at maximum limit and hole at minimum limit

41
Q
A

(a) Are cumulative

42
Q
A

(a) To test for the correct size of a hole so that it will produce the required fit

43
Q
A

(b) The hole based system

44
Q
A

(a) With a straight edge and feeler gauge

45
Q
A

c) The largest size allowed and the smallest size allowed

46
Q
A

(a) The hole will be machined using a standard sized tool

47
Q
A

(a) The difference in dimension that is necessary to give a particular ‘’class of fit’’

48
Q
A

(a) 1.876 +.002/-.001

49
Q
A

(a) Clearance fit, Interference fit, transition fit

50
Q
A

(b) a permitted variation on a dimension to allow for inaccuracy of equipment

51
Q
A

c) the same size as the hole

52
Q
A

(a) tolerance

53
Q
A

(a) a clearance fit

54
Q
A

c) difference between shaft and hole diameters

55
Q
A

(a) by a plus and minus sign preceding the permitted tolerance

56
Q
A

(b) Unilateral

57
Q
A

c) the hole basis

58
Q
A

(a) it applies to both parts that are to be assembled

59
Q
A

(a) a loose running clearance hole based fit

60
Q
A

(b) Go/noGo gauges, internal micrometer or callipers

Module 7: Maintenance Practices (B1) (20 decks)

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