Machine Translated by Google
AND 231 LINKS BETWEEN SOLIDS
SIDE CHAINS
1- Object of the functional rating
2- Chains of odds
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Machine Translated by Google
1 • Object of the functional dimension:
When manufacturing mechanical parts, it is impossible to achieve a "correct" dimension because of
factors such as tool wear or machine dispersion.
We call this rating which should be "ideal": nominal rating.
In order to make parts, we therefore set ourselves a margin of error, called Tolerance
Interval (IT)
All manufactured parts falling within this range will be considered acceptable.
Example:
Either the rating:
21
20ÿ1
20
ÿ1
19
The nominal dimension sought is 20 mm
The allowed margin of error ranges from +1 mm to – 1
mm, i.e. a tolerance interval IT = 2 mm
Will be considered as correct the pieces of dimension
ranging from 19 to 21 mm
IT
Remark:
The same tolerance interval can be distributed in different ways:
20ÿ1
ÿ1
;
20ÿ2
0
;
20ÿ0.5
ÿ1.5
This will depend on the type of manufacture, the machines used etc....
A permanent dialogue between the design offices and the manufacturing departments is necessary.
Once manufactured, the parts must be able to be assembled taking into account possible
dimensional variations.
This is where the notion of a chain of odds comes in.
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Machine Translated by Google
2 • Dimension chains:
Example:
We want to store sticks in a box.
- What problem can arise?
- Some sticks are too long
- Set minimum and maximum dimensions for the box and the
- What solution to bring?
sticks, as well as a set* allowing them to be placed easily in the box.
*
the game in question here is the condition for the sticks to enter the box, this
dimensional requirement is called dimension condition
48ÿ0.5
0
J
HAS
?
Rating condition:
The length of the box is defined by a
tolerance dimension
Length to be defined
The minimum play is 1 mm
The maximum play is 2 mm
Method:
Each side of an element (link in the chain) is associated with a vector.
The condition dimension is associated with the result vector of the sum of all the component vectors
the string (see the math lesson on vectors!)
ÿJ
ÿA2
HAS
ÿA1
2
We can write: ÿJ
1
A =ÿA1 ÿÿA2
• When will we have: JA maxi ?
– when A1 is max and A2 min:
YD max = A1 max - A2 min
• When will we have: JA mini ?
– when A1 will be mini and A2 maxi:
JA mini = A1 min - A2 max
STI2D
Machine Translated by Google
Digital Application:
•
YD max
= A1 max - A2 min ÿ 2 = 48.5 - A2 min ÿ A2 min = 46.5
•
JA mini
= A1 min - A2 max ÿ 1 = 48 - A2 max ÿ A2 max = 47
The stick may have odds of 47 ÿ0.5
0
Rule #1:
– The TI of the condition dimension must be equal to the sum of the TIs of all the links of the
chain.
Rule n°2: (practical rule)
– The vectors that go in the same direction as the condition dimension, have a "+" sign and the same
hint
– Vectors that go in the opposite direction to the condition dimension have a "-" sign and the subscript
opposite
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