Mechanical Drawings define the specifications of each component in
your product, as well as sub-assemblies and assemblies. They
control the size of each part feature, and they control how parts fit
together. When parts don't fit together or they don't function incorrectly,
there may be a problem with the parts or assemblies.
Mechanical Drawings are used to confirm that parts and assemblies are
correct or incorrect.
Let's say a manufacturer of one part in your product makes 10,000
parts that are out of spec. That is, they do not match the
specifications in the Mechanical Drawing of the part. Usually
this means that the part will not function correctly in the assembly of
your product. Do you have to buy the parts anyway?
The answer is an astounding no. When you order parts from a
manufacturer you order them using Mechanical Drawings. If a part
does not match the Mechanical Drawing, it is not what you ordered.
The manufacturer's responsibility is to provide you with parts that
match the specs in Mechanical Drawings. So a Mechanical Drawing
becomes the legally binding document in your agreement to purchase
This concept extends to any type of purchase you may make for
components and assemblies. For example, when you purchase prototypes,
they have to meet the specifications in the Mechanical Drawings. When
you have production tooling fabricated, the tooling has to make parts
that meet the specifications in the Mechanical Drawings of the parts.