Engineering - What Production – How

methods that avoid the need to purchase

expensive machines.

Products produced in either factory are acceptable

as long as they meet the specifications of the

engineering drawings.

WHICH DETAILS BELONG WHERE

It is easy to fall in to the trap of putting too much

detail on engineering drawings, in an attempt to be

helpful. For example, the designer of the

component with the screw that needed to be

tightened might realise that the screw is in an

awkward place and specify on the engineering

drawings that the tightening operation is to be

done early in the assembly process. But suppose

the factory where the product is made only had a

particular type of right-angled torque driver. It

might actually be more convenient for them to

tighten the screw later on, when they can get at it

from the side. By imposing the unnecessary

restriction the engineer might have just made the

product more expensive.

The key questions when considering if something

belongs on an engineering drawing are "Is the

proposed specification something that can be

observed in the finished product? Would a product

be unacceptable if this specification were not

followed?"

In the example of the screw the answer is that the

torque specification is important and measurable.

You can look at a finished widget and measure the

torque of the screw and say whether it is

acceptable. The torque specification, if it is

important to the correct operation of the widget,

properly belongs on the engineering drawing.

On the other hand, you can say nothing from

looking at the finished widget about which tool

might have been used to tighten the screw or

when the tightening might have been done. These

things do not affect the finished widget and thus

do not belong on the engineering drawings.

WHY TWO SETS

Separating production information from the

engineering drawings brings advantages to the

engineering department too. Every engineer is

familiar with the Project That Will Not Die. The

project he worked on five years ago but about

which he is still compelled to make mundane

decisions every other week. Decisions that have

nothing to do with the engineering specifications of

the product, but rather concern production details.

This problem is especially acute in smaller

companies without a dedicated production

engineering department, where all the information

about both engineering and production details is

on one set of drawings. Every mundane

production problem requires the involvement of

engineering staff to modify the drawings. Avoid

this problem by maintaining separate engineering

and production drawing sets. The engineering

drawings will rarely change and the expensive

engineers can work on developing new products.

The production drawings, which typically change

more frequently as problems arise or new

equipment is introduced, can be maintained by the

production staff.

CONCLUSION

Maintaining a clear distinction between

engineering and production drawings, and

ensuring that everyone understands which

information belongs where brings benefits to both

the engineering and production functions, both in

time and cost.

ABOUT THE AUTHOR

Matthew Kendall is a

principal of Ionocom

Communications Inc.,

Vancouver, BC.

He has worked in electronic

product design since 1987,

first in Reading, England,

and lately in Vancouver, BC, Canada.

He can be reached by email at

matthew@ionocom.com.

See http://www.ionocom.com for more articles like

this one.