Designing Parts for Small Batch Machining

CNC Machining when combined with 3D CAD/CAM has revolutionised workshop practice in recent years. It has opened up a whole new world of possibilities for designers who are designing machined components which are intended to be produced in small or medium sized batches.

But what has changed and what are the constraints from a designers point of view?

Ultimately the constraint on the designer is always cost. Almost anything can be made - somehow - if cost is not a constraint. What a designer needs to know is which features on a component are cheap and easy to produce and which are more difficult and therefore costly. This is not always obvious unless you have good experience of manufacturing parts using modern techniques.

As a starting point lets start with the easiest component to make and see what features can be added and what are the implications. What hasn't changed is that the easiest component to make is a parallel sided block with a pocket or other features on.
The reason this is so simple is that it can be held easily in a vice, machined around five sides and then put back in the vice upside down and skimmed to thickness. This process requires very little setting up and requires no special fixtures.

What has changed is that now the complexity of the pocket makes very little difference to the cost. When using a 3D CAD/CAM system the shape and depth of the pocket are simply picked from the model with a couple of clicks of the mouse and the software takes care of the rest. The complexity and size of the machine program produced makes no difference as modern machines have large memories and the files are transferred electronically.