6 Ways a Part Can be Considered Complex

10/03/2019 | Jim Herr


Some machine shops claim to manufacture “complex” parts, which surely sounds impressive. Yet, what really is a complex part and what skills does a shop need to work on them? Here are 6 different conditions that could cause a part to be classified as complex. Examples and photos are from actual Stecker Machine Company projects.

Casting Weight and Size

This one is simple. Some parts are large, usually making them heavy, too. A part over 70 pounds requires a lifting device as well as a plan on handling it throughout the process, from raw material to the machine tool to inspection to final packaging. Stecker Machine uses numerous cranes and has the ability to design and build lifting devices as they’re needed.

This lift system moves a 260-pound casting after machining.

Lift system moving a casting


Simply holding a part to be machined can be challenging. Stecker Machine Company may work with both the customer and the foundry to plan how to clamp and hold the part for machining before any cast tooling is made. The cast datum scheme typically ensures everyone is on the same page. Occasionally, cast datum points need to be moved to improve clamping and holding the part.

To improve holding while machining, clamping tabs may be added to a part, which may or may not stay on the part after machining.

Clamping tabs added to a part

While staying current on the latest hydraulic components may be a challenge for some shops, hydraulic clamping does offer some advantages over manual clamping:   

  • Repeatability of accurately locating the part in the fixture
  • Speed of clamping; can be seconds versus minutes
  • Ease on the operators; less fatigue

To have the bore come out round in tolerance, we created a way of holding this part without putting pressure on the bore. That solution has led to 8 years of trusted delivery.

Bore round in tolerance

Part Material

From aluminum to ductile iron to cast iron, there are different grades for each type of material. Reliable tool suppliers can help match the correct grade of insert to the material being run.

Stress in castings can affect a part as it’s machined. Once some material is removed, stress can cause a bored hole to be out of round or a milled surface to be out of flatness. Some cures to stress distortion include adding a finish operation to the part, changing how the part is held, adding a semi-finish tool, or having the casting stress relieved.

Print Tolerances

Tight tolerances can make a part complex. Here are some examples of when tolerance becomes a challenge: true position of .1mm on a bore; a diameter tolerance on a bore of .020mm; concentricity of several bores at .015 tolerances. These tight tolerances determine if specialty tooling is needed, how many operations are required, how the machines should be programmed, or if an outside operation is needed. Note: the larger the bores, the bigger the challenge.

Flatness of .05mm, or parallelism of .05mm, can be challenging on larger or thin-walled parts. Solutions include different face mills, inserts, and different ways of fixturing the part.


Part complexity and the number and types of components that need assembly determine how an assembly fixture is designed. Operator-friendly assembly fixtures are developed so that all necessary components are assembled ensuring that all assemblies ship with complete components.

Air cylinders, sensors, pressure switches, etc. help make sure no components are missed.

Air cylinders sensors and pressure switches

Another shop’s assembly of a 82.55mm diameter steel sleeve into an aluminum part (press fit of .18mm) marred the sides of the aluminum part and created leak paths. Our customer was thrilled that our solution — pressing in the sleeve with heat — eliminated leak paths.

Steel sleeve into aluminum part

Pressure Testing

The shape of a part can make it complex. When clamping a part to pressure test it, critical features — machined bores, machined flat surfaces, thin walls — must be scrutinized to prevent distortion. If the part to be pressure-tested is large and heavy enough to require a crane for lifting, all handling steps need to be accurately planned.

A water test is a standard pressure testing method during which the operator observes for air leaks to determine if a part passes or not.

Parts for water test for air leaks

Used for large quantities, air decay testing’s programmable test instrument provides the pass/no pass indication. This fixture’s test instrument and computer do cost more than water testing, yet they eliminate the potential for human error.

Programmable test instrument for air decay

So, while the description of “complex” may seem open for interpretation, it can really be explained in one of the 6 ways mentioned. Properly handling any one of them takes experience and knowledge. Taking on all 6 requires a machine shop that’s heavily invested in highly-skilled CNC machinists and equipment, including robots.

Stecker Machine Company takes pride in tackling complex projects that other machine shops refuse to attempt. It’s that level of confidence in our quality and people that truly sets us apart. Have a particularly challenging complex project? Contact us today!