Why ask before release
The cost of changing a design rises sharply once tooling is cut or parts are ordered. A short review before release is the cheapest quality step in the process. Run it with someone who makes the part, if you can.
The questions below suit most mechanical products. Adapt them to your process, material and volume.
1. Can it be made by a standard process?
Name the process for every part: machining, casting, forging, sheet metal, moulding, fabrication or another. Check that the shape suits it. Deep narrow pockets, thin walls, undercuts and sharp internal corners are common trouble spots.
2. Are the tolerances as loose as they can be?
Tolerances drive cost. Tighten only the features that need it, such as mating surfaces, bearing seats and sealing faces. Check that the tolerance stack of an assembly works, and that no feature depends on a tolerance the process cannot hold.
3. Is the material right and available?
Check strength, corrosion resistance, weight and cost, and also availability in the form you need. Specify standard sizes and grades where you can, to avoid long lead times and minimum order quantities.
4. Have you used standard parts?
Fasteners, bearings, seals and other catalogue parts are cheaper and easier to replace than special ones. Limit the number of different sizes in a product, so that purchasing and assembly stay simple.
5. Can it be assembled, and in what order?
Walk through the assembly. Check tool access, hand access and the order of operations. Make sure parts can only be assembled the right way, with features that locate them, and keep the number of parts as low as the function allows.
6. Can it be inspected?
Check that every critical dimension can be measured with the equipment available, and that the datum scheme in the drawing matches how the part is held for inspection.
7. Are the drawings and the model consistent?
Check that dimensions, notes, materials and part numbers agree between the model, the drawing and the bill of material. Inconsistent documents are a common cause of wrong parts.
8. Will it survive its service life?
Check the design against its loads, temperatures and environment. Where failure is costly, support the review with analysis. See our guide to choosing the right simulation.
9. Can it be serviced?
Think about the person who will maintain it. Can wearing parts be reached and replaced? Are lubrication points, filters and inspection openings accessible?
10. What does it cost, and what drives it?
Estimate cost with the supplier if you can, and identify the largest drivers. Often a few features, such as a tight tolerance, a special material or a long machining operation, account for most of it.