A tight tolerance sounds great from a design engineer's perspective. It forces the manufacturer to put out product that matches your specifications exactly. It ensures each part is nearly identical, creating a similar user experience for each customer. It makes your design comes to life just the way you want it.
But your tube bending design guidelines should actually include generous tolerances, when possible. From a practical production standpoint, specifying tight tolerances can be bad for both your project budget and your lead times. This leads to unhappy supply chain managers and executives.
If the success of your project doesn't rely on a perfect product, here's why you should loosen your grip on your tight tolerances.
Tube Bending Design Guidelines for Tolerances
Unnecessary costs
Presumably, your product requires more than one service. It may require multiple fabrications, like cutting, bending, slotting, etc.
How much money do you think is wasted if the part is discarded late in the process? If you demand a slightly-more-perfect component, you'll have to repay for:
- Machine upkeep
- Operator wages
- Materials
- Other overhead costs
Waste can make up a huge portion of unnecessary costs in the manufacturing process. Despite best efforts, machines don't always make perfect fabrications. There are multiple factors (some uncontrollable) that affect the specs of a finished part. The more fabrications and services you tack on, the more likely something will be slightly off.
The tighter your tolerances, the more money you're likely to waste on natural (and perfectly acceptable) deviations. Remember, it's not your money you're spending carelessly -- it's your CEO's.
Lead times
It takes time and effort to inspect each piece -- something that can be necessary if tight tolerance is specified. Staff will need to sort through the entire order, and rejected parts will need to be remade to meet quantities.
Do-overs and painstaking quality control measures can easily double or triple lead times. With a little more breathing room, parts can be produced much more quickly. Quality control is always a concern, but looser tolerances allow for quicker inspections and fewer eyeballs to watch for even the most tiny deviation.
Natural deviations (such as those caused by material or machine idiosyncrasies) will not cause part failure in most applications. Your part will function perfectly with your manufacturer's standard advised tolerance.
If your project requires a tight turnaround time, think about loosening your tube design tolerances.
Exceptions to the Ruler
Of course, some products and applications absolutely require tight tolerances -- minor errors can mean life or death for the user. If this applies to your product, DO NOT compromise on your tolerances.
Some industries that rely heavily on airtight tolerances include:
- Aerospace
- Medical
- Other mission-critical applications
Design, specifications, and tolerances should always be made with the customer in mind first. Once the customer is considered, then we can move on to cost and lead time optimization. If your product is not at risk for failure, tolerances are certainly a quick and easy way to streamline design production.
(Editor's note: This article was originally published in March 2017 and was recently updated.)
