Pop quiz: If your print calls out specifications that are difficult or impossible to achieve, what’s the best possible response a precision machine shop could have?
- No-quoting your project and moving on to the next one.
- Quoting your project immediately — no questions asked (making assumptions).
- Asking questions about specific requirements before quoting the project.
If your timeline and budget are tight, you might be inclined to pick #2 because it seems like the easiest path to receiving your parts. But let’s say there’s an issue with one of your GD&T callouts, or your tolerances are so tight they’re unverifiable even on a 5-axis CMM or with optical inspection equipment. In that case, the shop that doesn’t ask questions will need to make assumptions about your design and — even worse — the acceptable accuracy of your completed parts.
Assumptions are never a good thing in manufacturing.
That’s why, at Wagner Machine, we advocate for response #3: asking questions and collaborating with customers before quoting complex machined parts.
The Value of Collaborating on Complex Machined Parts
We’ve learned from experience that asking questions and collaborating benefits both parties: customers and machine shops.
The shop gains clarity about the callouts on the print and can provide recommendations to improve the part’s manufacturability without impacting functionality and performance. This can lead to more competitive quotes and reduce the risk of surprise price increases on subsequent orders. Updating prints to improve clarity also has the added benefit of better consistency on future orders regardless of who makes the customer’s parts. Even if changes aren’t made, a little communication can be the difference between a quote and a no-quote.
Success Stories: Collaborating to Find a Solution
Here are some examples of how we have collaborated to solve common design issues that often result in no-quotes.
Example 1: unverifiable tolerances
A customer recently came to us with a defense part they’d been having made for years that was no-quoted regularly because some of the tolerances are too tight to reliably machine or inspect.
Instead of no-quoting them, we began asking questions about the part. The problem was they had called out non-industry standard tolerances for several press fit and slip fit interfaces that were unnecessarily tight. Through our conversation, we found that there was already an approved process to use functional gages to verify the fits. Those functional gages didn’t actually guarantee that the parts met the spec on the print, but the customer had a proven and approved process that was to be used for inspection.
Ultimately, revising the print to adjust the tolerances wasn’t an option, as is often the case for defense parts. Once we understood the existing inspection procedures, we were able to quote the parts with a simple note about using the approved inspection process to verify specific tolerances. Our customer can now be confident that they will get functional parts, and we have a specific procedure for inspection that will ensure we make consistent parts every time.
Example 2: incorrect datum callouts
It’s not uncommon for prints to include GD&T callouts that don’t entirely make sense. For example, one customer called out a datum plane measuring .125” wide on a part measuring 4” in length and then referenced features to that datum on the opposite end of the part. An uncertainty of .0002” for points taken on the .125” wide surface can lead to variation of more than .006” for features measured at the other end of the part even if the part is actually perfect. It is very important to understand how datums will impact the repeatability of measurements.
Another common problem we come across is customers using threaded holes as datums, or calling out extremely tight true position tolerances on threaded holes. Either of those situations can cause a lot of variation in inspection results and should generally be avoided.
When we see GD&T callouts or other tolerances that don’t seem right, we always take the opportunity to ask questions, point out potential problems, and provide alternative solutions.
If you need a complex machined part that other shops have no-quoted, try Wagner Machine. Request a quote.