Top Reasons Orders Get Rejected and How to Avoid Them
Oftentimes, rejections don’t start at the machine. GroundControl, a software company that builds first-article inspection (FAI) reporting tools for aerospace manufacturers, reports that most FAI rejections stem from documentation errors, not from parts that fail to conform. You don’t have to work in aerospace to see the same thing: a wrong revision, a missing cert, or an undocumented deviation can fail an order on a part that measures fine.
That doesn’t mean every rejection is paperwork. Tolerance drift, poor-quality finishes, and material nuances that present machining challenges are also real issues to contend with. Below are the most common causes of rejections and what to check for on each job before they leave your dock.
When the Paperwork Fails Before the Part Does
GroundControl lists five repeat offenders on FAI rejections:
- Characteristics or notes missing from the drawing
- Special-process certs missing or expired (heat treat, plating, welding, NDT)
- Working against an outdated engineering revision
- Incomplete or incorrect form data, such as wrong part numbers, missing signatures, or incorrect tolerances
- Missing supporting documents: material certs, CMM reports, sub-tier FAIRs
Most of these can easily be caught by a second set of eyes before submission. Confirm revisions match and remain consistent across documentation, including POs, prints, and your travelers. Check cert dates, and make sure your processor’s approval covers the process called out. Check every dimension and note on the print against your report, line by line, so nothing gets skipped.
Print problems also account for a large portion of paperwork issues. You’ll find this story across forums: a shop quotes a looser tolerance than the print, gets approval over email from the customer, but a revised or redlined drawing never comes. Later, the part is checked against the print and fails, despite being built to the agreed-upon specs. Get approved deviations in writing, attach them to the job record, and ask for a revised or redlined drawing to cover your bases.
That’s where DFM and job review earn their keep. Xometry uses engineering experts on the front end to flag potential DFM issues, order deviations, and drawing ambiguities in jobs before partners see them, proactively catching problems and reducing downstream delays. If you need tips on requesting concessions, read our piece on negotiating DFM concessions with customers.
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When Parts Fall Out of Tolerance
3ERP points to three common causes of out-of-tolerance parts: CNC machine calibration issues, material variation, and temperature and humidity effects.
Calibration drift is gradual, so schedule calibrations rather than waiting for a bad part to prompt one. Include the gauges and probes you inspect with. A worn gauge will pass or fail parts that don’t deserve it. Our guide to best practices for tool calibration is a good place to start.
Material and temperature cause problems that show up after the cut. Buy consistent stock where you can, and don’t assume a new lot cuts like the last one. Stock with internal stress can move once you start removing material, so leave room to re-check after roughing thin or lopsided parts. Keep the shop temperature steady, let the machine warm up, and allow the parts and gauges to normalize before you take measurements. A part checked warm off the machine can read differently once it cools. Over-clamping a thin wall is the same kind of trap: the part measures good in the vise but is out of tolerance unconstrianed.
Before you accept a job, compare tight callouts against what your machines, tooling, and inspection equipment can reliably hold. If a feature is beyond your process, raise it at the quote stage, not after material is already cut. Customers can often relax a tolerance or explain what the feature does, but only if you ask early.
When the Finish Doesn’t Pass Visual Inspection
We agree with 3ERP's assessment that poor finishes are commonly tied to excessive machine vibration and improper feed rates. The fixes are sharp cutting tools, the right milling strategy, and the right feed rate and spindle speed. One note of caution from other machinists: slowing the feed way down doesn’t always help. A tool that rubs rather than cuts can burnish the surface and worsen the finish, especially on aluminum. Change one variable at a time.
Inspectors look beyond tool marks. QualityInspection.org lists surface porosity, scratches, dents, flow marks, sink marks, and flash as the appearance defects they check for. Some apply to molded and cast parts, but scratches and dents can come from the deburring bench, a loose bin, or after delivery due to poor packaging. Make sure parts are properly treated after they are off the machine, and incorporate common standards into your shop's practice, such as no dents, scratches, dirt/oils, or defects, even if the customer didn't specify cosmetic requirements.
When the Material Itself Is the Problem
3ERP also lists patterns most machinists know: aluminum forms burrs, stainless work-hardens and wears tools fast, and titanium generates excessive heat. Match speeds, feeds, and cutting fluid to the material. On stainless and titanium, a tool that dwells or rubs worsens work hardening, so keep it cutting and change inserts before wear shows up in the finish.
Not every material problem starts in your shop. AMPCO Metal notes that faulty deliveries from material suppliers increase rejects, so verify incoming stock before it's on the machine: make sure the cert’s heat number matches the bar's markings. QualityInspection.org notes that the test report must match the actual batch used for the order. Your supplier provides the cert, but you carry the heat or lot number through to the job record. More on understanding material traceability.
Catching Problems Before They Ship
LeanWorx recommends root-cause tools: 5 Whys, Fishbone diagrams, and a corrective-action log. It also finds that avoidable scrap and rework come roughly equally from tooling, unstable processes, and operator or training issues. There’s no single fix. When you run a 5 Whys, don’t stop at “operator error.” Ask why the process let the error happen, then log the fix with an owner and a date.
Not every shop has an in-house quality team to check a borderline part or an ambiguous spec. Xometry's Partner Community gives shops a Knowledge Base, forums, Partner Events, daily office hours, and a dedicated case manager on every job, so there’s someone to ask before a questionable part ships. To get work for your shop with that support behind it, join the Xometry Partner Network.
