Many procurement professionals assume that once the purchase order is issued, the rest is up to the supplier.
I used to think the same.
That changed after one aluminum machining project was delayed by more than 10 days because the parts got stuck at the surface finishing stage. The production schedule was disrupted, and we spent far more time solving the problem than preventing it.
Looking back, the supplier wasn’t the only reason. Several critical questions had never been asked during the quotation stage.
If you’re sourcing custom CNC machined parts, these are six common mistakes worth avoiding.
1. Treating Verbal Lead Times as a Commitment
“It’s no problem—we can deliver in two weeks.”
Many buyers hear this during quotation and take it as a confirmed schedule.
Later the explanation changes:
- Material hasn’t arrived.
- Programming is delayed.
- Surface treatment is still waiting.
- Another order was prioritized.
A realistic lead time should include every manufacturing stage:
- Material procurement
- CNC programming
- Machining
- Inspection
- Surface finishing
- Packaging and shipment
Requesting a detailed production schedule during quotation helps identify potential bottlenecks before production starts.
2. Sending Incomplete Drawings
Even experienced engineers sometimes overlook critical information.
Common missing details include:
- Material grade (304 vs. 316L stainless steel)
- Surface roughness requirements
- Tolerance specifications
- Heat treatment
- Surface finishing requirements
Every clarification email extends the project timeline.
Before sending drawings, verify that all manufacturing requirements are clearly specified. A complete drawing package reduces communication time and minimizes production risks.
3. Choosing the Lowest Price Instead of the Right Capability
The lowest quotation isn’t always the lowest overall cost.
Some suppliers may accept projects beyond their actual manufacturing capability.
Typical issues include:
- Tight tolerances beyond machine capability
- Thin-wall components with deformation problems
- Deep-hole machining challenges
- Complex 5-axis geometries
The result is often rework, rejected parts, or delayed delivery.
Ask suppliers whether they have manufactured similar components before. Relevant experience often matters more than a slightly lower unit price.
4. Underestimating Surface Finishing Lead Time
Many buyers focus on machining time but overlook secondary processes.
Anodizing, plating, passivation, powder coating, polishing, and heat treatment are frequently outsourced.
If the finishing subcontractor is fully booked, your completed parts may wait several extra days before processing.
During supplier evaluation, ask:
- Is surface finishing performed in-house or outsourced?
- What is the current turnaround time?
- Is there a stable finishing partner?
Knowing this early makes delivery schedules far more predictable.
5. Assuming Small Orders Receive the Same Priority
Prototype orders are often small.
Production orders from larger customers are usually much more profitable.
When capacity becomes tight, prototype jobs are frequently pushed back.
If rapid prototyping is important, consider suppliers whose primary business focuses on low-volume, high-mix manufacturing instead of mass production.
Their scheduling process is generally better suited for prototype and small-batch projects.
6. Focusing Only on Price in the Purchase Order
Many purchase orders clearly define pricing but say little about delivery expectations.
A well-prepared order should include:
- Confirmed delivery date
- Inspection standards
- Acceptance criteria
- Delay responsibilities (where appropriate)
Clear documentation helps both parties manage expectations and reduces misunderstandings throughout the project.
Final Thoughts
Successful custom machining projects depend on much more than competitive pricing.
Lead time, manufacturing capability, engineering communication, and project management all play equally important roles.
Many delays can be prevented simply by asking the right questions before production begins.
Whether you’re sourcing prototypes or production parts, investing more time during supplier evaluation usually saves far more time later.
Looking for a Reliable CNC Machining Partner?
At Tik Precision Machining, we manufacture custom precision components for industries including medical devices, semiconductor equipment, robotics, automotive, and industrial automation.
Our engineering team reviews every drawing before quotation, clearly communicates material sourcing and surface finishing lead times, and provides transparent project scheduling from the beginning.
Typical prototype lead time is 7–10 working days after drawing confirmation.
If you’re planning your next machining project, we’d be happy to discuss your requirements and help identify the most efficient manufacturing solution.