Your CNC supplier accepted the PO, then claimed your tolerances are “tighter than standard” and demanded an upcharge.
A post-PO tolerance upcharge means the supplier did not validate tolerance capability before quoting. Do not approve the increase unless they prove process and inspection control.
The sections below show how to verify the claim, protect your deposit, and decide—fast—whether staying or switching suppliers carries less risk.
Table of Contents
How do you verify if tolerance upcharge is real or supplier padding costs?
A post-PO tolerance upcharge is legitimate only when the supplier proves which critical features exceed their standard capability and how they will control them. If they can’t do that, the upcharge is padding.
Verification should happen on the drawing, not in discussion. Ask the supplier to mark the exact dimensions they claim are “non-standard” and state how each will be verified. This may involve functional gauges, bore gauges, fixtures, or CMM only where geometry or datum relationships require it. Then ask what actually changes in their process plan—additional setups, slower cutting windows, or added in-process checks at the operation that creates the tolerance.
If the response stays vague—“tighter than normal,” “higher risk,” “more difficult”—without feature-level explanation, capability was not validated during quoting. The upcharge is covering uncertainty, not tolerance.
We prevent this by validating tolerances at the critical-feature level before quoting, assigning the appropriate inspection method to each so pricing doesn’t change after PO unless the drawing changes.
Sourcing Takeaway:
If a supplier can’t point to specific features and explain how they’ll be controlled, pause the upcharge. That’s the moment to seek an independent capability check before committing more cost or time.
Can this CNC supplier actually hold your tolerances even if you pay more?
No. Paying more does not create tolerance capability — it only increases your exposure if control is missing.
A supplier that can truly hold tolerance will be clear about three things: where the tolerance is created in the process, how it’s controlled during machining, and how it’s verified. This doesn’t mean CMM inspection for every dimension. It means using the right method for the right feature—gauges and fixtures where possible, CMM only where geometry demands it, and in-process checks where tolerance is formed.
When a supplier accepts the upcharge but relies mainly on final inspection, the risk shifts to you. Most tolerance failures aren’t inspection problems; they’re process-control failures discovered too late.
Our approach focuses on controlling critical features during machining, not trying to catch problems at the end. First-article checks happen early so tolerance risk is confirmed before the full run proceeds.
Sourcing Takeaway:
If the supplier can’t explain how critical tolerances are controlled during production, paying more won’t protect you. That’s when validating capability elsewhere becomes the lower-risk move.
What happens to your deposit if you cancel PO over tolerance upcharge?
If you cancel after a post-PO tolerance upcharge, the deposit outcome depends on what changed—your drawing or the supplier’s capability assessment. If the drawing didn’t change, the risk is usually on the supplier.
In practice, many shops accept a PO before completing process planning. When they later discover tolerance risk and demand more money, they’re trying to shift that risk to you. If you cancel at that point, deposits are often negotiable because the supplier hasn’t materially started production—no fixtures, no first articles, no documented inspection plan tied to the original quote.
The danger is waiting too long. Once machining starts or fixtures are made, the supplier has leverage to claim sunk costs. That’s why the timing of your response matters more than the wording.
We’ve seen buyers protect deposits by asking one simple thing before agreeing to anything: show what work has already been completed against the original PO. If there’s no evidence beyond “engineering review,” the deposit is rarely defensible.
Sourcing Takeaway:
If the tolerance upcharge appears before real production starts, don’t assume the deposit is lost. Clarifying what’s actually been done often resets the leverage.
Is the tolerance upcharge real — or a capability issue?
What exact response to supplier protects your position right now?
The safest response is one that pauses cost escalation and forces capability clarity—without escalating conflict.
A short, controlled reply works best: ask the supplier to identify the exact features driving the upcharge, the inspection method for each, and what process steps differ from the original quote. Make it clear you’re reviewing feasibility before approving changes, not rejecting them outright.
This does two things. First, it documents whether capability was validated during quoting. Second, it prevents the supplier from treating the upcharge as automatically approved through silence or urgency.
Avoid emotional or accusatory language. Avoid negotiating price before understanding control. The goal is to convert a commercial dispute into a technical one—because technical claims can be verified.
If the supplier can’t answer cleanly, you’re no worse off for asking. You’re better positioned to decide whether to proceed, pause, or exit.
Sourcing Takeaway:
Your first response should slow the situation down, not speed it up. Turning the upcharge into a feature-level capability question protects your cost, schedule, and options.
Should you negotiate lower upcharge or refuse entirely?
Negotiate only if the supplier proves they can control the critical tolerances. Refuse if they can’t.
Lowering the upcharge without resolving the control gap doesn’t reduce risk—it just splits it. You may pay less, but you still face scrap, rework, or silent tolerance drift. In those cases, refusing is often safer than negotiating.
If the supplier provides clear control methods—specific inspection tools, in-process checks, and an early first-article plan—then negotiation makes sense. You’re negotiating execution cost, not uncertainty.
The mistake many buyers make is negotiating before capability is proven. That locks them into a supplier who already signaled uncertainty, with fewer exit options later.
We generally advise treating this as a go / no-go gate, not a price discussion. Capability first. Cost second.
Sourcing Takeaway:
If tolerance control is unclear, negotiation doesn’t help. Decide based on capability, then discuss price—or walk away.
Should you get backup quotes before responding to supplier’s demand?
Yes. You should secure at least one backup quote before committing to any tolerance upcharge. It restores leverage and prevents you from deciding under pressure.
Responding without alternatives forces a false choice: pay more or risk delay. A backup quote reframes the situation into a comparison—capability, timeline, and total risk—rather than a negotiation driven by urgency. It also reveals whether the upcharge reflects real difficulty or a single supplier’s limitations.
Timing matters. Ask for a feasibility-first quote focused on critical features, inspection approach, and earliest FAI timing. You don’t need a perfect price yet—you need confirmation that someone else can hold the tolerances without resetting the schedule.
If your current supplier senses you have options, the tone changes. If they don’t, escalation becomes the default.
Sourcing Takeaway:
Before you answer any upcharge, get a second capability check. Decisions made with options are almost always cheaper than decisions made under pressure.
How do you get backup CNC shop quotes fast enough to make a decision?
You get backup CNC quotes quickly by limiting the request to feasibility, critical tolerances, inspection method, and earliest FAI timing.
Send only what matters: the drawing, highlighted critical tolerances, target quantity, and required ship date. Ask for three things upfront—feasibility, inspection approach for critical features, and fastest realistic FAI timeline. Avoid long questionnaires and pricing debates at this stage.
Shops that can actually help will respond concretely. Shops that can’t will deflect or delay. That filtering alone saves time.
Also, don’t wait for a “formal quote” to decide. A clear yes/no on capability plus a credible timeline is enough to move forward—or to stop wasting time.
Sourcing Takeaway:
If a shop can’t confirm capability and inspection approach quickly, they won’t move fast later. Use speed of response as an early capability signal.
Should you place a parallel order with a backup supplier immediately?
You should place a parallel order only when schedule risk is higher than the cost of duplicating early work.
Parallel orders make sense when delivery failure would cascade—missed launches, line stoppages, or customer penalties. They don’t make sense if the current supplier has proven control and is only resolving price.
The trigger is uncertainty. If the supplier can’t clearly show control of critical features—or keeps extending “review” timelines—waiting becomes riskier than duplicating effort. Parallel starts buy time and optionality, even if one path is later canceled.
The key is scope control: run a limited parallel start (FAI or small pilot) rather than full production. That caps cost while protecting schedule.
Sourcing Takeaway:
Parallel orders aren’t about distrust—they’re about risk management. When tolerance clarity is missing and time is tight, optionality is cheaper than delay.
How do you switch CNC suppliers without missing delivery commitments?
You switch CNC suppliers without missing delivery by overlapping feasibility validation and first-article planning before stopping the original supplier.
The mistake is waiting for a clean break. That burns time. The safer move is to let the new supplier validate feasibility, inspection approach, and FAI timing while the current supplier is still “reviewing” or negotiating. This overlap preserves schedule without committing twice.
The handoff should be deliberate. Transfer only the drawing, tolerance intent, and delivery target—nothing else. Avoid forwarding emails or complaints. A capable shop doesn’t need the backstory; they need clarity on critical features and timing.
Once the backup confirms control and timing, you make a clean decision. Either proceed fully, or stop before real cost accumulates.
Sourcing Takeaway:
Supplier switching doesn’t start with production—it starts with validation. Overlap the thinking phase, not the machining phase, to protect delivery.
At what upcharge percentage does switching become cheaper than staying?
Switching becomes cheaper than staying once a tolerance upcharge increases cost without reducing delivery or quality risk—often above a 15–20% increase.
A 10–20% increase can be acceptable if it comes with proven control, early FAI, and schedule protection. Beyond that, cost alone stops being the issue. The real expense becomes rework, missed dates, internal firefighting, and explaining failure upstream.
Once the upcharge rises without added proof—no clearer inspection plan, no faster validation, no reduced risk—you’re paying more for the same uncertainty. At that point, even a higher-priced alternative supplier can be cheaper overall.
Buyers often fixate on unit price. Experienced ones compare total exposure: money, time, and credibility.
Sourcing Takeaway:
If higher cost doesn’t reduce tolerance risk or delivery risk, staying is already more expensive than switching.
Worried switching suppliers will cost weeks?
What’s the risk of paying upcharge vs losing deposit and switching?
Paying a tolerance upcharge risks delayed or non-conforming parts, while switching risks a fixed, known loss such as a deposit.
Silent failure is worse. Parts arrive late, out of tolerance, or “almost acceptable,” and now you own the delay, the rework, and the explanation. Deposits hurt, but they’re finite. Delivery failures spread.
The key question isn’t “How much do I lose today?” It’s “Which option limits future damage?” If the supplier has already shown uncertainty around tolerance control, paying more often delays the same problem instead of solving it.
Switching early contains loss. Waiting amplifies it.
Sourcing Takeaway:
A known loss is often safer than an open-ended one. When tolerance control is uncertain, early exit usually limits damage.
When should you exit immediately instead of negotiating?
You should exit immediately when the supplier cannot clearly prove control of the critical tolerances and continues pushing cost instead of evidence.
This is the point where negotiation becomes dangerous. If the supplier avoids feature-level explanations, delays inspection details, or repeatedly reframes the issue as “cost” rather than control, they are signaling uncertainty—not collaboration. Continuing discussions only burns time while risk compounds.
Immediate exit is also warranted when tolerance concerns surface after PO acceptance without any drawing change. That means capability validation was skipped. No amount of negotiation fixes a missing process window, missing inspection method, or missing in-process control.
Another hard stop is shifting stories. If the explanation for the upcharge changes—first “tight tolerance,” then “material issue,” then “inspection cost”—you’re no longer resolving a problem; you’re uncovering one.
Exiting early doesn’t mean failure. It means containing damage before schedule, quality, and accountability are compromised.
Sourcing Takeaway:
When tolerance questions produce evasive answers instead of control plans, negotiation is no longer risk management—it’s delay. That’s the moment to disengage and validate capability elsewhere.
Conclusion
When tolerance costs appear after PO, the real risk isn’t price—it’s losing control of quality and delivery. If capability can’t be proven, delaying the decision only increases exposure. Getting a second capability check early often costs less than discovering failure later.
Frequently Asked Questions
Only if the loosened tolerances don’t affect function, fit, or downstream processes. Loosening blindly to reduce cost often shifts problems to assembly, performance, or warranty—where fixes are far more expensive.
Treating a tolerance upcharge as a pricing issue instead of a capability issue. Once cost is negotiated without proving control, buyers lose leverage and discover problems when time and options are already gone.
That’s often true only if you wait too long. Early validation with another shop—before full production starts—usually protects schedule better than staying locked into uncertainty and late rework.
No. Getting a capability opinion does not obligate you to switch. It’s a standard risk-control step when new constraints appear after PO, and experienced suppliers expect buyers to validate feasibility before approving changes.
No. Inspection only detects problems; it doesn’t prevent them. If tolerances aren’t controlled during machining, tighter inspection just finds failures faster—it doesn’t reduce scrap or delay.
Not all tight tolerances are functional. Many are inherited defaults or legacy specs. The fastest check is to identify which dimensions affect fit, performance, or assembly—and which don’t. Only the former should drive cost or inspection planning.
