Missing Tolerances on a Parts Drawing: What to Resolve Before Quoting
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A supplier receives a drawing for a track-roller shaft. The nominal diameters are shown, but one shoulder has no local tolerance. The title block refers to a general note, while the request for quotation mentions a later customer specification that is not attached. The supplier could apply its normal shop practice and return a price. That price would look complete, yet the buyer and supplier might be pricing different parts.
A missing tolerance is therefore a quotation problem before it becomes a manufacturing problem. The useful response is not to guess a value or mark the whole drawing “unclear.” It is to identify the exact feature, show every requirement that might govern it, explain why the answer affects the quote, and obtain a controlled decision from the person authorized to define the part.
This task starts after the correct drawing package has been identified. If the open question is which revision applies, use a revision-control process. If the 3D model and 2D drawing give competing instructions, treat that as a specification conflict. Here, the focus is narrower: the applicable package is known, but a tolerance or the conditions needed to interpret it are absent or ambiguous.
Read the title block and general notes first
A dimension without a tolerance beside it is not automatically untoleranced. The drawing may apply general tolerances through its title block, notes, a referenced specification, or a defined class of dimensions. Before raising a question, record the drawing number and revision, units, projection convention, material and condition, referenced standards and their editions, finish or coating state, and every note that could apply to the feature.
The order of this check matters. A local callout may control one feature while a general note covers the rest. A referenced document may apply only to dimensions produced before coating, or only to features identified by a symbol. If the reference is missing from the request package, do not reconstruct it from memory or from a different customer's drawing. Record the missing document by title and revision, then keep the affected feature open.
Provider guides such as Xometry's technical-drawing overview illustrate why material, dimensions and tolerance communication belong together. They are useful examples of the information a manufacturer needs. They are not the governing specification for an undercarriage part, and their preferred drawing practices do not replace the buyer's released requirements.
Also check whether the nominal value itself is complete. A diameter may lack a depth, a hole pattern may lack a datum relationship, or a surface requirement may not say whether it applies before or after treatment. In those cases, adding a plus/minus value would answer only part of the question. The clarification must describe the complete condition that will be manufactured and inspected.
For background on why dimensional controls affect roller interfaces, see why precision CNC machining tolerances matter for track rollers. That background explains the consequence of unclear requirements; it does not supply the missing tolerance for the current drawing.
Identify the features that need an engineering answer
Do not turn every unlabelled dimension into the same emergency. First identify which missing condition can change fit, function, manufacturing route, inspection method, cost or lead time. A mating bore, bearing seat, seal interface, thread, datum feature or controlled spacing may need an explicit answer because a small interpretation difference can change tooling or acceptance. A reference dimension may require no manufacturing acceptance at all. The drawing and design authority, not the supplier's intuition, determine that status.
Give each open point a feature identity that another person can find. Use the drawing view, zone, callout, feature label and nearby geometry. A cropped image can help locate the question, but retain the drawing number and revision with it. “Please confirm the bore tolerance” is weak when the drawing has several bores. “Confirm the tolerance and finished condition for bore B-14 in section C-C on drawing revision D” creates a traceable question.
Then state why the answer affects the quotation. The supplier may need to know whether a feature requires a different process, dedicated gauge, additional inspection, controlled surface treatment or special handling. This is not a request for the supplier to redesign the part. It is a concise explanation of why the quote cannot be treated as firm on that line until the requirement is known.
Keep manufacturing capability separate from product acceptance. A supplier may be able to hold a tight range, but capability does not prove that the tighter range is the intended design requirement. Conversely, a supplier's usual process range does not authorize relaxing a requirement. Record capability information as a proposal or risk input, and keep the buyer's approved requirement in its own field.
Inspection needs the same discipline. The clarification should say whether the feature can be measured in the stated material and surface condition, whether the drawing identifies the relevant datum setup, and whether the result belongs to an individual part or a sampling plan. Do not invent a gauge, sample size or acceptance rule merely to complete a quotation. If these choices affect price, list them as unresolved quotation assumptions.
Separate supplier defaults from agreed requirements
Many manufacturers publish default tolerance practices for particular services. Those defaults can help a buyer understand what information a supplier normally needs, but they belong to that provider, process and service level. Protolabs, for example, explains its own machining tolerance approach. A different shop may use a different baseline. Neither provider's published value becomes part of your drawing unless the parties explicitly adopt it for the order.
When a supplier proposes a default, capture it as a proposal with its source and conditions. The quotation should identify which feature it covers, the assumed material or processing state, the inspection basis and the commercial effect. The buyer can accept it, replace it with a different requirement, or reject the proposal. Silence is not acceptance, and a price generated from an unstated default should remain conditional.
General-tolerance standards require the same care. Record the exact designation and edition shown in the applicable document. Do not select a standard because it is familiar or because a similar part used it before. If the title block cites one document and a purchase-order note cites another, that is a conflict to resolve, not permission to choose the one that makes quoting easier.
Surface condition can change the meaning of the requirement. A dimension controlled before heat treatment, coating or another finishing step is not automatically the same as the finished dimension received by the buyer. The clarification should identify the required state and any allowance or later operation only when supported by the released specification. Otherwise, the state remains open alongside the tolerance.
Consider an illustrative supplier response: “Quote assumes our standard machining tolerance.” That sentence is too broad. A usable response would link the assumption to a named feature, state the exact proposed requirement and inspection condition, show its effect on price or lead time, and request approval from the designated authority. Until the response is approved, the quotation record should say “conditional,” not “compliant.”
Return a closed clarification sheet with the quote
A clarification sheet should make each decision auditable without recreating the entire drawing. Keep one row per feature or connected issue. Attach the relevant drawing crop for navigation, but use the released drawing and referenced documents as the source of truth. The table below shows the minimum logic; all feature names and outcomes are illustrative.
| Feature and source | Current evidence | Supplier proposal or question | Authorized response | Quote status |
|---|---|---|---|---|
| Bore B-14, section C-C, drawing revision D | Nominal value shown; title-block general note clearly applies to finished bores | Confirm that the cited general note governs this feature and name the inspection state | Confirmed in the controlled response, with approver and date recorded | Ready to price on the confirmed basis |
| Shoulder S-3, detail view, drawing revision D | No local tolerance; referenced customer specification is absent from the RFQ package | Provide the named specification and confirm whether S-3 is within its scope | UNKNOWN | Conditional or on hold; missing evidence is not a pass |
| Seal seat F-2, drawing revision D | Drawing note appears to control the finished condition; RFQ text asks for inspection before coating | Identify the required measurement state and which instruction has precedence | Two conflicting replies received from different contacts; no design-authority disposition | Hold the affected line until one authorized answer is issued |
Record the question ID, drawing and revision, feature location, current evidence, proposed interpretation, response, approver, date, affected quotation line and open or closed status. If the answer changes another feature, inspection plan or previously quoted operation, link the affected rows rather than silently updating only the original question.
The final quotation should repeat any accepted assumption in language that purchasing and production can both see. Open questions should remain listed with their commercial effect. A closed row means the requirement and authority are recorded; it does not mean the part has been manufactured or inspected.
When the purchase order is issued, carry the clarification reference into the order package and supplier acknowledgement. That prevents a useful pre-quote answer from becoming detached from production. If a later drawing revision changes the feature, reopen the decision under revision control instead of overwriting the original record.
This approach lets a supplier price what is known, isolate what is conditional and return a focused question to the right owner. It also gives the buyer a practical stopping rule: no feature with a missing condition, conflicting source or absent approval is allowed to become an unstated manufacturing assumption.