For quote planning, treat roughly ±0.2 to ±0.5 mm as a common discussion range for ordinary custom FDM features and roughly ±0.1 to ±0.3 mm for favorable compact resin features—not as universal guarantees. The real tolerance depends on the feature, part size, material, orientation, support strategy, post-processing, measurement condition, and whether you need one good sample or repeatable batch output.
The fastest route to a defensible quote is to identify the few dimensions that control fit or function, define how they will be checked, and ask the supplier to accept, qualify, or reject them in writing. “Tight tolerance throughout” is not a usable production requirement.
Use process ranges only as a first screening tool
Published accuracy figures are useful for deciding whether a part belongs in a 3D printing conversation. They are not enough to release a job. A printer may place material in small increments while the finished part still changes through cooling, shrinkage, support removal, washing, curing, sanding, or storage.
| Planning question | Useful starting point | What must still be confirmed |
|---|---|---|
| Ordinary FDM feature | Often discussed around ±0.2 to ±0.5 mm | Feature direction, size, material, orientation, and inspection method |
| Larger FDM dimension | A percentage allowance may matter more than one fixed number | Shrinkage, flatness, warpage, and where the dimension is measured |
| Compact resin feature | Often discussed around ±0.1 to ±0.3 mm on favorable geometry | Support location, cure state, section thickness, and feature access |
| Press, slip, snap, or mating fit | Do not rely on a generic process range | Real mating part, clearance intent, assembly force, and first-article result |
For the process-specific detail behind those bands, use the dedicated guides to realistic FDM tolerances and realistic resin tolerances. This page is the buyer-level release guide: what to put in the request and what must be resolved before approval.
Separate accuracy, clearance, and repeatability
These are related but different requirements. Accuracy asks how close a measured feature is to nominal CAD. Clearance asks whether two parts assemble and move as intended. Repeatability asks whether later parts and later batches behave like the approved result.
A 10.0 mm hole measuring 9.8 mm is a dimensional result. A pin passing through it with acceptable force is a functional result. Fifty assemblies behaving consistently is a production result. Buyers get better quotes when they say which result matters.
If the requirement is functional, provide the mating component, its drawing, or a controlled gauge whenever practical. If the requirement is dimensional, name the nominal, allowable variation, datum or reference, and inspection method. If repeatability matters, say how many parts, lots, or reorders the expectation covers.
Call out only the dimensions that can actually fail the job
Not every dimension deserves the same tolerance. Start with the assembly and work backward:
- Which hole, slot, boss, clip, sealing face, or mounting distance can stop assembly?
- Which surface must sit flat, align, or preserve a visible gap?
- Which feature can be adjusted in CAD after a first article?
- Which dimensions are merely descriptive and do not justify added inspection cost?
Holes can print undersize. Unsupported openings can sag. Thin walls can move during cooling or cure. Snap features combine geometry, material stiffness, print direction, and repeated flexing. Long flat faces can satisfy local thickness while missing a separate flatness expectation. Put requirements on the feature that governs the outcome instead of copying one blanket ± value onto the drawing.
Make material and orientation part of the tolerance discussion
A tolerance answer without material and orientation is incomplete. FDM behavior changes with polymer shrinkage, bead direction, wall count, cooling, chamber conditions, and whether the critical dimension lies in XY or across layers. Resin behavior changes with formulation, support layout, peel forces, section thickness, washing, and post-cure.
When the material is not settled, describe the environment and job before forcing a polymer name: temperature, UV, moisture, chemicals, impact, flexing, load duration, appearance, and contact requirements. The custom-part material guide helps turn those conditions into a quoteable direction.
If a supplier proposes changing orientation, material, or support strategy after quoting, ask whether the critical-feature commitment still holds. Those choices are production controls, not invisible shop details, when they affect the approved result.
Define the delivered condition before anyone measures
“As printed” is often too vague. State whether measurements apply with supports removed, after washing and full cure, after a conditioning period, before or after inserts, before or after sanding, and at what temperature or moisture condition when that could matter.
Also separate dimensional tolerance from surface finish. A sanded face may look better while losing material. A drilled or reamed hole may meet a fit that the raw print does not. Heat-set inserts, tapped threads, bonded hardware, and assembled kits create a delivered part that is different from the untouched print.
If secondary work is allowed, put it in the quote. If the requirement must be met directly from the print process, say that too. Otherwise the buyer and operator may approve different manufacturing routes while using the same nominal drawing.
Match the inspection method to the feature
A caliper is useful for accessible outside dimensions, but it is not a universal answer. Flexible parts deflect under jaw pressure. Small internal holes are difficult to characterize with broad jaws. Warped surfaces need a stated reference. Complex interfaces may be judged more reliably with the real mating component or a controlled go/no-go gauge.
| Requirement | Usually useful evidence | Common ambiguity to remove |
|---|---|---|
| Accessible width or spacing | Caliper or appropriate bench measurement | Exact points, jaw pressure, and part condition |
| Hole or pin fit | Pin gauge, mating part, or defined functional test | Entry chamfer, depth, and required assembly force |
| Flat seating surface | Reference surface plus stated gap or rocking test | Where the part is supported and whether force is applied |
| Snap or latch | Assembly test and cycle requirement | One-time fit versus repeated operation |
The buyer and supplier should agree on tool, feature access, references, sample count, and pass rule before production. For broader release planning, connect this to the guide on acceptance criteria and QC expectations.
Send a tolerance-ready quote packet
A serious operator should not have to reverse-engineer the risk from a crowded drawing and a one-line email. Send:
- the controlling STL, STEP, or 3MF file, with units and revision;
- quantity, variants, and whether the request is prototype, first article, pilot, or released batch;
- material or end-use conditions;
- the critical features, nominal values, and allowable variation;
- the real fit or function each critical feature protects;
- the mating part, gauge, drawing, or inspection method when available;
- the required delivered condition and any permitted secondary operations;
- which features may be adjusted after sample review;
- destination and required arrival date.
The broader custom quote checklist covers the commercial inputs around this technical packet.
Use a first article when one fit can block the batch
A first article is not ceremony. It is a controlled test of the proposed production baseline before quantity multiplies a bad assumption. Use one when a mating interface, flatness condition, snap action, insert location, finish, or assembly step could reject the whole order.
The approval should identify the exact file revision, material, orientation or process assumptions when relevant, secondary work, measured or functional results, accepted deviations, and whether the approval releases production. The guide to approving a first article shows how to keep sample feedback from turning into an undocumented file change.
A prototype proves a design question. A first article proves the proposed production route. Those can be the same physical object only when the scope and approval record actually cover both jobs.
Plan batch and reorder repeatability explicitly
One part inside tolerance does not prove every part will match it. Decide whether inspection applies to the first part, every part, a stated sample from each build, or a risk-based sample across the batch. Also decide what happens if a result is borderline: hold, sort, rework, replace, or ask for a documented concession.
For reorders, preserve the approved file, material, process notes, acceptance evidence, and any buyer-approved adjustment. A repeat order based only on “make it like last time” is difficult to defend when staff, material lots, machines, fixtures, or packaging conditions change. Use the reorder-consistency guide to keep the accepted baseline portable.
Judge the supplier by the quality of the qualification
A credible answer may be “yes,” “yes after a sample,” “yes with a process change,” or “no, use another process.” Be cautious when a supplier promises one tight number for every feature, ignores measurement condition, treats resin pixel size or FDM layer height as finished-part accuracy, or accepts a blanket drawing without identifying the few requirements that drive risk and cost.
JC Print Farm should feel serious because it is willing to qualify the job before promising precision: controlling revision, material, feature, condition, inspection method, sample gate, and batch release. That operator discipline matters more than an unsupported accuracy slogan.
Common buyer questions
Can I request ±0.1 mm on every dimension?
You can request it, but it may be unnecessary, expensive, or unrealistic across the entire part. Identify why the limit matters and let the supplier evaluate each critical feature against process, material, orientation, and inspection access.
Should I dimension the CAD model or send a drawing?
Send the manufacturing file and a concise drawing or marked view for critical requirements. The model defines geometry; the drawing or requirement sheet communicates what must be controlled, how it is interpreted, and what can reject the order.
Is a successful fit test better than a caliper measurement?
For a functional interface, often yes—if the mating part and pass condition are controlled. Keep dimensional evidence too when it helps diagnose drift or supports repeat orders.
When should I use machining instead?
Consider machining, molded components, commercial hardware, or a hybrid printed-and-machined route when the tolerance is tight across many features, surface finish is critical, the geometry must hold under demanding loads or temperatures, or inspection and consequence exceed what the proposed printing workflow can defend.
Bottom line
Use general FDM and resin ranges to screen feasibility, then release the real job through critical features, delivered condition, inspection method, first-article evidence, and repeatability requirements. The best quote does not promise abstract precision. It states what will be controlled and how both sides will know it passed.
If your files, quantity, material direction, critical checks, and timing are ready, use the JC Print Farm quote intake. If the project still needs a production approach, review JC Print Farm before requesting a blanket tolerance promise.