Guides / For Shops

What to Check on a Bike Part Drawing

September 24, 2026

A bike part drawing takes ten minutes to review properly. Skipping that review is how a shop wins an order and loses money on it. Here is the checklist, in the order that catches the most.

1. Is there a drawing at all

A STEP file is geometry. It carries no tolerances, no finish, no surface finish callouts and no indication of which faces matter.

If all you have is a model, either ask for a drawing or state clearly that your number is budgetary and lists the assumptions you made. Quoting a bare STEP file as though it were a specification means you have silently chosen every tolerance on the part.

2. Material and temper, spelled out

“Aluminum” is not a material. 6061-T6 and 7075-T6 differ by a factor of nearly two in strength, meaningfully in tool wear and visibly in how they take anodize.

If the drawing says aluminum, ask. If it says 7075 with no temper, ask. If the part is a crank or a chainring and the drawing says 6061, ask whether that is deliberate, because it usually is not.

3. Before or after finishing

The question that causes the most disputes on machined and anodized parts.

A coating grows about half its thickness outward from the surface, so a bore loses roughly the full coating thickness on diameter. That is 5 to 25 microns for Type II and 25 to 50 for Type III, against bearing fit tolerances measured in single hundredths.

Look for one of these on the drawing: dimensions after anodizing with a stated thickness, dimensions before anodizing with masking called out, or a machining allowance. If none of the three is there, that is your first question.

4. Which dimensions actually matter

Count the tight tolerances. On a typical bike part three to six dimensions are real: a bore that takes a bearing or a steerer, a clamp face, a bolt circle position, a chainline offset.

If the drawing has thirty dimensions at plus or minus 0.02 mm, it is almost always a CAD default rather than an intention. Ask. You will save the customer money, save yourself an inspection routine and demonstrate that you read the thing.

5. Datums and how the part is located

Is there a datum scheme, and does it match how the part is used? A hub shell should be dimensioned from the axle bore, a stem from the steerer bore, a chainring from the center bore and the mounting face.

Chained dimensions are the other thing to look for. Five chained dimensions at plus or minus 0.05 mm give a plus or minus 0.25 mm position at the end of the chain, which is never what the designer meant.

6. Interfaces, and whether they are standard

Bike parts bolt to things that already exist. A 28.6 mm bore is a steerer. A 31.8 mm bore is a handlebar. A 44 mm bolt circle with six M5 is a disc rotor. The dimensions are in the interface standards reference.

Two things to check. First, that the drawing’s number matches the standard, because a transposed digit here scraps a batch. Second, whether the customer has named the standard or measured it from a worn sample, because those produce different drawings.

7. How many setups

Count the faces with features on them. That number, more than anything else on the drawing, sets your price.

Then ask whether the design allows any of them to be combined, and whether a 4th axis would collapse five setups into two. On stems and hub shells this is usually where the difference between your quote and a competitor’s comes from.

8. The features that will hurt you

• Internal corners under about 3 mm radius, which force a small cutter and a slow path
• Deep narrow slots and pockets more than four diameters deep
• Thin walls with a height to thickness ratio above roughly ten to one
• Non-standard hole sizes that turn a drill into an interpolated feature
• Threads to the bottom of a blind hole
• Large thin pocket floors that will drum under the cutter
• Highly pocketed parts that will move after machining as residual stress releases

9. Deburring, and who is doing it

On a chainring with 34 teeth there are 68 flanks. On a hub flange there are 32 holes, each with two sides. Bike parts are handled by riders and a burr is felt immediately.

If deburring is not on the drawing, it is still going to happen. Decide now whether it is in your number.

10. Quantity, repeat and what it is for

A prototype and a production part are different jobs with different right answers. Ask what this run is for and whether it repeats.

It changes whether you invest in a proper fixture, whether you offer a repeat price and how you present the setup cost. A brand that tells you 300 pieces follow in spring is telling you how to quote the 20 in front of you.

What to send back

Two or three specific questions, the same day, then the number. Not a list of fifteen, which reads as inexperience, and not silence followed by a padded quote.

Buyers judge shops on the quality of their questions. It is the cheapest competitive advantage available to you.

Register your shop to receive RFQ previews that already carry the material, quantity, tolerance, finish and deadline, so the review starts from a better place.

Frequently asked questions

Keep reading

• What Bike Parts Work Asks of an Anodizing Shop
• What Bike Parts Machinists Want From a Metal Supplier