CadVex blog · 3 October 2026

Quoting from a STEP file: a pre-quote checklist for CNC estimators

What to check before you price a CNC part from a STEP file: revisions, units, bodies, drawing notes, material, setups, tolerances and assumptions.

By CadVex · 6 min read

A STEP file tells you what the part looks like. It does not tell you everything you need to price it. The geometry is only half of the RFQ; the other half sits in the drawing, the RFQ text and the questions nobody has asked yet.

Run through the checks below before you open the costing sheet. Most take a minute, and each one catches a mistake that would otherwise show up on the machine.

What a STEP file does and does not carry

STEP is the neutral CAD exchange format standardized as ISO 10303. The application protocols you are likely to see are AP203, AP214 and AP242. AP242 can carry product and manufacturing information (PMI), such as dimensions, tolerances and GD&T attached to the geometry. In practice, many STEP files that arrive with an RFQ contain geometry only, because PMI was never added to the model or was left out at export.

So unless the customer states that the annotated model is the controlling definition, assume the requirements live on the drawing and in the RFQ text.

The checklist

1. Model and drawing revisions match
2. Units and scale are correct
3. You know what is actually in the file
4. Every drawing requirement has been read
5. Material and stock size are pinned down
6. Quantity, repeat potential and quantity breaks are clear
7. The part fits a machine you have
8. You know how many setups the features force
9. Critical tolerances are separated from general ones
10. Outside processing and its lead time are accounted for
11. Your assumptions are written into the quote

1. Match the model and drawing revisions

Compare the revision in the title block with the file name, the RFQ text and anything the customer wrote in the email. If the drawing says Rev C and the STEP file is named Rev B, or the model carries no revision at all, ask before pricing. A quote built on the wrong revision is a quote for a different part.

If the model and drawing disagree on a dimension, ask which one governs, then record the answer.

2. Confirm units and scale

STEP files declare their length unit, so a clean export normally opens at the right size. Problems come from parts modeled at the wrong scale, files converted through other formats, or a drawing dimensioned in inches next to a model built in millimeters. Measure the overall envelope and one or two key features, then compare them with the drawing. A ratio of 25.4 is the classic sign of an inch and millimeter mix-up.

3. Check what is actually in the file

You want one closed solid per part. What you may get instead:

• An assembly with mating parts, fasteners or the customer's fixture
• Several bodies that are really separate line items
• A surface model with gaps, which gives no reliable volume or removal figure
• One hand of a left and right pair, with the opposite hand only noted on the drawing

Decide what you are quoting and confirm the part count against the drawing or the RFQ.

4. Read the drawing for what the model does not carry

Threads are the usual trap. They often arrive as plain holes, modeled at the tap drill size, the nominal size or somewhere in between. The thread form, size, class, depth and any inserts are on the drawing.

Then read the rest: the general tolerance block or the standard it references, such as ISO 2768, local tolerances and GD&T frames, surface finish callouts, heat treatment, coatings and plating, part marking, edge-break and deburr notes, and inspection requirements such as a first-article report or material certificates. Read the general notes to the end. The expensive requirement is often a single line near the bottom.

5. Pin down material and stock size

Confirm the full grade and condition, not just "aluminum" or "stainless". 304 and 316 do not cost the same, and a temper or condition callout can change both the stock price and how the part machines. Then choose the stock you would actually buy or pull from the rack: form, size, saw and facing allowance, and extra length or thickness for workholding. Check whether certified material, a specific source or customer-supplied material is required, and note how long your material price is valid.

6. Confirm quantity, repeat orders and quantity breaks

Programming, setup and fixturing are fixed costs spread across the quantity, so unit price depends heavily on lot size. Ask whether this is a prototype, a first article before production, or a blanket order with scheduled releases. Quote the breaks the customer asked for, and say whether each one assumes a single lot. If the part is likely to repeat, decide whether a dedicated fixture is charged now or spread over future orders. More on this in what drives a CNC machining quote.

7. Check the envelope against machine capacity

The bounding box is easy to read from the model. The real question is whether the part fits with its workholding, whether tools reach the deepest features, and, for turned parts, whether the diameter fits your bar capacity or chuck. Also check part weight for handling. If only one machine in the shop can run it, that machine's rate and schedule set your price and lead time.

8. Count the setups the features will force

Look for features on several faces, side holes on turned parts, undercuts, deep narrow pockets, small internal radii, thin walls and features at compound angles. Each extra setup adds setup time and fixturing, and it can make tolerances between features cut in different setups harder to hold. DFM checks that change CNC part price covers the geometry that moves cost most often.

9. Separate critical tolerances from general ones

Most dimensions fall under the general tolerance. A handful, such as bearing bores, fits, datum-related positions or flatness on a sealing face, decide the process: finishing passes, reaming or boring, possibly grinding, and inspection time. Price those few properly instead of treating the whole part as tight or missing the one feature that needs extra work. Check that critical sizes still hold after coating or heat treatment, and if a tolerance looks tighter than the function needs, ask.

10. List outside processing and lead time

Heat treatment, anodizing, plating, passivation, painting and any subcontracted grinding or EDM each bring a supplier price, often a minimum lot charge, handling, freight and calendar days. Your lead time is your machining queue plus every outside queue plus transit. Use a current supplier price where you can, and note the sequence, for example heat treatment before finish machining.

11. Write your assumptions into the quote

A price is defensible when its basis is written down. At minimum, state:

• The model and drawing revisions quoted
• Material grade and whether certificates are included
• Quantities, and whether each break assumes a single lot
• Outside processes included, and anything excluded
• The inspection documentation included
• How unclear requirements were interpreted
• Quote validity and the lead time basis

If the customer later changes the revision, the quantity or the finish, written assumptions show exactly what changed and why the price moved.

Where CadVex fits

CadVex handles the geometry side of this checklist. Upload the STEP file, and drawings where needed. CadVex analyzes the geometry, detects manufacturable features and likely setups, and builds an editable estimate with DFM feedback tied to the model. In CadVex Cloud, supported drawing parameters such as material, tolerances, threads and finishes can be extracted automatically and filled in for review, with each value showing where it came from. Everything stays reviewable and editable before the quote is sent.

CadVex Desktop runs the STEP analysis on your Windows PC or Apple Silicon Mac, so CAD files stay on the shop computer during analysis.

Revisions, quantities, outside processing and commercial terms remain your call. If you want to try this on your next RFQ, compare CadVex Desktop and Cloud.