The short answer
A CNC machining quote is mostly a price for machine time and the human time around it. Material is part of the number, but on many small and medium parts it is not the biggest part. What moves a quote up or down is how long the part spends on the machine, how many times it has to be clamped, how much programming and fixturing the first piece needs, and how much checking the drawing asks for. If you understand those four things, you can usually find savings before you ever send the RFQ.
This guide is written for buyers and engineers who want to know why two similar-looking parts can be quoted very differently. It avoids price lists on purpose: rates depend on the shop, the machine and the region. Instead it explains the levers that change cost in any shop, gives typical engineering values where they help, and ends with a checklist of what to send so an estimator does not have to guess. When you are ready, you can upload a STEP file and drawing on the 3DWK quote page (quote-new.php) and an engineer will review it.
How an estimator builds the number
Most CNC quotes can be read as two buckets. The first bucket is paid once per order or once per revision: reviewing the model, writing the CAM program, designing or adapting a fixture, setting tools, and proving out the first article. The second bucket repeats for every part: raw material, cycle time on the machine, part handling between setups, deburring, finishing and inspection.
Per-part price is roughly the one-time bucket divided by the quantity, plus the repeating bucket. That simple relationship explains most of what buyers see. A single prototype carries the whole setup cost by itself. At larger quantities the setup is shared across many parts, so the repeating cost dominates and design details that shave cycle time start to matter more. Illustration 2, below, shows this curve in a generic form with no prices attached.
Reading tip: if a quote for 1 piece and 10 pieces looks almost the same in total, the job is setup-heavy. If the total grows nearly in proportion to quantity, cycle time and material dominate.
One-time costs you can influence
Programming effort
Complex 3D surfaces, many small features and unusual hole sizes all add CAM time. Using standard drill sizes, consistent corner radii and fewer distinct feature types keeps programming simple.
Fixturing
A block that can be held in a vise is cheap to fixture. Thin, organic or very flexible shapes may need soft jaws, a vacuum plate or a dedicated fixture. Adding flat clamping faces or a sacrificial tab can remove that cost.
Number of setups
Every time the part is turned over, the operator re-clamps, re-indicates and re-checks. Features that can be reached from one or two directions are quoted lower than features spread across six faces. Five-axis machines reduce setups but usually carry a higher hourly rate.
First article and documentation
A full dimensional report, material certificates or a formal first article inspection report are real work. Ask for them when you need them, and say so in the RFQ so they are priced, not added later.
Per-part costs, ranked by how often they surprise buyers
The table below lists the repeating cost drivers we see most often in drawings, what makes each one expensive, and the usual way to reduce it. None of these is a rule that always applies; they are starting points for a conversation with the estimator.
| Driver | What makes it costly | Typical way to reduce it |
|---|---|---|
| Tight tolerances everywhere | Slower finishing passes, more measurement | Apply a general tolerance such as ISO 2768-m and tighten only functional features |
| Deep narrow pockets | Long small tools, light cuts, chatter | Keep pocket depth within about 3 to 4 times the cutter diameter |
| Sharp internal corners | Small end mills or EDM | Use an internal radius slightly larger than a standard cutter radius |
| Thin walls | Reduced feeds to avoid vibration | Keep metal walls around 0.8 mm or thicker, plastics around 1.5 mm or thicker |
| Hard-to-machine alloy | Slower cutting speeds, more tool wear | Use 6061 aluminum or free-machining brass where strength allows |
| Fine surface finish | Extra passes or polishing | Leave as-machined (about Ra 3.2 µm) except on sealing or sliding faces |
| Deep tapped holes | Tap breakage risk, longer cycle | Thread depth of about 1.5 times diameter is usually enough |
| Cosmetic requirements | Handling care, rework, masking | State which faces are cosmetic and which are not |
Material: price per kilogram is only half of it
Buyers often compare alloys on raw material price alone. In machining, how fast the material cuts can matter as much as what it costs to buy. Aluminum alloys such as 6061 and free-machining brass such as C360 cut quickly with long tool life. Stainless steels such as 304 and 316 cut more slowly and work-harden. Titanium Ti-6Al-4V and many nickel alloys cut slower again and wear tools faster. So a part in a more expensive bar can sometimes cost less overall if it machines much faster, and the reverse is also true.
Stock size matters too. A part that fits inside a standard bar or plate size with a few millimetres of clean-up per side wastes less material than one that is a hair too large and forces the next stock size up. If the overall envelope is flexible, ask the estimator which stock size they plan to use. For alloy choice itself, see our guides on 6061 vs 7075 aluminum and on stainless steel grades.
Quantity, lead time and revisions
Quantity changes the cost structure, not just the total. Very small batches are dominated by setup. Medium batches let the shop optimise toolpaths and fixtures. At high volumes, other processes such as die casting or injection molding may become cheaper per part, which we cover in our comparison of CNC machining, die casting and injection molding by volume.
Lead time also has a cost. A standard lead time lets the shop schedule your job into an open machine slot. An expedited request may mean overtime, splitting the job across machines or bumping other work, and shops price that in. If your date is flexible, saying so can help.
Revisions are the hidden one. Each design change after the program is written can mean reprogramming and a new first article. Freezing critical dimensions before ordering, or ordering a small prototype batch first, keeps those costs predictable.
A worked comparison without prices
Imagine an aluminum mounting bracket with four tapped holes, one bearing bore and a pocket to save weight. Version A has a ±0.02 mm tolerance on every dimension, sharp internal corners in the pocket, a pocket depth of about six times the cutter diameter, all edges polished and tapped holes three diameters deep. Version B keeps the bearing bore tight, puts every other feature under a general tolerance, uses a corner radius just over a standard end mill, limits the pocket depth to about three times the cutter diameter, leaves faces as-machined and taps to about 1.5 diameters.
Both versions do the same job in the assembly. Version B needs fewer tool changes, shorter tools, fewer finishing passes and less inspection, and it can likely be made in fewer setups. An estimator would expect it to quote lower and ship sooner. Illustration 1, at the top of this article, maps each of those decisions back to the cost bucket it affects.
What to send with your RFQ
A complete package reduces both the price and the time to get a quote, because the estimator does not have to build in a margin for uncertainty.
- A 3D model in STEP or another neutral format, plus a 2D drawing for tolerances, threads and finishes
- Material and temper, or the property you need if you are open to alternatives
- Quantity, and any likely repeat or annual volume
- Which dimensions are critical and which can follow a general tolerance
- Surface finish and coating requirements, including which faces are cosmetic
- Inspection and documentation needs such as a dimensional report or material certificate
- Required delivery date, and whether it is flexible
Common questions
Why is my prototype so expensive compared with production?
A single piece carries the entire programming, fixturing and first-article cost by itself. At higher quantities that one-time cost is spread across every part.
Will loosening tolerances always lower the price?
Not always. Tolerances that are already easy to hold do not cost much more. The savings come from relaxing tolerances that force extra finishing passes, special tooling or measurement on a CMM.
Is five-axis machining cheaper or more expensive?
It depends on the part. Five-axis machines cost more per hour, but they can replace several setups on a multi-sided part and improve feature-to-feature accuracy. For simple prismatic parts, three-axis work is usually cheaper.
Can 3DWK suggest design changes to reduce cost?
Yes. When you upload files on the quote page, an engineer reviews manufacturability and will flag features that drive cost, such as deep pockets, sharp corners or unusually tight tolerances, so you can decide before ordering.