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Which Auto Parts Get CNC Machined, by Vehicle System
Nine groups cover most of the RFQs we read. Find the group your part sits in to see what it is usually made from and what a shop checks on the drawing before it quotes.
Nine groups of custom auto parts
The group tells a shop what the part has to survive. Materials and checks below are typical, not a rule for your part.
| Group | Typical parts | Usual materials | What shops check |
|---|---|---|---|
| Engine and intake | Intake manifolds, throttle body adapters, valve covers, timing covers, pulleys, crank triggers | 6061 aluminum, 7075 for pulleys, steel for crank hardware | Flatness of sealing faces, port and bolt positions, thread depth in aluminum |
| Turbo and exhaust | Turbo and manifold flanges, downpipe and v-band flanges, wastegate mounts, sensor bungs | Stainless 304, mild steel, titanium for weight | Flatness after welding, material that survives heat cycles |
| Drivetrain | Shifter bodies and linkage, differential covers, bellhousing and adapter plates, axle and driveshaft adapters | 6061 aluminum for covers and adapters, 4140 for splined and shaft parts | Spline and bore fits, runout, balance on anything that spins |
| Suspension and steering | Pickup points, control arm brackets, uprights, bushing sleeves, spherical bearing housings, column adapters | 6061 or 7075 aluminum, 4130 or 4140 steel | Load path, bearing bore fit, heat treat, material certificate |
| Brakes and wheels | Caliper brackets, hub adapters, wheel spacers, hub centric rings, master cylinder adapters | 6061 or 7075 aluminum, steel where load is high | Bore fit to the hub, thickness variation, stud and thread spec |
| Mounts and chassis | Engine and gearbox mounts, crossmember brackets, battery trays, radiator and accessory brackets | 6061 aluminum, mild steel, 4130 | Hole positions against the real car, weld prep, stiffness |
| Cooling, fuel and fluids | Thermostat housings, water necks, fuel rails, AN fittings and bungs, sandwich plates, oil cooler adapters | 6061 aluminum, stainless, brass | Thread form and sealing method, port finish, leak test |
| EV and electrical | Motor and gearbox adapter plates, shaft couplers, busbars, battery tray hardware, charge port mounts | 6061 aluminum, copper for busbars, steel for couplers | Concentricity from motor to gearbox, flatness, plating on copper |
| Interior and controls | Pedal assemblies, shift knobs, gauge pods and bezels, switch panels | 6061 aluminum, brass, Delrin | Cosmetic finish, anodize color, edge break |
What changes with where the part sits
Two parts with the same shape can need very different paperwork. Say which case yours is in the RFQ, because it changes the shops we pick and how they quote inspection.
- Holds the car on the roadSteering, brake, suspension and wheel parts. Ask the shop for a material certificate and an inspection report before you order. We do not certify parts or judge whether they are road legal.
- Seals against somethingFlanges, covers and ports. Flatness and surface finish on the sealing face decide whether it leaks, so name both on the drawing.
- SpinsPulleys, hubs, couplers and flywheel parts. Runout and balance matter more than the size tolerance.
- Sees heatTurbo, exhaust and engine bay parts. The material has to hold its strength hot, and the part moves as it heats.
- ShowsInterior parts, covers and trim. Finish, anodize color and edge break matter more than the last 0.01 mm.
Parts that are usually not worth machining
A straight answer saves you a quote. These are the cases where another route is normally cheaper.
Large cast housings in volume
Past roughly a thousand pieces a casting wins on price. Machining is for the critical faces after the pour.
Sheet metal panels and shields
Laser cutting and bending make these. A mill is the wrong tool.
Standard hardware
Bolts, studs, washers and fittings with a catalog number cost less off the shelf.
Parts with a good second hand original
If a clean original exists and fits, check that first. Send the RFQ anyway if it does not.
Springs, hoses, gaskets and seals
These are formed, molded or cut, not machined. A shop can make the metal parts they sit in.
Safety parts with no drawing and no sample
A shop needs something to measure. Photos alone are not enough for a load carrying part.
Guides for these parts
- Buying Guide
Custom CNC Auto Parts: A Buyer's Guide to Getting One Made
The whole job in one page: whether your part should be machined, what it costs, which alloy to ask for, what to send a shop and how to read the quotes you get.
- Process
Getting Custom Engine Swap Mounts and Brackets Machined
Swap parts are easy shapes in hard positions. How to define a mount or adapter plate so the first set fits, and where to leave adjustment and where not to.
- Buying Guide
Billet Differential Covers and Rear End Parts: Specs
Billet differential cover guide: bolt pattern, flange flatness, sealing finish, fill and drain ports, bearing cap support and material for rear end parts.
- Process
Reverse Engineering a Discontinued Car Part for Machining
What a shop needs when the only reference is the broken original: which dimensions to measure, when 3D scanning pays off and what to send with the RFQ.
Common questions
Something else? Email sales at autocncparts.com.
Do I need to pick a group when I send an RFQ?
No. Describe the part, the material and what it bolts to. The group only helps us decide which shops see it.
Can I get a part that is not on this list?
Yes. The list shows what we see most. Any part that can be cut from solid metal or plastic can go in an RFQ, and we tell you plainly if a shop route does not make sense for it.
Do shops machine brake and steering parts?
Some do, and they quote the inspection and material certificate with the part. We match on what a shop states about its machines and materials. We do not certify parts, so ask the shop for proof and check the part is legal for your use.
Do you stock any of these parts?
No. We are a matching service, not a machine shop and not a parts store. Every part is made to your drawing or your old part by a shop that quotes you directly.
Have a part in mind?
Send the drawing or photos of the old part and we will say which shops fit it, or that none do. We reply within 24 business hours.