How EDC parts are machined and finished
A knife scale, a pen barrel and a flashlight body go through different machines, different setups and different finishing lines. This is how the shops in the network route each kind of part, and what each step means for tolerance, cost and schedule.
Process, typical parts and what to expect
Typical ranges for small EDC parts, not promises. Material, wall thickness and finish move them, and the quote states what the shop will hold on your drawing.
| Process | Typical parts | Typical tolerance | Typical finish |
|---|---|---|---|
| 3-axis milling | Knife scales, liners, pocket clips, pry bars, bottle openers | ±0.01 to ±0.02 mm | Ra 0.8 to 1.6 µm |
| 4- and 5-axis milling | Contoured scales, sculpted handles, bevels, chamfers in one setup | ±0.01 to ±0.02 mm | Ra 0.8 to 1.6 µm |
| CNC turning with live tooling | Pen barrels, flashlight bodies, heads, tail caps, beads | ±0.01 mm on diameters | Ra 0.4 to 1.6 µm |
| Swiss-type turning | Pivots, standoffs, pins, pen tips, clip screws | ±0.005 to ±0.01 mm | Ra 0.4 to 0.8 µm |
| Wire EDM | Hardened lockbar inserts, tool steel parts, sharp internal profiles | ±0.005 mm | Ra 0.8 to 1.6 µm, finer with skim passes |
| Surface grinding | Hardened tool steel, liners, washers needing flatness | Flatness 0.005 to 0.01 mm | Ra 0.2 to 0.4 µm |
| Thread milling and tapping | Flashlight body threads, pivot and clip screw holes | 6g / 6H typical | As machined |
What each process does on an EDC part
Milling
Scales, liners, clips and pry bars start on a mill, usually from plate. Flat parts take two setups, one per face, with soft jaws or a fixture plate holding the profile. Contoured scales go to 4- or 5-axis machines so the bevel and the face are cut without re-clamping. Tolerances for knife scales
Turning
Pen barrels, flashlight bodies and beads are turned from bar. Live tooling adds flats, cross holes and clip slots on the same machine, so concentric features stay concentric. Thin-wall titanium tube needs light cuts and support to stay round. Titanium pen machining
Swiss-type turning
Pivots, standoffs, pins and pen tips under about 20 mm diameter. The guide bushing keeps slender parts straight, and the machine runs from bar without an operator between parts, which is why small turned hardware gets cheap at a few hundred pieces.
Wire EDM and grinding
Tool steel parts are machined soft, hardened to the drawing, then brought to size by wire EDM or surface grinding. EDM cuts hardened steel and titanium with no cutting force, which suits thin lockbar inserts and sharp internal profiles. Heat treatment for EDC parts
Threads
Flashlight heads and tail caps need threads that do not gall. Shops pair materials with care, thread mill where a broken tap would scrap the part and leave allowance for anodize. Flashlight threads and anodize allowance
Inspection
The shop measures the first article against the drawing before the batch runs, by CMM where the shop has one or with gauges and a height stand where it does not. Ask for the report on the RFQ. First-article inspection
Background reading: electrical discharge machining on Wikipedia.
Which route for which feature
If your drawing has one of these, the quote will reflect the route on the right. It explains most of the price gap between two similar-looking parts.
| Feature on the drawing | Usual route |
|---|---|
| Jimping, grip grooves, knurling | Milled with a form or slitting cutter, or knurled on the lathe. Spacing and depth belong on the drawing. |
| Lockbar cutout on a frame lock | Milled, with lockbar geometry and the lock face held tight. Hardened steel inserts are often wire-EDM cut. |
| Fine threads on thin-wall tube | Single-point turned or thread milled, with anodize allowance added before the finish. |
| Small holes for pivots and screws | Drilled and reamed or bored, often on the same setup as the profile to keep positions. |
| Sharp internal corners | Wire EDM. A milling cutter leaves its own radius, so give the largest radius the design allows. |
| Logo, serial number, batch mark | Fibre laser marking after finishing, or engraved on the mill before it. |
Finishes and what they do
Finish is where EDC parts are judged in hand, and where schedules slip if the shop hands the job to a finisher it does not manage.Finishes that survive a pocket
| Finish | What it does | Used on |
|---|---|---|
| Stonewash | Tumbled with ceramic media for a matte, scratch-hiding finish. | Titanium, stainless, aluminium |
| Bead-blast | Glass or ceramic bead for a uniform satin. Usually before anodizing. | All metals |
| Type II anodize | Dyed sulphuric anodize, about 5 to 25 µm. Colour options, moderate wear resistance. | Aluminium |
| Type III hard anodize | Thick hard coat, about 25 to 75 µm, half of it growth. Threads need allowance. | Aluminium |
| Titanium anodize | Voltage-controlled oxide colour, no dye. Bronze, purple, blue, gold. | Titanium |
| PVD / DLC | Thin hard coating, typically a few microns, black or coloured. | Stainless, titanium, tool steel |
| Passivation | Removes free iron after machining so stainless resists rust. | Stainless |
Drawing choices that cut machine time
- Give internal corners the largest radius the design allows. A 1 mm radius on a pocket forces a small, slow cutter.
- Call out tight tolerances only on fits: pivot holes, lockbar faces, thread pairs. Leave cosmetic faces to ISO 2768 general tolerance.
- State whether dimensions apply before or after finish, especially for anodized threads and press-fit holes.
- Keep scale and clip thickness consistent across a family of parts so one fixture serves the whole drop.
- Specify the finish by name and send a reference sample or photo. "Stonewash" means different media to different finishers.
Materials and parts
EDC materials: titanium, aluminium, zirconium, copper, steel, G10
Grades with UNS, EN and JIS designations, and how each one machines and finishes.
EDC parts: knife scales, clips, flashlight bodies, pens, beads
Typical materials, critical features and finishes for each part type.
Send a drawing
One RFQ, routed to the shops that run your material and batch size. Answered within 24 business hours.
Questions about EDC machining processes
- Is 4-axis or 5-axis milling needed for knife scales?
- Not for flat scales with a profile and pockets, which a 3-axis mill handles in two setups. Contoured or sculpted scales, bevels that wrap the edge and parts that would otherwise need four or five setups are where 4- and 5-axis work pays off.
- Why is Swiss turning used for pivots and pen tips?
- A Swiss-type lathe supports the bar right next to the cut, so long, slender parts stay straight and concentric. It also runs unattended from bar stock, which makes small turned parts cheap once the setup is paid for.
- Does anodizing change thread fit?
- Yes. Type III hard anodize grows outward by about half its thickness on every surface, so a thread cut to final size before anodizing will bind. The drawing should state whether dimensions apply before or after finish.
- Are hardened parts machined before or after heat treatment?
- Usually roughed soft, hardened, then ground or wire-EDM cut to final size. That sequence adds one to two weeks but avoids distortion from heat treatment ending up in the finished dimensions.
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