CNC Machined Spacers, Standoffs & Bushings
Round · hex · threaded · shouldered · OD 1.5–60 mm · wall from 0.3 mm · ±0.01 mm
CHX Metal turns spacers, standoffs and bushings from bar to drawing: round, hex, shouldered and threaded, OD 1.5-60 mm, bores from 0.6 mm, wall sections down to 0.3 mm, held at ±0.01 mm on length and ±0.005 mm on bore where the fit requires it. Aluminium, brass, stainless, steel, PEEK and nylon all run on the same bar-fed cells, and a 100,000-piece order is a normal production slot rather than a special case.
Spacers look like the cheapest part on the BOM and they are the part that quietly decides whether a stack of boards, a gearbox cover or a battery module goes together on the line or comes back. The failure mode is never dramatic: a burr left in a bore, a length that grew 0.05 mm, a thread that was tapped before anodising. This page covers what to specify, and what we control so the fifty-thousandth piece behaves like the fifth.
Geometry: what a bar-fed lathe can and cannot do
The constraint is not the drawing, it is the bar. Everything turned here starts as round stock, so any feature that is not a surface of revolution needs a second operation, a mill-turn cell, or a different process entirely.
| Feature | Practical range | Note |
|---|---|---|
| Outer diameter | 1.5 – 60 mm | Above 42 mm the part moves off the Swiss cell to a CNC lathe with a bar feeder or a chuck |
| Bore diameter | 0.6 mm and up | Below 1 mm, depth-to-diameter above 8:1 needs a gundrill or a peck cycle and is quoted separately |
| Wall thickness | 0.3 mm minimum | Thin walls deflect under clamping; we use collet support and light finishing passes |
| Length | 0.5 – 150 mm | Length-to-diameter above 10:1 needs a travelling steady or a second op |
| Hex flats | Across flats 2.5 – 36 mm | Cut on the sub-spindle or by a hex bar feed — hex bar is usually cheaper |
| Threads | M0.8 – M30, plus NPT/BSP | Rolled threads on ductile alloys; cut threads where the thread must run to a shoulder |
| Cross holes | Ø0.5 mm and up | Live tooling on the mill-turn cell; the hole position tolerance is what drives cost |
| Slots and flats | Yes, live tooling | A slot on one side is cheap; four slots at 90° indexes are not free |
If a spacer needs a cross hole, a flat and a slot, it is a mill-turn part and should be quoted as one. Splitting it across two suppliers produces a position tolerance nobody can hold.
Materials and the cost they carry
| Material | Density | Typical finish | Relative part cost | Where it is used |
|---|---|---|---|---|
| Aluminium 6061-T6 | 2.70 | Clear or black anodise | Low | Board standoffs, brackets, heat-sensitive stacks |
| Aluminium 7075-T6 | 2.81 | Hard anodise | Low-mid | High-load standoffs, aerospace brackets |
| Brass C3604 | 8.50 | Nickel or tin | Low | Threaded standoffs, EMI/RF shielding, earth posts |
| Stainless 303 | 7.90 | Passivation | Mid | Corrosion resistance without plating, food and medical equipment |
| Stainless 316L | 8.00 | Passivation, electropolish | Mid-high | Marine, chemical, medical; also lower magnetic signature |
| Steel 12L14 | 7.87 | Zinc, nickel, black oxide | Lowest | High-volume general purpose, then plated |
| PEEK | 1.30 | None needed | High | Electrical isolation, high temperature, medical and semiconductor |
| Nylon / POM | 1.14 / 1.41 | None | Low-mid | Insulating washers, low-load spacers, damping |
Cost index compares material plus machining at equal geometry, not catalogue price. Anodising and plating are quoted as separate operations with their own lead time.
Tolerance allocation: spend it where the stack needs it
A spacer has three dimensions that matter — length, bore, and the squareness of the ends — and a dozen that do not. Over-tolerancing is the single most common reason a simple part comes back expensive.
| Dimension | Sensible default | When to tighten | Cost impact |
|---|---|---|---|
| Overall length | ±0.1 mm | ±0.02 mm only if it sets a preload or a gap | +15–25% |
| Bore diameter | H9 / +0.05 | H7 or ±0.005 mm for a bearing or a pin fit | +20–40% |
| Concentricity bore to OD | 0.05 mm | 0.01 mm for thin-wall parts | +25% |
| End squareness | 0.03 mm | 0.01 mm where the part is a bearing shoulder | +10–20% |
| Surface finish | Ra 1.6 | Ra 0.4 for sealing or sliding surfaces | +20–30% |
| Thread | 6H standard | 4H6H or a specified torque requirement | +10% |
Numbers are what we see across production lots on bar-fed lathes, not a catalogue claim. Anything tighter is possible and is quoted after a capability check on the specific feature.
High volume without drift: how 100,000 pieces stay identical
The enemy at volume is not accuracy, it is drift. Tool wear moves a diameter a few microns per thousand parts; thermal growth moves it again when the shop warms up after lunch; and a new bar lot can move it once more. Three things keep a run stable:
- In-process gauging with offset feedback. The cell measures a sampled part and corrects the tool offset automatically, so the mean stays centred instead of walking to the limit and being pulled back.
- SPC on the critical feature. X-bar and R charts on the bore and the length, with Cpk reported per lot. We target Cpk ≥ 1.33 on drawing tolerances and ≥ 1.67 where a customer asks for it, and we will say when a feature cannot reach it.
- Bar lot control. Material certificates are held per lot and matched to the production record, so a drift that traces back to a mill lot is visible instead of mysterious.
For parts that feed automatic assembly, we also control what drawings usually ignore: burr height, chip residue in blind bores, and part-to-part orientation for the bowl feeder. A spacer that arrives with a 0.1 mm burr jams a feeder at 3 a.m. and the whole run gets blamed.
Finishing: the operation that most often goes wrong
Anodising grows a part by roughly half the coating thickness per surface, and it grows it unevenly on edges. Threads masked before anodising will not accept a screw afterwards if the masking is wrong. Two rules cover most of it: thread after anodising, or mask the thread and state the class; and never specify a tight bore plus a thick coating without telling the finisher which dimension is functional.
| Finish | Thickness | Effect on dimension | Typical use |
|---|---|---|---|
| Clear / black anodise | 5–15 µm | +5–15 µm per surface | Aluminium spacers, cosmetic and wear |
| Hard anodise | 25–50 µm | +25–50 µm per surface, edges more | Wear surfaces, sliding bushes |
| Chemical conversion (Alodine) | < 1 µm | Negligible | Electrical bonding, paint base |
| Nickel plate | 3–10 µm | +3–10 µm per surface | Brass and steel standoffs, solderability |
| Zinc / zinc-nickel | 5–12 µm | +5–12 µm per surface | Steel spacers, corrosion |
| Passivation | < 0.1 µm | None | Stainless, after machining to remove free iron |
| Electropolish | Removes 5–20 µm | −5–20 µm | Medical and semiconductor stainless |
Packaging, and why it belongs in the quote
A 50,000-piece order of small bushings is a handling problem before it is a machining problem. Parts leave here bagged in counted multiples, in trays that match the customer's feeder pitch, or on tape where the assembly is automated — and the packaging choice is quoted as a line item so nobody discovers it on the invoice.
Standard is double-bagged, desiccant, carton with a lot label carrying the part number, quantity, material certificate number and inspection report reference. VCI bags and moisture-barrier foil are available for sea freight to humid destinations, and this is one of the few places where a 2 % packaging cost avoids a 100 % rework claim.
Related guides and capabilities
CNC turned parts · Brass turned parts · Stainless steel turned parts · Aluminium turned parts · Mass precision hardware · Batch production
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Frequently asked questions
What is the smallest wall thickness you can turn?
0.3 mm on a Ø10 mm part in aluminium, with collet support and light finishing passes. Below that, deflection during turning and handling damage after it become the limit rather than the machine.
Can you tap threads and then anodise?
Yes, but the thread must be masked or cut oversize to allow for the coating. Our default is to mask threads on anodised parts and state the thread class on the drawing review, because an anodised M3 thread will not accept a plated screw at nominal size.
Do you deburr and clean before packing?
Every part is deburred as a process step, not an inspection catch. Blind bores and cross holes get a chip check under magnification before packing, and parts for automatic assembly are checked for burr height against the drawing limit.
How do you price 5,000 versus 500,000 pieces?
Setup is amortised over the lot and the cycle time is fixed, so the curve is steep at the start and flat afterwards. Below roughly 500 pieces the setup dominates; above 50,000 the material and the finishing cost dominate. We quote the actual curve rather than a single unit price.
Can you supply the mating screw as well?
Yes — screws, nuts and washers in the same material and finish are sourced or machined and packed as a kit if the customer wants one part number to receive. Kit assembly is a quoted operation.
What tolerance can you hold on hex flats?
Across-flats ±0.05 mm is standard from hex bar; ±0.02 mm when the flats are milled on the mill-turn cell. Hex bar is cheaper but limited to standard sizes.
Do you handle nylon and POM?
Yes. Both machine cleanly but move with temperature and moisture, so we control the coolant and measure at 20 °C after stabilisation. Tolerances tighter than ±0.05 mm on nylon are usually not meaningful and we will say so.
Send your drawing, get a price in 24 hours
Name, email and what you need. Attach a drawing if you have one — STEP, PDF, DXF or a photo of the print. We reply with unit price, MOQ and lead time, usually within one working day.
Prefer email? Send drawings to mc@chxmetal.com.