Casting routes used for bearing bronze
Machinability rating and machining behaviour of common bearing alloys
Industries, Provider of Bronze Alloys
CNC Bronze Machining and Custom Parts: Processes, Tolerances
Bronze machining behaves differently from steel. Chip formation, work hardening, tool wear and the way a pressed bushing closes after installation all depend on the alloy and the casting route. This page sets out how bronze parts are produced, what dimensional accuracy is routinely achievable, and the information a supplier needs to quote accurately.
1. Machining characteristics by alloy
Machinability rating is expressed relative to free-cutting brass C36000, set at 100. The spread across bearing bronzes is wide, and it governs tooling choice, cycle time and unit cost more than any other single factor.
| Alloy | Rating (C36000 = 100) |
Chip formation | Main machining risk |
|---|---|---|---|
| C93800 | 80 | Short, easily broken chips | Built-up edge if the tool edge is not sharp; lead swarf needs separate handling |
| C93200 | 70 | Short chips | Smearing on the rake face at low speed; keep speed up and edge polished |
| C95400 | 60 | Continuous, stringy chips | Work hardening if the tool dwells; abrasive iron-rich phases accelerate flank wear |
| C95500 | 50 | Continuous chips | Work hardening and higher cutting forces; needs rigid setup |
| C95800 | 20 | Tough, continuous chips | Notable work hardening; requires sharp carbide, consistent feed, no dwell |
| CuSn12-C (CC483K) | 20 | Tough chips | Work hardening; abrasive wear from tin-rich phases |
| C86300 | 8 | Hard, segmented chips | Highest cutting forces and tool wear of the group; carbide tooling and rigid fixturing required |
| CuSn8 (CW453K) | Not recommended as machined stock |
— | Wrought strip alloy; wrapped bushings are formed and sized rather than machined from solid |
Ratings are from the Copper Development Association database and mill data sheets. They compare relative machinability under standard conditions; actual tool life depends on tooling, machine condition and the operation.
Two practical consequences follow from this table. First, a part specified in C86300 and the same part specified in C93200 are not comparable in machining cost. Second, aluminium bronzes and manganese bronze punish interrupted cuts and tool dwell: the cut should be continuous, the feed steady, and the tool withdrawn rather than allowed to rub.
2. Processes: turning, milling, drilling, grooving
Turning
Used for bushings, sleeves, washers, rings and round wear parts, from bar, tube or centrifugal castings. A typical sequence for a precision bushing is rough turn outside diameter, face both ends, rough bore, then finish bore in a single continuous pass with a sharp tool, leaving the finish allowance low enough that the final pass cuts rather than rubs.
Milling
Used for flat wear plates, slide plates, L-gibs and T-slot nuts, and for drilling patterns in plates. Climb milling with a sharp, positive-rake cutter reduces work hardening on aluminium bronze. Plates are rough-milled, then finish-milled with a light, consistent cut; the final pass should not re-cut a hardened surface layer.
Drilling
Bronze tends to grab on drill exit and to produce a burr. Sharp drills, a steady feed, and backing support at exit reduce breakout. For deep holes, peck cycles clear chips and limit heat. Where graphite plugs are to be inserted, hole depth and diameter tolerance control the plug fit and the resulting coverage ratio.
Grooving and internal features
Internal grooves, oil pockets and lubrication indents are produced with form tools on the lathe or with a grooving cycle. On wrapped bushings with lubrication indents the features are formed in the strip before rolling, not machined afterwards.
3. Casting routes and their effect on machining
| Route | Typical product | Effect on machining and performance |
|---|---|---|
| Continuous casting ASTM B505 |
Solid bar, tube, rectangular bar | Fine, uniform grain with low porosity. Consistent machinability along the length; the usual stock for machined bushings and wear parts in standard sizes. |
| Centrifugal casting ASTM B271 |
Rings, tubes, hollows | Dense outer structure; impurities and porosity migrate to the bore and are machined away. Suited to large-diameter rings and bushings where solid bar would waste material. |
| Sand casting ASTM B148, B584 |
Large or complex shapes | Coarser grain, more allowance needed, and properties vary with section thickness. Used for large wear plates, housings and one-off shapes. |
| Permanent mould ASTM B806 |
Repeat shapes in volume | Finer grain than sand casting with better dimensional repeatability. |
| Wrought EN 1652, EN 12163 |
Strip, plate, bar | Tin bronze strip is rolled and formed into wrapped bushings, then sized. Plate is used for wear plates machined to drawing. |
The route determines the stock allowance, the achievable surface integrity and the mechanical property values that apply. A drawing that names the grade but not the route leaves all three open.
4. Tooling and cutting parameters
Tool selection
- Carbide is standard. Fine-grain, uncoated or PVD-coated grades are used for the abrasive alloys; sharp polished edges reduce built-up edge on the soft leaded bronzes.
- Positive rake geometry with adequate relief, typically 8–12° clearance, keeps cutting forces down and limits work hardening.
- Chip control matters on aluminium bronze and manganese bronze, where stringy chips affect finish and operator safety. Chip-breaker geometry and high-pressure coolant both help.
- Rigidity — short tool overhang, rigid workholding. Bronze absorbs less of the tool pressure than a soft steel, so any compliance shows directly as chatter and dimensional drift.
Indicative cutting speeds
| Alloy group | Cutting speed Vc m/min |
Feed, finishing mm/rev |
Depth of cut, finishing mm |
|---|---|---|---|
| High-leaded tin bronze C93800, C93200 |
200–400 | 0.05–0.15 | 0.2–1.0 |
| Tin bronze, cast CuSn12-C, CC484K |
150–300 | 0.05–0.15 | 0.2–1.0 |
| Aluminium bronze C95400, C95500 |
100–200 | 0.08–0.20 | 0.3–1.5 |
| Nickel aluminium bronze C95800 |
80–150 | 0.08–0.20 | 0.3–1.5 |
| Manganese bronze C86300 |
60–120 | 0.08–0.20 | 0.3–1.5 |
Validate before releasing to production
The ranges above are starting points for roughing-to-finishing operations with sharp carbide in a rigid setup, not recommended production parameters. Cutting speed, feed and depth of cut interact with tool geometry, machine condition, coolant strategy, section thickness and the required surface finish. Confirm the parameters on a first-piece trial and adjust against measured tool wear and surface finish before running a batch.
Coolant and swarf
- Flood coolant or oil mist is used for most bronze turning and milling; it stabilises temperature and flushes chips.
- Graphite-plugged bronze is often machined dry with extraction. Graphite dust mixed with coolant forms a paste that is harder to manage than dry dust, and wet graphite can complicate subsequent assembly.
- Lead-bearing alloys generate lead-containing swarf. Segregate and dispose of it under local regulations rather than mixing it with general steel swarf.
- Stress relieving before finish machining is worth considering on aluminium bronze parts with tight dimensional requirements, because residual stress from casting and roughing will move the part when material is removed.
5. Tolerances, fits and surface finish
Routinely achievable tolerances
| Feature | Typical production capability | Notes |
|---|---|---|
| Unspecified dimensions | ISO 2768-m | State the general tolerance standard on the drawing instead of leaving it implicit |
| Bushing outside diameter | IT7–IT8 | IT6 achievable with fine finishing |
| Bushing bore, before installation | IT7–IT8 | Final bore is often obtained after pressing — see below |
| Bore to outside diameter concentricity | 0.02–0.05 mm | Depends on wall thickness and workholding |
| Roundness | 0.01–0.03 mm | Measured on finished bore |
| Flatness, machined plate | 0.05–0.10 mm per 300 mm | Thin plates may need stress relieving between operations |
| Length and shoulder dimensions | ±0.05 mm | Tighter on request |
Press fits
A bushing pressed into a housing deforms elastically. The bore closes by an amount related to the diametral interference and the wall thickness ratio: thin-walled bushings close by close to the full interference, heavy-walled bushings by less. Where running clearance is critical, the bore is finish-machined, reamed or burnished after installation, or the pre-installation bore is adjusted to compensate.
| Interface | Common fit | Application |
|---|---|---|
| Housing bore | H7 | Standard reamed or bored housing |
| Bushing OD — light press | m6 | Light duty, where the bushing may need removal |
| Bushing OD — normal press | r6 | General industrial application |
| Bushing OD — heavy press | s6 | Heavy load, shock, or where rotation of the bushing must be prevented |
| Shaft | h6, f7, e7 | Selected to give the required running clearance |
Running clearance is commonly set at 0.1–0.2% of shaft diameter, subject to a practical minimum in the region of 0.025 mm. Solid-lubricant bearings run with larger clearance than oil-lubricated ones. Confirm the clearance against thermal expansion, shaft and housing materials, and the bearing supplier’s recommendation for the specific bearing form.
Surface finish
| Surface | Ra, µm | Ra, µin | Why it matters |
|---|---|---|---|
| Shaft journal | 0.2–0.8 | 8–32 | Drives wear rate on both parts; a rough shaft abrades the bearing |
| Bushing bore | 0.8–1.6 | 32–63 | Supports film formation; too smooth can hinder lubricant retention |
| Housing bore | 1.6–3.2 | 63–125 | Affects press-fit retention and heat transfer |
| Slide plate working face | 0.8–1.6 | 32–63 | Wear rate and stick-slip behaviour |
µin values are converted from µm at 39.37 µin per µm and rounded. Where a drawing specifies roughness, name the parameter, the value and the assessment length.
6. Groove and lubrication patterns
The groove pattern is part of the bearing design, not a cosmetic detail. It controls where lubricant is held, how it reaches the contact zone, and how much load-carrying area is lost.
| Pattern | Motion | Function | Design caution |
|---|---|---|---|
| Straight axial | Rotating or oscillating | Distributes lubricant along the length | Should stop short of the ends to limit end leakage |
| Circular Annular |
Rotating | Feeds lubricant around the circumference | A groove at mid-length effectively halves the load-carrying length |
| Figure-eight Double figure-eight |
Oscillating and rotating | Distributes in both directions without a full circumferential break | Pattern depth and land width set the load-bearing area |
| Spiral Helical |
Rotating, one direction | Pumps lubricant along the bearing | Direction of rotation has to be known before manufacture |
| Lubrication indents Pressed pockets |
All | Holds grease in wrapped bushings; formed in strip before rolling | Common in CuSn8 wrapped bushings for agricultural machinery |
| Graphite plug grid | All, dry or boundary | Provides solid lubricant at the contact surface | Coverage commonly 20–30% of the sliding area; raising coverage improves dry running and reduces load capacity |
Where graphite plugs are used, the base alloy, plug diameter, grid pitch and resulting coverage ratio belong on the drawing. See graphite-plugged bronze bearings for plug layout and alloy combinations.
7. Parts produced
| Component | Common alloys | Governing features |
|---|---|---|
| Straight and flanged bushings | C93200, CuSn12-C, C95400, C95500 | Bore tolerance, wall thickness, groove pattern |
| Split bushings | C93200, CuSn12-C | Split-line fit, reassembly register, clamping |
| Thrust washers | C93200, C95400, CuSn12-C | Thickness, flatness, groove or pocket layout |
| Wear plates and slide plates | C86300, C95400, CuAl10Ni5Fe4-C | Flatness, hole pattern, countersink depth, graphite coverage |
| L-gibs and guide rails | C86300, C95400 | Profile accuracy, mounting face, lubrication pattern |
| T-slot nuts | C95400, CuSn12-C | Thread accuracy, slot profile, wear on the sliding face |
| Bronze gears and worm wheels | C95400, C95500, CuSn12Ni2-C | Tooth profile, concentricity, backlash, mating worm hardness |
| Screw-down nuts and rolling mill nuts | C86300, C95400, high-tensile brass | Thread form, load flank, lubrication provisions |
| Spherical and journal bearings | C95400, C95500, CuSn12Ni2-C | Spherical contour, contact pattern, clearance |
| Machined turned and milled parts | All of the above | Per drawing |
8. Inspection and documentation
- Dimensional report — measured values for the features marked as critical on the drawing, against the stated tolerances.
- Material certificate — EN 10204 type 3.1 with the heat analysis, or a mill test certificate showing composition and mechanical test results against the ordered specification.
- Hardness — Brinell, with the load and indenter recorded, since the value is only comparable at a stated load.
- Surface roughness — measured on the specified surfaces, with the parameter and cut-off recorded.
- Graphite coverage — where plugs are specified, coverage ratio can be verified from the hole layout and plug diameter, or by image analysis of the working surface.
- Non-destructive examination — dye penetrant or ultrasonic on request for cast parts with load-critical sections.
Agreed inspection scope belongs in the enquiry, not after the first article is made. Adding ultrasonic testing or a full CMM program after machining changes cost and lead time.
9. From drawing to production
An enquiry that includes the items below can usually be quoted directly. Missing alloy, tolerance or lubrication information is the most common cause of a quote that has to be revised later.
- DrawingSTEP or DWG preferred, PDF acceptable for a first review
- Alloy and standardGrade plus the governing specification and year, e.g. C95500 to ASTM B505/B505M
- Casting routeContinuous, centrifugal, sand or wrought — if the drawing is silent, state the intended stock form
- Heat treatmentAny solution treatment, quench and temper, or stress relief requirement
- QuantityPrototype and production quantity, and the expected annual volume
- TolerancesGeneral tolerance standard, plus any IT grades or explicit limits on critical features
- Surface finishRa values on functional surfaces
- Lubrication featuresGroove type and dimensions, plug pattern and coverage, or indents
- InspectionCertificate type, dimensional report scope, any NDT
- Service conditionsLoad, sliding speed, temperature, environment — needed to flag feasibility, not to set allowable limits
- Packaging and markingIncluding any export packaging or part marking requirement
- Target lead timeAnd whether a first article is required before the batch
10. Frequently asked questions
- Which bronze is cheapest to machine?
- Among the alloys listed, C93800 has the highest machinability rating at 80, followed by C93200 at 70. Both are leaded tin bronzes. C86300, at a rating of 8, sits at the other end and usually carries a noticeably higher machining cost for the same geometry.
- Can aluminium bronze be machined to tight tolerances?
- Yes, but the process has to account for work hardening. Sharp carbide, a positive rake geometry, consistent feed, no tool dwell and adequate rigidity are the main requirements. Stress relieving before finish machining helps hold tolerance on parts where a large amount of material is removed asymmetrically.
- Why is the bore machined again after the bushing is pressed in?
- Pressing a bushing into a housing compresses it, and the bore closes by an amount related to the interference and the wall thickness ratio. Where the running clearance is tight, the bore is finished after installation, or the pre-installation bore is compensated so the installed bore lands in tolerance.
- What fit should be specified between bushing and housing?
- H7 on the housing bore with r6 on the bushing outside diameter is a common general-purpose combination. m6 is used for a lighter press and s6 where shock loading or rotation of the bushing has to be prevented. The shaft fit is chosen separately to give the required running clearance.
- Is graphite-plugged bronze machined wet or dry?
- Often dry with local extraction. Graphite dust mixed with coolant forms a paste that is awkward to handle and can contaminate the assembly. Dry machining with appropriate dust extraction is the common approach, subject to the shop’s health and safety rules.
- What tolerance applies to dimensions not individually toleranced on the drawing?
- Whatever general tolerance standard the drawing names. If none is named, ISO 2768-m is a common default for machined dimensions, but it should be stated explicitly to avoid ambiguity between the drawing and the quote.
- Do you need the service conditions to quote a machined part?
- Not to quote, but the information helps flag problems early — a groove pattern that suits rotation but not oscillation, a clearance that closes up at temperature, or an alloy that is difficult to source in the required section. Load, speed, temperature and environment are useful context for a feasibility review.
Applications
As a primary source for bronze alloys, our products are utilized across a wide range of industries and applications. If you’re facing a challenge or have an application where self-lubricating bearing bronze could be the solution, contact us today. Below is a list of some of the most common industries and applications we serve:
Bronze alloys and grade selection
Composition, properties, cross-reference
Bronze bushings and sleeve bearings
Types, dimensional standards, fits
Bronze bushings and sleeve bearings
Types, dimensional standards, fits
