CuSn12 Flanged Trapezoidal Nuts for Screw-Jack Travelling Carriages
A CuSn12 flanged travelling nut for a screw-jack carriage must match the complete thread system and the axial load path. Specify pitch, lead, number of starts, hand, tolerances and the flange mounting arrangement. A bronze grade and nominal screw diameter alone cannot establish travel speed, backlash, load capacity or load-holding behaviour.
Specify the alloy and the complete nut separately
Bimeccanica documents CuSn12 bronze flanged trapezoidal nuts and identifies the historical UNI 7013-72 material reference in its CFB literature. It also emphasizes lubrication for its screw-and-nut pair. This is evidence of a manufacturer’s specified construction, not a BONIU catalogue item or a rating for an independently machined nut.[1]
For a new purchase, state the agreed alloy standard, edition, casting route or stock condition, and required inspection documentation. Do not convert the historical reference into an unconditional modern EN or US equivalent. If the drawing simply says “CuSn12”, resolve the acceptance specification before approving a substitute.
Application boundary: this guide concerns a proposed drawing-defined bronze nut in a rotating-screw, travelling-carriage arrangement. BONIU’s current plain-bushing pages do not establish availability of a threaded load nut, a complete screw jack or a safety-rated lifting system. Request manufacturing review first.
Compare the thread fields that change the mechanism
| Specification field | What it determines | What to send with the enquiry |
|---|---|---|
| Nominal diameter and thread form | Mating thread geometry, not the final assembled fit by itself | Complete screw and nut thread designation and applicable standard |
| Pitch, starts and lead | Axial advance for one screw revolution | All three values; do not use “pitch” as a substitute for lead |
| Right- or left-hand thread | Direction of carriage travel for a given rotation | Explicit hand and the required operating direction |
| Thread tolerance and engagement length | Fit, contact distribution and available threaded section | Tolerance classes, effective engagement and end reliefs |
| Flange and locating pilot | How axial force reaches the carriage and how the nut is aligned | Section drawing, supporting shoulder, bolt pattern and datums |
| Lubrication and protection | How lubricant reaches the threads and how debris is excluded | Approved lubricant, access, wipers or covers and maintenance space |
The drawing should distinguish a mounting hole from a load-carrying shoulder, an anti-rotation feature and a lubrication passage. Their functions are different even when they are close together on a compact flange.
A lead error can double carriage speed
Original kinematic example: assume two hypothetical screws with the same 6 mm pitch, one with one start and one with two starts. Lead equals pitch multiplied by starts. At an assumed 120 rpm, carriage speed equals lead multiplied by rpm.
| Assumed construction | Lead per revolution | Travel at 120 rpm |
|---|---|---|
| One start, 6 mm pitch | 6 mm | 720 mm/min |
| Two starts, 6 mm pitch | 12 mm | 1,440 mm/min |
The example shows why a replacement nut cannot be ordered from pitch and bore size alone. The screw must mate geometrically, and the resulting motion must match the machine’s limits and control settings. These calculations do not establish thread strength, efficiency, motor torque or whether the load can drive the screw backwards.
Load holding needs a separate equipment-level decision. Do not infer a verified self-locking function from “bronze trapezoidal nut”. The responsible designer must review the screw geometry, friction conditions, wear and any required brake or independent restraint.
Draw the axial force path through the flange
Identify whether normal operation pushes the nut flange against a carriage shoulder or tends to pull it away. Draw both directions if the machine reverses axial load. The mounting fasteners and surrounding structure must be reviewed for their actual forces; a matching bolt circle alone does not prove a replacement.
Keep carriage guidance separate from screw transmission. Off-axis payloads should be resolved through the designed guides and supports. A nut forced to compensate for a misaligned carriage can contact the screw unevenly, increasing drag and concentrating wear.
Bimeccanica’s CFB literature distinguishes flange mounting arrangements for vertical use, illustrating that installation orientation matters for its system. Use the machine’s approved arrangement rather than copying a supplier illustration into a different assembly.[1]
Measure backlash without confusing it with system movement
Define the measurement position, applied force direction and how the screw is restrained. Carriage movement on reversal can contain thread clearance, screw-end bearing movement, coupling play, guide motion and elastic deflection. A single indicator reading does not automatically measure nut wear.
Compare results under a repeatable, safely isolated inspection procedure and retain the baseline. Ask the equipment designer to set the service limit and replacement method. Tightening an adjustable nut to remove every detectable movement can raise drag and heat; it is not a universal acceptance procedure.
Where a separate safety nut is fitted, its clearance and monitoring function are distinct from ordinary positioning backlash. ZIMM’s maintenance guidance includes inspection of the safety nut, connections and surface protection, with trapezoidal-drive relubrication dependent on duty. Its guidance does not supply a universal BONIU inspection interval.[2]
Installation and lubrication review
- Inspect the mating screw along the full working travel. A new nut on a locally worn, damaged or contaminated screw may bind in one position and remain loose in another.
- Verify thread hand, lead, engagement, locating surfaces and burr control before assembly. Use the approved inspection method; free spinning without load is not a capacity test.
- Align the screw, carriage guides and nut mounting without forcing the flange into position. Confirm clearance to thread runouts and end stops over the intended stroke.
- Use the lubricant and replenishment method approved for the actual screw/nut pair, temperature, speed and environment. Copper-alloy content does not make this a dry-running screw assembly.
- Check protection against abrasive dust and keep inspection and lubrication access available. Commission under the machine builder’s procedure and retain torque, movement and temperature observations.
Frequently asked questions
Is pitch the same as lead?
Only for a single-start screw. For a multi-start screw, lead is pitch multiplied by the number of starts. State both values in the enquiry.
Can CuSn12 be ordered as an automatic C90700 equivalent?
No. Resolve the actual material standard, edition, limits and product condition. A tin-bronze family description is not a substitution approval.
Will a longer bronze nut automatically carry a proportionally larger load?
No. Thread contact is not necessarily uniform. Review engagement, manufacturing accuracy, flange section, screw capacity, lubrication and duty together.
Can BONIU quote from a damaged sample alone?
A sample can support inspection, but provide the screw specification and assembly drawing as well. Thread manufacture and the proposed supply scope require explicit feasibility confirmation.
Technical sources
- Bimeccanica: CFB bronze flanged nuts. Manufacturer material reference, lubrication guidance and mounting distinctions; no supplier dimensions or ratings are assigned to BONIU.
- ZIMM: What maintenance does a screw jack require?. Manufacturer inspection and maintenance context for its screw-jack systems.
Request a drawing review
Send the screw and nut drawings, complete thread designation including lead and starts, thread hand, mounting section, carriage guidance, axial loads in both directions, speed, stroke, duty cycle, environment, lubrication plan, quantity and inspection requirements. Identify any safety-nut arrangement separately. Ask BONIU to confirm material and thread-manufacturing feasibility before treating this as a supply proposal.