How to Milling Connecting Rod jJurnal With Mini Milling Machine?

Recently, a Russian customer of Shanghai ANTISHICNC has enquired about the process of machining #20 steel connecting rod journals using a mini milling machine. The customer’s connecting rods have a length range of 30–103mm and a diameter range of 10–50mm. The operation steps are as follows:

I.Workpiece pretreatment

The connecting rod journals shall first undergo rough machining (milling both end faces, drilling and reaming positioning holes) to ensure flat reference surfaces.

A finishing allowance of 0.3–0.5mm shall be reserved for the journal machining area.

As connecting rods are irregular parts, special fixtures must be fabricated:

Positioning shall be based on the big end hole, small end hole and end face of the connecting rod.

Secure the connecting rod firmly to the milling machine table using bolts and pressure plates to prevent displacement during machining.

If no special fixture is available, a vise + positioning block can be used for auxiliary fixation. However, the workpiece position must be repeatedly calibrated to ensure the machining axis of the journal is parallel to the spindle axis of the milling machine.

II. MillingProcess

Rough Machining

1.Start the spindle of the mini milling machine. Manually move the worktable to bring the milling cutter close to the blank surface of the connecting rod journal machining area.

2.Lightly touch the workpiece edges in the X-axis and Y-axis directions respectively, and record the tool setting origin in the machine coordinate system.

Lower the Z-axis until the cutting edge of the milling cutter just contacts the workpiece surface, and set the Z-axis zero point.

3.Spindle Speed Setting:

For rough machining of steel connecting rods: 1000–1500r/min

For rough machining of aluminum alloy connecting rods: 2000–2500r/min

Feed Rate Setting: 50–80mm/min. Avoid excessive feed rate to prevent tool chipping.

Adopt the layered cutting method: set the Z-axis cutting depth to 0.1–0.2mm per pass, and mill layer by layer until a finishing allowance of 0.1–0.2mm is reserved for the journal size, while shaping the basic cylindrical surface of the journal.

Finishing Machining

Increase the spindle speed by 30%–50%:

For steel workpieces: 1500–2000r/min

For aluminum alloy workpieces: 2500–3000r/min

Higher speed reduces cutting force and workpiece deformation.

Reduce the feed rate to 20–40mm/min to ensure a smooth machined surface.

III.Milling Key Notes

1.Positioning Accuracy ControlThe coaxiality and parallelism of connecting rod journals directly affect assembly performance. Repeatedly calibrate the workpiece positioning datum during machining. If necessary, use a dial indicator to monitor the movement accuracy of the worktable.

2.For steel machining: Use emulsion or cutting oil to reduce cutting temperature, minimize tool wear and prevent workpiece thermal deformation.

3.For aluminum alloy machining: Dry cutting is acceptable, or a small amount of kerosene can be applied.

4.Tool Wear MonitoringDuring finishing, if scratches appear on the machined surface or burrs increase significantly, replace the tool in a timely manner to avoid accuracy deviations.

The core advantages of using a mini milling machine for journal machining lie in its high flexibility, cost-effectiveness and precision compatibility with small-sized workpieces. It is particularly suitable for small-batch, multi-variety connecting rod journal machining scenarios. For machining the customer’s #20 steel connecting rod journals, we recommend the following model X2 Mini Drilling and Milling Machine:

Specifications	Units	X2
Drilling capacity	mm	13
End milling capacity	mm	16
Face milling capacity	mm	30
Longitudinal axis (X)	mm	220
Crossaxis (Y)	mm	100
Headstock travel (Z)	mm	180
Max. distance spindle to table	mm	280
Spindle speed Low range	rpm	100-1100 ±10%
High range	rpm	100-2500 ±10%