Pin-Point Gate Bushing Accessories: Extensions, Electrodes & Pairings
The Complete Pin-Point Gating System
A pin-point gate bushing is the centerpiece of a three-plate mold gating system, but it works with several supporting components:
| Component | Function | When Required |
|---|---|---|
| Pin-point gate bushing | Creates the gate orifice and flow path | Always — the core component |
| Pin gate extension bushing | Extends gate reach for thick plate stacks | When plate stack > max bushing length |
| EDM electrode (gate) | Machines the gate orifice in cavity steel | When gate is in cavity plate, not bushing |
| EDM electrode (SR) | Machines the nozzle touch radius | For sprue bushing processing |
| Runner lock pins | Hold runner during first-stage opening | Always in three-plate molds |
| Runner ejector sets | Eject runner during second-stage opening | Always in three-plate molds |
| Runner change pins | Redirect flow between plates | Complex multi-cavity layouts only |
Extension Bushing Pairing
Pin gate extension bushings bridge the gap when your mold plate stack exceeds the maximum available gate bushing length. Key pairing rules:
- Bore diameter match — Extension bore ID must match the gate bushing runner-side bore diameter within ±0.01 mm
- OD match — Extension OD must match the plate bore diameter (typically h7 slip fit)
- Length calculation — Extension length = total plate stack − gate bushing body length − runner plate bore depth
- Material compatibility — Use the same steel grade as the gate bushing (SKD61, SKD11, or stainless) for thermal expansion matching
Electrode Pairing
Gate processing electrodes are needed when the gate orifice is machined by EDM into the cavity steel (rather than being integral to the gate bushing tip). Selection depends on the gate type:
- Pin-point gate electrode — Thin cylindrical tip matching gate diameter minus EDM overcut. Use copper for standard gates, tungsten copper for sub-1.0 mm or multi-cavity.
- Submarine gate electrode — Tapered conical electrode for tunnel gates below the parting line. Always specify the included taper angle to match your gate design.
- SR processing electrode — Spherical-tip electrode for machining the nozzle touch radius on the sprue bushing.
According to ScienceDirect's EDM engineering reference, electrode overcut (spark gap) varies with EDM energy settings and workpiece material. Always run a test burn on sample steel to establish your machine's actual overcut before processing production molds.
Runner System Pairing
Every three-plate mold with pin-point gates needs a runner handling system. The minimum components per mold are:
- Runner lock pins — 1 per 50–80 mm of runner length. Select tip type based on resin: standard for commodity resins, hard lock for glass-filled or high-shrinkage.
- Runner ejector sets — 1 per 60–100 mm of runner length. Stroke must exceed runner depth + 2 mm.
- Runner change pins — 1 at each point where the runner transfers between plates or changes direction.
According to JIS B 5111 mold component standards, all runner system components should be specified on the mold BOM (bill of materials) with their exact positions and specifications.
Ordering Checklist
When ordering a complete pin-point gating package, specify:
- Gate bushing: body diameter, tip diameter, tip length, material (steel/carbide), transition type (round/angle)
- Extension bushing: body OD, bore ID, length, material
- Electrode: gate type (pin-point/submarine), tip diameter, material (Cu/WCu), quantity per mold
- Runner locks: body diameter, tip type, shaft type (straight/tapered), quantity
- Runner ejectors: body OD, stroke, pin diameter, quantity
- Runner change pins: type (Z-pin/ejector/fixed-side), bore diameter, length, quantity
Frequently Asked Questions
What accessories do I need with a pin-point gate bushing?+
Do I need an extension bushing for every gate bushing?+
Which electrode do I need for pin-point gate processing?+
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