Your stock extruder skips on retractions, grinds filament on long prints, and produces inconsistent extrusion widths that show up as vertical banding in the final print. The single drive gear with an idler bearing was fine for PLA at 40mm/s, but the moment you push PETG faster or try flexible filament, it fails. A dual-gear extruder replaces that single drive gear with two meshed gears that grip filament from both sides. Here’s how to pick one, install it, and recalibrate everything that changes.
Why Dual-Gear Matters
A single-gear extruder pushes filament with one toothed drive gear and a smooth idler bearing. The idler provides pressure but zero grip — all the push comes from one side. When back-pressure increases (partial clogs, fast retractions, high-flow hotends), the drive gear tears a chunk out of the filament and slips. That’s the clicking sound you hear when a print fails at hour 3 of 6.
A dual-gear extruder meshes two toothed gears together. Filament passes between them and gets pushed from both sides with equal force. The grip surface area doubles, which means:
– Zero filament slip at retraction speeds up to 60mm/s
– Consistent extrusion with flexible filaments (TPU actually works now)
– No grinding on long prints with abrasive filaments
– More consistent E-steps that don’t drift over time
BMG vs BMG Clone vs Other Dual-Gear Options
The Bondtech BMG is the reference design. Original BMGs use hardened steel drive gears, a 3:1 gear reduction, and tight-tolerance housings. They cost $80-100. BMG clones use the same geometry with cheaper gears and looser housings. They cost $15-25. For most users, a decent BMG clone (Trianglelab, Mellow, or FYSETC) performs identically to the original — the gear reduction ratio is the same, and the 3D-printed housing tolerances don’t affect extruder function.
Other dual-gear options: the Creality metal extruder upgrade ($15, single gear in a metal housing — just a more durable single-gear, not a true dual-gear), the E3D Hemera ($120, integrated hotend+extruder — overkill unless you’re running a volcano hotend at 100mm/s), and the Orbiter v2 ($60, lightweight direct-drive dual-gear — best for speed-focused printers but harder to mount).
Step-by-Step BMG Clone Installation and Calibration
Step 1: Disassemble and remove the stock extruder. Unload filament. Remove the extruder motor from the bracket. Remove the stock extruder assembly from the motor shaft — this usually means loosening the grub screw on the drive gear. Take photos of the wiring before disconnecting anything. The motor direction matters — you’ll need to know which pair of wires to flip if the extruder direction reverses.
Step 2: Install the BMG extruder. Mount the BMG to the motor using the included bracket. The drive gear goes onto the motor shaft — tighten the grub screw against the flat side of the shaft. If your motor shaft is round (no flat), file a small flat spot or use threadlocker on the grub screw. A spinning drive gear on the motor shaft means zero extrusion.
Step 3: Connect the filament path. The BMG has a specific filament path — in through the top, between the two drive gears, out through the bottom to the hotend. Push filament through by hand before powering on to verify it feeds smoothly. If it binds, check that the PTFE tube is fully seated and the hotend is hot.
Step 4: Calibrate E-steps. This is the most important step. The BMG’s 3:1 gear reduction means the motor has to spin 3 times further to push the same amount of filament. Stock E-steps (usually ~93 for Creality printers) will be way off. Expected BMG E-steps: 400-420 for a standard NEMA 17 motor with 1.8° step angle and 1/16 microstepping.
E-step calibration procedure:
1. Heat the hotend to printing temperature (200°C for PLA)
2. Mark the filament 120mm above the extruder entry
3. Command the printer to extrude 100mm: G1 E100 F100
4. Measure the remaining distance from the mark to the extruder entry
5. Calculate new E-steps: New = Old × (100 / (120 - remaining))
6. Example: you marked at 120mm, 33mm remains after extruding. Actual extrusion = 87mm. New E-steps = 93 × (100/87) = 107 (stock single gear). For BMG, starting E-steps should be around 415.
Step 5: Tune retraction. The BMG’s aggressive grip means you need less retraction distance. Stock retraction (6.5mm at 25mm/s on a Bowden setup) is too much — the dual-gear grip rips the filament so hard it creates air pockets in the melt zone. Start at 3.5mm distance, 35mm/s speed for Bowden setups. For direct-drive BMG: 0.8-1.2mm distance, 35-45mm/s speed.
Step 6: Reverse motor direction if necessary. If the extruder runs backward (pulls filament out when it should push), flip the connector or reverse the direction in firmware. The BMG’s internal gearing reverses the output direction relative to many stock extruders. In Marlin: change INVERT_E0_DIR from false to true (or vice versa). In Klipper: add or remove ! from the dir_pin.
Dual-Gear Extruder Comparison Table
| Extruder | Type | Gear Ratio | E-Steps (est.) | Price | Best For |
|---|---|---|---|---|---|
| Bondtech BMG | Dual-gear | 3:1 | 415 | $80-100 | Reference standard |
| Trianglelab BMG Clone | Dual-gear | 3:1 | 415 | $20-25 | Best value clone |
| Mellow BMG Wind | Dual-gear | 3:1 | 415 | $18-22 | Lightweight clone |
| Creality Metal Extruder | Single-gear | 1:1 (metal housing) | 93 | $12-15 | Durability only, no grip improvement |
| Orbiter v2 | Dual-gear | 7.5:1 planetary | 690 | $55-65 | High-speed direct-drive |
| E3D Hemera | Dual-gear | 3:1 + integrated hotend | 409 | $110-130 | All-in-one, very heavy |
| Sherpa Mini | Dual-gear | 5:1 gearbox | 650 | $25-35 | Ultralight direct-drive |
Common Mistakes & What Most Pilots Get Wrong
Mistake 1: Installing the BMG and forgetting to change E-steps. The print starts, the extruder motor spins, and nothing comes out of the nozzle. Or worse — a tiny amount does come out, so you think it’s working, but the entire print is 70% under-extruded and falls apart when you remove it from the bed.
Consequence: Hours of wasted prints. You re-level the bed, change the nozzle, dry the filament — all because you didn’t update one number in firmware.
Fix: Before the first test print, set E-steps to 415 (BMG default). Then run the calibration procedure. The calculated number will be within ±15 of the default. Save with M500 and verify with M503.
Mistake 2: Keeping stock retraction settings. The BMG grips filament so hard that 6mm retractions pull molten filament up into the cold zone, where it solidifies and creates a partial clog. The print continues for another 30 minutes with random under-extrusion before the clog becomes complete and everything stops.
Consequence: Phantom clogs that clear themselves when you pull the filament and push it back in. You think the hotend is defective and replace it.
Fix: Halve your retraction distance when switching to a dual-gear extruder. 6mm → 3mm. 4mm → 2mm. For direct-drive: 1.5mm → 0.8mm. Run a retraction tower test (Teaching Tech calibration site has a great generator) to find the exact sweet spot.
Mistake 3: Overtightening the BMG tension screw. The BMG has a spring-loaded tension arm with an adjustment screw. You crank it down because “more grip is better.” The filament deforms into an oval shape under the pressure, then jams in the PTFE tube or hotend throat.
Consequence: The filament enters the hotend with an oval cross-section. It binds in the perfectly round heatbreak. Extrusion stops. The extruder clicks. You can’t push filament through by hand either.
Fix: The tension screw should be tightened just enough that the extruder doesn’t slip during a hard pull test. Grab the filament above the extruder and pull firmly while commanding an extrusion — if the motor clicks, tighten ¼ turn. If no clicking, the tension is fine. More is not better.
Mistake 4: Using a BMG clone with the stock Creality V4.2.2 board’s TMC2208 drivers in stealthChop mode. The BMG’s 3:1 gear reduction means the motor spins 3x faster than stock. At high print speeds, the step rate can exceed what stealthChop can handle, causing the driver to drop steps silently. The print shows random under-extrusion that doesn’t repeat at the same layer height.
Consequence: Prints with unpredictable, non-repeating extrusion gaps. You chase hardware issues that don’t exist.
Fix: If your board runs TMC2208 or TMC2209 drivers, switch to spreadCycle mode for the extruder driver. In Marlin: #define STEALTHCHOP_E to //#define STEALTHCHOP_E. In Klipper: stealthchop_threshold: 0. The extruder will be slightly louder but won’t miss steps.
⚠️ Safety Notice — 3D Printer Electrical and Fire Safety: Upgrading your extruder involves modifying motor wiring, current settings, and firmware parameters. Incorrect VREF or motor current settings can cause stepper drivers to overheat or motors to stall, creating a fire hazard. Always verify motor current settings after an extruder upgrade. Ensure all electrical connections are secure and insulated. Use a thermal fuse or fire-resistant enclosure if printing unattended. Verify your printer’s electrical components meet 2026 safety certification standards applicable in your region.
Once your extruder is gripping consistently, the next calibration to dial in is linear advance — it uses that consistent grip to compensate for pressure buildup in the nozzle. We covered the full procedure in the linear advance calibration guide. And if you’re chasing extrusion consistency, our E-step calibration guide walks through the full dimensional accuracy workflow.
A dual-gear extruder that grips reliably is also the key to printing flexible TPU — which means you can start printing your own FPV camera mounts and antenna holders. Pick up a Trianglelab BMG clone and a spool of SainSmart TPU at uavmodel.com and print parts that survive real crashes.