Your stock single-gear extruder has one job: grip filament and push it through. After 1000 hours, it does that job poorly — slipping on retractions, grinding soft TPU into dust, and losing steps on fast travel moves. A BMG-style dual-gear extruder solves all three problems with one mechanical upgrade. The trick isn’t the install — it’s the reconfiguration that 90% of guides skip.
BMG-Style Dual Gear Extruder Upgrade: Complete Installation and Configuration
Dual-gear extruders use two interlocking drive gears that grip filament from both sides. Unlike single-gear designs where an idler bearing passively presses filament against one driven gear, dual-gear systems actively drive both sides of the filament. Grip force roughly doubles for the same spring tension. The geared reduction (typically 3:1) means the stepper motor spins 3 times for every 1 rotation of the drive gears — multiplying torque while increasing resolution.
Step 1: Choose Your BMG Extruder
Three tiers of BMG extruders exist:
- Genuine Bondtech BMG: Swiss-made, hardened drive gears, precision-machined housing. $80-100. Tolerances are perfect — install and it just works.
- TriangleLab BMG Clone: The best clone. CNC aluminum housing, decent gears, good tolerances. $25-35. I’ve run these for 3000+ hours without issues. The gears are slightly softer than genuine but still outlast brass single-gear drives 3:1.
- No-name BMG Clone: Injection-molded plastic housing, mystery-metal gears, inconsistent tolerances. $8-15. The gear mesh can be rough, creating inconsistent extrusion. The housing flexes under tension. Fine for experimentation, but expect to replace within 500 hours.
For most users, the TriangleLab clone hits the sweet spot. The genuine Bondtech is worth it for production machines running 24/7 where downtime costs more than the price difference.
Step 2: Physical Installation
The BMG mounts in place of your existing extruder, but with two critical differences:
Motor direction: BMG extruders reverse motor direction. The 3:1 gear reduction inverts rotation — the motor spins clockwise to push filament instead of counterclockwise. If you install without changing direction, the extruder retracts instead of feeding on the first print.
Filament path: BMGs feed from the top and exit from the bottom at a slight angle (the housing is designed for direct-drive mounting where the outlet feeds straight into the hotend). For Bowden setups, use the included Bowden coupler fitting. The PTFE tube must seat flush against the internal guide hole — a 0.5mm gap here creates a filament buckling point that jams on retractions.
Installation steps:
1. Remove old extruder, clean the stepper motor shaft
2. Press the BMG drive gear onto the motor shaft. The set screw must land on the flat of the motor shaft. If your motor shaft has no flat, file one — the gear will spin freely under load otherwise.
3. Mount the BMG housing to the motor using the included screws. Do not overtighten — the plastic housing cracks at the mounting ears above 0.6 Nm.
4. Insert the PTFE tube fully into the Bowden coupler
5. Load filament and verify smooth manual feeding before connecting electronics
Step 3: E-Step Recalculation
BMG extruders need dramatically different E-steps than stock extruders. Stock Creality single-gear extruders typically use 93 steps/mm. A BMG with 3:1 reduction and the standard drive gear circumference requires approximately 415 steps/mm. This is not a small adjustment — if you leave E-steps at 93, the extruder feeds 4.5x too little filament.
Calibration procedure:
1. Heat hotend to printing temperature
2. Mark filament at 120mm from a fixed reference point (the extruder entrance)
3. Send G1 E100 F60 (extrude 100mm at 60mm/min)
4. Measure remaining distance from reference point to mark
5. Calculate: New E-steps = (Current E-steps × 100) ÷ (120 − remaining distance)
6. Store with M92 E<value> then M500
Example: Current E-steps=415, remaining distance=23mm. 120-23=97mm actually extruded. New = (415×100)÷97 = 427.8. Round to nearest whole step: 428.
Run the test twice. The second measurement should show exactly 20mm remaining (100mm extruded). If it doesn’t — if you’re getting 18mm or 22mm — something is slipping. Check gear tension.
Step 4: Retraction and Slicer Adjustment
Dual-gear extruders grip better, which means retraction settings change:
- Retraction distance (Bowden): Drop from 5-6mm to 3-4mm. The better grip means less filament “spring-back” during retraction — the filament moves exactly the commanded distance instead of slipping slightly.
- Retraction speed: Increase from 25-30mm/s to 35-45mm/s. The dual-gear grip handles faster retraction without grinding.
- Retraction extra prime amount: Set to 0. The single-gear used extra prime to compensate for slip during retraction. The BMG doesn’t need it, and adding it causes blobs at layer starts.
- Extruder acceleration: Increase from 500-1000 to 2000-3000 mm/s². The higher torque lets the extruder accelerate faster without losing steps, reducing print time on models with many retractions.
Test print: Print a retraction test tower (available on Printables). Start at 2mm retraction, increase in 0.5mm steps. The BMG should produce clean results at 2.5-3.5mm for Bowden — much lower than the 5-6mm a stock extruder needed.
BMG Extruder Comparison Table
| Extruder Type | Steps/mm | Max Retraction Speed | Filament Grip Force | TPU Performance | Lifespan | Cost |
|---|---|---|---|---|---|---|
| Stock Single-Gear (Creality) | 93 | 25 mm/s | ~3 N | Poor — slips constantly | 1000-2000 hrs | Included |
| BMG Clone (TriangleLab) | 415 | 45 mm/s | ~7 N | Good — prints 95A easily | 3000-5000 hrs | $25-35 |
| Genuine Bondtech BMG | 415 | 50 mm/s | ~8 N | Excellent — handles 85A | 10000+ hrs | $80-100 |
| Orbiter V2 (planetary) | 690 | 60 mm/s | ~6 N | Very good — lightweight | 5000+ hrs | $60-80 |
| BMG Setting | Bowden Value | Direct Drive Value | What Happens If Wrong |
|---|---|---|---|
| E-steps | 415 (baseline) | 415 (baseline) | Severe under/over-extrusion |
| Retraction distance | 2.5-3.5mm | 0.4-0.8mm | Stringing (too low), heat creep (too high) |
| Retraction speed | 35-45 mm/s | 30-40 mm/s | Filament grinding (too high), stringing (too low) |
| Extruder current | 650-800mA | 500-650mA | Motor overheat (too high), skipped steps (too low) |
| Tension screw | Just past flush | Just past flush | Filament deformation (too tight), slip (too loose) |
Common Mistakes & How to Avoid Them
Mistake 1: Forgetting to Reverse Motor Direction. You install the BMG, flash the firmware, hit print, and the extruder runs backwards — retracting when it should feed. Consequence: Filament grinds for 30 seconds while the hotend runs dry, then clogs because the molten plastic at the nozzle tip carbonizes with no fresh material pushing through. Fix: Reverse the extruder direction in firmware (#define INVERT_E0_DIR true in Marlin) or swap two of the four motor wires.
Mistake 2: Tightening the Tension Screw All the Way. Maximum tension seems like the safe choice for better grip. On a BMG, the dual-gear design means overtightening actually crushes the filament from both sides simultaneously — creating an oval cross-section that jams in the PTFE tube. Consequence: Filament feeds fine for the first 10mm, then the deformed section hits the tube constriction and stops. The extruder keeps pushing, grinds a flat spot, and the print fails with an air print. Fix: Tension screw should be just past flush with the housing. Load filament and verify you can see very light tooth marks on the surface, not deep grooves.
Mistake 3: Using Old Slicer Profiles Without Changes. You install the BMG, change E-steps, and keep your old slicer profile. Retraction distance is still at 6mm. The BMG pulls molten filament 6mm up the heat break — into the cold zone where it solidifies and creates a partial clog. Consequence: Under-extrusion gets progressively worse through the print as retractions accumulate. Fix: Halve your retraction distance, increase retraction speed by 30%, zero out extra prime, and print a retraction tower to dial it in.
Mistake 4: Expecting the BMG to Fix a Bad Hotend. The extruder pushes filament — it doesn’t melt it. If your hotend has heat creep or a partial clog, the BMG will grip better and push harder, but it still can’t push solid filament through a restricted hotend. The symptom shifts from “extruder slipping” to “extruder motor skipping steps” — a thunk-thunk-thunk sound. Consequence: You now have a great extruder on a bad hotend, and the skipped steps look exactly like the slip you were trying to fix. Fix: Verify the hotend is flowing freely before attributing extrusion problems to the extruder.
⚠️ Safety Notice: When working with extruder upgrades, disconnect power before handling stepper motor wiring — energized stepper drivers can be damaged by plugging/unplugging motors while powered. Use proper ventilation when printing with any filament type. All electronics should carry appropriate safety certifications (CE, UL, or equivalent) for your region. Verify firmware thermal runaway protection is enabled after any firmware changes.
The BMG upgrade pairs well with a hotend that can keep up. Our all-metal hotend upgrade guide covers the hot-side upgrade, and our E-step calibration article provides the detailed calibration procedure for any extruder swap.
A reliable extruder is the foundation of every successful print — and it’s the same foundation that lets you print TPU camera mounts and PETG frame braces for your FPV builds. The TriangleLab BMG clone delivers Bondtech-level grip at a third of the price. Available at uavmodel.com alongside the Capricorn XS PTFE tubing for a complete filament-path upgrade.