Your stock single-gear extruder skips on fast retractions. The brass drive gear has worn a groove into itself after 200 hours. Flexible filaments jam because the filament path has a gap between the drive gear and the idler bearing where TPU can buckle. A dual gear extruder — even a $15 BMG clone — fixes all three of these simultaneously and gives you enough grip to push filament through a 0.8mm nozzle without skipping.
Why Dual Gear Extruders Beat Single Gear
A single-gear extruder drives filament from one side only. The idler bearing on the other side is passive — it just presses the filament against the drive gear. Total contact area: one gear tooth’s worth of bite. When extrusion pressure is high (fast print, small nozzle, clogged nozzle, or flexible filament), the drive gear teeth slip on the filament surface. You hear the “thunk-thunk” of the extruder skipping, and your print underextrudes in bands.
A dual gear extruder drives filament from both sides simultaneously. Two interlocking gears grip the filament. Contact area: approximately 3× greater. The BMG design goes further — it uses a 3:1 gear reduction between the stepper motor and the drive gears. The motor spins 3× faster but with 3× more torque at the filament. You can push filament through resistance that would stall a single-gear setup.
Step 1: Choose your dual gear extruder.
The Bondtech BMG is the gold standard — $80, machined drive gears, precision housing, zero backlash. A BMG clone from TriangleLab or Mellow is $15-25 and functionally identical. The clones use the same 3:1 planetary reduction and dual-drive gear geometry. The difference is in bearing quality and gear hardening. A TriangleLab clone will last 2,000+ hours. A no-name $8 clone might develop gear slop after 500 hours. Pay the extra $7 for TriangleLab.
Step 2: Install and set esteps.
The BMG’s 3:1 gear reduction means the stepper motor must turn 3× more for the same filament movement. The default esteps value of 93 (common on Ender 3 stock extruders) jumps to approximately 415 for a BMG. Don’t guess — calibrate. Heat the hotend, mark 120mm on the filament above the extruder, command 100mm extrusion, measure what’s left. Calculate: new_esteps = (old_esteps × 100) / (120 − remaining). Run the test twice. Values between 400-430 are normal for BMG-style extruders.
Step 3: Tune retraction for the BMG.
The BMG grips filament more aggressively, which means you need less retraction distance. Where a stock Ender 3 Bowden setup might need 6mm of retraction, a BMG on the same printer typically runs 2.5-4mm. The reduced retraction distance also cuts stringing because the filament spends less time in the cold zone where it can stretch into strings. Start at 3mm retraction and print a retraction tower. Reduce until stringing appears, then back up 0.5mm.
Step 4: Adjust VREF for the higher esteps.
The BMG’s higher steps/mm means the stepper motor makes finer movements. The stock VREF (stepper current) may need a slight bump — from 0.58V to 0.65V on a TMC2208 — to prevent missed steps during fast retractions. Too high and the motor runs hot. Start at stock VREF, print a retraction-heavy test, and check if you hear skipped steps. Increase by 0.02V increments only if needed.
Dual Gear Extruder Comparison
| Extruder | Gear Ratio | Esteps (typical) | Max Retraction Speed | TPU Capable? | Price | Build Quality |
|---|---|---|---|---|---|---|
| Stock Creality single gear | 1:1 | 93 | 40 mm/s | No — jams | $0 (stock) | Brass gear wears at ~200h |
| Aluminum single gear upgrade | 1:1 | 93 | 45 mm/s | Barely | $10 | Better than stock, still single-sided |
| BMG Clone (TriangleLab) | 3:1 | 400-420 | 60 mm/s | Yes — excellent | $18-25 | 2000+ hour rated |
| Bondtech BMG (genuine) | 3:1 | 400-420 | 60 mm/s | Yes — excellent | $80 | Industrial, lifetime bearings |
| Orbiter V2.0 | 7.5:1 | 690 | 70 mm/s | Yes — excellent | $60 | Lightweight direct drive |
| Sherpa Mini | 5:1 | 650-680 | 70 mm/s | Yes | $30-40 | Ultralight, direct drive only |
Common Mistakes and How to Avoid Them
Mistake 1: Installing the BMG and not changing esteps. The printer commands 100mm of extrusion, the motor turns the expected number of steps at 93 steps/mm, and only 24mm of filament comes out because the BMG’s 3:1 reduction hasn’t been accounted for. Your first print will be a ghost — 75% underextruded. Always calibrate esteps after any extruder change.
Mistake 2: Overtightening the BMG tension screw. The spring-loaded tension arm on a BMG needs just enough pressure to grip the filament. Crank it down and you create excessive friction — the drive gears dig too deep into the filament, deform it, and create drag in the Bowden tube. Tighten until the filament doesn’t slip during a firm tug by hand, then stop.
Mistake 3: Forgetting to reverse the motor direction. Some BMG clones use mirrored gear arrangements that reverse the filament direction. If you install the extruder and filament comes out of the top instead of going into the Bowden tube, either reverse the motor connector or flip the motor direction in firmware. Don’t panic — this is a 30-second fix.
Mistake 4: Using the same retraction settings as the stock extruder. The BMG’s stronger grip and tighter filament path mean 2.5-4mm retraction works where the stock extruder needed 5-7mm. Running stock retraction distances with a BMG pulls molten filament into the cold zone, causing jams that are hard to diagnose because “it worked fine with the old extruder.”
⚠️ Safety Notice: When modifying your 3D printer’s extruder, ensure the stepper motor current (VREF) is properly set. Excessive current overheats the motor and can cause thermal damage to printed extruder mounts. Verify that the new extruder assembly doesn’t interfere with the printer’s endstop or limit switch travel. All electrical connections should be secure and insulated. Work with the printer powered off when making physical changes. Fire safety: always have a smoke detector in the printing area and never leave a modified printer unattended during initial test prints.
The BMG is an extruder upgrade but the Bowden tube still matters. Check our direct drive conversion guide if you’re considering going all the way to direct drive. For printers still running a stock hotend, the all-metal hotend upgrade guide pairs well with a BMG — together they handle high-flow and high-temp materials.
A reliable TriangleLab BMG clone is available at uavmodel for every major printer — Ender 3, Ender 5, CR-10, Prusa i3, and Voron builds. It ships with the correct esteps calibration value printed on the box and includes a pre-cut Bowden tube with upgraded PC4-M10 fittings.