Extruder system
Bondtech BMG extruder: gear ratio, E-steps and drive gears
Bondtech's BMG: advertised 3:1 but 50:17 in Klipper, 415 E-steps at 16 microsteps, heat-treated drive gear, and what Bondtech found in one clone.
Also listed as BMG
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Short answer
Bondtech says the BMG uses a 3:1 gear reduction, and lists 415 E-steps at 1.8° steps and 16 microsteps (double it for a 0.9° motor or 32 microsteps). Klipper's documentation notes the BMG's actual gearing is 50:17, which is what you enter as gear_ratio. Bondtech says its primary drive gear is heat-treated and nickel-coated.
Key facts
- Type
- Geared extruder[1]Bondtech's FAQ covers the BMG and BMG-based extruders.
- Filament size
- Not confirmedBondtech's troubleshooting guide gives a 2.0 mm filament channel for its 1.75 mm extruders and 3.5 mm for 2.85/3.0 mm extruders, without naming BMG variants.
- Gear ratio
- Advertised 3:1; Klipper says the actual gearing is 50:17[1][2]Enter 50:17 as gear_ratio in Klipper.
- Published E-steps
- 415 at 1.8° steps and 16 microsteps; double for a 0.9° motor or 32 microsteps[1]Bondtech's FAQ table. Other Bondtech extruders have their own values.
- Drive gears
- Heat-treated, nickel-coated primary drive gear (Bondtech)[3]Bondtech reports that one clone it examined had gears that were not hardened. That is one unit, examined by an interested party; it is not a finding about all clones.
- Max temperature
- Not confirmedThe temperature limit belongs to the hotend paired with the extruder.
- Nozzle standard
- Not confirmed
- Nozzle change
- Not confirmed
- Heater
- Not confirmed
- Printers the maker names
- Not confirmedBondtech's FAQ calls its extruders 'open use units', which is not a list of supported printers.
- Maker flow figure
- Not confirmed
- Outside measurement
- CNC Kitchen, 2020: Prusa MK3S (E3D V6 with Bondtech gears), PLA at 215 °C: about 3% under-extrusion at 9 mm³/s; audible skipping from 15 mm³/s[4]One setup, measuring the MK3S extruder with Bondtech gears, not a BMG unit. It shows under-extrusion can start before skipping.
- Where the maker sells
- Bondtech lists authorized resellers in the US and Canada and ships worldwide directly from Sweden[5]Bondtech's page names no Amazon or AliExpress store. Reseller lists change, and its delivery times are not a promise.
- Not confirmed
- Not confirmedBondtech's FAQ gives no BMG printer list.
Watch out for
- Klipper uses 50:17 for the BMG, not the advertised 3:1. Copying '3:1' into gear_ratio gives the wrong extrusion.
- Bondtech's 415 E-steps assumes a 1.8° motor at 16 microsteps; double it for a 0.9° motor or 32 microsteps, then calibrate on your printer.
- Bondtech's 1.75 mm extruders have a 2.0 mm filament channel, so oversized sections of filament can jam and be ground by the gears.
- Annex Engineering's BMG-vs-LGX force figures are a calculation from motor curves, not a measurement. Do not rank extruders by them.
What fits
Product details below are the seller's own description unless a source is shown. Pick the variant named for each item.
BMG extruder
Bondtech BMG extruder, 1.75 mm (standard)Choose the standard (right-hand) BMG for 1.75 mm filament; the Mirrored version is a separate listing.
Bondtech sells the BMG without a motor, for 1.75 mm filament only, with a 3:1 gear reduction and a groove-mount hotend retention for E3D V6-style hotends.
Questions
What gear ratio do I enter for a BMG in Klipper?
Klipper's documentation says the BMG is advertised as 3:1 but actually uses 50:17 gearing, which is entered as gear_ratio. See E-steps and rotation distance.[2]
What are the BMG E-steps?
Bondtech lists 415 E-steps at 1.8° steps and 16 microsteps, and says to double it for a 0.9° motor or 32 microsteps. Calibrate on your printer after fitting it.[1]
Are BMG clone gears hardened?
Bondtech says its own primary drive gear is heat-treated and nickel-coated, and reports that one clone it examined had gears that were not hardened. That is one unit, examined by Bondtech.[3]