Nophead's Extruder Tweaks

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The extruder design has moved on, getting ever more complicated, but I have stuck with the original version with a lot of minor tweaks to make it reliable. It gives good results with ABS, PCL, PLA and HDPE and has higher throughput than any of the geared designs.

NopsExtruder.JPG

Starting from the top :-

Shaft encoder

Using a shaft encoder gives the following advantages: -

  • Ensures a constant filament feed, independent of friction and temperature.
  • Allows the speed to be reduced without stalling, but also does not reduce the top speed as gears do.
  • Requires no trial and error calibration of feed rate as it can be calculated from screw pitch, etc.

Details of my optical implementation here. Zach's magnetic version available from the [rrrf.org RRRF] here.

Interference suppressor

DC motors give off a lot of RF interference which can corrupt comms, crash nearby micros and affect radio and TV reception. I designed a small suppressor circuit which solves the problem. Details here and here. An RRRF version is under devlopment details here.

GM3 Gearmotor

  • This must be the the 12V version. The 5V motor has very thin brushes that quickly wear away.
  • The clutch may need locking for touch plastics like PLA and HDPE. See Zach's instructions.
  • I have found that the output shaft sometimes starts slipping (even without the clutch being locked). This can be fixed by gluing it with a two part cynoacrylate superglue that states it is suitable for polyethylene and polypropylene.
  • Running in the motor by connecting to a low voltage supply for a few hours will allow the brushes to wear in before having to handle high currents. This reduces arching, producing less RFI and prolongs the life of the brushes.
  • Adrian Bowyer recommends lubricating the gearbox with silicone grease.

Direct drive

The flexible drive has limited life due to metal fatigue and is not required for any plastics tried so far. The direct drive motor holder for the older design extruder is hard to dig out of SVN so I have posted it here: Media:Old-motor-holder.stl

Old-motor-holder.jpg

Pump

  • The poly holder channel needs to be low friction, particularly for PLA. HDPE is ideal for this as it can be RepRapped and is is almost as slippery as PTFE.

TBC