Extruders and Hotends

Preamble

Are you confused as to which extruder and hotend combination to get? So was I.

Do you want to spend as little money as possible, and are thinking about getting a cheap Chinese extruder from eBay for $20? So did I.

However, you could be wasting your money. It is advisable that, should you skimp on every other part of your 3D printer, you should, definitely, not skimp on the extruder, as this is the business end of the whole machine. Failure to get the right extruder will result in bad prints, clogged extruders and endless frustration.

The featured image, above, comes from Maintaining 3D printers.

A most informative article is A Comprehensive Introduction to 3D Printing Technology, which, extensively, covers extruders, dual extruders, retraction, and hotends (as well as Printbeds and Filament).

What is the difference between a hotend and an extruder?

The 3D printing head can be divided into two parts:

  • Hotend – this is the part that melts the 3D printing filament, and puts the molten drops on to the print base. This has three parts:
    • Nozzle;
    • Heater cartridge, and;
    • Heating barrel.
  • Extruder – this is the mechanical part that pushes the 3D filament through to the hotend.

Which type of extruder?

From Best 3D printer extruder, there are two main types of extruder:

The Direct type has the extruder and the hotend mounted as one unit, with the stepper motor directly connected, and feeding the filament, to the hotend.

The Geared type is similar to the Direct, but uses printed gears to push the filament to the hotend. Common on DIY printers.

The Bowden extruder separates the extruder and the hotend, so that the print end becomes lighter and more agile, with the heavier extruder, containing the stepper motor is mounted apart, on the frame. the two are connected via a PTFE conduit.

This thread on RepRap forums, Bowden vs Direct Feed Extruder? has some real world examples. The lighter print head of a Bowden extruder reduces artifacts in the resulting prints, removing the ghosting effect left from the heavy carriage of a direct extruder oscillating. However, for softer filaments, a direct extruder may be preferable. Bowden can exhibit greater hysterisis, and have retraction speed issues – longer retracts and faster travel speeds may be required. The Bowden feed tube may add friction, as well.

If the frame is rigid/solid/heavy enough then the weight of a direct extruder should not be an issue (although this may be contended by some).

Both types of extruder can have issues though:

The direct drive does have shadowing and rippling in it. The bowden has a problem that when you suddenly change speeds … for example go from 70 mm/s infill layer to a 40mm/s solid layer you will see a little extra flow of filament causing bands to appear in the prints… The direct drive doesnot have this issue… I have the exact same hot end on both the printers and have printed with the same filament…

There is a third option, the Flex3Drive:

Flex3Drive, which is a direct drive extruder, but driven with a flexible driveshaft whereby the motor is mounted off carriage. Flex3Drive gives the benefits of low moving mass, improved speeds without compromising quality, whilst retaining a direct drive extrusion method.

The same thread also makes mention of 12 mm lead screws with Nema 23 steppers.

Which hotend?

There is a good comparison of hotends on the RepRap wiki, Hotend comparison.

There are a number of factors to consider:

  • Voltage – 12 V or 24 V – neither is better, but requires compatible components;
  • Filament size – your hotend has to match either a 1.75 mm or 3 mm filament;
  • Nozzle size – 0.35 mm to 0.5 mm (0.4 mm is a happy medium);
  • Temperature:
    • All metal – higher temperature, works with all filament material types, but requires active cooling, with a fan;
    • PTFE lined – limited to PLA and ABS filaments.

Extruder Recommendations

To choose from:

  • Flexion Extruder Retrofit Kit

Hotend Recommendations

PTFE lined

Pros

  • Cheaper
  • Quieter (no dedicated cooling fan)
  • Typically faster due to larger melting area
  • Easy to change nozzles

Cons

  • Hard to find, older design
  • Limited to PLA and ABS only, some models can go a little hotter but this is rare

All metal

To choose from:

  • Lulzbot Hexagon Hot End with TAZ Single Extruder body
  • e3D v6 – can be used with Direct or Bowden extruders (any J-head compatible extruder body)
Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s