09 - All Metal hot end (12/26/14)

Post date: Dec 27, 2014 1:30:49 AM

One reality of 3D printing is that hot ends jam. Some reasons I have seen this occur are:

• • Heat levels rise too far up from the transition zone into the cold zone and the filament hardens

  • The design of the hot end allows for expansion of parts

  • The first layer is too close to the print surface causing too much back pressure

  • The flow rate is too high for the design to handle it (this would often be because the attempted print speed is too high), this also results in too much back pressure, the size of the melt zone is one big factor in how fast you can push/melt plastic through the hot-end

  • A particle of debris gets trapped and doesn't disintegrate from the heat as it is pushed through the melt zone

It's a combination of the first four reasons above I see most common with my printer.

Here is an example of a jam and it's result

Jams happen rarely, and are easy enough to repair, in the above case the inner PTFE sleeve was replaced, it was reassembled and printing commenced once again. Though the jams are rare enough, they can happen deep into a multi-hour print. This can be very frustrating because of wasted time and plastic.

The hot end pictured above is featured in most of my blog posts up to this point. It is a low-cost ($10 unassembled! $20 assembled), simple J-head design and is very reliable. The 0.40 mm nozzle being the most so. After using it for quite a few months now, I have come to the opinion that it shares weaknesses of many similar designs, primarily that of PTFE expansion and stretching when heated, therefore too much back pressure causing bulges that will eventually jam or burst. I have had some success mitigating the problem by putting a 1/2" spring clamp around the outer PTFE rod and mounting a cooling fan to blow across the heat sink and PTFE rod. This did not eliminate the problem however and I started looking at employing a new design even if it was higher cost, so the research began.

One starting point for doing such research is the reprap wiki hot end comparison page.

Since in my mind the failures I've experience came down to the PTFE expansion, I considered using a design that has PEEK but decided in the end that I wanted to get away from the plastic all together. I eventually compiled the following criteria as my highest priority hot-end attributes:

• All Metal (use of PTFE has pretty much been the cause of all failures I've seen)

• Serviceable (some have heater and thermistor permanently mounted)

• Multiple/exchangeable nozzle hole sizes

• Supports 1.75 mm direct feed (don't care about Bowden)

• Groove mount (or an easy way to adapt to my extruder)

Given these attributes I then narrowed the choices down to :

• E3D-V6 - met all criteria except still uses an inner PTFE sleeve for 1.75 mm filament but it's a very thick walled sleeve and is only in the cold zone

• Prometheus - adjustable cold, transition and melt zones, but only available in one nozzle diameter (.4 mm)

• Budaschnozzle - just seemed like too many parts making it more difficult to service

• Trinity Labs Metal Magma - lack of info and couln't determine if there was a 1.75 mm version

• Pico - just wasn't sure about the mounting and couldn't find much in the way of reviews/users.

Ultimately I ordered the E3D-V6 since it met most of the criteria, plus they have a good track record with the V5. They have good online assembly instructions so after assembly, I designed and printed an adapter that would allow me to insert the new hot end into my keyed mounting system. This caused me to lose about 30mm of print height but it's very rare that I need much height.

I did experience one jam and it was due to turning on the attached fan late into the heat-up (they recommend tying the fan to constant 12v while I just wired it to the fan control on the RAMPS board). The jam was very easy to fix and nothing was broken or needed replacing. The attached fan is noisy but once the motor whine is moving the axes, it isn't as noticeable.

I recommend this hot-end.