An Interview (of sorts) with E3D’s Nozzle Expert – Mike Sherlock #AskAnExpert

An Interview (of sorts) with E3D’s Nozzle Expert – Mike Sherlock #AskAnExpert

 With more than 10 years of experience making E3D HotEnds & Extruders, we have gained a wonderful wealth of knowledge at E3D. We'd love to share this with the wider community, in a sense returning to a simpler RepRap mindset. 

Mike Sherlock is a Senior Design Engineer and our certified nozzle expert here at E3D! Recently, we invited our community to pick Mike’s brain about all things nozzles and received a tremendous response with many questions asked – far too many to include in one blog. So without further ado, here are a selection of our favourites from the questions posed to Mike: 


Who are you and what does your role at E3D entail? 

My name is Mike Sherlock and I’m a Senior Design Engineer at E3D. Although working across a few different projects, a large amount of my focus is spent working on nozzles and the future of nozzle technology at E3D, which I suppose makes me the designated nozzle expert. 

Outside of work I'm a huge NFL fan (go Bills!), I love heavy metal music and have a multitude of nerdy interests including tabletop wargaming, comic books and sci-fi but please don't let that put you off! 


What is the best way to DIY a good nozzle? 

Start with an M6 brass bolt, drill a 2mm hole from the threaded end and then machine the orifice hole with as small a drill bit as you can find from the other. That's how E3D started! 



Why is brass the mainstream material for nozzles?  

Brass is a great balance of material cost, machinability and thermal properties. 


Have you ever tried an aluminium nozzle? 

Yes, but we found that molten plastic really loves to stick to them. 


What challenges have there been in designing/manufacturing a tungsten carbide nozzle, and if you're not, why not? 

It is expensive to machine precise geometry in tungsten carbide. While moulding is also possible, this makes it difficult to maintain the tolerances needed to ensure E3D’s level of component quality and reliability. We’ve chosen to direct our R&D focus elsewhere… 


What difference does the thermal conductivity of a nozzle material make on printing performance? 

Thermal conductivity quantifies a material’s ability to conduct heat, which gives you an indication of how well a nozzle will transfer the heat from the heater block to the filament. When you set your printer to a temperature, this is controlled based on the reading at the temperature sensor, not the temperature in the nozzle. If you change nozzle material (and alter the thermal conductivity) you impact the heat transfer to the filament flowing through the nozzle. As a result, for a given temperature reading at your sensor and consistent filament extrusion speed, the temperature of the filament exiting the nozzle will be different. 

This is why a PLA print that comes out with a glossy finish when using a brass nozzle might appear more matte when printed using a different nozzle. This is also why some users increase the print temperature when they change to different nozzles. Increasing the temperature of the heater block to compensate for the reduced thermal performance of the nozzle can result in the correct temperature in the filament. 

Another relevant property is thermal diffusivity, which is a combination of thermal conductivity, density and specific heat capacity.  


What's the reason for a 2mm bore inside a 1.75mm HotEnd?  

Originally this hole was made at 2mm because that’s the drill size that the team had access to. However, through testing we’ve found that the extra clearance allows the system to be forgiving of variations in filament diameter/straightness when being pushed through the system. 


Which specific drills are used for the 2mm hole, and what's the point angle? 

When E3D started the 2mm hole was machined with a standard 118° point drill as this is what they access to. As the company grew they were able to justify custom form drills to create more optimised geometry for flow. As you can see here, the point angle is now 60°. 



How does the length of the 0.4 diameter part of the nozzle impact print quality?  

A shorter orifice length generates less backpressure and as such allows for greater precision from your extruder. However, if it's too short then the filament flow isn't appropriately controlled and it exits the nozzle orifice erratically.  


In your technical drawings the length of the orifice seems to be different for each nozzle size (e.g. 0.8 mm nozzle orifice length is 1.6mm and for the 0.25 mm nozzle it is 0.38 mm). Does this have to do with the limitations of machining or are they derived to achieve less ooze? How would extrusion be affected by changing the angle that leads to the orifice? On a V6 nozzle this angle is 60° what happens if the angle is more narrow or wide?  

The different orifice lengths are the result of testing in R&D to balance backpressure and flow straightening in each case. More adventurous internal geometries are an area of active research. 


Is there a difference in how well smaller and larger nozzles handle retraction? 

Yes. Larger orifice holes contain more plastic, meaning a longer retraction distance is required to clear the material and prevent ooze.  


What are the issues with going smaller than a 0.25mm nozzle? Any luck with your 0.15mm nozzle? 

Besides being much more difficult to machine, small orifice holes also generate very high backpressure. The short orifice length needed to control the backpressure on small-diameter nozzles means the 2mm drill extends quite far into the cone. The 0.15mm nozzle actually has a different cone geometry specifically to prevent the 2mm drill from breaking through. 


Give me the charts of nozzle material, material printed, and wear over time or amount of material printed. Wear designated in microns of enlargement of the nozzle orifice. 

I can’t give you that data, but it wouldn’t give you the true picture anyway. Although printing abrasive materials may enlarge the orifice diameter, the primary wear-case for nozzles is actually recession of the tip flat.  


What makes one nozzle better than another? 

The king of nozzles would be accurately manufactured with precise geometry. It would have superb wear resistance to allow users to print abrasive materials while also having excellent thermal properties to efficiently transfer heat to the filament. The nozzle would also be resistant to polymers adhering to it during printing, minimising print artifacts and the potential for them to cause failed prints. You’d also be able to clean your nozzle without the risk of negatively impacting any of the listed features. Sounds great doesn’t it?…   



What is the primary reason for having the nozzle "not quite touching" the heater block before hot tightening? I know that it's for making a proper seal between the heat break and nozzle, but wouldn't a seal between the nozzle and block be perfectly fine as well?  

Hot tightening the nozzle to the heat break ensures a good seal along the filament path. If you were to tighten the nozzle to the block then there likely wouldn’t be an appropriate seal at the interface between the heat break and the nozzle. Extrusion pressure can then force melted filament through this gap and out of the top of the heater block. This can create oozing, lead to jams and generally makes a real mess. 


What makes your nozzles better than the usual selection off Amazon where you can get 10 of them for $1? I'm aware that the machining is better, but I don't understand how simply machining a nozzle better reduces clogs.  

E3D parts are made to our exacting standards and are checked by our excellent quality control processes. Our nozzles also come with access to our fantastic aftersales support team. 

When buying third-party nozzles you’re accepting parts that haven’t been manufactured and verified in this same way. We’ve seen all sorts of issues in parts like you describe, including but not limited to: 

  • Completely blocked nozzles where swarf hasn’t been removed. 
  • Holes being machined the wrong size.  
  • Orifice holes being very poorly aligned with the tip flat. 
  • Burrs where the orifice hole breaks out into the tip flat. 
  • Lower quality material grades. 
  • Poor internal surface texture leading to increased extrusion force requirements and less reliable retractions. 


Have you ever considered using high frequency accelerometers to determine the instantaneous pressure and temperature of the flow inside a nozzle?  

Not accelerometers but you can do some very interesting things with laser interferometers (and sharks). 


What is your favourite nozzle for CF-Nylon when printing functional parts? 

Nozzle X, for now… 



Y’all REALLY love that optical inspection device.  

Yes we do, it’s a fantastic bit of kit and really good at checking the roundness of holes, something I can’t do with my phone camera. 


How do you inspect the machining quality inside nozzles? 

We’ve found the winning combination to be an enthusiastic member of the QC team and a shrink ray.  


Any closing thoughts? 

Thank you to the community for submitting so many excellent questions. Hopefully this post is worth the wait and be sure to say hi if you ever see me at an event!  


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