Here some remarks I made in the facebook group. Certainly easier to find it back here...
Extruding is physics and has to follow its rules ...
Speed and nozzle and heater and heater block and type of plastic : it all influences each other.
I made the following simulation for melting PLA.
I took the following properties :
density 1,3g/cm3 (between 1,2 and 1,4 depending on origin)
specific heat : 1.800J/kgK
The specific heat varies from 1.200 to 2.200 depending on were you are in your heating path.
Plastics behave different than 'normal' liquids that have a linear behaviour when increasing temperature in a phase and have nice fixed temperature when they change phase (solid/liquid/gas)
So just for having a demo model let's assume it's 1800J/kgK
I used nozzles from 0,4 to 1,2mm and for each one the maximum commonly used width(120%) and height (80%).
The table shows the power you would need to melt it. for different speeds (30, 60 and 90mm/s)
for a cube of 50x50x50 your extruder would need to melt 125.000 mm3 of plastic independent of the nozzle size.
Another issue is that the hotend doesn't produce the heat IN the plastic but in a heater that heats a block of metal.
The heat from the heater has to travel from the heater to the plastic through several barriers : heater-Aluminium block-plastic.
The path through the aluminium block is not an ideal path. It varies from short next to the heater to long at the opposite sides
There are also important heat losses through radiation (you can feel the heat whith your finger even when not touching ) and convection (cold air is heated and flows away), during the movement of the block and also by 'undesired' cooling with the part cooler. I assumed an efficiency of 60%.
If the melting chamber is in parallel with the heater and if the heater is fully in the aluminium block, as with the volcano, the hotend becomes more efficient. Also the melting chamber is longer, has a larger surface with the block and a better heat transition to the plastic.
This also means that insulating the hotend is actually a good idea.
Just have a look at the images I included and take your conclusions about nozzle size, speed, layer thickness and heater capacity... It shows that with a large nozzle, lower speeds and sufficient heatercapacity, you actually get your result faster in your hands
Additional there are several heat losses : the hot end block has a hot surface and radiates heat away as well looses heat through convection, air flows through movement and part cooler fan.
When looking at normal hot end, one also has a path the heat has to follow from the heater to the melting chamber. This resistance of the path to transport the heat (read : transported quantity of usefull heat per time unit) is depending on several factors : the amount of material between source and target, kind of material (mostly aluminium), the length of the path, the the orientation heater/melting chamber to each other, the material used, the section to travel ... see graphs below :
Example 1 : E3D V6
Example 2 : E3D Volcano
When put together in another graph, one can see the trade-off between speed and detail ...
So now you know why I use a Volcano ...