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I understand the principle of why a heater block is used. Helping to reduce temperature variation as the filament is extruded using the heat capacity of the block.

But I’m wondering why it takes the form it does? I imagine it is cuboid in shape just for convenience as it’s easy to machine?

From a surface area to volume ratio a cuboid appears to be one of the worst shapes to use.

Note: I am currently doing a project which requires me to increase the tool clearance of the nozzle of a 3D printer. Hence why I am exploring alternative print head configurations and heater block design trying to minimise the profile of the print head as much as possible.

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    $\begingroup$ A heater block's primary function is to transfer heat from the heating element to the parts after the heat break where the filament is melted. Heating elements could be custom-made to incorporate some sort of melting chamber, but it is cheaper to use common off-the-shelf ("COTS") cylindrical heaters and fit them into an adapter. I could be wrong. $\endgroup$
    – Andrew Morton
    Nov 10 '19 at 17:06
  • $\begingroup$ I had wrongly assumed the cuboid geometry had originated from the reprap project, interestingly enough they used a cylindrical heater block. $\endgroup$
    – FEA42
    Nov 10 '19 at 17:20
  • $\begingroup$ If you could find two heating elements which are thinner, you might be able to place them either side of the nozzle to get a thinner profile. $\endgroup$
    – Andrew Morton
    Nov 10 '19 at 17:37
  • $\begingroup$ @AndrewMorton You forget the screws to mount the heater element. There are reasons to mount several heating elements, but that is to achieve faster heating, not a smaller form factor. $\endgroup$
    – Trish
    Nov 10 '19 at 18:32
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A heater block has its shape designed simply by the necessity of the needs and the ease to manufacture them. Functionally, a heater block serves as:

  • a structural component holding the following components in a well-known position to one another:
    • heatbreak
    • nozzle
    • heater cartridge
    • thermosensor
  • a transmission medium of heat energy from the heater cartridge to the thermosensor and filament path.
    • this dictates the use of high thermal conductive metals
  • a thermal energy storage to equalize the heating pattern of the heater cartridge.

While this dictates the internal geometry of the block, it does not say anything about the external geometry. This is chosen entirely because of manufacturing, which strongly prefers square items in a vise with stop positions to allow repeatable machining.

While other heater designs are existant, for example wrapping a heater wire around the meltzone, the use of a machined structural element that houses bought components saves a lot of time in assembly Quality Control and subsequent repairs, as each component (heater, thermosensor, block) can be rejected or replaced on its own. This makes the machine all in all more serviceable.

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No the heater block does not need to be cuboid.

Maxiwatt hotend (from http://hot-end.com/)

This heater block from Maxiwatt is mostly cylindrical. My self and another college use them on our machines and I can say from experience that they heat up faster.

In the early days of 3D printing people were even making their own "heat blocks"

In the video link, the person is describing how to wrap nichrome wire around a brass wood insert to create a heat block.

The reason for it being square: It's easy to hold and thus cheap to make.

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    $\begingroup$ Note that these heater blocks use an integrated heater or are the heater and have to be replaced as a whole component. $\endgroup$
    – Trish
    Nov 11 '19 at 12:00

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