Needle Hotend for nonplanar printing

Question

To minimize retractions and travel when printing several objects, some slicers produce gcode for sequential deposition when each object is built in a traditional manner bottom up layer by layer before starting a new object. Of course, there are limitations caused by the hotend geometry :

So bulky hotends don't allow for this trick to be used wen sequential pieces are closer than several centimeters. If there where hotends with minimal end effector geometry (needle like, much like drill bit on CNC) we might even do things like spiralizing contours of a single object. This has also potential for other tricks like producing interlacing layers for better layer bonding etc. I wasn't able to find any ongoing work on minimal geometry hotends. Any links? And what might be the challenges in making one? heatblocks and heating cartridges are out of the question but nichrome wire and a fast PID heat controller might do the job.

Answer 1

The site is not well-suited to crowd-sourced invention, but the drawbacks to your suggestion are (I think) on topic.

The hotend has two main tasks. Accurate control of extrusion, and maintaining the desired volumetric melt rate. One factor which influences extrusion quality is the size of the melt-zone - generally, you want this to be as small as possible because rigid filament is easier to extrude/retract without ooze/stringing. Equally, the melt zone needs to be provided with a thermal mass (physical or virtual) to stabilize its temperature under extrusion.

Whilst it might be feasible to prototype your concept quite easily, it is likely to be expensive in volume - and there is no great direct advantage. So this is a concept which might enable an area of research but it doesn't look like a development objective with its own intrinsic value.

Answer 2

A conventional hot end needs only to be obstruction-free to the desired printing height on two adjacent sides to achieve what you want. The only other requirement is to be able to tell your slicer in what order you want your models to be printed.

For example, if your hot end is free of obstructions on the front and left sides, all that you need to do is lay out your models in a rectilinear grid, and tell your slicer to process them front-to-back, and left-to-right.

I have thought of doing this myself. By mounting my E3D V6 hot end as low as I can on its carrier, I should be able to print models up to 50mm in height, and only spaced 20mm apart. I may have to forego part-cooling, but I mainly print PETG without part-cooling, so no problems there.

Answer 3

Yes, using a needle to extrude will result in a smaller diameter extrusion. All that is needed is to find a one with a suitable bore size. The problem however is in generating enough hydraulic pressure, needed to extrude hot plastic through a nozzle of that size. If you can form an extruder that can, then go for it. The second problem is that the thin wall of such a nozzle won't have the same "ironing" effect that current nozzles have. From the picture referenced below you can see the nozzle hole and then a ring of metal around it. That ring flattens the filament out into the desired layer which helps with layer adhesion. With out it, the filament might not even stick to the previous layer, or the bed.