Blowing air to improve overhange

The pieces I have seen where people have tried to build parts with a long horizontal free span have had lots of dropping lines and loops and other problems. This is a basic limitation of fusion deposition of thermoplastic material.

However, I was originally thinking about greatly slowing the extrusion rate, so that the plastic can cool and harden just after coming out of the nozzle. That would make the strand strong enough to span a long gap. But, it would still tend to come straight down, not come out sideways. We could make a nozzle that extruded sideways, but then it would need to turn back and forth for every strand in one layer, then change to two new directions for the next layer. Rotating the whole extruder would make it heavier, more complicated, and less accurate. Rotating just the nozzle means a complicated gearing system that all works on the hot end, so it must be complicated metal, not plastic.

Some people have suggested blowing air at the nozzle tip to more rapidly cool the strand coming out, and that can help. But it can also blow the strand in the wrong direct. Then I thought, why only one cooling air nozzle? If we place 8 cooling air flow nozzles, and find some way to buy/make 8 tiny solenoid valves, then by selecting which one or two nozzles to blow compressed air out of, we can not only cool the strand rapidly, but help push it in the sideways direction we want. With 8 nozzles, and sending compressed air out one or two adjacent nozzles, we can control the airflow down to 22.5 degree steps. No need for any rotation or large moving parts other than the air flow controlls. The solenoids can even be replaced by a disk with one offset hole that is rotated around to select which nozzle(s) will get air, and this assembly can be all RP plastic parts. A further advantage of using the disk is that mixing air pressure from two nozzles at ratios of other than zero or 100% can allow for even finer control, down to 10 degree steps or less.

It will still be complicated adding 8 more nozzles to the tip of the extruder, but in return for possibly being able to make any hollow or free span shape, it may well be worth the effort.

Mike

Hey Mike,

Glad that you started a topic about this. What about just two nozzles that blow cold air from opposite directions, so that there's not much force put on the hot filament?

That would be fine for normal operation. No valves or solenoids or other controls needed. It simply would not help much for overhangs and horizontal free spans. I think that the simple, two nozzle approach will eliminate the need to extrude slowly, and might help to bridge small gaps, but without bending the strand 90 degrees to come out horizontally without anything under it pushing it up, I think the improvement will be modest. We should be able to go from 60 degrees down to 45 or even 30 degrees from horizontal, and should make internal holes and threaded holes practical, which is a big step.

Mike

I think if you cool it quickly enough, it should work... It's something I'll be testing along with the glass nozzles this or next month. We'll see. =)