Completely eliminate ooze.

Hello Everyone.

I have an idea that I believe will completely eliminate ooze, and also allow for FAR more precise control of extrusion. It is very simple and should be easy to implement on nearly all extruder and hot end designs.

The biggest reason that retraction does not perfectly stop the ooze of material out of the nozzle, is that retraction does not create suction. Air simply is drawn down the feed tube around the edge of the filament, allowing gravity to pull molten material out of the nozzle. The solution is very very simple.

In much the same way as placing your finger over the top of a drinking straw allows you to pick it up out of the glass while keeping fluid in the straw, and air-tight seal at the top of the feed tube should prevent any ooze what-so-ever. In fact, retraction might not be needed to stop extrusion, or rather an extremely small amount of retraction to compensate for the expansion that occurs as the material is heated.

The seal can most probably be implemented with a simple neoprene washer at the top of the support barrel of the hot end. The washer should have a hole of 2.8mm or so. Actually, you could pancake two .2mm washers between two .5mm washers. The .5mm washers would have a much larger hole, say 3.5mm and the thinner washers would have 2.8mm holes. That would provide something akin to a dual O-ring type of seal. The washer would be glued to the top of the support barrel with the holes perfectly lined up with the hole in the feed tube.

This should completely eliminate ooze and also provide for precise control over much slower extrusion, allowing for even thinner layers than is possible currently.

I will be implementing this on my printer this afternoon to test. I'll post complete results along with photos and a youtube video if successful.

I've searched, but haven't found anyone else attempting this approach. It seems like such a simple and obvious idea that I can't imagine that it hasn't been tried. If it works, and is a new idea, can we call it the Loughin hot end mod?

Kevin Loughin

I will definitely give it a try, I was thinking about o-rings, but washer is a pretty good idea too!

Don't bother. I built a two stage neoprene seal yesterday and set it all up. I had a completely airtight seal at the top of the feed tube and verified that I was airtight at the nozzle end.

It made no difference in ooze. Further investigation lead me to discover that the molten plastic is not liquid enough for surface tension to come into play. Therefore, it's much like trying to suspend some honey in a drinking straw by plugging the top end. Without surface tension, the honey just moves aside to let air bubbles past. The same thing happens with the molten plastic. Ooze is the same.

Oh well.

You've said airtight at the top of the feed tube, does this mean that you are using a bowden setup?
If it is the case, it might be possible that there is enough air so that the pressure can vary very much in your airtight zone. I wanted to try adding a o-ring inside the hotend, as close as possible to the melting zone.

Also gases from the melted plastic would cause ooze.

An idea would be to modify nozzle to have a shutoff valve. I've seen somebody do it with an external solenoid and piano wire but the design was leaking a lot.

scouted through some patents and found these: