Theory to reduce oozing

[soofle616]

Before I pursue this line of thinking I'm curious if anyone else already has and what the results were. Weeks ago I pulled one of the nozzles of my creator pro because it kept scraping ever so slightly on my prints and causing problems with certain geometries. In doing so I realized what should have always been obvious, the ptfe liner is cut off square but the hole in the feed side of the nozzle is tapered due to the shape of the drill that was used to bore it. The result is that as the filament is pushed into the nozzle, there is an area where it is no longer guided by the liner but not yet being extruded. Plastic has to fill this area up before it will consistently exit the nozzle. During printing that doesn't seem like it would be a problem but when the carriage is moving without printing (or when the other nozzle is being used) that leaves a reservoir of molten plastic that can ooze out and ruin prints. Retraction only helps so much because you're never going to pull out that molten reservoir of material (as evidenced by the need to purge when changing filaments). So my thought is that if the shape of the liner and the interior of the nozzle were more closely matched, that reservoir could be eliminated or at least reduced resulting in less plastic sitting around waiting to drip out.

So then it seems there are two options to look into
1) bevel the end of the liner to match the angle in the nozzle, this would allow the liner to seat further down in the nozzle. Cheapest and easiest option to test but would be a pain in the ass to do regularly without some sort of bevelling fixture
2) bore the nozzles with an end mill or similar to remove the drill point chamfer. More expensive up front because it requires a new nozzle to be custom made but it means that future liner replacements need only be cut off square as is the current practice.

Thoughts or experiences?

[soofle616]

Bueller???

[Davo]

Soofle616,

I haven't seen this problem with our equipment, but your theory seems sound.

Our nozzles are brass, with the appropriate extrusion diameter all the way down to the lowest point of the nozzle. There is no cavity in which material can accumulate.

-Davo

[soofle616]

It's not the extrusion diameter that I'm referring to but the diameter for the ptfe liner (perhaps your nozzles don't use a liner?)

[Davo]

No, no liner inside our nozzles.

Our nozzles are brass, with the appropriate extrusion diameter all the way down to the lowest point of the nozzle.

[ole_blue_moon]

I have had the same problem with oozing or dripping from the idle extruder, mostly the one with PLA in a 2 extruder setup. My first preference was to use PLA for raft and support, and ABS for object. Printing the raft in PLA is no problem and gives good adhesion from both the bed to raft and from raft to object. Once the object starts to print on top of the raft two problems arose, first the idle extruder is not receiving heating power so cools down...then when needed printer has to pause and heat extruder. Takes way to long to print while waiting for each extruder to reheat. Second problem is the PLA oozes and creates whiskers in the object which pretty much ruin it. My solution is to use PLA for raft and ABS for both object and support. Works quite well most of the time, just have to break away the support with needle nose pliers. The main thing lost is the ability to dissolve the PLA support in a ultrasonic tank.

My thought was it would take a way to close off the idle extruder with some type of closing iris but this is probably too complicated and expensive for the current market. Your idea of less volume to pool melted material at the end of the head sounds like a good one. If some extruders now have no ptfe tube at all as person responded that would appear better also.

I'm about to replace my second generation Rapman printer with a replacement. It still works mainly because almost 100% of the parts I remade in aluminum by hand so it would quit falling apart. Leaning towards Flashforge Dreamer.

Ole_blue

[richardphat]

If you mean that PTFE that guide the filament to the brass, then you need to change it frequently.
They wear out and become loose and plastic will leak at that point. I bought 6 feet PTFE tube and cut them with the dremel to replace them when I feel it needs to be changed.

[3DPBuser]

Removing the reservoir would not reduce ooze, because retraction creates a vacuum inside regardless of reservoir or not, correct ?

[soofle616]

Removing the reservoir would not reduce ooze, because retraction creates a vacuum inside regardless of reservoir or not, correct ?

Why would it create a vacuum? The other end of the nozzle is open to atmosphere and would draw in air to fill the void where the filament was.

[Mjolinor]

Why would it create a vacuum? The other end of the nozzle is open to atmosphere and would draw in air to fill the void where the filament was.

It creates a reduction in pressure.