Really weird hollow cold pulls. What am I doing wrong.
I would add a photo but it's hard to get one of the issue. So basically Im trying to do a cold pull using some nylon. I heat it up and it loads fine but when I go to do the cold pull the end of the filament looks like a hollow tube. I've done it now 3 times in a row and all the same. Hollow at the end for about 12mm or so and perfectly symmetrical.
I suspect some old filament is stuck in the hotend but how could it be perfectly symmetrical making a hollow tube?
RE: Really weird hollow cold pulls. What am I doing wrong.
I've never heard of doing a cold pull with Nylon. Usually PLA or special cleaning filament.
Having said that, I've indeed seen one case (with my other printer, Ultimaker) where multiple cold pulls would not remove all of the scorched filament residue in the barrel of the nozzle. It still had the characteristic weak flow to one side even after needling and cold pulls.
I ended up disassembling the snap-in hot end and chasing out the nozzle barrel from the top with a drill bit. There was a lot of scorched residue in there that the cleaning filament would not grab well enough to pull out.
RE: Really weird hollow cold pulls. What am I doing wrong.
Well, how about that I haven't heard of cleaning filament. Any recommendations?
RE: Really weird hollow cold pulls. What am I doing wrong.
Here's what I use:
https://www.amazon.com/eSUN-Cleaning-Filament-Extruders-Clogging/dp/B08RSCP95X/ref=sr_1_1
There are other brands as well.
Some use it for cold pulls, some just run it through the extruder to clean it, some do both.
how could it be perfectly symmetrical making a hollow tube?
If your filament has a low viscosity when melted it's possible for a loaded filament to dribble out of the nozzle, running preferentially from the centre and remaining coating the sides as it cools. This is the reason that a short, extra, pre-printing extrusion is made after a manual colour change; to refill the nozzle and repressurise the hot end.
Nylon is a little odd when cold pulled. It is possible to pull a nylon monofilament from almost any shaped path. It is used in cold castings to make convoluted channels ... when tensioned nylon stretches and narrows so pulling away from the sides, losing adhesive friction and passing the stress along the filament which repeats the deformation and eventually frees the whole thread.
Cheerio,
RE: Really weird hollow cold pulls. What am I doing wrong.
This makes a lot of sense. Thanks for the reply.
I ordered some of the cleaning filament and hope it works.
Thanks, everyone.