One piece teflon liner for 1.75 mm filament

[wshelley]

Hi guys,

I've been playing with a single piece teflon liner for the stock hot end for the Rostock Max. I've been working at printing PLA and even with a fan and the EZshroud fan mount still have jams. I believe one of the jams resulted in a larger diameter section right near the melt zone where the PLA could expand and jam. I turned a solid piece of teflon on the lathe and installed it yesterday to give it a try. The first attempt used a center bore just under the nominal 2mm on the supplied liner. The PLA continues to jam. I'm using the basic settings Steve suggested 170c, bed at 55c, fairly slow print speeds of about 50mm/sec at .25mm layer thickness.

Here are a couple of pictures.

Overall liner

Relief for easy filament insertion

Nozzle end

Thoughts? Comments? I have plenty of teflon on hand so I can try variations...

[626Pilot]

Funny you should ask. I just did something similar with a Dremel tool five minutes ago. Two suggestions: Try 195C/65C (works like a charm for me) and shorten the narrower part a little. I think ideally it should be as short as possible while still helping the PLA not leak, because if it's too long the PLA won't heat enough.

I think there is probably a sweet spot for how long it should protrude into the nozzle tip, balancing amount of contact (heating) vs. keeping the volume as low as possible to help with retraction.

You might also want to add another PEEK fan. I am using two of them and find it takes much longer to jam.

[wshelley]

Interesting, I'll give that a go. I've been concerned that my PEEK fan is a bit weak so I've ordered a couple of new ones that will hopefully push more air. I'm using the EZshroud so it should use one fan more efficiently. I did most of my PLA testing at around 190 but Steve at SMCNC said the higher temps tended to cause more jams so I was trying his recommendation of 170. If I learn anything useful I'll be sure to post...

Ward

[626Pilot]

I read a few days ago that there are three varieties of PLA, each with different optimal melting temps. I had great luck at 195 degrees with the stock tube... until I didn't anymore. I spent all day yesterday trying different configurations of inner PTFE tube with differing lengths of "snout" sticking into the nozzle end, and temps from 170 to 225. None of it seems to make any difference.

Here's what I think is happening. The "snout" is doing two things - shortening the melt zone, and taking heat that would have gone to the melt zone and conducting it upwards. Theoretically a shorter melt zone is a good thing, but it also reduces the thermal mass, which could make it more prone to temperature swings. Since the "snout" is in direct contact with the nozzle, rather than sort of floating above the melt zone, some heat that would have gone to the melt zone is going into it instead, and rising.

I saw you milled out a cone into the top of the PTFE to make it easier to insert the filament. Maybe you should try milling one into the BOTTOM. It would create a lensing effect that might "encourage" the PLA to flow downwards, especially if it begins to get rubbery. (Think of it like a rocket engine nozzle... just way slower.) There might be a sweet spot where what you lose from the snout intruding into the melt zone is offset by the lensing effect.

You might also try milling the "snout" to be a little narrower, so it doesn't grip the side of the nozzle. That would allow some melted plastic to get up into the gap you create. That plastic would still conduct SOME of the heat from the nozzle to the PTFE tube, but it would also conduct some of it downwards into the melting reservoir. (Probably more than it would conduct to the PTFE since in its liquid state it would be directly interfaced with that plastic.) It could boost retract performance as well by resisting the vacuum created by retraction.

[626Pilot]

After messing around with different ideas for several hours, I've come to the conclusion that just using a PTFE tube long enough to go from the PTF connector to the shelf of the nozzle tip is as good as it's likely to get, unless someone has a degree in fluid dynamics or something. I've wasted loads of time on this, so now you don't have to.

Long story short, I'm printing ABS on kapton and the PLA can just wait until I get my Budaschnozzle mounted. 2 days of work is enough, I think. John from SeeMeCNC says he rarely prints in PLA so I don't think the stock hot-end was designed with it in mind. Even with one or two 10mm fans blowing across the PEEK, it is just far too finnicky to be worth the trouble.

[bvandiepenbos]

Most everything I have read says the J-Head prints PLA well. I do not know from personal experience, I have not printed with PLA yet.
However, I am running a J-Head with ABS and it works great... so much better than the OEM Steves hot-end.