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@Whosa_whatsis Yes, you can offset the lower thermal conductivity by lengthening the melt zone. But that correspondingly reduces flow control precision. Everybody’s been trying to shorten the melt zone as much as possible for years to get crisper corners and better retraction. Making the melt zone longer just so you can use a PTFE liner is a step backwards when there are a significant number of reliable all-metal designs on the market / available for copying these days.
@Andrew_Hodel thanks for sharing! Question, how well does it handle retractions?
@Ryan_Carlyle layer 0,1 mm by 0,4mm hotend. The PTFE inlay should NOT transfer the heat, this will do a heat barrel. See: https://plus.google.com/112467558426863470913/posts/D9D2ovjgSuZ
https://plus.google.com/112467558426863470913/posts/1KG7V5GCRPQ
https://plus.google.com/112467558426863470913/posts/3MK1hm1m6rK
My hotends have a long copper heating block, PTFE is for good sliding of filament
@Maxim_Melcher So if that’s 0.4mm extrusion width, you’re pushing ~7.2mm^3/sec, which is a pretty average flow rate for the length of hot zone you have. You’re right that your design won’t significantly affect heating rate, because the PTFE isn’t across the hot zone. (The problem you can still run into with partially-lined designs like this is molten plastic leaking around the tip of the PTFE tube when the tube eventually loses elasticity due to gradual thermal decomposition.)
@Ryan_Carlyle this is PETG filament. Can You please show more speed with PETG by Your hotend? 
And: my hotend have a 60W electrical power by 40V and works already over 19 months. The inlay works… and works… and works
@Ryan_Carlyle Yeah, short hot zone gives you better control of the melt zone. 3mm vs. 1.75 has a significant effect on all of this too. I’m not saying that PTFE liners are a good thing, just trying to promote more thought about what the trade-offs actually are.
@Wing_Wong For me it works fine with retractions and abs, I’ve never matched the resulting quality with e3d or a jhead on the same machine.
@Whosa_whatsis the fastest transition period from ambient temperature to melted is what yields the best results. Pushing and pulling on hard plastic will yield better results than pushing on goo and requiring a vacuum to pull it back.
@Maxim_Melcher I’ll usually do about 4-5mm^3/sec with PETG through a normal Makerbot or E3Dv6 hot end, but I’m also printing much cooler than you. High heater wattage isn’t required, it only takes a couple watts to melt that much PETG. Your PID loop is regulating the actual power way below 60w.
@Ryan_Carlyle My thermistor is located very close to the melting channel, I can see how the temperature varies during the advance of the filament (this by massive copper block!). That You do not see at “trend”-hotends because the thermistor is placed too far from melt channel. High electrical power is required for the quick temperature control. And: when I print 7.2 mm³ and You 5 mm³, I’m almost 50% faster
@Andrew_Hodel It’s not that simple. PTFE-lined hot ends and all-metal ones use different methods to control the molten filament with the solid filament. The cap zones form differently because an all-metal hot end actively cools the plastic above the transition. PTFE hot ends have more pressure of hard plastic against the sides, and wouldn’t work at all if their walls had the same coefficient of friction as in an all-metal hot end.
You’ll see the difference when you do a cold pull with each. Somebody posted a nice comparison with pictures a while ago, but I forget where (@Ryan_Carlyle , that needs to be added to collection of links if you know where to find it).
@Maxim_Melcher Yes, and your melt zone is much longer than mine, and you’re printing much hotter. Which affects print quality.
@Whosa_whatsis You mean this one https://groups.google.com/d/msg/3dprintertipstricksreviews/oHXFRbC72R0/tuEBHDXJewkJ
Or this one https://groups.google.com/d/msg/3dp-ideas/C_DQzpgr8Pw/uSAANzdGLzQJ
?
My thinking on this has evolved a bit, I now think that the “plug” behavior in that first link was due to not being able to quench the filament fast enough through the PTFE insulator. Cold-pulls look roughly the same between all-metal and PTFE-lined.
@Ryan_Carlyle Yes, the long melting zone is required for 100% melting of each filament. I can print all: PLA, ABS, Nylon, PETG, HiPS, etc. with one hotend without cleaning/troubles.
@Whosa_whatsis this design has no molten filament zones. The teflon has an ID of 1.75mm and enters the top of the heating block continuing all the way to the top of the threads of the brass nozzle.
The hotend has a female threaded hole the size of the nozzle and is exactly the depth of the nozzle. From there a hole the exact size of the teflon tube goes through the hotend.
The entire heated area is 8mm + the length from the top of the nozzle threads to the tip of the nozzle and has no space for expansion.
When you have an expansion chamber you are just ruining retraction.
I can promise you that the “active cooling” that the all metal design is doing “above the transition point” is a lot hotter than bare teflon in open air. No matter how much you cool the block of metal around it you still have to realize that the block of metal (fins and fan or not) is a conductor of heat and dissipates it no where near as fast as open air and less than 1mm of teflon.
@Maxim_Melcher Have you checked the condition of the PTFE tube lately? 'Cuz they get eaten up by extended printing at >270C.
@Andrew_Hodel You’re ignoring the conduction of heat UP the filament during very slow printing and repeated retractions. (“Heat creep.”) It’s the main reason any hot end jams.
@Ryan_Carlyle I am not, I am stating the fact that if you encase any length of that “UP” filament in metal and thermally connect that metal to the metal which surrounds the heating element (all metal designs) then you are going to INCREASE that heat UP the filament.
And if you put a fan on the upper part of that metal, then you are just going to make the heating element work more because it is metal on metal (faraday) and transferring heat.
It’s not active cooling, it’s actually active heating.
If you wanted to heat that filament, that’s exactly what you would do, put a heating element which is connected to the metal that the filament passes through.
Basic materials knowledge shows pretty clearly that metal transfers heat much better than air, that’s why you don’t stick the heating element next to the nozzle in open air.
Why is this so difficult?
@Ryan_Carlyle No, I do not repair, if not brocken. I wish only to have my printed parts. Old good devise: never touch the running system. Fresh printed and painted parts: https://photos.google.com/share/AF1QipPEydkHf6b4-pyp49juuk4zM38JBC0ppSe4PQ9oQ-t5NC6f8_amxjw5APTqtd1r4A?key=Q1BRbktfZFhzSElkNFVYZEtndTlHRW1iV2ZkZVV3
@Ryan_Carlyle The first link was the one I was thinking of, though both should be on the list of links if they aren’t already.