Thermodynamics and filament retraction.

I think you might be misunderstanding the purpose of the retract function in the slicer. The purpose is to remove pressure on the hotend so you won't get strings when the hotend moves from one end point to a start point on another part of the model.

If you are looking for a way to clear the plastic from the extruder then you are looking for what is called the cold pull or atomic pull as some call it method and that has to be cone manually and will vary from roll to roll.

The issue in your request is that the properties of every spool is different so there is no set curve that you are looking for. Even spools from the same manufacturer and same lot will still have variations due to the mixing of the pellets and colorant during extrusion. I find the most consistent properties come from natural filament with no colors but even that varies due to impurities and even air that might get trapped.

Ok so what happens if the logic craps mid print and your script never runs? For your request just add the retraction move to the end gcode before the hotend is turned off. Look up gcode commands and just use that command with the desired length.

Well I tried heating up the hot end, inserted some filament, tried to roll back the extruder

All I get is an echo message saying

Cold Extrusion Prevented.

Ok, lets bash this out in stages, see if it can be ironed out a bit...

G28 ; home all axis

Park the extruder

M140 S0 ; turn off hotbed

Turn off the hotbed, its not needed anymore

M106 S255 ; set fan to full

Switch fan on to full as we are cooling down to the temperature being set from 250degC

M109 S160 R170 ; set hotend temperature 160 - 170.
M116 ; wait for temperature

Set and wait for the cooler temperature

G1 E-5 F300 ; retract 5mm of filament
M107 ; turn fan off

retract filament 5mm and turn off the fan. Fan indicate job done

M84 ; after that turns motors off

to me, that makes a logical order to do things with, remember its END CODE here and cooling down to an optimal temperature (which no one has yet said what the temperature is and I can't find anything other than people quoting the ideals for extrusion)

Ideas, I am open to them...
M300 doesn't make a beep, so I haven't bothered and not that I want anything beeping at me in anycase...

The reason you find no temperature specced is that there is none. It varies by as much as 50 degrees +/- per roll/machine and it also depends on how much heat is in the core of your hotend versus the read temperature. Notice in hotend design the thermistor is not reading the exact core temp but a temp a few mm from the core and even a few more mm from the heater. That could be as much as 20 degrees different. This is why when people attempt the Atomic or cold pull it takes multiple attempts till they get it at the right temp.

In the world of 3d printing there are no exact or set temps as each machine varies due to their PID settings, hotend configuration, accuracy of the thermistor and it's location, quality of filament used, and many other variables that cannot be controlled. Even the temp that the printer is setting in will effect the actual temp of the hotend.

If you mean to change the cold extrusion prevention setting then that requires a firmware edit in Arduino then a recompile and reflash. The reason for the limit is for safety that you don't damage your extruder while trying to push or PULL cold filament.

As for your peev with programming, gcode is as old as the first CNC based machines as that is what it was written for. It was actually ported to 3d printers since they are essentially a CNC machine as well. So gcode programming is older than Windows.

You should have a copy of your firmware saved. If you don't then that is a bad on you as there is a chance it can get corrupted and you need a safe copy. IF you have then copy then all you need to do is open it in Arduino then open the configuration. h tab.

Once you get that tab open find the line that looks like this.

//this prevents dangerous Extruder moves, i.e. if the temperature is under the limit
//can be software-disabled for whatever purposes by
#define PREVENT_DANGEROUS_EXTRUDE
//if PREVENT_DANGEROUS_EXTRUDE is on, you can still disable (uncomment) very long bits of extrusion separately.
#define PREVENT_LENGTHY_EXTRUDE

#define EXTRUDE_MINTEMP 170
#define EXTRUDE_MAXLENGTH (X_MAX_LENGTH+Y_MAX_LENGTH) //prevent extrusion of very large distances.

The line a made bold is the one you will need to change to temp lower than what you will need. Or you can just comment it out by placing // in front of it instead of the #. Once you edit it, save it as a different copy from your safe backup. Then compile it and upload it to the printer.

Again I think you have this entire 3D printer market confused. 3D printing is a hobby and as such we are used to editing code and making changes to the machines to do what we want then to do. Heck some of us even write custom codes to make it do things others may not need.

The point is, it is not a consumer market like some advertise it as. It is not plug and play and it does require some work/skill/know how on the owner/operators part. You will need to change firmware, you will need to make mods to your machine, you will always be making updates and mods to make your machine better and to perform as you want. That is the fun part and what makes it a hobby. It will consume time and it take away part of your life. If you are not prepared for this then maybe look at another hobby.

I don't know anything about your hotend, but with my E3D's I simply release the tension lever on my extruder and pull out the filament manually either to change colors or just reload a spool. I have done it at full heat every time and have no issues pulling out or reinserting...and to Heartless' point above, I never had the need to pull the filament every time a print is finished; just let it all cool down and next time it fires up and extrudes just fine.

But keep trying different things until you are happy with it...that is part of the fun...AND BE SAFE!

Sounds to me your "PROBLEM" is self imposed. For one you are allowing your printer to run while you sleep or are away. That is a big nono. Your printer should never run unattended. Another issue is that you are wanting to change a standard. Many of us in fact most of us have all had to tear down a hotend to soak or burn out over heated filament many time till we learned how to prevent it or find the cause of it happening. This IS a standard practice. Again you seem to think this is a consumer market and as such you are imposing consumer level rules and expectations.

This is a HOBBY market. We make our printers the way we want. That being said, it is YOUR printer so edit the firmware, mod it, to do what YOU want and become a potential safety hazard as well. But don't expect others to do it for you or to take on your modifications that suit YOU. What YOU want may not fit or be right for OTHERS.

What you want violates a safety feature that was built into the firmware to safeguard those who might forget to heat the hotend and then try to advance or retract the filament.

The nannying as you call it is only unwanted by you. It has been this way since the firmware was ported to 3d printers from CNC and no one till you have voiced an issue. If they had an issue then they quietly modded their firmware to perform the way they wanted and life went one. Most of us only print when we can keep an eye on the printer if by some chance we do have to print a long print that will require running while sleeping or being away then we build or buy a fire proof box to house the printer in the event that things go wrong. We do not leave our machines running unwatched in a living area unless we have taken safeguards in the event of a failure that could happen at some point.

If your logic is crashing or your endcode is set up wrong and the hotend is not turning off then rather than band-aid the problem by modding firmware, fix the actual problem. Find out why your logic is crashing. Could be a bad power supply or faulty logic board. That is not normal. Find out why your hotend is not shutting off when the print ends, that is not normal.

Maybe be creative and add a motion sensor to the system that will shut power to the hotend off if it sees no motion within the print area say for 30 minutes. The function you want to add is not there for a reason because no one till YOU has found issue with it. Again instead of complaining about a function you want, just create it and move on. If tearing down a hotend in a HOBBY machine is too much trouble for you then make the changes for YOU that suit YOU or consider another HOBBY. This is NOT A CONSUMER market, these are NOT CONSUMER MACHINES, and YOU are expected to make the changes needed to make the machine perform as YOU want it.

1. I never operate or leave the printer running unattended.
2. The printer is in a cupboard that is sealed with a fire-proof door
3. Because of the location being some 30 ft from my desk and has to be controlled remotely I don't get to hear when the print has finished.

SO...

A simple retract feature to stop the hot end plugging up so I can remove the filament when I do discover that the printer has finished, it is hard to tell how long a print takes because NONE and I really do mean that NONE of the slicers used to date has given a real or close time to finish, I started a print one night at 8pm and it didn't finish until 4am when the slicer reported it to be a 3hr 57min print.

So the reality is this, the filament NEEDS to be retracted WHEN the temerature of the hot end has been cooled enough to stop the filament deforming or getting stuck when its pulled out the hot end, thats the problem here, the last several manual retactions has ended up with the filament getting jammed in the motor despite releasing it properly.

So this is a very much needed feature.

BTW...

Before the printer was fullt built, there was a glitch that allowed me to move the filament, it does not damage the hot end if a command is issued to move the extruder motor, I know, I have done it and all it does is chew in to the filament and clog the drive so that the teeth have no grip. If the command was issued to extrude several feet and no protection was in place, then yes, I can imagine that the stepper wouldn't be too happy and it is possible that the driver may burn out. NOTHING serious can happen in that regard and I wonder if this is yet another urban myth like I see on the sites I moderate for programmers, favourite of the moment is SEO and boy, have people produces some myths about what you have to do to get your site ranked number one in Google...

So you have to excuse me if I am a bit sceptical and keep poking around for information, its hard enough when you have several sites on the same subject all contradicting each other. Like a puzzle it will be solved.

as for contempt claim... Sorry, not me, it feels like there is reluctance to part with information to assis in this, I will look in to flashing the board with my mods in as I have to add mesh levelling to the printer.

Then I plan to take the printer apart and put the good bits in to a frame I designed and eventually I plan on installing my own interpreter, been fleshing one out as an idea the past couple of days. A more logical approach I believe, looking at Marlin GCode it can be improved on.

Oh and I found a standard for AMF additive processes AKA FFF as in Fused Filament Fabrication, so I wonder who coined FDM...  Anyway, there are standards and I will find them.

Nope, sorry - the actual reality is that your hotend is the problem.

In a properly assembled hotend, there is a straight path from the inlet to the nozzle, there is nowhere for the filament to go other than down and out of the nozzle, or be pulled back out the top

But an improperly assembled nozzle potentially has gaps between the parts, which would allow soft/melted plastic to expand into them, thus causing the problem you are experiencing - the filament getting stuck.

So again.. there is NO need to do what you are trying to do.
The problem is in the hotend itself, and the RIGHT way to fix it, is either disassemble and reassemble correctly, or replace it with one that IS assembled correctly.

As for slicer times being incorrect, yeah, that is a common issue since every printer has different print speeds, acceleration speeds, jerk settings, etc.. slicing programs can not typically take every possibility into account when calculating print times - the times are estimates based on ideal conditions for the print speed chosen.

However - with that said - I, personally, use Repetier Host to run my printers, and Slic3r for slicing, and I have successfully adjusted my time estimates to be within a couple of minutes either way on 98% of my prints.

the other 2% are typically within 10-15 minutes of the estimated time (very long prints tend to be further off)