gcode for quieter printing

[Graham]

I wish you were correct about the "poor design" but the facts show otherwise.
To clarify, unless FF has changed the Dreamer (It would be a simple change and there have been several revisions to the core board) the "potential"problem is real and certainly not over thinking. The "theory" is a physical characteristic of thermocouples and cannot be questioned. The voltage generated in the thermocouple wire is almost directly proportional to the difference between the temperature at the thermocouple junction (hot junction) and the temperature at the end of the TC wires (cold junction) or where the TC wires connect to copper wires or traces. For more detail sees:
http://www.acromag.com/sites/default...tters_926A.pdf
In the Dreamer, the thermocouple connections to copper are in the wiring box above the extruders. The cold junction is measured by the TC Amp (Texas Instruments ADS1118) on the core board in the bottom of the printer.
For the TC amp data sheet see: http://www.ti.com/lit/gpn/ads1118

The practical application is, of course, subject to other variables.... especially how the firmware uses the TC data but unless the actual temperature of the cold junction (interface between the thermocouple and the copper wiring is measured), it is not possible to obtain an accurate temperature. I do believe that FF has some kind of fudge factor in their firmware that uses an arbitrary cold junction offset that is higher than that measured by the TC amp located on the core board which has built in cold junction compensation. They could even be using the chamber temperature as measured by the existing thermistor and while I would still consider this a poor design, it would certainly be better than not having any reliable measure of cold junction temperature.

However, I also would agree that if you use the Dreamer within its published recommended temperatures i.e. <=230°C, it is unlikely that you will ever have a problem.

I have done extensive temperature tracking using a second FF thermocouple in the front hole in the extruder and a third monitoring the cold junction temperature in the wiring box above the extruder and the under reporting of the extruder temperature has always <=10°C so no real problem with extruder temperatures set to 235°C or below. The error increased significantly (up to 15°C ) on the rare occasions that I used higher temperatures but I still found no evidence of the potential for thermal runaway. I believe this is because the temperature of the area above the extruder at the location of the actual cold junction does not increase as fast some have theorized due to its location at the top and the fact that the fans will come on when the chamber temperature reaches 50°C. The risk is definitely real, but unlikely within reasonable operating temperature ranges.

It should be noted that I no longer have the top on the Dreamer when printing. Before I was aware of this design issue, I followed the conventional wisdom at the time and closed up the Dreamer for ABS printing. On my first multi hour print, I melted the extruder carriage. It was replaced under warranty, and this is what led me to research this issue.

Graham

p.s BTW the easy field fix is to replace the copper wires that run from the wiring box to the core board with Type K thermocouple wire. http://www.omega.com/search/esearch....ch=gg-k-24s-25