Insulating the heater block... more data!

I recently posted on the topic of Insulating the Heater Block and a few days later received some great data (graphs) from Alzibiff, a Mendel90 owner and keen RepRaper. Alan (Alzibiff) was in the process of insulating his J-Head heater block with some silicone tape, as per Nopheads design improvements, when he kindly captured some before & after data. This is great data in many ways. I hope I can do its interpretation justice...

{By the way, Alan is the proud owner of that 'pin-up' of 3D printers, the Black Dibond one with the Christmas Tree, which famously featured on the cover of the Mendel90 build manual for some time!)

The target temperature for all graphs was the same, 220 Deg C. The power resistor in the J-Head v5b, running on 12v, had no difficulty bringing the heater block up to temperature in all tests. The significant observable differences between graphs was in the average % power draw, the blue line along the lower (green) graph in each case. Alan has two fans on his x-carriage, one ducted under-carriage PEEK cooling fan (same as this), which I'll call the "Upper Fan". He has a standard M90 work cooling fan, which I'll call the "Work Fan". The latter fan duct was unmodified, no insulation cooling hole (another of Nopheads mods.)

Small Tech Note: I've checked that the power draw of the fans do not impact on the power graph. It only shows % power draw by the heater.

Figure 1. No (heater block) Insulation, Upper Fan ON, Work Fan OFF. 45% power to maintain temp.

Figure 1

Figure 2. No (heater block) Insulation, Upper Fan ON, Work Fan ON. 55% power to maintain temp. This is interesting because it's suggesting there is extra power needed to maintain temperature when the Work Fan is on. There must be air drift from the downward facing cooling fan that is impacting on the heater block, causing it to draw more power to maintain temperature.

Figure 2

Figure 3. Heater block insulation fitted (Silicone Tape), Upper Fan ON, then Work Fan ON at the '31' mark, so both fans on for the latter half of the graph. 38% power (Upper Fan ON), 48% power (both ON), approximately.The power draw to maintain temperature after the insulation is fitted to the heater block is nicely reduced. The insulation is doing it's job. But, once the Work Fan cuts in the power usage increases again slightly. This suggests that cool air drift from the work fan is cooling the heater block somehow. I expect the heater block would benefit from some insulation on it's base also, to further improve the insulation, but the nozzle probably doesn't protrude enough to permit this with the present j-head design.

Figure 3

Figure 4 is probably the most impressive. It shows the insulated heater block in operation with both fans OFF. To me it's the most impressive because the power draw (green graph) is barely above 25%. It shows that the silicone tape is a very good insulator, and really outperforms my skinny Teflon jacket. I must add that this particular test (Fans off) did unease Alan, and he didn't run it very long as he has had his share of extruder jams in the past.

Figure 4

Quick Conclusions:

The silicone tape is an excellent insulator, and an enhancement worth considering.

Indirect cool air (air drift) from fans has a greater impact on the power required to maintain hot-end temperatures than one might think, due to the cooling effect of such air.

Thanks to Alan for the graphs. Hope folks found it of interest. Questions and comments welcome as always.

Regards,

NumberSix



Installing and PID tuning new J-Head Extruder

I recently received my new J-Head V Extruder Nozzle. Hotends.com are also now selling a 15mm long 30W cartridge, which fits the J-Head nicely. This is good since the fan ducting on the Mendel90 surrounds the heater block, and it wouldn't fit very well, if at all, with a larger heater cartridge. The 15mm cartridge is neater, and the currently popular 20mm 40W cartridges I've seen around. I also like that it draws slightly less power, at 30W, as I'm always concious of the risk of overheating connectors, wires or even some component a controller board.

The bits and pieces came well packaged. It included a heat resistor, but I plan to use the cartridge. It's good to have the heat resistor as a spare. It has a 100K thermistor, and since the last time I ordered, now includes suitably sized PTFE sleeves for insulating the thermistor and resistor wires. All the heater cartridges seem to sell with wires pre-crimped on and very well insulated, which is great.

The cartridge heater was a close fit to the hole in the J-Head brass heater block, and with one or two wraps of tinfoil it pushed snugly into place. (Cartridge wrapped in tinfoil and partially fitted, in photo above.)

I fitted the little PTFE sleeves to the thermistor, soldered some wires on and insulated the joints with heat-shrink. I inserted the thermistor into the hole in the heater-block, and surrounded it with some car exhaust putty. The wires from both the thermistor and heater cartridge where then zip-tied to the barrel (photo below.).

I thought about using car exhaust putty to secure the heater also, but the wiring is quite stiff, and it's a good fit to the block so it doesn't seem to be drifting. The one reservation I have about the cartridge arrangement is the bend in the wires. I was careful not to kink the very stiff wires, and hopefully they will be fine since they are secured well to the peek barrel. We'll see how it goes.

The J-Head Nozzle is secured to the extruder with three M3 bolts, M4 washers and M3 star washers to ensure nothing vibrates loose. This is Nophead's design, an excellent method of securing the nozzle. The M4 washers sit against the shoulder of the groove in the PEEK barrel and lock it firmly into the perfectly sized hole in the base of the extruder. It's not going anywhere!

I left the exhaust putty to dry for a few hours, connected the thermistor and heater into my connector board, plugged in my ribbon cable and gave the block a few hours at 100 Deg C to bed dry out the putty completely.

PID Tuning

A purchased printer kit, such as Nophead's Mendel90 will have pre-established PID values in the firmware, which will have been set for the characteristics of the extruder. The purchased M90 kit ships with a power resistor (at time of posting), but since I've chosen to try out a cartridge heater in the J-Head nozzle I've retuned the Marling firmware PID values using an auto-tuning feature. The auto-tuning is called on using an M303 Gcode command which is manually sent to the controller from the host software. If the command is executed on it's own it sets a target temperature of 150 Deg C, but to calibrate for different target temperatures the S parameter is added, e.g. M303 S230. You may want to obtain separate PID values for different target temperatures (different materials). 

Once the PID tuning has completed its process it will return a set of constants for you to note and enter.

The PID values can be later sent via a Start-Gcode, written to EPROM if supported, or hardcoded to the firmware. For hardcoding, the values are entered in the Configuration.h file, the firmware compiled and downloaded to the controller.

e.g.

// J-Head Mk V with cartridge heater. IOS 20131002

    #define  DEFAULT_Kp 27.95

    #define  DEFAULT_Ki 4.22  

    #define  DEFAULT_Kd 46.25

Repetier Host has a convenient temperature plotting capability which illustrates what's happening as the auto-tuning runs. You will see it tuning (pict below) to a target temperature of 220 Dec C, although I later repeated it to a target temperature of 230 for ABS, and at 185 for PLA, noting the value set for each.. The nozzle should be allowed to cool completely before repeating a calibration.

The graph shows the calibration process in action. The power is first applied fully, then as the target temperature is reached it is cut, then applied in cycles, reducing a little each time. The power is shown as % over time in Green, and Temperature plotted in Red. The concluding values and finishing message is also shown in the picture below.

After writing the new PID values to the firmware I set a target temperature and turned the heater on. The graph below nicely illustrates the rate of heating, climbing quickly on full power to well over 200, then PID Control cuts in within 10 Deg of the target, set in this firmware line "#define PID_FUNCTIONAL_RANGE 10",  and from there you see the temperature curve climbing again but quickly smoothing out to the target temperature. Also visible is how the power delivery settles to modulate at a much reduced level, maintaining the target temperature nicely (green graph below.). The red curve drops down when the heater is turned off.

Finally, for comparison purposes I generated the same graph on my older printer, with it's Gen6 Controller, J-Head IV Extruder and 5.6 ohm power resistor. See picture below.

There are a number of aspects to compare, the rate of temperature rise and time to reach target temperature, the draw on power, the quality of PID control. There are explanations for the difference in each comparision, but one major conclusion... my new set-up is significantly better in all respects and I look forward to printing with it!

As always, thanks for viewing!

NumberSix