Thing-O-Matic / MK5 Extruder: Insulated Heating

Having found the thermal coefficient between the MK5 Extruder’s resistor and Thermal Core without any insulation wrapped around them, the next step is to do the same thing with insulation. In an ideal situation, the coefficient wouldn’t change: the same power flowing through the same area should produce the same effect. In actual practice, it decreases because the Core receives heat from the resistor that doesn’t pass through the interface.

I used the left-side resistor for this test, as the clip lead dislodged the brass tube atop the other one during the previous test.

I used cotton fabric (harvested from an old sheet in the Rag Box) rather than the delicate ceramic cloth tape normally used with the MK5 head; I figured that plenty of cloth would be at least as good, as long as I didn’t run the temperature up all the way.

A second wrap around the outside pretty much mummified the Thermal Core. Apart from a few small gaps & cracks, the only paths for heat to get out are the Thermal Tube and the four screws. There’s no ABS filament in the extruder head and the cloth covers the nozzle on the bottom.

I didn’t instrument the Core quite so thoroughly, having already established that the metal Core block is pretty much isothermal.

Name	Meter	Location
TOM	MK5 t-couple	Top of core
T1	Fluke 52	Resistor
T2	Fluke 52	Core edge adjacent to resistor
CA	Craftsman A	Bottom of core
CB	Craftsman B	not used
MPJA	MPJA meter	not used

The adjusted data looks like this:

Power	TOM	T1	T2	CA	Time	Current
0	19.5	19.4	19.7	20.0	1634	0.00
1	26.8	29.2	27.7	27.2	1644	0.45
1	31.0	32.6	32.3	31.6	1654	0.45
1	35.3	36.2	35.1	34.4	1704	0.45
1	36.3	37.9	37.0	36.1	1714	0.45
1	37.4	39.1	38.1	37.2	1725	0.45
2	44.7	48.6	46.1	46.6	1735	0.63
2	50.0	52.5	50.3	48.3	1745	0.63
2	52.1	54.9	52.7	51.1	1755	0.63
2	53.2	56.3	54.3	52.2	1805	0.63
4	67.9	74.6	69.7	66.1	1817	0.58
4	76.3	81.9	77.4	73.8	1827	0.58
4	80.6	85.8	81.4	77.7	1837	0.58
4	83.7	88.0	84.0	79.9	1848	0.58
4	84.8	89.7	85.6	81.6	1858	0.58
4	85.8	90.7	86.7	82.7	1908	0.58
6	101.6	109.6	102.8	97.1	1919	1.10
6	109.0	116.3	109.8	103.8	1929	1.10
6	112.2	120.0	113.6	107.7	1939	1.10
6	114.3	121.7	115.6	109.4	1949	1.10
6	115.3	122.7	116.6	110.5	1959	1.10

The temperature differences between interesting points is:

Power	R – Edge	Top – Bot	Edge – Top	Edge – Bot	R – Amb	Edge – Amb
0	-0.3	-0.5	0.3	-0.3	0.0	0.0
1	1.5	-0.4	0.9	0.5	9.8	8.0
1	0.3	-0.6	1.3	0.7	13.2	12.6
1	1.0	0.8	-0.1	0.7	16.8	15.4
1	0.9	0.2	0.7	0.9	18.5	17.3
1	1.0	0.2	0.7	0.9	19.7	18.4
2	2.5	-1.9	1.4	-0.5	29.2	26.4
2	2.3	1.7	0.3	2.0	33.2	30.6
2	2.2	1.0	0.6	1.6	35.5	33.0
2	2.0	1.0	1.2	2.2	36.9	34.6
4	4.9	1.9	1.8	3.6	55.2	50.0
4	4.5	2.5	1.0	3.6	62.5	57.7
4	4.4	2.8	0.9	3.7	66.4	61.7
4	4.1	3.8	0.3	4.1	68.7	64.3
4	4.0	3.2	0.8	4.0	70.3	65.9
4	3.9	3.1	0.9	4.0	71.3	67.0
6	6.8	4.5	1.1	5.6	90.2	83.1
6	6.5	5.2	0.8	6.0	96.9	90.1
6	6.4	4.5	1.5	5.9	100.6	93.9
6	6.2	4.9	1.3	6.2	102.3	95.9
6	6.1	4.9	1.3	6.1	103.3	96.9

And the corresponding thermal coefficients…

	R – Edge	Top – Bot	Edge – Top	Edge – Bot	R – Amb	Edge – Amb
1 W	1.0	0.2	0.7	0.9	19.7	18.4
2 W	1.0	0.5	0.6	1.1	18.5	17.3
4 W	1.0	0.8	0.2	1.0	17.8	16.8
6 W	1.0	0.8	0.2	1.0	17.2	16.1

The R-to-Edge coefficient is down to 1 °C/W, but that still means the resistor temperature is far too high at 30 W dissipation.

The R-to-Ambient and Edge-to-Ambient coefficients are up much less than I expected: the insulation helps, but not a great deal. I think there’s plenty of energy going out the Thermal Tube toward the Filament Drive and Extruder Motor; as the Core insulation gets better, conduction along the Tube becomes a larger fraction of the loss.

One last test looms: what’s the improvement with thermal compound between the resistor and the Core?