MK5 Extruder: Thermal Riser Temperatures – Operating

Thermal Switches in place
Thermal Switches in place

My Parts Heap disgorged a somewhat larger TO-5 heatsink (a Thermalloy 228B, which they no longer make) with three fins and a collar having enough spring to fit tightly around the Thermal Riser Tube. It was intended for transistors on PCBs with horizontal air flow, but I hoped it would be more effective than the smaller heatsink that comes stock with the TOM.

There’s certainly some air flow through the heatsink at the top of the arches, but I have no way of measuring that. The picture there shows another, much flatter, heatsink that I’d been using to cool the Thermal Riser after I found out how hot it was getting near the top.

This heatsink didn’t get a thermocouple mount epoxied to it and, given my experience with the first set of measurements, I didn’t bother stuffing a thermocouple between the fins.

The Thermal Switch Block now has a 100 °C NC Thermal Switch epoxied to it and, barely visible to the lower right, a 40 °C NO Switch is taped to the Z stage in the corner of the acrylic support base. The switch cable looks like this:

Themal Switches - prepped and mounted
Themal Switches - prepped and mounted

With the meter’s T1 thermocouple bead behind the 40 °C switch and T2 tucked into the Thermal Switch Block, the results look thusly:

Thermal Riser and Z stage Temperature Graph - block top
Thermal Riser and Z stage Temperature Graph - block top

The core went to 220 °C this time, with the ABP at 120 °C, and I started extruding at 20 minutes when the temperature had stabilized. The Switch Block temperature promptly dropped 6 °C as room-temperature filament entered the top of the Thermal Riser Tube at 2 rev/min × 10 cm drive dia × π = 63 mm/min ≈ 1 mm/sec.

The previous test showed that the Thermal Switch Block stabilized at 90 °C and I think this one will be about the same, despite the larger heatsink, although the while-extruding temperature hovers around 70 °C. That’s better than 90 °C, so I’ll keep monitoring it and see how it plays in warmer weather inside a cozy build chamber. Obviously, having the Extruder ram cool filament into the Thermal Core holds the temperature down.

Given those numbers, a 110 to 120 °C NC switch would be better; I’m sure one will eventually appear in my usual surplus sources. With a 30 °C margin and an assumed rise of 7 °C per 25 °C Thermal Core increase, the switch will trip when the Core passes 225 + (4 × 25) = 325 °C. That’s rather toasty, but the alternative seems to be having a switch that kicks out on a hot day.

As expected, the Z stage temperature passed 40 °C at 10 minutes and the (yellow) Low Overtemperature LED blinked on. I wasn’t too surprised at that; the previous test had a cold ABP. I’ll move that switch to the top of the acrylic arch, taped against the base of the Filament Drive frame where it can measure the effect of the Thermal Riser on the plastic base. That picture shows the potential for high temperatures at that spot.

The original data:

Thermal Riser and Z stage Temperatures - block at top
Thermal Riser and Z stage Temperatures - block at top