A simple test of additional insulation below the Makergear M2’s heated build platform, measuring the time required to heat the platform from 30 °C to 80 °C:
- As-shipped without insulation: 8:20
- Cardboard + cotton cloth: 8:30
- Cardboard + aluminum foil + cotton: 8:00
That’s with a resolution of about 10 seconds and 1 °C. Ambient temperature was 25 °C; I preheated the platform to 30 °C for a repeatable starting point. The heater was full-on for the entire time and I tried to record the time until it first turned off at the setpoint temperature.
So my initial insulation didn’t make any difference; ten seconds (in the wrong direction!) seems down in the noise.
Adding aluminum improved the situation, but not by much.
The platform wasn’t moving, so there’s no air circulation on either surface. I think it will be possible to record / plot the platform heater duty cycle during printing using LinuxCNC’s HAL components, so some useful data should emerge from that.
I think the bottom line is that there’s so much heat transfer up through the glass plate and away that reducing the heat flow from the bottom by a little bit doesn’t matter…
The Smell of Molten Projects in the Morning 
How about temporary insulation on top of the glass?
Nope, that must remain clear for the nozzle. A whole bunch of homing & zooming about happens before the printer starts pooting out filament, so you’d be forced to clear more area than just around the object, then ensure the nozzle stayed away from the obstructions. I have enough trouble not hitting those screws in the corners!
I’ve seen some zoned heaters out in the wild that only heat up an area under the object. That probably works OK, but introduces more power conductors and control complexity than seems justified.
I think we’re on different pages. I’m talking about the initial warm-up PRIOR to printing. A way to reduce the 8 minutes.
Can you maintain 80 C during printing?
What is the max bed temperature you’ve seen on your M2?
Ah, you mean cover the platform while it’s warming, then snatch the tea cozy away before starting. That’s too fiddly for me: I would inevitably start the print with the cover in place…
A man’s gotta know his limits. [sigh]
I’ve only printed PLA at 70 C, but the temperature remains stable; the LED blinketh, even if I haven’t measured the duty cycle, so it’s not running flat out.
Folks on the Makergear Google group report running well over 100 C for ABS. One guy attached a 500 W 240 VAC silicone pad to the glass plate and cranked it to 125 C…
Just throw the whole printer under a bell jab and pump it down to 10e-4 torr or so. :)
And watch that hot plastic foam!
As soon as I get an idea of how long the new desiccant lasts in the safe, I’ll toss that logger in the can of filament stock along with another bag of beads to see if bone-dry plastic works differently than stuff stabilized at 55% RH. Rumor has it dryer is better, but it’s not clear by how much.
Re humidity + filament, just picked up a few of these : http://www.ebay.com.au/itm/20-pcs-6-Dot-Humidity-Indicator-Card-/130938233648?pt=AU_Storage&hash=item1e7c86e330&_uhb=1 . You are correct that dryer filament works better – a higher water content leads to things like excess oozing (as the water converts to steam and creates nozzle pressure) and layer adhesion issues. You don’t want it bone dry… I’m seeing on datasheets of raw pellets recommendations to keep it anywhere from 10% to 15% by weight…
As for heat bed performance – you just can’t beat a quality silicone heat mat! :) I can post the repetier-host temp graph if you want – but I get ambient (15°C at the moment) to 90°C in 4mins 30… 80° is achieved in a mere 3 minutes. I use a QU-BD silicone bed under some borosllicate glass… 200×200 if its of value as a comparison between build plates…
I suppose I can dry out a spool, weigh it, then put it in a bag with just the right amount of water. [grin]
Practically speaking, I have two choices: 50 to 60% RH ambient basement or bone dry in a bucket with desiccant. The former works OK, using my loose criteria for OK, and we’ll see about the latter.
Makergear stuck a 130-ish W silicone heater under the 200×250 mm aluminum plate: somewhat less power driving a larger plate under an air gap. In very round numbers, I think it delivers equivalent performance to your heater. Given that I really like the glass, I should probably just glue a heater to it and eliminate the aluminum plate, but that’s in the nature of fine tuning.
Update: Some doodles on the power density…
The M2’s initial warming is slower than yours, because this heater distributes less power over a larger area:
I’ve been thinking of boosting the voltage a bit to increase the power: 200 W probably wouldn’t burn the thing out, which would be about 13 V at the connector. Assuming the DC SSR drops a volt, that’s 14 V at 15 A, which would be a stock 15 V brick dialed back a few percent. It works well enough to keep that on the, uh, back burner…
Heres the QU-BD Curve:
