The temps on the bed have a large gradient from the center to the outside of the bed. The thermocouple that I have kapton taped an inch or so from the edge reads 65C while the center of the bed reads 100C. I've checked independently with a IR temperature gun, and it's showing me the same thing. The edges are staying way cooler than the center. This has caused some issues where the far side of a print will start to curl a little and the center will stay (while doing ABS at least). This issue is somewhat understandable as the aluminum is very thin and because of that, acts like a heatsink in the open air; the edges dump their heat quickly while the center is trying hard to keep things warm. I need something with a better heat transferrance and capacity.
I had previously purchased a larger heater mat cause I intended to buy one of the Mendel-Parts.com beds, since they're made from almost 5mm thick aluminum. That'd have some serious heat transfer abilities.
Unfortunately, it's kind of pricy to get that shipped from europe here, especially with such a commodity material as metal. So I started looking around for places to get the bed from, as it's simply a 9"x9" sheet with some holes drilled in it. The little notch is optional for me as it isn't there for clearance, just as a hole for the extruder to dump test extrusions into.
However, I got to thinking. If aluminum is good, then copper must be better! It has almost twice the thermal conductivity of aluminum (Copper: ~ 385 W/m K, Aluminum: ~ 204.3 W/m K) and I can get it relatively easily (though not cheaply). I went to OnlineMetals.com and purchased a 9" x 9" x 0.125" sheet of copper. It's nice because they will cut the sheet to your specs for you, and it can make things cheaper as well! It was about $70, so to bump things up to the $100 mark (where you get a discount) I added a couple pieces that my friend would need for his RepRap on there, as well as a version of the bed in 5mm thick aluminum, just in case the copper didn't work out.The items came in today, and wow! The copper really is heavy. I hope that the steppers can drive this thing around. The Aluminum bed is also quite large.
I can't wait to get the new heater glued in so I can see how well the copper plate reacts to the temps, and if the temp gradient is the same.
http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html
ReplyDeletehttp://www.coolmagnetman.com/magconda.htm
According to the sources above: copper is only 1.6 times more conductive than AL but it is 3.3 times heavier. So you are better off with thicker AL. For the same conductivity it will be lighter, warm up faster and much cheaper.
Oops! That was a mistake on my part there. Shoulda been almost double. Fixed it and put in the thermal conductivities according to the Wikipedia page https://secure.wikimedia.org/wikipedia/en/wiki/List_of_thermal_conductivities
ReplyDeletePLA usually sticks to Kapton better than ABS. You're not running it at ABS temperatures, are you? PLA won't stick to a bed that's too hot, but it should stick well to Kapton from room temperature up to about half of the recommended bed temperature for ABS.
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