Monday, December 22, 2008
Roast-in-a-bag Duck...
...tape.
The hair dryer works remarkably well as a means of creating a constant warm environment for building with ABS. This prevents both curling and delamination. But it can be a bit hit-or-miss, and is also noisy and uses a silly amount of power (1.4 kW according to its rating plate, or - to put it another way - over 20 times as much as the whole of the rest of the RepRap machine...).
Forrest had a brilliant idea: use an oven roasting bag to enclose the build in a bubble of warm air. So, from a suggestion by Nophead, I built a miniature fan convector (above). It's an old processor heatsink and fan with two 10-ohm pieces of nichrome wire woven in among the heatsink fins. They're in parallel, and at 12v will give about 30 W. As an alternative you could obviously just bolt a fat 4.7-ohm resistor on the back.
Then I phoned Christine and Sally (w. and d.; they were out buying things for some sort of festival that they claim is imminent; I think they're trying to pull the financial wool over my eyes...) and asked them also to buy oven bags. I bolted a sheet of balsa (previously used to build on) just under the extruder mechanics and duck-taped the bag to it and to the build base.
I moved the machine about to make sure there was enough slack to accommodate a build. This was a bit tricky, as too much and folds would have got in the way.
The cream object to the right of the picture is a thermometer. With both the extruder on and the mini fan convector the temperature in the bag stayed pretty constant in the top sixties.
I ran a test build:
Another part of the newest granule extruder. Holding a rule against its base and squinting at the light in any gaps reveals it to be as flat as a pancake in Flatland.
Clearly the bag arrangement could be considerably tidied-up with the addition of some concertina folds and springs and so on. I don't know what polymer they use, but the extrude head (internal temperature 240 oC) came to rest against it several times and didn't cause any damage at all.
A rather good side effect was that the slightly acrid smell of molten ABS was completely enclosed and thus eliminated. Even when I opened the bag at the end no smell emerged, implying that the volatiles had condensed inside.
The hair dryer works remarkably well as a means of creating a constant warm environment for building with ABS. This prevents both curling and delamination. But it can be a bit hit-or-miss, and is also noisy and uses a silly amount of power (1.4 kW according to its rating plate, or - to put it another way - over 20 times as much as the whole of the rest of the RepRap machine...).
Forrest had a brilliant idea: use an oven roasting bag to enclose the build in a bubble of warm air. So, from a suggestion by Nophead, I built a miniature fan convector (above). It's an old processor heatsink and fan with two 10-ohm pieces of nichrome wire woven in among the heatsink fins. They're in parallel, and at 12v will give about 30 W. As an alternative you could obviously just bolt a fat 4.7-ohm resistor on the back.
Then I phoned Christine and Sally (w. and d.; they were out buying things for some sort of festival that they claim is imminent; I think they're trying to pull the financial wool over my eyes...) and asked them also to buy oven bags. I bolted a sheet of balsa (previously used to build on) just under the extruder mechanics and duck-taped the bag to it and to the build base.
I moved the machine about to make sure there was enough slack to accommodate a build. This was a bit tricky, as too much and folds would have got in the way.
The cream object to the right of the picture is a thermometer. With both the extruder on and the mini fan convector the temperature in the bag stayed pretty constant in the top sixties.
I ran a test build:
Another part of the newest granule extruder. Holding a rule against its base and squinting at the light in any gaps reveals it to be as flat as a pancake in Flatland.
Clearly the bag arrangement could be considerably tidied-up with the addition of some concertina folds and springs and so on. I don't know what polymer they use, but the extrude head (internal temperature 240 oC) came to rest against it several times and didn't cause any damage at all.
A rather good side effect was that the slightly acrid smell of molten ABS was completely enclosed and thus eliminated. Even when I opened the bag at the end no smell emerged, implying that the volatiles had condensed inside.
Labels: delamination, heated chamber
