It happened while both myself and my wife were at work so the machine finished the build. When I came home the room stank of fumes.
The bed temperature will have been limited to about 170°C by the thermal cut out I have in series with the heater for safety. Since it was making a bed of six and it went wrong about 1/3 of the way through the build, they will have been cooking for about 4 hours.
Unsurprisingly the bottom of the object shrank and went brown. What was surprising was that the bottom layer became transparent and glass like. So glass like that I cut my finger on it. The meniscus edge was razor sharp. It seems to have softened over time though, this happened a few weeks ago.
Perhaps it might be a useful process if you want a transparent window on the base of an object. You could lay down a single layer and then cook it for a few hours at 170°C and then deposit the rest of the object on top of it.
Interesting, has it made the part brittle? or stronger? has the height of the part lowered by much.
ReplyDeleteI wonder what it would have looked like cooking for longer.
The bottom layer seems to be harder and more brittle.
ReplyDeleteThe height is correct because it was still building the top after the bottom had shrunk, so last layer was deposited at the correct height above the bed regardless of what was underneath. The bed then cooled down.
I wonder if perhaps the butadiene is getting cooked out of the bottom layer? If so, that would essentially leave SAN plastic, which is more transparent, harder and more brittle than ABS.
ReplyDeleteCan i ask if there is any reason why you use a termocouple for heated bed and termistor for extruder? I mean, wouldnt it make more sense the other way around? Is it just for convenience - or i may be missing something? Tyvm - Noobman
ReplyDeleteNo there isn't a good reason. I started using a thermocouple when I was using HydraRaptor to control an oven for SMT re-flow as that is what is used traditionally. I then used it for the heated bed on HydraRaptor as it was already implemented in my hardware and firmware. Then when I made my Mendel I used the same firmware so I copied the hardware.
ReplyDeleteI am thinking of switching to a thermistor for the heated bed on my next machine as they are a lot cheaper to interface to and mount on a bed. The main downside is I calibrate them all individually to get the same accuracy as a thermocouple.
Also i havent realised the first time, but -on short- what firmware changes are needed in order to use both termocouple and termistor at same time? I dont currently have a heated bed, but i will make one fairly soon, just dint got into it yet.
ReplyDeleteI don't know, I use my own electronics and firmware.
ReplyDeleteI don't suppose you ever weighed the thing to see what the difference with a typical joint was...?
ReplyDeleteNo sorry. I still have the part but I have changed various parameters so the parts I am making now will have a different weight.
ReplyDelete