Custom Heat Pad and thermistor question
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There's more than one way to crack an egg.
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Here is the big mac sandwich
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That bed is thicc.
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@phaedrux
Has to be as big as it is... if it were a skinny bitch it would flex -
I am going to stick my head out here and comment on your heated bed configuration ....
Sorry to be a downer and all that but there is a good reason why everybody else uses the heat bed configuration that they use. The heat pad has, as you pointed out, individual wires that generate the heat. This has to be evened out which is done by the aluminum build plate.
The cork has two functions - one is to insulate the bottom of the heat pad so you don't radiate a good portion of all that heat into space and it is also used to apply pressure to the heatpad to keep it in touch with the build plate. Of course this only works if you have some sort of mechanism under the cork to press it against the heat pad. This is usually done with another aluminum plate.
The glass on the very top is your actual build plate but it could be a myriad of other solutions. You do NOT want to print directly on the aluminum build plate.
The arrangement that you are using makes zero sense! -
@jens55 I think you're looking at his picture upside down. The glass is the build surface. The aluminum is the support base underneath.
Definitely not traditional and I would worry a bit about the heater not having a large sink source to smooth out the heat, but that glass is very thick so maybe won't be so bad.
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@phaedrux, I think the op has explained it sufficiently .... from bottom to top, it is aluminum plate, cork, heater, glass.
IHO nothing good can come from that and I wanted to express my thoughts rather than be quiet and politely not say anything. OP can do with my opinion what he wants (I expect the opinion will be dismissed) but at least I know I tried to warn him .... -
@jens55
As i mentioned earlier i have the exact same setup on my other printer and it has been flawless for several years. The only difference here is the glass is thicker than on my other printer due to originally i had a thinner piece of mirror. When i took it to a glass cutter to cut it to size he screwed up the dimensions and wasted a $60 sheet of mirror. He replaced it with this thick ass glass for free. Essentially though its the same setup as my other printer and works just fine.I like when people say something wont work. When i modified my FT5 from two z lead screws to 4 (one in each corner rather than the two in the center) several people with college degrees said it will never work, it will be over constrained and will bind blah blah blah... I built it and its been printing just fine for years
https://youtu.be/Y-mI4nO2WIM part 1 (why i was doing the mod)
https://youtu.be/-Rz560F4oiY part 2 (the actual mod completed) -
@wingtip, I didn't say (I hope) that it would not work but rather that it makes no sense at all. Just keep it in mind if you run into odd problems down the road.
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Let me approach this from a slightly different perspective just for argument's sake .... and I am not saying it won't work but just throwing ideas around.
So people spend money on special cast and machined aluminum print beds to get as flat an area as possible to print on. While average printed layer height may be 0.2 mm there are plenty occasion when I am printing 0.1 mm layers.
Cork is a natural product. Natural products such as wood are not known to be precision surfaces, they change based on humidity, temperature and the phase of the moon. Cork is also not produced in a precision thickness.
Your heat pad is not manufactured as a precision thickness part.
So you built a surface that is hopefully very level and flat and you add two layers of non precision parts to it. I am ignoring the fact that glass also has variations but you can't directly print on aluminum so some reduction in precision is unavoidable.
In your case you are introducing substantially more opportunity for error to the overall equation.
You could probably replace the aluminum build plate with a slab of wood and possibly get a good print when conditions are right but that doesn't make wood a good product for making a build surface out of. -
@jens55 I had a mirror but the guy cut it wrong so i am stuck with this glass that he says is just as accurate as the mirror being flat... and with auto mesh leveling it has to be better than my other printer which has no auto leveling at all...
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@wingtip, yes, mirrors are made with standard glass so the two are functionally equivalent.
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This is a thermal image of a Taz printer with a heater affixed directly to the glass bed.
Printing on that machine was very difficult due to the almost 30C variation in temperature across the bed (among other reasons).
This is a thermal image of the same heater mounted on a 1/4" cast aluminum bed that replaced the glass bed that broke (as glass will do under the right circumstances):
I think it clearly shows why you want to heat up the aluminum.
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@mrehorstdmd .... wow!
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@mrehorstdmd
What were you trying to print abs or something extreme like that? Im not... as i said, this method has worked on my other printer for years and is how ive made this one... The problem i usually have is the prints stick to well and i have trouble getting them to release.
Im not changing it all now after its been built as the alum bed is designed with the adjustment wheels in mind. mounting it directly to the alum sheet would require ordering another heat pad slightly smaller and restrict my building area even further after losing 20+ mm in x axis already due to binder clips.
It is what it is at this point and if there are issues then i will address it then. But the same setup has worked for me already for several years... -
The OP's aluminum is not a cast plate, but an extruded or rolled sheet which will not be flat enough to print on. That also means that if you were to put the thick glass on that aluminum, the glass will not heat evenly because of air gaps between the glass and the aluminum and the poor thermal conductivity of the air and glass. A thinner, more flexible piece of glass would be better in this case, at least for heat transfer, but then you have the problem of unflatness (which can be solved with flatness compensation and a sensor on the extruder carriage).
A closer to ideal situation is to put a piece of glass, probably not especially thick, on a piece of cast tooling plate with the heater attached to the bottom of the plate. The flat aluminum will contact the glass surface with fewer and thinner air gaps and do a better job of transferring the heat. This way you get flatness and good heat transfer.
Do you want to ride a bike with square wheels?
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It's untraditional, but I think it will work. I guess I'm most worried there will be hot spots on the heater if it's not making great contact with the glass. It is 1500w afterall. Glass isn't a great heat conductor but the traces on the heater pad look pretty evenly spread out and close together. And that glass is thick as hell.
Don't forget to PID tune the bed heater.
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@phaedrux
its 6061 t5 alum sheet that a machine shop drilled and milled to accept 4mm nuts in place. As for the airgaps its sandwiched with giant Fing binder clips to clamp it all together. Again this is the exact same method that is working on my other printer just fine. -
@wingtip hey I'm on your side! fire it up and show us!
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@phaedrux Im getting there....
