Need options for a large heated bed.
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@deckingman said in Need options for a large heated bed.:
After pouring it in and letting it set, I checked with a level and still had a 2 to 3mm slope. Much better than the 16mm I started with but not truly horizontal.
Perhaps it shrunk a little, and the thicker sections shrunk more?
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@dc42 said in Need options for a large heated bed.:
@deckingman said in Need options for a large heated bed.:
After pouring it in and letting it set, I checked with a level and still had a 2 to 3mm slope. Much better than the 16mm I started with but not truly horizontal.
Perhaps it shrunk a little, and the thicker sections shrunk more?
That's a possibility. Although I'd have thought that if it shrunk, it might have come away from the battens that I put around the edges to form a "bunded enclosure", and there is no sign of that having happened. It set quite quickly so I thinks it's more likely a combination of that and the rather viscous nature of the "thick use" type product. As I said, if I did it again, I'd get it somewhere near with a smoothing trowel before letting it "do it's own thing".
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Use Borosilicate Glass and for that size of build platform consider using 10-12mm. I have a 300 x 600 printer I had tried aluminum that didn't work the expansion of aluminum is too great.....I tried granite....it was much better but the glass is the best
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@percar Borosilicate Glass in 800mm x 800mm would cost me about $600.
I decided to give a regular 1/4” glass plate a try at $55.
Good results so far.
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@percar f you use a kinematic mount, the expansion doesn't cause any problems.
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@jdumoulin said in Need options for a large heated bed.:
Borosilicate Glass in 800mm x 800mm
What nozzle size are you going to use? For those sizes, you will need to extrude a lot of plastic.
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@zapta I am using a super volcano with 1mm right now mounted on a hermera. I want to try the 1.4. Yes it pushes a lot of plastic.
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@jdumoulin, I saw a review of an IDEX printer the other day and wonder, does it make sense to have let's say 1.4mm in one nozzle, 0.4mm in another, and tell the slicer to use the 0.4mm only for outer shell. This will require different layer heights for the two nozzles.
Could provide very large object with very good surface quality.
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@zapta said in Need options for a large heated bed.:
@jdumoulin, I saw a review of an IDEX printer the other day and wonder, does it make sense to have let's say 1.4mm in one nozzle, 0.4mm in another, and tell the slicer to use the 0.4mm only for outer shell. This will require different layer heights for the two nozzles.
Could provide very large object with very good surface quality.
It does make sense for a tool changer / IDEX machine, however this functionality can be limited by the slicing software. Cura is great in that you can make the infill be at a different layer thickness and be printed with a different tool (can also set different tools to outer/inner walls, support infill, etc). However there is a limitation when using settings like "Extra Infill Wall Count" (under Infill settings), zero extra walls will be printed if the infill layer height is greater than the standard layer height. I think I understand why the have it setup this way, but I would like to be able to have extra infill walls at a different layer thickness.
I don't think in Cura at this time you can change the inner wall layer thickness relative to the default layer height.
What can be easily done, however, is setting extremely large extrusion widths when using these large nozzles.
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I thought I'd add my experiences on this subject. I've built a very large printer. The heated bed and build surface have been two of the biggest concerns, but so far both seem under control. The build area is about 870 x 800, and I'm using 6mm aluminium as the structural element, with 20+ adjustable screws on the underside supported by a 40x40x4.0mm EA aluminium frame. Heating is done with a custom bed heater from China with holes for the screws - it's about 2300W on 240VAC. I looked at getting Borosilicate glass for the build surface, but I was quoted about $1200 + freight from the states (probably another $1200), and PEI sheet was pretty similar. I ended up using a large mirror from IKEA ($60 for 2!), which I cut to size. Before the heated bed went in, I had all kinds of surface adhesion issues, but since then it's been great.
Mesh bed levelling hasn't been perfect, I get about 1-2mm max error across the whole area, but given the size I'm not concerned with that.
So far I havne't printed anything particularly large, I'm still debugging the design, but I have a project coming up that will start to use more of the area, so I'm keen to see how it goes. -
I can't resist to reply to this thread ...
I am one of those people that think that a glass plate by itself is not appropriate for a bed. It needs to have an aluminum spreader plate underneath. Further, unless you use Borrosilicate glass, it is quite possible that the glass will fracture from thermal stress unless you heat up very slowly. I realize I am speaking against first hand experience but just because it is working for one person, it doesn't mean it's a good idea to do this.
If you want to level concrete (or any other fairly thick fluid), you need to vibrate the pour to overcome surface tension. Vibration from below is best but I would think vibration from above (or from the side) would achieve a similar result. While vibration will get you horizontal, I would still expect to have to do some surfacing after te material has cured.
A smoothing trowel will give you grief!I would think that past 300mm * 300mm, a kinematic mount would be an absolute requirement!
As far as I know, Cura does NOT offer the ability to do two different layer thicknesses. I have a 0.8 mm nozzle as well as a 0.4 mm nozzle mounted. I could print the outside with the small nozzle and the inside with the large nozzle but layer height, as far as I can see, is linked so that both nozzles do the same layer height.
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@jdumoulin said in Need options for a large heated bed.:
Borosilicate Glass
Go with the Borosilicate Glass option....for large build printers this is the only way. Even if using kinematic mounts there are still distortions then the aluminum heats up. The outer perimeter of the build plate is always cooler then the internal and this creates distortions of the build plate. If you want to go into the physics of the phenomenon I have not problem discussing this in another part of this forum. Yes the glass is more expensive but in the end it is a better option.
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@jens55 said in Need options for a large heated bed.:
Cura does NOT offer the ability to do two different layer thicknesses
If you want to print the infill with heigher layer, there is a solution:
https://community.ultimaker.com/topic/32034-why-cura-doesnt-support-different-layer-height-at-the-same-layer/
You could try multimaterial print with the bigger nozzle for the infill. -
@JoergS5, I sit corrected ... I will have to try this out.
Thanks!
