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I'm /relatively/ new to 3d printing (I'm getting pretty good prints from my Wanhao di3 plus, but haven't done any DIY kits or anything) and materials engineering is probably the furthest thing from my area of expertise so I thought I would pose this to more experienced makers:

If I'm building a large scale printer (probably a similar size to substation33 - sub33D's 1200x1200 printer) that I'm only going to print in PLA and MAYBE ABS occasionally, can I substitute the heated bed for simply heating the entire enclosure? The idea would be to have a thermistor measuring the ambient air temp inside the enclosure with a heat gun or two to hear the entire enclosure as necessary. I want to do this to try and reduce the cost (significantly as far as I can tell) as it seems 400*400 silicone heat pads tend to go for about 80 bucks a pop. An alternate idea I had was to use two or three heat pads and space them evenly under a glass bed, although I feel that this won't work as well because the heating won't be homogenous...

Any input is appreciated :)

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I tend to agree with Davo, that you might want both. But I'd probably try the enclosure first. My printer is about 1200 by 400. I looked at options, and found some difficult trade-offs:

First, the big heatbed approach:

  • as you know, getting a single heatbed that big will be expensive (and if it ever breaks or fails, you have to replace it all).

  • a big heatbed also draws far more power than a RAMPS board can switch, so you'll have to use the on-board control to control a power relay (solid state or mechanical).

  • a big heatbed will also waste a great deal of power when you're doing small things.

Second, the heated enclosure approach:

  • more costly to heat up at the beginning, but if insulated it may be cheaper for long prints (with a bed that large, your prints might take really long, too) because it can retain the heat better.

  • if you keep the air circulating inside, you'll get much more uniform heat, rather than hot first layers and cooler higher layers.

  • consider the effect of the heat on all the other components: motors, electronics, pre-heating the fibers, thinning any lubricants,....

  • you could save some heating cost and time by providing a way to shrink the space to be heated: perhaps just a partition you can insert when doing smaller prints. It wouldn't have to be nearly airtight to make a big difference.

A third option is several small heatbeds:

  • this lets you turn on just the ones you need for any given print

  • still expensive, but cheaper than one big one, especially when any of them fails.

  • there will be uneven heat at the seams, but if you place the boards tight together I doubt it's enough to matter. You could also carefully trim the boards' edges to get the spacing closer to uniform.

  • temperature regulation will be tricky. If you want to support a temperature sensor for each board, you'll have to start hacking at the control software, because (as far as I can tell) there's no provision for multiple heaters. Probably easier to create a completely separate unit with a big power supply, and a simple thermostat for each of the beds, that you just set manually before starting a print.

Overall, I think the heated enclosure may be best. I like the hair dryer idea or heat gun idea, of course you'll need a little extra circuitry to switch it, but you can use the usual software for temperature regulation by installing thermistor or thermocouple in the case (just be careful about circulating the air well enough to avoid "hot spots").

You may want to add an extra cutoff to protect against runaway heating -- I had that happen once when a thermistor literally fell out of the mounting hole in the hotend. Something like https://www.grainger.com/product/SUPCO-Thermostat-407L11.

Let us know how it turns out.

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With a well-insulated and well distributed (or perhaps well-mixed is a better term - even heating) enclosure you should have a veritable heated bed by dint of heating the enclosure (with the bed in it), unless the bed needs to be hotter than the enclosure. I think that would be bit more elaborate than "a couple of heat guns" and involve several fans to distribute and mix air continuously.

But - heated enclosures are not a freebie - everything inside the heated enclosure needs to be happy running at the sort of temperatures the enclosure is running at, and that can be hard on some electronic parts, shortening their lifetimes at least. Likewise, your calibration needs to be done on the hot enclosure - mechanical parts (particularly on a large scale printer) will change size due to the temperature.

Insulation will both reduce your running cost (the more heat you keep, the less you have to add) and help keep the temperatures even, by slowing the cooling at the edges of the enclosure.

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If you want to print ABS at even one third of that scale, you will want a heated bed and a heated enclosure. Posts here (and my personal experience) support this; unfortunately, I can't find an impartial, non-anecdotal source to cite.

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    $\begingroup$ I think the commercial (stratasys) FDM printers have only a heated enclosure. The bed is plastic. However, the enclosure is heated to a fairly high temperature. $\endgroup$ – Tom van der Zanden Aug 22 '17 at 12:16
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The point of using a heated bed it's to keep the part within a certain range of temperature while printing.

So, it's all about thermodynamic. It will be easier to keep the part at the desired temperature if the contact surface with the hot environment is larger, so, it might reduce warping and other related problems.

Anyway, it might be enough to have just the heated bed in contact with the part and not the whole environment to reduce the problems of abs printing.

You can check Tom3D's post, 3D printing with ABS: Hotter nozzle or hotter ambient? #Filaween, and video, YouTube - 3D printing with ABS: Hotter nozzle or hotter ambient? #Filaween, it might help you choose what to do.

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  • $\begingroup$ So, can you get away with not having a heated bed and have (only) a heated enclosure instead? That's what the question is. I think you answered the opposite question. $\endgroup$ – Tom van der Zanden Aug 24 '17 at 10:08
  • $\begingroup$ I just read my answer again and it feels dumb right now. Using a heated gun might work, but it will have a weird heat distribution on the case. There will be really hot spots and hot spots, so, might work but not sure at all... Anyway, the key point of the heated bed it's to keep the part hot, so... it might work $\endgroup$ – Luis Diaz Aug 24 '17 at 10:19
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If it is yours first DIY 3D printer try building smaller version first with just one silicone heat pad. 400^2 mm^2 is good enough.

From my experience:

  1. I used 500W silicon heater with SSR (AC mains) and it heats as fast as hotend (on DC 12V).

  2. I also recommend tooling plate (CNC machined Aluminum plate), it is better for heat transmission (Al) and it is more flat (machined to +-50um).

  3. You might consider thermal insulation under the silicone heater and also some foil on build plate itself - to minimize thermal losses. Cork might be useful for bottom. For top I use blue foil (in which it was originally wrapped).

Enclosure I think it is also necessary, combined with heater, but then you must also have tubes for cooling of printed part, motors, fridge on hot end, etc.

Word of caution: You must realize that you will be probably using 1.0mm nozzle or even more, since on 1200x1200mm you will just wait for weeks for part to complete. For reference: I print on 340mm diameter (delta) with 0.3mm nozzle and works just fine. But if I use just 0.1mm instead of 0.2mm layers it takes more time, but at the end it looks fantastic. So in your case even layer height must be big to reduce printing time. So you can increase speed, but then there could emerge some artifacts on printed object and also consider heater on hot end, which might be lagging behind.

There are a lot of problems when you go this big and all are not even closely to be considered solved, but if you have time..

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  • $\begingroup$ This doesn't answer the question, which asks whether you can get away with not using a heated bed at all and substitute just heating the enclosure. This is good general advice, but I think it would be better to just stick to answering the main question. $\endgroup$ – Tom van der Zanden Sep 6 '17 at 5:44

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