Heated Sand print bed?

[PaulS]

I am building a large machine with roughly 5 cubic foot build volume. Since trying to heat 5 sq feet of surface is such a daunting task not to mention a print surface that size, PEI would cost a fortune even if it was available so looking for an alternative. I was watching someone doing some sand casting recently and got to thinking, as crazy as it sounds would a heated packed sand bed even work? I know i am way outside the box here so any other ideas for a 5 foot by 5 foot heated bed, i am all ears! Bed will be stationary.

[Ron]

Because it isn't moving you could do many things.
You could try casting a "cover" over a bed of sand having embedded heating elements.
Any common casting resin should work OK for this purpose.
Polyester with catalyst (as opposed to two part epoxy) would be easier to deal with and would self-level a bit better most likely.
Plus you can thin it down even more using solvents.
Then plane it to be completely smooth by any of a number of methods.

I saw a commercial process by which silicone pads of roughly that size were made commercially for dye transfer printers.
The silicone was mixed in a large paint pot and then it was evacuated for a few minutes to get rid of entrapped air.
After that it was carefully poured onto a sheet of thick plate glass.
When cured (about 24 hours later), both the top and bottom of the resulting pad were very, very smooth and extremely parallel.

You could also have such a plate cast and polished smooth by almost anyone who does architectural cement floors.

I want to know how many kilowatts of heat you are going to embed into it though.
That is assuming that you are planning to heat the bed in the first place of course.
Since our 300x300 mm FT-5 beds seem to like around 400-500 watts, a 5x5 foot bed (~1500x1500mm) would need roughly 25x as much power to achieve the same power density.
So 10-12kw?
But that's not as bad as it appears at first glance really.
Common kitchen oven elements can easily do that.
Getting it evenly distributed could be a bit of a problem.
A grid work of heating tape would be better but you'd need a lot of it.
They do that sort of thing in homes now (heated floors), so such resources do exist.

[PaulS]

you are spot on there @Ron thinking some sort of heated chamber would be better. I run a 120v 750w pad on my ft5 and it heats up about as fast as the print head so probably a little overkill there. I was thinking of going with 2 of them on some sort of metal plate covered in glass but the thought of blue tape and or some sort of slurry to print on is not pleasant. I use pei now which is awesome IMHO but 5x5 feet would be big $ i am guessing. Heated chamber might be just the thing but i have no experience with them so looking for 1st hand experience. i am guessing sustained temps would be more stable in a chamber right?

[Dave]

Holy cow... I read "5 cubic feet build volume" and thought OK, that's pretty big...
...
but 5'x5'x5' is going to be MASSIVE! That's not 5 cubic feet, that's 5x5x5 = 125 ft^3!

[Dave]

You know what though, being a stationary bed REALLY helps you out here.

I'd be inclined to look at the technologies used for radiant floor heating. A coil of PEX tubing, laid out in a maze shape on forms and with a pour of fine self-leveling concrete to make a slab, then that surface polished. Heating could be one of those mini (~2-gallon?) electric point-of-use water heaters designed to mount under a sink. You would need a pump to circulate the water, and some valves and such since it would be a closed system. The bed temp would be whatever you set the water heater to.

Man... 5x5'... You would probably have to have TWO bed surfaces, and let this slab float/slide on top of another surface so it doesn't walk itself away during the heat/cool expand/contract cycles... sort of the opposite of frost heave.

I bet you could get a 5x5 piece of glass though for the actual print surface. It's a bit large to find a glass table top (like a coffee table), but I bet a window supply shop could get a sheet that size.

Looking forward to what you come up with.

[Ron]

If you watch the "bruised and reduced" section at your local IKEA (assuming you have one of course) you can often find tempered plate glass table toppers in sizes up to and including 5'x5'.
I bought a bunch of very large table top glass plates for $5 each a few years ago.
They are very, very flat and have rounded edges and so forth.
I plan to build some fancy display cases with them.
You never know what you'll find there.

Or check at a local glass shop and see if they have some scraps, or a mis-cut from someone else's job.

The PEX tubing and a point-of-use water heater would work quite nicely for the bed, and also for a space heater if it is enclosed.
There are probably twenty ways to do this, all courtesy of it being stationary.

[MadDog]

Hello @PaulS;

I am having trouble with dimensions...

You said 5 sq. feet of surface - which is about 27 inches x 27 inches
Also 5 foot x 5 foot - which is about 60 inches x 60 inches

Somewhat regardless, the ideas of glass or poured resins with heating elements embedded sound doable. Thought being lay the glass down flat, pour a bit of resin (resin impregnated sand??), place heater elements on resin, pour resin to cover elements, then flip over. Insulate this sandwich from below. Possibly mold-in some short legs to support the bed.

One issue might be how to keep all this heat from affecting other stuff within the printer.

[PaulS]

My bad @MadDog, you are correct. X rail is 1540 mm y and z are 1500 mm so yeah 5 foot x 5 foot is my guestimate but dont forget the objective is both heat and a functional print surface like pei. I didnt think to embed the sand in a resin... if you recall, i replaced all my "less than idea"l... wood parts with fiberglass parts from the get go so this would be a simple thing for me. I will have to keep an eye out for glass but no idea if i even need it yet considering i am looking for an alternative maintenance free print surface. Anyone know of a paint on maybe? i expect a lot of abs and or asa printing so chamber will be vented and ducked outside. I am pretty sure two 750 watt mats on a plate with a piece of glass would get the heating done but that still leaves me with a reliable maintenance free print surface. considering the potential surface contact area, something tells me a removal tool may not get it done so thinking way outside the box here as far as sand print surface. since bed will be static, i don't have to worry about part moving during print. Question i have is will extruded plastic drag print around sand. scary to think of sand around movement but think i can contain it to be somehow...need to experimane with sand coated resin surface to see if it will take a print i suppose. surely i can be the first to be this kind of crazy... never mind the peanut gallery there @csorrows

[PaulS]

aren't typos fun lol

[PaulS]

yup @MadDog i do plan on getting y and z outside the heat zone but not sure what i can do for x or extruder.

[Ron]

If you run a CoreXY or an "H" drive setup and that should help get the X motor out of harm's way.
The extruder is more of a problem of course because it you ran a Bowden setup it would have a very long feed tube for a printer of that size.
However, you could try running a very long tube with a Bowden feed on the FT5 just to see what happens.
Who knows, it might not be so much of a problem after all.

[PaulS]

was running a bowden on ft-5 was a nightmare for retract so probably not a good ideas for something with this long a feed...

[Ron]

I concur, having attempted the same thing and then gave up on the idea.
However presumably you will be using larger filament (3mm?) because of the positively huge build volume and perhaps ultra-fine details would not be quite as much of a goal?
Or am I missing your intention entirely?

P.S.- when I saw a 3D printed automobile (a full-sized road-worthy car) at a trade show last year it appeared to have been printed from melted plastic rope.

[Dave]

However presumably you will be using larger filament (3mm?) because of the positively huge build volume and perhaps ultra-fine details would not be quite as much of a goal?

At that build volume, filament costs could easily become prohibitive... I would think one would be considering either a pellet extruder, or creating your own filaments from pellets? A Filastruder would probably have paid for itself by the third thing you printed.

[PaulS]

Hi @Dave, you are reading my mind. still looking for a possible pellet extrude setup Also heard a possible 6 mm filament standard coming so hoping that happens before i get to buying the extruders and hot ends... Just got all seven 1500+ mm linear rails so time to start figuring out dimensions and movement..."this is going to be big" Since i will be blowing some things up so big, i expect to be able to print around 1 mm layer height so 10 times faster than my other machines printing at .1 mm as i understand it, really large objects blow up the detail too so hopefully quality will be somewhat maintained but from E3D's demo, clearly get a strength bonus from these big layers so should be interesting to say the least!

[Ron]

6mm filament?? Oh my.
That would be more like a rigid rod I would think because the stiffness of a column of material goes up exponentially when compared to its diameter, all other things being equal.

Unless of course the pellet extruder was mounted at the carriage and hot end.

[PaulS]

yes and yes i wondered that same thing but that was the you tube rumor. Standards for filaments and spools as well So far i have seen so interesting auger type pellet extruders and yes they are local no bowden option there but otherwise appear do able just not sure about print quality. anyone run anything like that yet?