heat bed vs heat chamber?

Hi guys, i have one question.

im preparing to build my first 3d printer, and ofcourse i am in big dilemma, so much availble designs....


so when i look stratasys fdm printer, i see that they dont have heated bed, but also i see on mojo printer, they use chamber heating.


my question is simple, can i have heated chember without heated bed,and avoid warping?

if yes, how high should be temperature in chamber?



sorry if that question is answered, i searched but didnt find any results..

I think you need will a raft if you don't use a heated bed.

Yes a heated chamber reduces warping. Ideally is should be just below the glass transition of the plastic. For ABS it would 70-80C so it needs to be all metal with external cooling to the hot end.

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[www.hydraraptor.blogspot.com]

... AFAIK stratasys is heating their chamber with hot air - 50 to 60degC could be enough to reduce most of the warping ... can remember an old thread, where someone (Vic?) stated, that the most warping effects take place when cooling down from 40degC to room-temp ...

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Viktor
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I use 45C plus heated bed but it doesn't eliminate all warping for ABS.

The warping is proportional to how much the plastic shrinks when cooling from it's glass transition to room temp. That is why PLA warps so much less, because it has a very low glass transition.

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[www.hydraraptor.blogspot.com]

... then maybe better heat your chamber to 60degC and put bags around the plastic parts, which will be cooled by passing air ...

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

few interesting pics....


as seen, mojo has closed printing chamber, here we can see paper "heat wall" so actually all components are in room temperature...

and mojo heat bed....

My Stratasys machines run the chamber at 70 deg C for ABS.

As shown, the Mojo (unlike the FDM series and P-class machines) puts all the motion control elements (steppers, belts, etc.) outside the heated envelope, so they can use a lot more plastic for such components. It probably reduces the power consumption as well, since they don't need to heat as large a volume.


VDX Wrote:
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> ... AFAIK stratasys is heating their chamber with
> hot air - 50 to 60degC could be enough to reduce
> most of the warping ... can remember an old
> thread, where someone (Vic?) stated, that the most
> warping effects take place when cooling down from
> 40degC to room-temp ...

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[haveblue.org]

Huh, anyone else just notice that the belt layout in that machine looks like an h-bot?

yes, and it fits perfect to whole concept of machine. easy to make heat wall, they can use weak and cheap motors because low moving mass etc.


they have done very good homework

2 haveblue:
thank you for information about heat temperature.

how do you cool your printed part? do you leeve it in machine and let part to slowly cool itself in heated chamber(some sort stress relief) or just take it out when finished?


2 nophead: theoretically, its all Physics.


all materials shrink when cooled.

so when none heatbed first layer shrinks and second is printed on allready shrinked bed.

with heat bed we have few centimeters heat to avoid cooling, so everything is shrinked and cooled together.

in heated chamber whole printed part shrinks and cools in same time.



now one of last two options is better...thats why i asked for opinions because i dont have experience

Edited 1 time(s). Last edit at 05/07/2013 01:17AM by woo.

crispy1 Wrote:
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> Huh, anyone else just notice that the belt layout
> in that machine looks like an h-bot?


Yeah, interesting. I saw a similar picture a while back and asked on here if anyone knew if the Mojo was an H-bot, and I think people explicitly said no. Very interesting, and gives me hope in the dimensional accuracy feasibility of the H-bot design if Stratasys is using it in their mass-produced machine that relies on accuracy and consistency.

woo, I generally just leave the part in the machine to cool. Unless I'm feeling impatient, in which case I just yank it right out of the chamber as soon as the print is done :-) Even in those cases, I haven't noticed any warping (but I did find that the transparent ABSi, a methyl methacrylate ABS, is still pliable at envelope temperatures and does need a full cooldown).

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[haveblue.org]