Thursday, February 11, 2010


the anti-heated-bed?

I've been following this "heated bed" technology recently, as it seems to do a reasonable job of reducing warping... but its not "perfect", so I was thinking of alternatives.

In the commercial machines, they enclose the entire unit, and make a "hot box", which aparently works well. Everyone says "repraps can't do that because the printer parts will soften/melt", so instead we have:
"headed beds" :-
"heated bags" :-
"heated blower fans" :-

So I thought: "there has to be a way to just put the whole thing in a simple heated box".

So I Ask myself, and you all.....
What temperature should a "heated box" run at?
Is it less than the critical melting/softening temperature of ABS ( or PLA )?
If it is OK, then why haven't we tried this?
If the box temperature is "too high" for the normal parts, then what change/s need to be made to a mendel to make it more "temperature resistant"?
The wooden/aluminium mendel/s would be an instant winner here, but is there something we can do to ABS to make it heat-resistant? ( eg: perhaps build an entire from pewter using lost-ABS casting? like: )

I don't have all the answers, I just pose these questions for group input. Comments please!


I started to think about an heated-box too. But maybe the temperature can be quite low.
I don't know about "professional" printer, probably I can ask to see and test one.
To eliminate warping completely it needs to be about the temperature the plastic goes soft at so by definition you can't use the same plastic for machine parts inside the chamber.

I think commercial machines heat the bed as well.

One could imaging taking the roasting bag idea a bit further on Darwin by having a bellows to form the walls of the chamber and a very elastic membrane to form the roof with the extruder nozzle going through it.

The bellows could be frames cut from thick plastic sheet with Kapton tape making the hinges. The roof would have to very elastic, perhaps a thin sheet of latex rubber if it will handle the temperature.
This something I think could be improved on RepRap! Thanks for working on this ;-)

As for commercial printers, I think room temperature is about 70ºC, after looking at this videos:
"To eliminate warping completely it needs to be about the temperature the plastic goes soft (...)"

I am not sure for what you said, because on videos of commercial printers we see that they heat room at 70ºC for ABS printing. Also your and mine experimentation with just the bed, don't put heat on all layers of piece! Maybe a lower temperature than that 120ºC would be ok for avoiding all the forces if all the piece is at 70ºC and not just the base at 120ºC...
The Dimension machinery I have briefly used heats the build chamber to 80 Degrees Celcius for ABS. The Bed is'nt heated directly but the machine does appear to wait for everything to come up to temperature before commencing the print.

The parts sometimes do warp and ping off the bed's (the beds are an interchangeable plate) particularly after the bed has been used a couple of times and the surface has lost its "key".

So all in all a lot of effort for not much gain. But if there is no other way......
Just thinking about the warping and the bits that always lift. It is usualy always the corners first. Being right angled they concentrate the forces. It may be worth trying changing component designs to eliminate right angled corners, as this may help. Forrests guying technique looks to have some mileage in it as well.
Maybe, but logic would suggest that if the plastic goes hard at a temperature that is higher than the chamber then it will contract slightly after it has gone hard, which will leave some stress in it and hence cause some warping.

Does anybody know if very large Stratasys objects have any warp at all, or are they completely flat?

I am quite happy with the results I get from a heated bed as the object are as flat as glass except at the corners which lift a small fraction of a millimeter. I think rounding the corners would fix that, or using Forrest's apron technique.
I hear there are two problems with a heated bed.

First there is the plastics softening issue, which you've addressed.

Second there is the hot motors issue. The steppers run at ambient + 30c, if you heat the chamber they are in they will not only wear their bearings much, much faster, but will also themselves get hot enough to melt the plastic they are mounted to.

Because of #2, particularly the additional motor wear, I think that heating the entire machine is a non-starter.

Personally I favor the roasting bag approach. I think that if you put a fan on it to inflate it it'd keep entirely out of the way of any possible machine motion, and with a weighted square base that just fits around the bed, it'd be simple to seal and unseal.

But I haven't tried it, still trying to get that elusive first print...
Everyone says "repraps can't do that because the printer parts will soften/melt", so instead we have

Not me. There is in theory quite a simple way around the melting parts problem. Make molds of the raprap parts and then use epoxy that will take the temp into the molds.

In one way using molds could speed up creating new RepRaps. Since filling a mold with plastic is faster than control flow to make the shape.

IE total number of hours to make the machine would be less.
Moulds can only make a subset of the shapes that reprap can make and the process is manual and the materials expensive compared to filament.

With a heated bed it is relatively easy to make a machine the runs 24/7 unattended, dropping finished parts into a bucket. The brings the part price down to cost of the filament.
Moulds Look at the frame pieces of the RepRap itself. nophead.

I can not see one of them taking advantage of any special shape that only a RepRap can produce compared to a moulds.

Lot of the information to make the basic moulds already exists.

Again it depends on the type of moulds you are producing the expense.

A good mould will last for quite a long time.

If moulding the parts means more stable temp and less risk of defective parts.

Moulds can be used with filaments and beads of plastic. Its just melt and poor for thermal reacting.

Big point here until RepRap gets sacrificial support materials. Most of the time it cannot out do double and tripple moulds. Ie mounding sacrificial materials to use inside mound.

Also another point mould closing opening and filling does not have to be manual. No one so far has made a small scale machine doing it. Now if it turns out to have some major advantage moulded over RepRap produced why not make one of the auto machines.

There are companies here to CNC cut the moulds then into machines for filling and item production. So no human is need to even replace the moulds as they wear out. This could be another way to rapstrap as well.

You could say that what RepRap does could be done manual as well and it would be insanely slow.

Basically a little expense to make a machine that can be both inside a heatbox and use a heat bed would be good for sorting out if there is any real advantages to a heatbox.
oiaohm, that tecnology seems intewresting! I am glad that I can read about it on that pages :-)

Maybe a table comparition between this 2 tecnhics would be good and let people choose.

I think this is a no discussion for here.
oiaohm Taking the mould approach you suggest will make a machine that could not be called a RepRap as it would then not be able to self replicate >50% of its parts.

The only gain in having moulded parts, laser cut, machined or cast parts is increasing the RepRap community quickly by means of what could only be called mass produced Repstrap Mendels/Darwins.

Users of these mass produced machines would then replace the parts by printing their own parts.

Thus only a repstrap Mendel/Darwin would be able to overcome the problem of the Heated chamber effect on Replicated parts as it would not have any to be affected.

So you can use a Makerbot or RapMan with the the heated chamber. Or any other non REPRAP 3D printer.

The only compromise that could improve printing is to stabilize the internal temprature of the RepRap to a temprature above ambient but within the working temprature of the plastic that the Reprap was made from.

So for ABS we might maintain an ambient of 35C say allowing for steppers to add their 30C of operating temprature. for Pla it might only be 27C Ambient I don't know.

I don't know if doing this will make any improvement warping but it will improve the temperature stability of the work area.

Reduce the power required to heat the bed and print head, provide fume extraction from the print area.
The big deal about molds that I think nophead was thinking of, is the fact that molding of components cannot create parts that have a sparse infill.

Molding produces solid components with a solid skin.

Printing of components produces components with a solid skin but an infill that is settable within the slice and dice software to have a percentage of air in it.

All in all if the material that a component was made of was cheaper to purchase in a resin state (solid cast) and mold, we wouldn't be having this conversation.

Everyone would prototype one copy as a plug (molding master) and cast the rest.
Has it been considered to create a water based radiator system with thin wall tubing to address some of the problems with the plastic parts within the heated zone, in combination with some form of spray on heated insulation or material?

The disadvantage would of course be complexity. The advantage might be that, other than the tubing and pump itself, it should be printable.
Word on the street is you can print ABS on unheated acrylic and it adheres so well it won't warp at the bottom. You can't print PLA directly on acrylic because it bonds like glue, so for that use blue or kapton tape.
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