How to get extrusions to stick well?

Or you could stick some black tape on it, as used on for BGA rework stations when the chip you are putting down or taking off has a shiny top.

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[www.hydraraptor.blogspot.com]

@nophead: thanks! i have not tried dropping the temperature during a build, but it is a good idea. right now my heater is run at setpoint control, separately from the arduino running the reprap, so i don't have a good way of coordinating between the two. i guess i could try it manually for starters...

@forrest: i was thinking along the same lines, of using nichrome and cement to build a heated plate without needing the power-resistors. i am curious how it would work out, but i have a feeling that the thin layer of cement would have a high tendency to crack, what with the different coefficients of expansion and all the heating and cooling... if you try it let me know how it works.

another thing people could try if they have the resources, is just to extrude onto a commercial hot-plate.

One of the big problems with using especially anodized aluminum (most usually available) is that it has a high emissivity. That means that you are going to have substantial energy loads from radiant heat loss. In that sense, Metalab's using of copper clad printed circuit boards was brilliant, because copper has quite a low emissivity till it gets very heavily oxidized. Even then, it's quite easy to clean down to shiny again.

Doesn't convection swamp emission in this case?

Would a low wall around the edge reduce the convection loss by preventing cold air from being sucked in sideways.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
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> Doesn't convection swamp emission in this case?
>
You can't swamp radiative loss. You can just add to it with convection.

The little simulation model I did indicated that if you use forced convection on the print surface, a very common option that I think you use, iirc, you are absolutely right. You can see in the main blog that I did a scaling up exercise on the Metalab surface heater and discovered that you need about 150 Watts to properly heat a print table using their design. To get that from a 12 v power supply you're talking about 12.5 amps. My power supply will do that, but I wonder if most of the ATX systems that people are using can supply that in addition to what the Reprap machine needs to operate.

You're also talking about a 0.9 ohm heating element to deliver that kind of wattage at 12 v.

Edited 1 time(s). Last edit at 11/28/2008 11:41AM by Forrest Higgs.

I have been battling with the warping/lack of adhesion problem when printing HDPE.

I have tried all sorts of different plastics borrowed from the tech department's scrap bin and nothing worked as the bottom of the raft would not adhere.

I also tried using copper strip board and heating it with a hot air gun and this worked quiet well but it bent the strip board (which could be fixed by holding it down better) and it damaged the strip board when I removed it.

I then tried heating the MDF table I extrude onto but again not much adhesion unless I pushed the plastic into the surface.

Then I noticed some old Evostick glue on the side and painted it onto the MDF and extruded straight onto it while it was wet.

This worked really well. No peeling or warping and when it was time to remove it a swift tap with a screwdiver and it came straight up.

This worked on a 4cm2 raft extruded in HDPE at 230 degrees and the temperature in the garage was about 2!

Tomorrow I will try a large long thin object.
Andy

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emcreprap.blogspot.com/

Forrest- I haven't read your blog post about scaling up the heated baseplate (I couldn't find it ). So this will have to be a decidedly amateur post.

What about making a heated baseplate with a number of separate controlled regions, so only some of the base plate has to be heated at a time. So hopefully you wouldn't be drawing near 150w.
This would only help if you were doing a number of separate parts, trying to do one big part would mean having it all turned on anyway.

Though I guess this would mean more channels of PWM, so were back to the custom electronics.

[disclaimer] I'm new (..fresh meat..) and don't (yet) own a reprap, so I may have missed some crucial piece of reasoning.

aGrazy Wrote:
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> I haven't read your blog post about
> scaling up the heated baseplate (I couldn't find
> it ). So this will have to be a decidedly
> amateur post.
>
No problem...

[www.3dreplicators.com]
>
> What about making a heated baseplate with a number
> of separate controlled regions, so only some of
> the base plate has to be heated at a time. So
> hopefully you wouldn't be drawing near 150w.
> This would only help if you were doing a number of
> separate parts, trying to do one big part would
> mean having it all turned on anyway.
>
> Though I guess this would mean more channels of
> PWM, so were back to the custom electronics.
>
I've got nothing against custom electronics. Right now, however, I'd rather use more electricity for a while and make sure that the heated surface concept really works well before running off and designing a complicated thing like that.
>
> I'm new (..fresh meat..) and don't (yet) own a
> reprap, so I may have missed some crucial piece of
> reasoning.
>
Doesn't sound like you have.

I just tried extruding ABS onto sugar today and it worked! I did not have time to finish making the object, and clearly there is a lot of work that still needs to be done before it works flawlessly, but the ABS stuck to the sugar very well.

I melted the sugar in an aluminum foil 'cup' and then poured it onto an aluminum foil surface, then flattened it with the underside of a pan. The surface was really smooth and flat, but it was not completely flat when I mounted it onto my base (I just taped it to existing paper, and the paper bowed up a bit), so one corner of my raft was sunken into the sugar a lot more than the other corner, but even the non-sunken corners stuck pretty well, and in those cases the tip of the heater barrel was about a millimeter or two off the surface.

The sugar cracked when I tried to remove the sunken-in corner, but it was not very damaged when I tried to remove the other, less molten-in corner of the raft. This definately shows promise! I will adjust my extruder to make sure it's running more consistently and try again.

[www.flickr.com]

destroyer2012 Wrote:
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> I just tried extruding ABS onto sugar today
>
EXCELLENT! Somebody finally tackled the question of what sort of support material plastic will actually stick to! Bravo!



BTW! Why is your sugar red?

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Hell, there are no rules here - we're trying to accomplish something.

Opportunity is missed by most people because it is dressed in overalls and looks like work.

Thomas A. Edison

Forrest Higgs Wrote:
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>
> BTW! Why is your sugar red?

No clue. It's baker's sugar, if that makes any difference. Gonna mess with my extruder's speed and try again. Maybe I can get better extrusion thickness. Maybe it has to do with the temperature at which I melted it?

Doing this in an oven seems like overkill. I was thinking of using a heat gun or something to melt the sugar down, or maybe eventually even make the base heat up and re-form the sugar-surface after a model is removed. Even wrapping nichrome wire around a small heat-resistant cup would melt the sugar quickly and efficiently for re-application.

Nice work on the sugar base. Glad to see this idea tried.

The "red" sugar seems very similar to the color of the sugar I melted earlier in this thread. It was a brown with a red tint to it that results from the sugar caramelizing. The candyfab folks have some very dark sugar creations as well.

Yes good work.

I wonder if the raft is still needed?

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[www.hydraraptor.blogspot.com]

Yeah, melting sugar is a materials science unto itself. There are all sorts of different categories of melted sugar. Have a look here: [www.baking911.com]

I'm guessing what destroyer2012 has would be "caramel - medium brown".

Might be interesting to create "candy" of various forms and see which ones have useful properties. For example, can you extrude "soft ball" sugar?

By the way, the standard way to make candy is to dissolve sugar in water and boil off most of the water. The reason the table linked to above works is that the boiling point of the solution changes as the concentration increases. Plain water boils at 100C but a 99% solution of sugar in water boils at 150C. As the water boils off, the boiling point increases, giving you a handy negative feedback loop (as long as you don't pump too much heat in too quickly). In theory, a thermostatically controlled pot could be set to maintain the desired concentration.

Another variant that might be worth exploring is sugar glass: [www.instructables.com] Not sure if it'd stand the heat, though.