ABS Coating on Aluminum Build Plate: Thickness Thereof

Printing ABS objects on an ABS film atop a heated aluminum plate works just about as perfectly as I could want, as witness those calibration objects. It turns out that the thickness of the ABS film makes a big difference in how well the first layer bonds to it.

I’m coating the plates with scrap ABS objects dissolved in MEK, because MEK seems to be less aggressively flammable than acetone. It smells horrible, though, and spreading a layer of toxic gunk with the consistency of honey can’t possibly be good for me. I use dead credit cards as spreaders and wonder if there’s a better way; a brush would clog up almost instantly.

The rough rule of thumb:

  • If the ABS layer isn’t obvious, then it’s too thin.

A Companion Cube growing out of a good pink film layer:

Companion Cube on ABS coated plate

Companion Cube on ABS coated plate

Peeling a smaller Cube off a plate shows how well it bonds to clear film. Notice how the film peels off the build plate without leaving any residue except for a tear in the film covering the hollow underside of the Cube.

Companion Cube - Bottom surface with ABS coating

Companion Cube - Bottom surface with ABS coating

These outline extrusions show the effect of a too-thin film, where the extrusion simply peeled off the film. Where it’s thick enough, the extrusion is welded right to the surface. Intermediate thicknesses tend to rip on both sides of the extrusion.

ABS coatings from aluminum build plates

ABS coatings from aluminum build plates

In round numbers, the perfectly formed film at the lower left is between 0.05 mm (the darker regions) and 0.09 mm (the deepest pink). The others range from 0.02 mm to 0.05 mm and are too thin for good bonding. Even the thickest film doesn’t add much to the first layer thickness.

The other part of the secret is extruding the first layer at 10 mm/s, which is 25% of the 40 mm/s I use for the rest of the object layers. The platform is at 120 °C, the Thermal Core at 210 °C, and the extrusion sticks like it’s welded… which, in fact, it is.

I think that a too-thin film cools the extrusion before it can bond with the film, while a just-right film melts slightly on contact. Extruding at 10 mm/s guarantees enough contact time for the filament to melt the film and cool down before the nozzle puts any tension on it: corners come out perfectly.

The other part of the puzzle requires an absolutely level build platform at a constant height from the nozzle. The platform leveling described there helps, but it’s a hassle to get everything set up.

  1. #1 by Ben on 2011-04-15 - 09:02

    It’s interesting to see the different methods people are using to get a decent adhesion on the first layer for raftless printing. My setup is similar to yours, but I use a single aluminium plate on top of the heated PCB, with a high temp. thermal paste between the two. Before using the paste I just had the foil between them and warping on edges of objects that were 10-20mm from the plate edge was too much of a problem.

    I’ve got a single layer of 3M tape on the Alu. build surface that I replace every 5-10 builds, the adhesion is so good now, that I have problems removing objects off the tape once builds complete. Which in itself is a sign that it’s ‘good enough’.

    Have you tried tape as opposed to a film of ABS? Using two plates with tape on them to swap out when builds complete might be easier than repainting with ABS each build.

    • #2 by Ed on 2011-04-15 - 09:56

      a high temp. thermal paste between the two

      I admit to being a coward: the thought of smooshing that blue thermal compound in there, then having it wind up everywhere inside the TOM, gave me the shivers. But I think you’ve got it right: the air gap causes problems.

      I must summon up my courage and Do The Right Thing.

      tried tape as opposed to a film of ABS?

      Kapton tape worked reasonably well as part of tape-and-paper ABP belts, but when I switched to aluminum plates I also started using the ABS coating. Mostly, I wanted a uniform bottom layer, didn’t have any tape wider than 25 mm, and wound up with unsightly gaps no matter how hard I tried: if I was going to use a flat plate, I didn’t want ridges on the bottom of the parts!

      From your experience and what I read elsewhere, 100 mm Kapton tape, especially the undoubtedly counterfeit stuff from halfway around the planet, works very well. I like the no-fumes aspect a lot

  2. #3 by smellsofbikes on 2011-04-15 - 13:24

    Would it help to mill 0.010″ wide channels in the aluminum, maybe a cm. or two wide, with the ribs between pretty much as thin as you can get them, so when you’re spreading the mung on the plate you’d essentially be screeing the mung the way people do with levelling the surface of concrete?

    • #4 by Ed on 2011-04-15 - 13:56

      Nah, it’s what happens when I must take the plate off: that stuff goes everywhere.

      I suppose I could just ignore the whole thermal expansion mismatch issue, epoxy the plate on top of the heater, and be done with it.

  3. #5 by Billy Zelsnack on 2011-04-15 - 14:36

    I think there are two things going on
    1. Thread adhesion
    2. Part cools too fast

    Just to get a part at all the threads have to stick for the first layer. After the first layer is down I believe that the part cooling off too quickly is the main culprit of edge warping. Part of that is due to poor thread adhesion at edges that allow air to circulate. However I think most of it is from just plain heat conduction into the build platform. Try printing onto your aluminum platform without the heat on! A heated platform prevents much of this because there is less of a heat differential. No matter what it is impossible to get even cooling over the entire part, but I think that as long as you limit the rate of cooling you can end up with uncurled parts.

    I’ve been experimenting with a wood insulated platform plus two layers of kapton and have had some good success with superglue or threadlock for extra adhesion.

    The superglue on kapton on a heated platform allowed me to crank down the platform to 80C. I actually had to because the part would stick too well at 120C. Moving to the wood platform with the kapton and superglue gives enough thread adhesion that combined with the lower heat conduction of the wood allowed for large flat raftless prints. When I did have issues I manually added a heat skirt around the object and ended up with unwarped parts. Maybe in the future support material could be used as an insulator too.

    My printers are torn apart at the moment, but next want to try the dissolved ABS in acetone with the insulated wood platform. I think they both may work (for adhesion) for the same reason.. It chemically melts the ABS into the kapton.

    • #6 by Billy Zelsnack on 2011-04-15 - 14:52

      oh geez. I didn’t know the video would be embedded so huge in the post. Sorry.

      • #7 by Ed on 2011-04-15 - 15:23

        First time for everything… now we all know!

    • #8 by Ed on 2011-04-15 - 15:43

      superglue on kapton on a heated platform

      The levels of absurdity required to get the thread to stick to the build platform gives me pause; I don’t know what those spendy commercial printers do, but it definitely doesn’t involve heated cyanoacrylate!

      The ABS-in-MEK works surprisingly well, although I really want to find something less noxious.

      Spray adhesive likely isn’t going to be attractive, either…

      • #9 by Billy Zelsnack on 2011-04-15 - 15:58

        I don’t think superglue is the answer at all, but it along with a wood platform is making me think that it is possible to do an unheated platform. I know nophead has said that unheated parts warp later, but I’ve not noticed it so far and maybe I am not building tall enough parts. I dunno. Maybe just slowing down the cooling process is enough to prevent future warping.

        I believe commercial 3dprinters get around both the adhesion and warping by using a heated chamber. I find that much less attractive than requiring a little platform adhesive. Also.. Nothing stopping the application of (whatever) adhesive from being automated.

  4. #10 by John Rehwinkel on 2011-04-15 - 14:37

    I see your notes written directly on the ABS scraps – another good example of putting your notes where they’ll do you the most good!

    • #11 by Ed on 2011-04-15 - 15:31

      I thought about keeping a logbook and that led to ID numbers and that led to … it started to look a lot like work, is what it started to look like.

      So I recalled how Eks told me to just write it where you’d need it and did so. I save the samples until I bayquake the TOM or otherwise render them irrelevant, then they go into the pot for eventual dissolution / recycling.

      I do save the better ones for Show-N-Tell sessions, of course…

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