This is a variation of Thing 6384: an aluminum plate sitting atop the Automated Build Platform’s bare heat spreader, minus the belt. HIs truly ingenious idea was to cover the plate with a thin layer of ABS to ensure adhesion: an ABS filament bonds very well to ABS!
I started with a big sheet of 3/32 inch aluminum, a bit thinner than the 1/8 inch sheet he used, which is what I had in the Parts Heap. Bandsawed three chunks to rough shape, squared up the edges on the Sherline with manual CNC:
That was complicated by the Sherline’s cramped work envelope. The 5/8 inch lathe bit on the right sits at exactly right angles to the X axis and serves as the reference plane. To make it happen:
- Stack the three plates, clamp to table aligned against lathe bit
- Whack off the far edge
- Put clean edge against lathe bit
- Whack off another edge
- Measure / scribe 120 mm from each new edge (thus the blue stripes)
- Align & cut
That actually worked quite well, although you’d think the angular error would build up as I rotated the plates. I checked and tweaked the angle after the first cut and it was all good.
Then drill six clearance holes for the socket head cap screws holding the heater plate to the ABP; a #1 drill gave a few mils clearance, which is all it needs. The holes are 4 mm in from the edges of the 120 mm square, with the two middle ones at, yes, 60 mm.
However, there’s not much meat between the edge of the plate and the holes: call it 1.1 mm. If you do this, using 122 mm plates would produce less scary-close results. That’s why I like manual CNC for this stuff: no need to lay it out, tap in the numbers and it just Works.
My APB heater has a static drain connected to the heat spreader, so I milled a 2 mm recess around the right-hand screws to clear the lugs, wires, and Wire Glue blob. The silicone wiper gets its own cutout, which I made a snug fit so that the rubber would push the plate against the screw heads and hold it in place.
I machined recesses on only one plate, so I could incorporate any changes in the other two. The initial setup was atop a scrap plastic sheet which, as it turned out, wasn’t particularly flat. The edges of that not-quite-complete hole on the left were nasty-sharp.
Then clean off the ink with xylene, scrub the plate with a 220-grit sanding sponge, and it looks really nice. Impossible to photograph a uniform gray surface, though: the autofocus goes nuts.
While all that was going on, I’d dumped some MEK into a polyethylene jar along with a handful of calibration cubes and similar debris. I used MEK, rather than acetone, because it’s somewhat less aggressively flammable while still being a good solvent for ABS. Right now, the gunk has the consistency of thin honey, which may be too thick to spread easily; I’m still figuring this out. I apply the gunk with a folded coffee filter: scrape the puddle around to cover the whole plate, then let it dry. This is best done outdoors, except that right now it’s well below freezing out there.
Here’s what the film looks like under the start of a quartet of dodecahedrons I ran off to see if they stuck properly:
The bottom surface looks like it was machined: dead flat,nice edges, good thread definition. The parts stick like they were glued to the surface, with no tendency to pull up at the corners.
The Outline thread shows some adhesion trouble for the first 10 mm or so. After that, it’s nailed right to the ABS film. That’s why I use Outline, at least until I figure out a better way to start the thread.
After I finish the next two plates, I’ll have a somewhat quick-change build platform: pull the hot plate off (holding it with pliers!) and slap a new one on. Not as convenient as the ABP, but much better for building precision parts like gears and extruder motor mounts.
The Smell of Molten Projects in the Morning 
This is a great idea! The materials science behind picking the build surface is very interesting. We tried dozens of things before picking Kapton as our build surface. Unfortunately this method doesn’t seem to be re-usable, and unless you can apply an even coat every single time, you might get uneven buildup of coatings.
Zach
It certainly lacks user friendliness along a number of critical dimensions! I don’t like it, but for printing out stuff with dimensions that matter, it’s better than anything else I’ve tried.
The ABS film peels off the aluminum plate and leaves a clean field for the next application. The dried film is well under 0.05 mm (at least after I diluted the “thick honey” down to “thin honey”) and slathering another layer over some small scraps that didn’t peel doesn’t add any real thickness; they pretty much melt together.
What it does highlight, though, is the non-level-ness of the ABP heater, because with an initial nozzle height of 0.35 mm, that 0.2 mm front-to-back tilt pretty much guarantees a well-glued thread at the back and a barely touching thread in the front.
The front-to-back arch (caused by all the copper on the top surface?) pretty much negates any benefit of my tedious ABP shimming. The combination of 0.1 mm tolerances, heat distortion, and the air gap under the surface poses a real conundrum… but it’s pretty close as it stands.
Hi Ed, it’s WiggyG again. If you’re looking for a way to coat the plate, I’ve been using a small paint brush (like you might use for detailing a model airplane). I initially used a thick “goo” of ABS to coat the plate. I’ve found that I can get away with a very thin watery coat and still get good results. The fun of using such a thin coat, is that after removing the part from the plate, you can just fill in the bare area with the thin slurry and be back to printing almost immediately. Since the ABS coating is on the order of 1 to 2 thou thick, “buildup” is a non-issue. I’ve done a dozen sequential prints on the same plate without stripping/recoating. I just touch-up the bare area from the previous print and keep going.
Best regards,
WiggyG
I’m following right behind you with the thin layer!
Rather than using a brush, which either clogs up or requires cleaning, I’ve been pouring a narrow line of liquid along one edge of the plate, then spreading it with the edge of a (scrap!) credit card. As you observed, covering the plate is good enough: there’s no need for an exact layer thickness because it dries to a very thin film anyway.
And, yes, it dissolves the previous layer and merges seamlessly into the scraps, so there’s no need to peel anything off. I was delighted to discover that!
I’ve been exploring the low-temperature end of extrusion around 200-210 C with the plate at 110 C. The thread doesn’t bond perfectly and tends to pull up at corners, so a higher extrusion temperature seems like a Good Idea.
Fortunately, I’m printing a series of fairing clamp plates for our bikes that serve perfectly well as adhesion tests: they’re usable even if they’re not perfect.
Ed,
You’ve many choices: Here is mine to you. I’ve just spent a few hours testing a Metal Leaf Adhesive purchased from a hobby store (Michael’s). I’m working another project but, I saw your efforts and the point is – This spray adhesive survived my 25 minute 350 degrees F oven testing without loosing adhesion. So, the idea is for you to, instead of using your homemade ABS goop adhesive, use an easy aerosol spray adhesive on your aluminum plate. The spray adhesive cures to tacky within two minutes. Plenty of time for your setting up. It remains tacky for up to 24 hours. Plenty of time for your setup. ;-)
Application: Spray a thin coating of adhesive and if you are able an even layer. Even if you aren’t able you would be hard pressed to spray enough to effect a height difference to your parts. Prepare your build-setup. I’m sure your machine warm-up cycle is enough time for the adhesive to be set for proper tack.
Clean-up: Dampen a cloth with ‘Goof Off’ (My fav. – its like magic.) or the competitor ‘Goo Gone’ (Not magic but, it sort of works.) Re-spray and print again. Fast, clean, efficient and pro-fes-sion-al?
My bot is down. Maybe you can try sooner than I can get new electrics. Even though I know it’ll work well.
There’s a can of 3M Super 77 spray adhesive sitting on the shelf that’s probably exactly the same stuff, what with there being only a few manufacturers of spray sticky, and I’ve been wondering what I bought it for… this may be the reason.
I’ll certainly give it a try, because the ABS-in-MEK mixture is just so nasty. On the other paw, the reason that can has been sitting on the shelf is that I really dislike spraying sticky stuff indoors: the overspray stays with you forever. If it works, I’ll need a downdraft vent hood in a big way.
Thanks for the suggestion…
Op – I just thought. If you really want your cancer causing MEK home made adhesive then a cheap spray bottle will work. Or you can get techy and use one of those kit aerosol spray bottles filled with your stuff. Or an airbrush. That’s how the composite shops do their spray release agents. You just need a layer of your non-release agent. :-)
Not with the syrup-like viscosity I’ve been using!
It turns out that a very very thin ABS layer isn’t as effective as a relatively thick layer, because the extruded thread doesn’t bond as well to thin ABS. I think the thread chills too quickly to melt its way into a thin film, but has enough time to soften a thick film.
A “thick film” is still much less than 0.1 mm, though, so it’s not much plastic at all.