More build surfaces that don’t work

Since I’m pretty much out of support material for the Stratasys (well, not really, but I hate to break open my very last reel of OEM P400 support), and my extruder hasn’t yet run the HIPS that I hope will be a suitable substitute, I’ve been playing with alternative bases for building.

When I first started making the build platform, one of the surface materials I ordered was a very fine stainless wire mesh. My thinking was that it would provide enough surface roughness to mechanically bond with the ABS, but could be peeled off after cooling. I placed the wire mesh over the silicone sheet I had originally tried using and clipped it to the Garolite platform.

The mesh didn’t lay perfectly flat, but it seemed like it should be okay.

However, after coming up to temperature, the silicone sheet under the mesh expanded and buckled.

I tried running a part outline anyway, but the flex of the mesh prevented a good bond between it and the ABS in most places.  Some spots did have decent adhesion, but given the flexibility of the mesh, warping and curling would undoubtedly remain a problem even if I had decent adhesion all around.

The next idea came to me after seeing that Makerbot started offering PVA 3mm filament. Given that PVA has such a low melting point (and that the material is highly hygroscopic), I’m skeptical that it would be a good support material for ABS, but it did give me an idea. I recalled that PVA is commonly used as a water-soluble release agent when molding fiberglass. What would happen if I put down a base of MG47 ABS, brushed on PVA as a release, let it dry, and continue building the ABS part?

I used a Mendel part and modified the Quickslice parameters so that it would create the base layers using model material rather than support material.  Annoyingly, there appears to be a bug in Quickslice 6.4 that results in a single layer of support material being laid down regardless of if you tell it to use the other tip!  Thankfully I still had enough adhesion between the second layer (first deposit of ABS) and the foam base to keep it stuck down reasonably well.

I added a ;PS command to the generated .SML file so that the machine would halt after creating the base, and then used a sponge brush to brush on a few coats of PVA.  I noticed some crackling sounds from the ABS/foam bond when brushing, but didn’t think much of it at the time.

I put the PVA coated base back in the machine, let it dry for about 15 minutes, and hit the pause button to let it continue with the build.  I noticed that the model tip seemed to be trenching through the PVA layer, but let it continue onward.

D’oh!  When I checked back later, I realized I hadn’t seated the tray carrier fully to the rear during the base build, and the model was hanging off the front edge.  This was far enough into the build to see if the PVA would serve as a good release, so I halted operation and pulled out the tray.

I was able to peel up the two ‘tabs’ on the base a little to separate them from the part, but the rest of it (as indicated by the green area where there is still PVA) wasn’t going anywhere.  Time to let the piece soak in water overnight to remove the PVA.

Well, the results were not as good as hoped.  Despite the PVA layer, the model ABS bonded quite well to the base ABS, and clean separation of the two wasn’t really possible.  Well, what if I tried increasing the distance between the base and model?  Between each layer in the .SML file, there is a relative move upwards in the Z-axis, followed by a relative move downwards in Z.  I modified the move between the base and model in the .SML file to provide 0.002″ of gap in addition to the pause needed for me to brush on the PVA.

I went through multiple iterations of this, with warp/lifting of the model layers always happening, even as I decreased the gap between the base and model and reduced the amount of PVA applied.  Finally, I was running with no gap and realized that thermal stress during the first run must have raised up the base slightly causing the model roads to plow through the PVA and bond to the top base layer.

As it turned out, I later found that Dr. Adrian Bowyer (founder of the RepRap project) had investigated this concept nearly 6 years ago.  Instead of PVA, he had used plain old kitchen pantry corn oil, with reasonable success.  Of course, his build size was not as large as what I was attempting.  The idea probably still has merit (I’m curious about using acrylic spray paint as a release layer), but there’s plenty of other things to investigate…

I finally got around to opening up the bag of 4043D PLA from MakerGear to see if it might serve as a good support material. iFeel Beta has had promising results with this, so hopefully it would run on the Stratasys.  The material is certainly the most brittle filament I’ve tested so far, and I had a number of breaks when trying to wind it on a spool.  As such, I decided it was best to try feeding it through the rollers alone to see if it would break.

Fortunately, it fed fine through the rollers with no breakage, so I put the drive block back onto the head and tried pushing the filament through the liquifier.

This resulted in the highest feed torque values I had yet seen – this was not an easy feeding material.

Sure enough, the material eventually jammed as the toothed drive roller stripped into the filament, losing traction.

Still, running the material through a Stratasys is indeed possible – another user with a Prodigy Plus has done so successfully, and sent me this photo of the drive assembly.  The idler wheel is solid metal, unlike the one on my 1600, which has a urethane center section.  Machining such an idler may be a future project, but for now I’ll abandon the work with 4043D PLA.

I decided to try using ABS as a base material and simply saw the parts off the base as needed.  As such, I manually added a base in Solidworks rather than adding a base (and faking the material) in QuickSlice.  I dotted the base with holes to make Quickslice generate perimeter roads to provide a little additional support, and then ran the part.

After the base was mostly complete, I halted the build, as there was a lot of sinking on the surface since the crosshatch infill had too large of a road width for the limited die swell of the MG47.  I recreated the base on the part, as the big 3/8″ thickness was definitely overkill, and it extended much further outward than needed.  With a reduced crosshatch road width of 0.0132″, I tried the part again.

The carpet-like top of the base layer reminded me that I had neglected to adjust the road width for the other layer types as well, but as the crosshatch infill was looking great, I let the build run until completion.  I also dropped the nozzle temperature down to only 240° C, as the feed torque wasn’t very high, and lower temperatures would droop less.

At the end, I had prototype paintball hopper halves and a pump for my Phantom paintball gun.  As noted, I had drooping filaments due to not having adjusted all of the road widths.

I expected a bit of drooping on the overhangs, as I wasn’t using any supports.

Rather than having to cut and sand the parts off of the base, they were able to be peeled away without too much fuss.  The crosshatch infill came out great, with no drooping all the way through the part.  I had intended to just tear out this infill, leaving the hollow shell, but the filament is a lot tougher than I had expected.

The base did lift from the foam base on one side, unfortunately, which let the hopper halves warp a bit.  With this build complete, I went back to QuickSlice to adjust the road widths for the other layers and tried running a small test part that used aligned roads as the top of the base.

While the dome on the part didn’t come out perfect, I didn’t have the same sagging as before.  The stubs on each side were John Branlund’s idea as a way to check for backlash. Fortunately, I had no discernible backlash in the system.

The part separated quite nicely from the base – only minimal sanding would be needed to remove the traces of support from the bottom of the part.

I ran 2 more parts at increasingly higher temperatures (left was 240° C, center was 255° C, right was 270° C) to see what the results would be.  Sagging on the top aligned roads of the base increased as the temperature went up.

Separating the part from the base also became more difficult with the increase in temperature, as the layer bonding became stronger.

Fortunately, more OEM support material has now arrived, so I can finally be back to proper operation shortly.