My ABS is all droopy

I ran some more parts with the New Image Plastics ABS, and noticed something odd:

No, not the horrific brightness/contrast I needed to apply (natural ABS does not photograph well if you’re trying to capture detail)  – the sunken, spongelike top surfaces of the parts.  I had been using a crosshatch fill pattern for parts within the Quickslice software which worked just fine with the Stratasys ABS, but the NIP ABS acts a little differently.  Here’s what the internal crosshatch fill should look like:

The pattern is about 0.15″ square – the important part is that the filaments are entirely straight and do not sag.  Unfortunately, this isn’t what happened with the NIP ABS:

In this case, the extruded filament did not stay taut, and the insides of the parts resembled the world’s smallest Golden Gate Bridge convention.  When the final top layers were laid down, they draped over the peaks in the internal fill, leaving a lumpy final top surface (though the outer contours were just fine).  None of the process parameters were changed from the Stratasys material, so I’ve started to wonder what the difference in formulation or processing might be?

In any case, I’m not about to lose sleep over it – the order of magnitude difference in price between Stratasys and NIP materials means that I can dispense with the crosshatch interior fill and use the standard ‘fast’ fill.  Sure, it takes longer to build, but the parts are notably stiffer with the extra density, and the Stratasys has proven to operate reliably when run unattended.

Perhaps tweaking the parameters will help some, but if I have to run with standard fast fill instead of full crosshatch, I can certainly survive.  It’s not as if I currently have a need for ultra low density parts.

5 thoughts on “My ABS is all droopy”

  1. Heat was my first guess – I tried dialing down the temperature by a few degrees, but it didn’t appear to have much effect. I’ve been assuming that unless otherwise noted, ABS is ABS (the Stratasys MSDS sheet says simply “Acrylonitrile/butadiene/styrene resin”), but in looking at the Wikipedia page on ABS, the material properties (including heat resistance) can indeed be modified by adjusting the proportions of the component acrylonitrile, butadiene and styrene monomers. I wonder if it’s possible to determine the exact mix of the Stratasys ABS versus the NIP ABS?

    Good call – I’ll try doing some experimentation at lower temperatures.

  2. I’ve found that color additives (or lack thereof) can change the proper extrusion temperature to up to +/- 10’C. Stratasys probably “calibrate” their different colors to all work well at the same temperature.

  3. I had actually been wondering if trying a colored ABS might improve the sagging. You’re probably right about Stratasys formulating all their colors to run at 270 degrees C. Obviously Stratasys puts a lot of effort into allowing for consistent output by way of material formulation and careful calibration of machine parameters. I’ve been digging through the definitions files in Quickslice, and someone did a lot of work to come up with all the flow curve charts – there’s a separate definition file for each tip size/layer thickness/material combination, and each machine model has its own set of files.

    I’ve been wondering how RepRap might be able to achieve this level of turn-key simplicity. Sure, people can now build their own Mendel or even get a Makerbot or RapMan, but it seems that there’s still a great deal of end-user experimentation required to get usable prints. Meanwhile, I had a whopping 5 minutes of instruction from the seller of my Stratasys (followed by perhaps an hour of skimming through the machine manual), and I was full steam ahead in making good parts after a couple of tests.

    I’m wondering how Stratasys actually developed the various flow curves in their software, and if something similar can be done for RepRap. Perhaps some sort of calibration pass that puts down beads at different speeds and flowrates so that the results can be measured with a micrometer, then have the user enter in these measurements so that the software can self-adjust?

  4. “Perhaps some sort of calibration pass that puts down beads at different speeds and flowrates so that the results can be measured with a micrometer, then have the user enter in these measurements so that the software can self-adjust?”

    Should work… that’s basically how we calibrate monitors/printers.

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