Putting MG47 to the test

John Branlund has been starting to try out the MG47 ABS filament, and I finally was able to do my first proper test on Tuesday. Last week I had tried running ten feet or so of the filament through the machine, but had mixed results – there was zero die swell (0.012″ filament out of a 0.012″ orifice), and running the first few layers of a Mendel z-bar-top-clamp_4off showed the same sort of warping and lifting that I was getting with the Chi Mei Polylac PA-747 material. Meanwhile, however, John’s first test with MG47 didn’t look too bad. I figured that the difference must be in the fact that John had actually dried his filament, whereas I was running it just as it had come from extrusion. Though the reels had been packed with a desiccant packet, the filament had still been fresh out of the cooling water bath – although it was technically dry, it had probably absorbed a great deal of moisture between the exit of the extrusion die and the start of the air drying rack.

I tossed my 3 lb. reel into the kitchen oven for an extended period in an attempt to remove as much moisture as possible.  In retrospect, I should have also put in a proper thermometer, as the knob on my oven is not exactly calibrated to an established standard (even when cooking the very simplest of frozen pizzas, I have to set the knob a good 25 degrees under the recommended temperature to keep from turning crust into carbon).  As such, my spool took on a slight set – while it it looks a little wavy if you gaze down a length of it, it should prove entirely usable.

With the dried filament spooled onto a reel, I loaded it into the machine and ran a foot or so through the 0.012″ nozzle.  Given how liquid the material seemed during my brief initial test, I dropped the temperature down to 250°C rather than the 270°C that Stratasys P400 ABS runs at.  Checking the torque load on the motors showed values in the low 60s, which I think was even less than what P400 at 270°C was running.  I checked the die swell again, and it was improved – about 0.0145″ (still 0.0025″ short of what P400 swells to, but certainly better than what the wet material was).  Checking for ooze (turn off the feed, wipe tip, wait 10 minutes and see how much material has leaked out) showed minimal seepage – this was certainly the driest filament I’ve yet run, and I need to start drying all my material under the Z-stage in the machine just like John craftily does.

I flipped around the polystyrene sheet on my build platform (it was getting warped a bit in one area) and brought the model tip down so that it was actually slightly buried into the styrene sheet (I should really start using feeler gauges for this, as it’s nearly impossible to eyeball correctly – I miss building on foam).  I started feeding the machine the Mendel z-bar-top-clamp_4off part sliced at 0.007″ layers (the smaller road width had helped when trying to run the PA-747 material, as it also had less die swell than the P400).  The first layer was a bit spotty – the tip was so low that the material couldn’t even exit the nozzle in a few areas, but things appeared to be running pretty well regardless, so I let it continue on.

The crosshatch infill was nice and straight with minimal filament droop.

Once done, I was amazed at the surface quality – this was one of the nicest parts I’ve gotten from the machine (the 0.007″ slice height certainly helps).

The bottom of the part turned out to be straight as can be thanks to superb (perhaps too good) adhesion to the polystyrene sheet.

The next test was to try running the MG47 on blue painters tape.  Unfortunately, the platform doesn’t come up far enough to let the tip come right down to the tape surface, so this run had the filament dropping about 1/32″ from the tip to the tape.  Notice the zig-zag of the outlines as this run used 0.010″ slice heights and hence wider road widths – without the die swell of the P400 material, the extruded filament is longer and has to bunch up.  I let this run for about 3 layers, but there just wasn’t enough adhesion between the tape and the ABS, and corners started to lift.

This led me to wonder how the Bolson ABS would work in the same setup – since the Z height would be identical (stage raised as far as it can go), I could get a suitable comparison regarding warp.  I loaded in the Bolson ABS, flushed the MG47 out of the liquifier, and let the same part file run once again.

The Bolson ABS still had corner lifting after the same number of MG47 layers, though not as bad as on the MG47.

The Bolson ABS also had better adhesion to the blue painters tape (perhaps the reason for less warp).  A good bond between model and support is absolutely essential, it appears – no wonder heated beds on RepRaps and Makerbots are all the rage.

Overall, I’m very happy with the MG47 thus far, as it beats the Chi Mei Polylac PA-747 in every way when it comes to use on a Stratasys:

• More die swell (though to be fair, I should try fully drying the PA-747 for a proper comparison)
• No visible vapor of volatiles coming from the tip when extruding at 270°C
• Filament doesn’t cling to the hot nozzle for dear life – the brush wipe actually wipes the filament off instead of smearing it on more
• No spiderweb thin ‘hot glue gun’ filaments coming off the part at path exits

No, the MG47 isn’t quite a match for the Stratasys P400 ABS (or even the Bolson ABS), but it appears that I’m on the right track.