Thursday, December 21, 2017

Wood filaments, finishing, Simplify3D

Someone where I work asked if I could make a base for mounting an unusual object as a trophy. I remembered that wood-infused filaments are available, so I said I'd give it a try. It turned into quite a project, and I learned quite a few new things:
  • Printing with wood filament
  • Switching filaments during printing
  • "Engraved" lettering
  • Section analysis in Fusion 360
  • Sanding, staining, varnishing and gluing wood-infused PLA
  • Simplify3D instead of MatterControl

Filaments

Globs that would need to be ground off and sanded.
Because I had a timeline of about 3 weeks, I bought the only wood filament available at my local retail store, GP3D wood light, which says it is 40% wood. It prints a lot like PLA, but it's more brittle and rough: one time the source filament actually broke while I was printing. It tended to produce little globs on the surfaces. My model had "engraved" or negative-space lettering, which I figured would be tricky, so I printed several chunks of my model with the wood, trying to get good smooth results. Time was running short and I was not getting the results I wanted, and I could find no user discussions of the material on line, so I ordered some Hatchbox wood filament that looked very popular.

While waiting for the Hatchbox to arrive, I figured out that I was using too high a temperature, which was causing some material to scorch inside the nozzle and then come out as a hard lump. Once I dropped to the low end of the temperature range, 190C, that seemed to settle down and I started getting smoother prints.

The Hatchbox printed nicely the first time, and I ended up using it for the final product. To be fair, the GP3D probably would have done fine as well with the lower temp and (as discussed below) Simplify3D. The Hatchbox seemed to come out smoother and more plastic-looking; it does not say what its wood percentage is. So maybe I'll give the GP3d another try on another project. Being a more woody texture, the GP3D took stain better.

Switching filaments

Contrast layer samples, between wood layers, after staining
Rather than a monolith of wood, I wanted to insert a contrasting layer to make it a little classier. I printed some samples with glossy black PLA, and also with some rather translucent PET-G in magenta or green. Eventually I decided to go with the black. The contrast layer was just a short ways down from the top deck, so I could "engrave" letters all the way to it, so the letters would have a black background.

Switching filaments is certainly possible, but there is a lot of discussion on the Internet on who to do it well. I learned a few things:
  • By default if you just pause MatterControl, it leaves the head in place. It can ooze filament, and when you insert new filament some needs to come out to get it flowing. This could land on and mess up the previous layer.
  • By default the stepper motors release after 60 seconds, so if you can't switch in that amount of time, the head or bed can move and ruin the print when it resumes. I spoiled one after 4 hours of printing, so I went looking for a solution.
  • I found some custom G-Code to add to the pause and resume actions. I set the pause to move the head up 20 mm and lock the motors for 10 minutes, and set the resume to lower the head back down. This worked well. I also slipped a piece of paper on top of the model to catch the ooze.
  • Pausing is not an instant action. I wanted a clean transition of colors, so I learned to preview the layers to see where the head would be at various times, so I could select an optimal location inside the model, not on a perimeter. The different colors would be hidden in the infill. Depending on the specific situation, sometimes it's in the layer before, and sometimes in the next layer.
The final model was going to take over 6 hours to print. I needed to switch colors after about 4 hours. In one of my test prints, and then in my second attempt at the final model, when I paused to make the switch the head moved up but would not stop extruding! There was nothing I could do to stop it and I had to cancel the print.

Engraved lettering

My design has a couple of "nameplate" surfaces on the sides with lettering cut into them at an angle. One of them includes a company logo which I had to learn how to import into Fusion360. The first tries used lettering way too small, which came out rough and globby, so I went with a larger font and simplified what I wrote (I had the design flexibility to do that). It also has some letters cut into the top surface, all the way to the contrast layer, which would give them a nice dark background.

Section analysis in Fusion 360



To attach the object to the trophy base, I designed a little round pedestal which would fit into a hole on the top. I wanted to see how all the pedestal plug fit, and how close the bottom came to the bottom of the hole so I could glue it in. I found the section analysis option, which was very helpful.





Finishing

The globby lettering needed some cleanup with my Dremel, and some sanding to get rid of the "pimples". Since it's 40% wood, the material sands better than regular PLA does. Regular PLA tends to turn white when sanded. This does a bit too, but not bad. Unfortunately it is still plastic, so when I trimmed some things with an Xacto knife, they tended to stick and remain as fibers, rather than cutting off cleanly as wood would.

The wood filament is pretty light in color. That's nice for some things, but I wanted a richer color for a trophy. I tested some stain that I had on hand. The stain tended to penetrate the grooves between the printed layers, which looked like wood grain. But it did not penetrate much in the smoother areas, even after 30 to 60 minutes, especially where I had sanded. I needed to leave the sanded areas a bit rough if I wanted them to stain.

I had some Varathane on hand, which is really a plastic and not a varnish. I was concerned that its solvent might dissolve the PLA, but it worked just fine.

I knew I would need to glue some of the final parts together, so I looked to see what was compatible with PLA. A very comprehensive article pointed me to Loctite Gel Control. It worked great!

Software

I didn't think that the runaway extrusion was the fault of the printer, but rather of the software. It became apparent that I was going to need to reprint just the upper sections of the model due to the aborted filament switch. I also was not thrilled with the little bumps caused by filament oozing when retracting on moves. The wood filament was not sticking to the bed well, causing wrinkles and flaws. And I was having trouble with the completeness of the top layers, and was futzing with extrusion factors to try to fix it. 

I've been using MatterControl, which came free with my Robo3D printer. Some reading earlier and when trying to solve these issues led me to Simplify3D as a more professional option. Many people have raved about it, so I bought a copy, although it is $150. If there was a chance it was going to help me not foul up a 6-hour print (I only had a few days left for this job), it was worth it.

I printed a test object (in PET-G, since that's what was in the printer at the time) and I was shocked at
how smooth the print came out. The sides and top were silky smooth, no nubs. The lettering was sharp and had nearly no globs. Nice!

For my next try at the full model, I used S3D. The sides and the lettering on the nameplates came out perfectly smooth, dramatically better than what I had achieved before. I saw that there was still a lot of discussion on how to properly change filaments, so instead of attempting that I stopped the print, and printed the contrast layer and top deck separately, and planned to glue them together. S3D's ability to start and stop at certain points is easier to use than MatterControl's, though I wish it were specified in layer numbers rather than measurements.

What a huge difference in print quality! I could see it right from the start, with great adhesion and smoothness in the first layer, and perfect smoothness all through the infill. The lettering was incredible. I spent maybe two minutes cleaning up a couple tiny globs with an Xacto knife, and NO Dremel work at all. I decided I did not need to sand the nameplates at all either, which would let them stain better. As one of the reviewers pointed out, the saving in post-processing time alone justifies switching to Simplify3D. I'm sold! (Though it does have a few quirks...)

The finished product

The first finished iteration was from MatterControl with a lot of cleanup. The customer loved it. "Just one thing... could you move this to there instead?" Um... sure... I'll just do another 6-hour print, stain, varnish...  The second iteration was done with Simplify3D, which required very little cleanup. It came out much smoother, with much sharper lettering, though slightly less woody-looking due to the poorer stain penetration. The customer loved the final result!


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