Perko Knot Reprint: Dissolvable vs. Breakaway Supports

Round 0: Dissolvable Supports

When the Ultimaker 3 came out a few years ago, we were really excited about the prospect of water-dissolvable supports. Imagine printing your model and then just letting the supports melt away in water! It sounds too good to be true, but it does work pretty much just like that, except for a some messy goopy things that happen along the way. To show off the power and usefulness of dissolvable supports we created a difficult spiky model that really needed those dissolvable supports, our Giant Spiky Perko Knot.

We printed the knot in Ultimaker Orange PLA, with Ultimaker PVA dissolvable support material. It was kind of a rough journey, especially with the “prime tower” that helps transition between the two different materials; you can read the whole saga at our original Giant Spiky Perko Knot article. Here’s how it looked when everything was said and done:

You can download this model from Thingiverse at Giant Spiky Perko Knot if you want to try printing it yourself! It’s not so bad at a normal size, but printing a huge one can cause all kinds of issues, no matter what kind of support you use.

Cat-astrophe :(

So life was fun, life was great, until our little gray cat Sackett decided he wanted to sit on top of the bookshelf where we kept our giant spiky orange knot, and…

This model had taken SIX DAYS to print, and plenty of filament and heartache. But it was one of our biggest and best models to bring to shows and conferences, so we had to try reprinting it. Trying to look on the bright side, we had to admit that our original model had some problems that maybe we could try to fix the second time around. Specifically, we had a lot of problems getting PLA to adhere properly to the dissolvable support material, and during the original print a lot of the teeth along the bottom of the model didn’t print correctly, or just fell off:

In addition, dissolvable support material is really expensive… and we had this unused spool of “breakaway” support material we had never tested…

Round 1: Underextrusion and Not-So-Breakaway

For our first reprint attempt we used Matterhackers Orange Pro PLA with Ultimaker BAM Breakaway support material. We got about halfway through the print before the orange stopped extruding for some mysterious reason. Click on the text in the Tweet below to open the entire thread of how things progressed including photos and video along the way:

If all goes well, then in 6 days and 6 hours we will have reprinted the giant spiky Perko knot that our kitty broke. Cross your fingers for me please! @Ultimaker pic.twitter.com/0zuNYduS4O

— Laura Taalman (@mathgrrl) November 20, 2018

Breakaway supports are exceptionally great at leaving a clean finish, but they are still very strong and hard to cut through, tear off, and remove. I’m actually glad this first reprint failed because I don’t think I ever could have extracted the knot from this diamond fortress:

Round 2: Interface and Out of Bounds

At this point we thought it might be good to economize. For our second reprint attempt we used the much less expensive filament Matterhackers Lime Green MH Build Series PLA, and went back to our good friend, Ultimaker PVA dissolvable support material. PVA is very expensive, but we only used it in the “interface” between the knot and the main supports, in the hopes that not much would be needed even for this very large model. We wrote about this on-the-cheap method for using PVA in our previous article Dissolvable Support Interface is Everything You Need. Click this Twitter thread to see how things went (spoiler alert – it doesn’t go well):

Giant spiky knot print redux, everybody please cross your fingers again! Will post progress in this thread over the coming days pic.twitter.com/SzKY6p9qZ4

— Laura Taalman (@mathgrrl) November 25, 2018

This time what stopped us was an unexpected “outside of normal printer volume” error. I have to admit that I scaled the knot up as large as I possibly could in Cura for this print, re-rotating and re-placing the knot until it just barely fit on the build platform. Cura let me do it, and managed to slice it, but I must have been just one tiny tooth over the line somehow, alas.

We did try to dissolve the interface support on the resulting partial print, but it didn’t work as well as we had hoped. The model and supports are just so dense and twisty that the water couldn’t effectively get to the interface to dissolve it. We didn’t have enough of the expensive PVA to do a print with full dissolvable supports, so we went back to breakaway…

Round 3: Breakaway and Elbow Grease

For our last (and ultimately successful!) print, we used Matterhackers Yellow Pro PLA and Ultimaker BAM Breakaway filament. This time we reduced the amount of support and switched to “zig-zag” instead of the diamond/cross-hatch pattern that was so impossible to remove in Round 1. In retrospect we really should have done the breakaway just in the interface, but here we used it for all of the supports. Click on the text in this Twitter thread to see the print from start to finish, with videos and photos along the way:

Round 3 of trying to reprint the giant spiky knot our kitty broke. It’s a four day print even at fast/0.2mm layer height. This iteration will use Pro Yellow PLA and “breakaway” supports. Fingers crossed! pic.twitter.com/fEoJ2QHKvL

— Laura Taalman (@mathgrrl) December 7, 2018

Taking off the supports took many days, and it was a serious and literal pain. Here’s just a piece of the process, in which we get some serious new snips from the hardware store, find our flush cutters, and then pull off part of a tooth by mistake:

But after an unreasonable amount of work that I do not care to repeat, in the end the breakaway supports delivered what was promised: an absolutely beautiful separation from the print, with no damage at all to the surface finish:

And here’s our new girl, cleaned up and ready for the next show:

Sackett says… I WAIT HERE FOR NOW BUT I WILL FIND WHERE YOU PUT THIS KNOT

tl;dr

Hey I 3D printed a giant spiky knot and you can too. To see how we designed it in the first place and then printed with dissolvable supports, check out our previous post, and to see how we reprinted the knot with breakaway supports, just scroll up :)

You can download the STL file from Thingiverse:

You can also order 3D prints of various Perko-related things at my geekhaus Shapeways shop:

 

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