[3d Printing] You're a Mean One, Mister Grinch

A lot of the time the things that we build are done because we have a need and a purpose in our households. For example, my household is full of pervy hobbit fanciers and connoisseurs of 80s cartoons. We make no bones about it, we pretend to be nothing that we're not, and a good time is had by all.

Given the season, my roommates had certain demands. One of them is that they want cookie cutters. Not just any cookie cutters, but once appropriate to the household and to the season.

The Grinch, not to put too fine a point on it.

Now, yes, the Grinch is a licensed property of a significant IP stakeholder which has no compunctions about going after anybody for anything at any time. That's why having your own 3D printer is amazing.

So I sat down with Onshape and made a stab at creating an appropriately interesting cookie cutter.

(It's always best to cover yourself whenever possible. Also, I can't resist a good pun.)

You can tell from the last captured state in Onshape how this essentially went. I pulled in a piece of line art with the original Grinch in a very classic pose and then I set to tracing out the bits that I knew I wanted in the cutter with splines. Much like rotoscoping, this is a tedious piece of work. Unlike rotoscoping you actually have to think about how much line density is too much because you actually have to worry about bits of goo squirting between pieces of plastic.

The prototype took a couple of hours to put together, not the least reason being that figuring out how to extrude splines and get them to create surfaces which can then be thickened into walls with volume which then get merged into a single object along with a base which gives you something press against – this is an interesting problem if you've never solved it before.

I love interesting problems that I've never solved before. Total win for me.

Once the basic design was complete, it was time to take it over to the printer.

And this was where the nightmare began.

For whatever reason, bad day, bad temperatures, bad experimental settings, just the wrong phase of the moon – I had adhesion problems. Not small adhesion problems, the kind of adhesion problems that end up with a pile of spaghetti sitting on your build plate. Not the tasty kind of spaghetti your mom made, either. The ugly, weirdly brittle filament kind of spaghetti.

Some days are harder than others.

Six times I juggled settings and modified model, to bring it back to the OctoPrint server and out of the Mini Delta – and I ended up in a world of disappointment every time.

Finally I just decided that the best idea was to solve the problem with a hammer, put a raft on the bottom of the build (and for those of you who are not familiar with 3D printing, a raft is essentially just saying "squirt several layers of plastic in an area slightly larger than the thing I'm printing and then start printing on top of it, because I can't figure out how to get this thing to stick and stay stable on a smaller base that's not made out of semiliquid plastic").

I suppose it's obvious that that worked, but I'm not thrilled with it.

There's a fair amount of stringing, which I generally attribute to an experimental printing at way to high temperature. You can't tell it from either of photos but there is a bit of warping of the raft where it let go of the BuildTak on the platform right there under the peak of the hat. It doesn't make much difference beyond the first couple of layers, but that's the sort of thing that should "never happen." I'll blame that on the fact that I was experimenting with printing on a totally unheated bed.

Do you need a heated bed for PLA? Absolutely not. Does it make everything easier and less frustrating if you actually use your heated bed? Absolutely.

So this morning was back to the drawing board, kind of literally. I've simplified some of the facial features, I've modified the printing parameters, I've re-extruded and re-thickened the walls so that they match up properly after the edit. I've taken off the raft and instead I'm printing the bottom of the model directly on the heated bed – and the printer is working its way through the model right now.

I'm only printing at 60 mm/s, even though I could probably drive it at 80 mm a second or more and still come out with a pretty nice print at 0.2 mm layer height. Making sure that you've got enough extrusion of the filament getting hot enough to come out of the nozzle that fast – that's where things start getting questionable. So today, after a pile of failures yesterday, 60 mm/s.

At the moment it looks like we've got good adhesion, good temperature control, not a lot of stringing, and things are pretty copacetic. But as any of you who have played with 3D printing yourselves now, everything can change in the blink of an eye and there's always 30,000 eyes watching.

Hopefully, I will get to report a nicely completed cookie-cutter in PLA before the end of the day.

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(For all you people hunched over the keyboard ready to send the message, "but PLA isn't rated a food-safe material!" Yes, you're right. Particularly FDM-printed PLA is not rated as food safe because it can be somewhat difficult to get particles of food loose from some of the layers if you have some textured exterior, and at 0.2 mm layer height, you're guaranteed to have some texture.

Personally, I don't care. This thing is probably only going to see use once or twice, then get run under hot water, and then my roomies will end up giggling helplessly as the thing deforms with a very light touch because the glass transition temperature of PLA is amazingly low.

And that's all right.

It's really all right.)