Stepper Extruder Calibration Objects: Barbie Style

After a few ranging shots, I printed coasterman’s calibration set. Much to my surprise, they came out very nicely… after the obligatory bit of tuning.

Everything printed at 40 mm/s, 0.33 mm layer thickness, 220 °C first layer / 210 °C all other layers, 120 °C aluminum platform. The first layer prints at 25% of normal speed/feed atop an aluminum plate covered with a thin layer of ABS. I’m still tweaking temperatures, first layer speeds, and ABS thickness on the plate.

All the pix have been contrast-stretched and lightly sharpened to bring out the detail. You’re going to start seeing a lot of Barbie style objects, because I want to use up that pink filament, OK?

The single-wall open box has an actual filament width of 0.55 mm, suggesting a w/t of 1.7. The Cool plugin throttled the speed down to 15 sec/layer and it’s just about perfect.

Calibration - Thin wall box
Calibration - Thin wall box

Here’s what it looked like in progress:

Calibration - Thin wall box - extruding
Calibration - Thin wall box - extruding
Calibration - 50 mm tower
Calibration - 50 mm tower

I simply didn’t believe the 50 mm tower would print until I saw it emerge intact. This is with 2 extra shells and 25% fill, at 15 sec/layer. The suck-in along the right edge comes from laying down the perimeter shell before doing the fill: that’s where the nozzle departs inward after finishing the perimeter. The distance to the fill was less than the Reversal threshold, so the stepper extruder didn’t reverse.

A few passes with the perimeter width/thickness tester resulted in a block that fits into the slot all eight ways with w/t=1.75 (with some orientations, mmm, much tighter than others, I’ll admit). The fill w/t=1.5 is obviously too low, because the top layer got overcrowded even with 25% fill on the internal layers.

The suck-out at the left corner shows where Reversal starts inhaling filament on alternate layers.  This was with 35 rpm and 100 ms, which seems too aggressive. It’s not bad-looking, mind you; I touched up the sides of the block with a bit of sandpaper to smooth out the tallest ridges.

Calibration - Perimeter Width
Calibration - Perimeter Width

The second classic 20 mm solid box looked good at w/t=1.75 and fill w/t=1.65, apart from the corner that pulled off the ABS and grew a tab that messed up half the layers. That’s what caused me to junk the ABP; about which, more later. The first one came out with the top looking a bit thin at fill w/t = 1.75.

Calibration - 20 mm solid box
Calibration - 20 mm solid box

The first hollow box just didn’t work at all, because setting w/t=1.75 built a single shell wall and the overhung top didn’t connect to the walls.

Calibration - 20 mm hollow box - failure
Calibration - 20 mm hollow box - failure

Changing to w/t=1.5 produced a reasonably good result, although the lid didn’t quite attach to the walls across the long diagonal. I always drop a scrap ball bearing inside to prove it’s hollow in there.

Calibration - 20 mm hollow box - success
Calibration - 20 mm hollow box - success

The Oozebane tests looked great, even though I’m not using Oozebane: a stepper extruder pretty much eliminates the need for that plugin. The front one had a few strings at 85 ms / 75 ms, the back one was clean at 100 / 75, but the fill got strangely thin.

Calibration - Oozebane test
Calibration - Oozebane test

Skeinforge 39 handles bridge layers oddly: no extra shells, fill parallel to one axis, and I really didn’t have it set up right. The holes look OK, albeit with poor contact with the fill.

Calibration - Precision - top
Calibration - Precision - top

The aggressive overhang didn’t work at all, but the 45 degree slope looks passable if you’re not too fussy. Small overhangs may be OK, but you really can’t do them without support material underneath.

Calibration - Precision - bottom
Calibration - Precision - bottom

All in all, the combination of a stepper extruder, spring-loaded filament tensioner, and an ABS-coated aluminum platform seems to produce good results. Maybe I can finally start printing useful objects…

However, as we all know, cranking out good calibration cubes doesn’t guarantee anything else will print the same way…

10 thoughts on “Stepper Extruder Calibration Objects: Barbie Style

  1. Very nice calibration prints. I’ll be interested in hearing your thoughts on the thing-o-matic ABP, the one on my makerbot has been responsible for a lot of gray hairs.

    1. Well, that should give you a clue. [grin]

      Basically, the ABP simply doesn’t work and I gave up on it. For my purposes, “mass production” isn’t a big draw; I want accurate parts in onesie-twosie quantities.

      I’m in the midst of setting up an adjustable HBP with a removable aluminum plate to get better control over the build surface alignment. Getting a good first layer requires a flat build surface at a constant distance from the nozzle, held to about 0.1 mm. Ideally, that’s repeatable without fussy adjustment for each build session.

      That’s a difficult requirement for a box made of plywood and plastic, but I’ll see how close I can come.

  2. 40mm/sec and .33 layer with a .25 first layer @220C core and @120C bed is what I am using! Both w/t’s are 1.8 though so we are totally different! haha.

    It’s hard for me to peg w/t’s because I am having slight XY precision issues on my cupcake. The threads are not exactly the same distance apart. This results in inconsistent packing so I have to compromise.

    My biggest issue now is that large objects curl at the extents. I think this is due to my HBP being up on adjustment springs. I’m hoping once I insulate the airgap the borders won’t be at such a lower temperature than the center.

    1. large objects curl at the extents

      The aluminum build plate with an ABS film, plus printing the first layer at 10 mm/s, killed that problem stone cold dead!

      In recent days, a 90 mm outer diameter ring, a 90 mm square, a 55 mm block, and a 3 inch cylinder all look like they grew right out of the coating: no shrinkage, no peeling, no warping. The first layer welds itself to the film, to the extent I must pry the object off the build plate and the film peels off with it.

      Now, with that in mind, there’s a lot not to like: spreading ABS dissolved in MEK can’t possibly be good for you, manipulating a hot plate requires three hands, and I’m not at all satisfied with the platform leveling.

      But the objects come out just about perfect!

  3. I insulated my build platform . . . partially to keep the ABS lowrider parts cool, and also to allow higher temperatures on the build platform. With the insulation and a paper “table cloth” I can get the build platform pre-heated to 150 with build at 130. I just used three nuts between the wood and the aluminum+PCB sandwich, and filled the now open area between with bits of left over ceramic nozzle insulation.

    Having it this hot keeps the lower layers pliable and seems to stop the lifting. If a build is aborted at say 5 layers, the pieces can be rolled off with pliers :)

    I use a smooth kapton tape like this:
    http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180427091024
    on the build platform.

    At normal build platform temperatures, I do have the worst peeling at the corners of the build platform. The heat loss is greater at the edge, and the MBI PCB gives away heating at the edge for the LEDs. A better design would concentrate the heat around the edge and have less heat in the center. Do you have access to thermal modeling software? I’ll lay out the PCB :)

    1. the build platform pre-heated to 150

      What bothers me about the platform heater: it’s a PCB with circuitry on the bottom side. Nothing in there has a rating much over 100 C, which means it’s Yet Another Case of Component Abuse.

      It’s a nice compromise that achieves light weight and compact layout where those are important, but it’s really a consumable part. While I was fiddling with the cartridge heaters, I though this would be a nice place for a 1/8 inch heater: right in the middle of a thick aluminum sheet.

      But, so far, I’ve just been using an aluminum sheet atop the PCB and carefully not thinking about re-doing the heater design.

      MBI PCB gives away heating at the edge for the LEDs

      The V1.1 heater design (good pix halfway down there) has heating traces right out to the edge in all directions. The aluminum-tape “heat spreader” isn’t quite wide enough, but I’ve been ignoring that problem, too.

      The 3 mm aluminum build plate I’ve been using distributes the heat just about perfectly.

      smooth kapton tape like this

      Shipping something bulky halfway around the planet gets really spendy really fast, doesn’t it? Ouch…

    1. It was part of an MBI Rainbow Pack. Word has it that pink has since gone out of stock…

      I’m thinking that’s not due to a sudden spike in demand, though.

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