What with printing this and that and those and some other things, we ran through a pound of red filament in short order. That’s fine with me, because I could never figure out a good combination of settings to photograph the objects; the cameras I have on hand seem blind to saturated red and overexpose the daylights out of it, even with the flash turned down a stop or two.
We picked yellow as our least favorite of the remaining colors, yanked out the last few feet of red filament as a show-n-tell for presentations, rammed in the yellow, and extruded a red-to-orange-to-yellow plastic tangle over the platform.
The two filaments had somewhat different diameters:
- Red: 2.91 mm dia → 6.65 mm2 area
- Yellow: 3.00 mm dia → 7.07 mm2 area
The area ratio is 1.06, so the yellow filament puts 6% more plastic through the nozzle at a given extruder speed. I’d been running the red filament at 1.40 rev/min for 20 mm/s feed, so the yellow should produce the same results at 1.40/1.06 = 1.32 rev/min.
My Shop Assistant designed some beads for a cloak she’s repairing and we tried one at 1.25 rev/min (better to err on the low side, I figured) that came out thoroughly overstuffed. She deemed it usable and whisked it off for painting before I could get a picture.
I ran another one at 1.15 rev/min that was still a bit overstuffed. A pair (using Multiply) looked better at 1.10 rev/min. This is a group photo:
So I ran off two polyhole test sheets at 1.15 and 1.10 rev/min, the latter of which looked much better. At 1.10 rev/min, the holes run a consistent 0.3 mm smaller than the programmed diameter: 3% on the 9 mm hole. Close enough!
Then it’s time for some things from coasterman’s calibration set.
A thin-wall box at 1.10 rev/min and 20 mm/s came out with exactly 0.66 mm wall width, so that extrusion speed produces a physical thread that matches the Skeinforge thread parameters used to make the extrusion: 0.33 mm thickness and 2.0 w/t.
And then a perimeter test box came out perfect. After scraping off some Reversal zits, the small block fits into the recess in all possible orientations. The base is slightly larger than the top, but that just makes for a somewhat more snug fit. The block is upside-down in the recess so you can see both sides of the printed objects:
So.
The initial extrusion speed ratio based on the filament area gets you close, but it still takes a few calibration objects to achieve perfect results. What’s really nice: after that calibration, it’s spot on!
The Smell of Molten Projects in the Morning 
See also:
– http://www.thingiverse.com/thing:5310 (+ variants)
– http://makerblock.com/profilemaker/
Profilemaker suggests 1.27, a bit lower than my initial 1.32 guesstimate, so it’d still take a few calibration runs to reach 1.10. There’s certainly enough windage in the effective drive gear diameter and gear swell to put us in violent agreement, though.
I simply want consistent results from the printer, so finding one set of parameters that works will be fine. Given that, I can design parts around its capabilities and expect to get finished plastic lumps with reasonable dimensional accuracy… if the bunnies look a tad funny, that’s perfectly OK!
> Profilemaker suggests 1.27, a bit lower …
Sure – they’re not perfect. Or, rather, the consistancy & tolerances of the machines & materials aren’t going to let you get a perfect result every time.
These sorts of tools do save you a few cycles of brain power, though. Once you get them dialed in a bit, make it very easy to change the printing profile – a different layer height or feed rate or w/t or whatever is just a minute away. After getting a grip on this stuff, I went from meticulously creating a bunch of profiles for various needs to just having the software generate new profiles every time, on the fly, for whatever attributes I wanted. I even stopped keeping skeinforge profiles – I just have a base one with the defaults I want.
> I simply want consistent results from the printer..
That’s fine too! :)
Truly a scarce resource these days!
For all the thrashing around I’ve been doing, it’s only lately that I’ve been actually printing stuff. It’s time to switch gears and not think about printer hackage; it’ll take a while to get out of that mindset…