Saturday, 27 August 2016

Printing with flexible filament is fun

I'm just about out of the purple Innofill plastic. For purposes of printing things for our kitchen, I'm looking for a matching red color. Turns out there's a color scale I hadn't heard of until recently, namely RAL, and some things I spraypainted were RAL 3003, a nice deep red. So let's see if that's available in filament!

At they offer any color filament you can pick out of RAL, but you have to buy 10 kg at a time, which is a bit much. They don't state the RAL for their regular spools.

At I find exactly the right color, at an almost suspiciously low price, 16€ for 800g. Looks like they're quite active on the forum, and I don't see any complaints there. (argh! When did "berlin" become a top-level domain?) has a nice overview of their colors, but alas no 3003. it is. Got here just before we left for the US, but not in time to do anything with it. Also got a sample of PETG, which I hadn't heard of before, but sounds like it's worth trying.

I'll need to do a better filament setup. From what I'm reading, the way I've just had the spool hang loose with no guiding and letting go of the end, I've set myself up for the tangles I now suffer from. I broke the spool holder that came with the kit, plus it was for larger spools AFAICT, so now I'll just use the rest of this spool to print the holder for the next.

For a quick test print, I reduced infill from 20 to 5%, set 1 top and 2 bottom solid layers, set infill_only_when_needed to true. Then I printed a reduced version of this filament holder to check that it matches my spools. Looks good, though it was probably designed to just let the spool sit loose and accept the bit of friction. I started designing a spool holder rolling on four ball bearings, so there's practically no friction, but then it struck me that a bit of friction may be a good thing. Instead I might just want to guide the filament better, maybe with a bit of PTFE tubing and a longer way from the spool to the extruder. Only problem with that is that cold pulls become harder.

And because I was running low on the normal filament, I decided it was time to try out the flexible filament. At the same settings as my regular PLA, it came out quite nice:

This is not an extremely flexible filament, just enough that I can compress the sides of this cube. I was going to print at 25% speed, but it didn't get picked up, and printing at 100% worked just nicely. Let's move on to testing ObPhoneCase by intersection the design with some cubes and printing that.

I realize now that placing the design centered in 0,0 would have made some things easier, for instance scaling.

Looks like I set the Z adjustment a teeny bit high, but the flexible filament doesn't seem to curl when cooling, so all that does is make the bottom layer less flat. That simplifies things!

The trickiest part of the phone case is getting the holes right. While some overhang is doable, it's not so predictable. However, printing with support doesn't work so well for this kind of structure, the support generated by Slic3r is fairly heavy-handed and doesn't come off nicely in this case:

Overall the case looks good, though:

Eventually I just decided to do my own support for the holes, with little cubes literally hanging in mid-air, but with a fraction of a millimeter distance. That actually came out really nice:

They come off at a light touch (actually some fell out just due to the bending when getting the print off the bed) and leave only the smallest of marks.

Saturday, 6 August 2016

More printing success than you can shake a piece of filament at

After cleaning the stripped filament from last time off the hobbed bolt, I printed the phone cover with my regular filament, just to see if it would fit. And it does! My calibration is great! My design, however, needs a bit of tweaking, but that was exactly the point of this print. The bottom holes should be a bit higher, the audio jack a bit further right, and both possibly enlarged. I'm quite amazed, though, that the overhang for the USB-C jack came out so nice - that's without any support:

The hole on the side needs a bit of enlargement, and the sides of it should be slanted for easier access:

On the back, there is a little bit of offset to the left, and the hole for the fingerprint is up too far. Plus, the sphere I used to make the fingerprint scanner easier to touch left a few strands. That might just be the effect of having a part that's thinner than the layer height. I can reasonably make it more steep.

Most importantly, at the very start of this print, I caught the extruder skipping a few steps, and just to attempt to save the print, tightened the idler screws somewhat, to where the springs are almost fully compressed. That helped! So now I know that the stripping has been partly due to the idler being too loose. That clears up one of my remaining questions.

After that, I printed the AAA battery dispenser again, this time at 90% scale. Unfortunately, part way up it the hotend came a bit loose (the mounting system is crap and I want to print a better one), and I had to fasten it again while printing. The result can store batteries, but isn't as nice, and tends to have the batteries go sideways:

Having noticed the very nice overhang on the phone cover, I thought it'd be nice to have a test piece for overhangs. So I maded one (shared on Thingiverse):

Overhang test with the overhang width in mm.
This shows that I can actually do up to 18mm of overhang, which is pretty incredible. It also shows "ringing", especially after the letters, which I should fix. While most troubleshooting guides seem to blame speed or acceleration settings, I think in this case the slightly loose hotend may be to blame.

The back side of the test piece has circles, where while the overhang is technically smaller, the ends fall down, making them a bit unclean:

I tried also doing this test without my fan running, to see what difference that made. Not quite as much as I expected, but still there's a lot more drooping:

Closeups, first without fan:

Then with fan:

The difference is striking. Having a fan is definitely helping. And this is just with a simple front-mounted fan, no fancy ducts. I have an idea for a fan duct setup with the fan mounted separately and blowing through a tube, but haven't gotten around to it yet. That would at least solve a bunch of annoying mounting issues. It might be more easily done with the radial type fan, possibly mounted on the left side of the extruder motor. The "ducts" could be a wide ring with four little blowers instead of a hotend-specific circle. The quality I'm getting from just blowing in the side tells me that getting every last drop of air placed just right is less important than actually being able to easily mount it. Plus, I want to be able to see the print in progress.

I also finally got around to fixing the loose wires I had had hanging around, getting rid of the last crocodile wire. It's better, and I won't have to worry about the fan wires falling down and catching on the corner clamp, but I still need a few cable ties to make it perfect:

Friday, 5 August 2016

Designing a phone cover, part I

For my next project, I want to play around with my flexible filament. Because I've overcome so many problems, it's time to add some more. But also because I want to make a case for my Nexus 5X.

While designing this case, I got to try out some OpenSCAD operations I hadn't done so much with before, in particular the minkowski() operator. While it works nicely for giving the case an outer rounding, I ran into a nice little problem when doing the interior. You see, the Nexus 5X isn't just a rounded box with rounded edges. The backside is tapering off towards the edges:

So my first model of the phone itself (to be used negatively) using just a hull of four cylinders wouldn't work. Instead, I tried to use an intersection of the hull with a minkowski of a similar hull:

module doubleround(size, corner, chamfer)

    hull() {
      for (x = [0, size[0]]) {
        for (y = [0, size[1]]) {
          translate([x, y, 0])
            cylinder(r=corner, h=size[2]);
    // Using a sphere is possible, but will kill performance

module nexus_5x_case() {
  intersection() {
    hull() {
      for (x = [rounding, width-rounding]) {
        for (y = [rounding, height-rounding]) {
          translate([x, y, 0])
            cylinder(r=rounding, h=thickness);
                   thickness], rounding, under_round);

Thanks to nophead for providing me the excellent word "chamfer", though he does it by subtracting an inverted corner.

This unfortunately led to some bumps in the corners:

The better approach turns out to be doing a hull() of an intersection of a cylinder and a large sphere:

module nexus5x_base() {
    under_round = 20;
  intersection() {
    hull() {
      for (x = [rounding, width-rounding]) {
        for (y = [rounding, height-rounding]) {
          translate([x, y, 0])
            intersection() {
              cylinder(r=rounding, h=thickness);
              sphere(r=under_round, $fn=50);


Much better. Alas, my first attempt at printing it fell prey to stripping again, though this time in a rather artistic manner:

So currently my two main problems are stripping and tangling filament. Stripping comes partly from poor Z adjustment and the tangling, but possibly also from poor adjustment of the extruder idler. 

I'm not sure what to do about the tangling filament. I haven't seen any conclusive tips on how to best prevent it, and it seems to be getting worse - I have to babysit the printing process now.

Wednesday, 3 August 2016

A pedal is born (with difficulties)

Finally, after several weeks of on-and-off experimentation, I have a fully functional foot pedal to replace the one that broke off our trashcan:

Due to the odd break, the difficulty of looking at the relevant parts, and difficulties printing, I went through quite a few prototypes before getting it right:

But by now I have my printing procedure down to a regular practice and can get good results as long as I Z-calibrate properly and my filament doesn't tangle. Tangling filament, apparently a side-effect of my repeated cold pulls, is becoming more of a problem, and I need to pick a good solution. The other repeating problem was various parts coming loose from the bed, especially the support pillars and a thin strip of the main part touching the bed. Also happened with some of the first tests. Adhesion for thin things is problematic and they should be rafted, or I should get a better hair spray (currently using Nivea Volumen Kraft & Pflege strength 4 of 6 possible.

Other things recently printed:

A guard for the X shaft, since I didn't have a properly stiff piece of plastic.

(On the right) A AAA battery dispenser that didn't scale quite right

First test of a holder for the RC-1 Canon remote control.
A yarn bobbin. Came out perfect on the first try.