Cable holder in magenta PET-G, but at a price

One of my daughters saw the phone cord holder I had made (designed by Lay3rWorks) and wanted a smaller version. Fortunately it was provided as a Fusion 360 file so I could import it and make changes. Although it was a parametric design, it wasn't fully automatic so I had to manually split the parts and recombine them. Not a very big deal.

She liked the magenta PET-G I have (by eSUN) so that's what I used. The first one had a problem: I had used a 15% infill and the top deck did not bridge that nicely, so it ended up with holes. Usable, but ugly. It also had a moderate amount of stringing between the upright dividers. And there were a couple of dark patches, like scorched plastic.

So I put some more thought into the settings. Now that I'm using Simplify3D I have more options.

• I set the base to 50% infill both to fix the upper deck, and to give the product more weight and a lower center of gravity. The upright dividers are joined to the base by a pretty narrow rectangle, and I was a bit worried about it breaking in the long term, so I set several layers around the joints to be 100% solid. Then the rest of the layers (most of the dividers) back to 15%.
  
• I had been using 245C for all my PET-G prints so far, and that's in the upper end of the recommended range. That can cause stringing. So I varied the temperature in the different sections of the print. The base was still 245C for good adhesion. I reduced the joint area to 240C, and the dividers to 235C to try to reduce stringing and scorching. The bed temp remained at 85C throughout.

Here's the result:

I was away for a while after the second print finished, so the print had time to cool on the bed. It popped off easily by hand, no razor blade needed. I've found that PET-G usually comes off nicely after it cools.

But the print had some weird lumps on the bottom, in a slightly different color. Chips of glass, stuck very tightly! I had to use a perpendicular X-acto knife to clean them off.

So now my print bed is chipped, right in the middle. Two big chips and a little one. Plus a scratch.

I imagine I've set the stage for the chips by using a putty knife to pry or tap off other prints that have been very stuck. PLA can do that. Often PLA will self-unstick if I let it cool thoroughly, but I've learned that only recently. And in trial-and-error printing, it's inconvenient to wait 30 minutes or so to remove a trial print.  So I imagine I had caused some tiny chips. Repeated heat stress probably caused tiny cracks to propagate. With PET-G I use a much higher bet temp, 85C. But I hadn't done that since in two months, so maybe the glass was damaged during that time and was prone to chip the next time it got really hot?

It seems unlikely that the PET-G just really stuck in those spots and caused the break, since I did not apply a lot of pressure to remove the print. I'll have to do some research to see if this is common. Will these chips now propagate worse? Will that scratch turn into a crack? I know from limited experience that that's how we cut glass: scratch a line with a tool and then stress it. I'll do some test prints, and will have to avoid the center of the bed.

I could just buy a replacement bed from Robo3D, but I think there are options. I have seen mention of some removable, flexible bed materials which make prints pop off more easily. So I'll do some reading before buying.

VR adapter for OWL Stereoscopic Viewer

Background

This project requires some explanation. For Christmas I received a copy of Queen In 3-D, the new book by Queen's guitarist Dr. Brian May. It seems he carried stereoscopic cameras throughout Queen's career and took a bunch of photos backstage and out and about. It's a terrific book. It comes with the OWL viewer, produced by Brian's London Stereoscopic Company.

LSC also developed an adapter which attaches a smartphone to the OWL and enables you to watch virtual reality videos. It's like a nicer version of the Google Cardboard viewer. The design is brilliant - very simple and elegant! I wrote to LSC to ask if the adapter is available separately since I already have the OWL, but got no response. Since I have a 3D printer, it should be easy to print a 3D adapter. No one has published one on Thingiverse, and out of respect for Brian's and LSC's intellectual property rights, I won't publish mine either.

Design

It's a simple rectangular plate that slips into the OWL viewer where one would normally put a stereo photo card. On the back I made some circular holders where I mounted some round Neodymium magnets (ceramic magnets are not strong enough). My iPhone already has a magnet on the back that I use with a magnetic mount in my car. So it will just stick right to the plate. I designed it parametrically so I can adjust the size for a snug fit in the OWL.






Printing

I printed a few partial samples to fine-tune the dimensions by a few millimeters. Here is a sample
with large chunks of the back plate cut out to reduce the print time but still give me the full width and height so I can test the fit. I used blue Hatchbox PLA filament for the test prints, and black Shaxon PLA to give a darker background to the videos.




Final Product

Using it

I was puzzled for a while about what software the smartphone needs to play VR. Then I learned that the YouTube app itself includes a VR mode (intended for Google Cardboard). For VR 360-degree content it displays the left and right halves and responds to motion of the phone to let you look around. For regular videos it simulates 3D by splitting the video into left and right, but can't respond to motion because the video is just a straight-ahead view.

I imagine there are dedicated VR apps for games and simulations etc. but I haven't looked into those yet. I saw a reference on Brian May's web site to some astronomical VR video's he has produced... he is also an astrophysics after all. I'll have to go back and find that link!

Christmas light storage frames

Here is a short and simple project. I bought new Christmas lights this year and decided to make some frames to wrap them around instead of the cruddy old cardboard I had been using. These have "ears" to keep the wires from falling off, and little clips on the sides to grab the plugs.

I recently listened to a blog which said many projects can do with much less infill than we often think. Since I needed to print several of these, I decided to vary the infill and see how it worked out. I went all the way down to 0%, forgetting about the issue of bridging. Since the sides are not that far apart, even with some drooping bridges, the the second and third layers fixed it and it came out with nearly no surface gaps. (For a project like this appearance doesn't really matter anyway.) So as little as 5% infill worked just fine.

Each of these used about 72 cents of PLA, and took about an hour to print. That really doesn't make much sense... I could probably have bought something like this for less... but this was more fun and printed while I was doing other stuff.

Wood filaments, finishing, Simplify3D

Someone where I work asked if I could make a base for mounting an unusual object as a trophy. I remembered that wood-infused filaments are available, so I said I'd give it a try. It turned into quite a project, and I learned quite a few new things:

• Printing with wood filament
• Switching filaments during printing
• "Engraved" lettering
• Section analysis in Fusion 360
• Sanding, staining, varnishing and gluing wood-infused PLA
• Simplify3D instead of MatterControl

Filaments

Globs that would need to be ground off and sanded.

Because I had a timeline of about 3 weeks, I bought the only wood filament available at my local retail store, GP3D wood light, which says it is 40% wood. It prints a lot like PLA, but it's more brittle and rough: one time the source filament actually broke while I was printing. It tended to produce little globs on the surfaces. My model had "engraved" or negative-space lettering, which I figured would be tricky, so I printed several chunks of my model with the wood, trying to get good smooth results. Time was running short and I was not getting the results I wanted, and I could find no user discussions of the material on line, so I ordered some Hatchbox wood filament that looked very popular.

While waiting for the Hatchbox to arrive, I figured out that I was using too high a temperature, which was causing some material to scorch inside the nozzle and then come out as a hard lump. Once I dropped to the low end of the temperature range, 190C, that seemed to settle down and I started getting smoother prints.

The Hatchbox printed nicely the first time, and I ended up using it for the final product. To be fair, the GP3D probably would have done fine as well with the lower temp and (as discussed below) Simplify3D. The Hatchbox seemed to come out smoother and more plastic-looking; it does not say what its wood percentage is. So maybe I'll give the GP3d another try on another project. Being a more woody texture, the GP3D took stain better.

Switching filaments

Contrast layer samples, between wood layers, after staining

Rather than a monolith of wood, I wanted to insert a contrasting layer to make it a little classier. I printed some samples with glossy black PLA, and also with some rather translucent PET-G in magenta or green. Eventually I decided to go with the black. The contrast layer was just a short ways down from the top deck, so I could "engrave" letters all the way to it, so the letters would have a black background.

Switching filaments is certainly possible, but there is a lot of discussion on the Internet on who to do it well. I learned a few things:

• By default if you just pause MatterControl, it leaves the head in place. It can ooze filament, and when you insert new filament some needs to come out to get it flowing. This could land on and mess up the previous layer.
• By default the stepper motors release after 60 seconds, so if you can't switch in that amount of time, the head or bed can move and ruin the print when it resumes. I spoiled one after 4 hours of printing, so I went looking for a solution.
• I found some custom G-Code to add to the pause and resume actions. I set the pause to move the head up 20 mm and lock the motors for 10 minutes, and set the resume to lower the head back down. This worked well. I also slipped a piece of paper on top of the model to catch the ooze.
• Pausing is not an instant action. I wanted a clean transition of colors, so I learned to preview the layers to see where the head would be at various times, so I could select an optimal location inside the model, not on a perimeter. The different colors would be hidden in the infill. Depending on the specific situation, sometimes it's in the layer before, and sometimes in the next layer.

The final model was going to take over 6 hours to print. I needed to switch colors after about 4 hours. In one of my test prints, and then in my second attempt at the final model, when I paused to make the switch the head moved up but would not stop extruding! There was nothing I could do to stop it and I had to cancel the print.

Engraved lettering

My design has a couple of "nameplate" surfaces on the sides with lettering cut into them at an angle. One of them includes a company logo which I had to learn how to import into Fusion360. The first tries used lettering way too small, which came out rough and globby, so I went with a larger font and simplified what I wrote (I had the design flexibility to do that). It also has some letters cut into the top surface, all the way to the contrast layer, which would give them a nice dark background.

Section analysis in Fusion 360

To attach the object to the trophy base, I designed a little round pedestal which would fit into a hole on the top. I wanted to see how all the pedestal plug fit, and how close the bottom came to the bottom of the hole so I could glue it in. I found the section analysis option, which was very helpful.

Finishing

The globby lettering needed some cleanup with my Dremel, and some sanding to get rid of the "pimples". Since it's 40% wood, the material sands better than regular PLA does. Regular PLA tends to turn white when sanded. This does a bit too, but not bad. Unfortunately it is still plastic, so when I trimmed some things with an Xacto knife, they tended to stick and remain as fibers, rather than cutting off cleanly as wood would.

The wood filament is pretty light in color. That's nice for some things, but I wanted a richer color for a trophy. I tested some stain that I had on hand. The stain tended to penetrate the grooves between the printed layers, which looked like wood grain. But it did not penetrate much in the smoother areas, even after 30 to 60 minutes, especially where I had sanded. I needed to leave the sanded areas a bit rough if I wanted them to stain.

I had some Varathane on hand, which is really a plastic and not a varnish. I was concerned that its solvent might dissolve the PLA, but it worked just fine.

I knew I would need to glue some of the final parts together, so I looked to see what was compatible with PLA. A very comprehensive article pointed me to Loctite Gel Control. It worked great!

Software

I didn't think that the runaway extrusion was the fault of the printer, but rather of the software. It became apparent that I was going to need to reprint just the upper sections of the model due to the aborted filament switch. I also was not thrilled with the little bumps caused by filament oozing when retracting on moves. The wood filament was not sticking to the bed well, causing wrinkles and flaws. And I was having trouble with the completeness of the top layers, and was futzing with extrusion factors to try to fix it. 

I've been using MatterControl, which came free with my Robo3D printer. Some reading earlier and when trying to solve these issues led me to Simplify3D as a more professional option. Many people have raved about it, so I bought a copy, although it is $150. If there was a chance it was going to help me not foul up a 6-hour print (I only had a few days left for this job), it was worth it.

I printed a test object (in PET-G, since that's what was in the printer at the time) and I was shocked at
how smooth the print came out. The sides and top were silky smooth, no nubs. The lettering was sharp and had nearly no globs. Nice!

For my next try at the full model, I used S3D. The sides and the lettering on the nameplates came out perfectly smooth, dramatically better than what I had achieved before. I saw that there was still a lot of discussion on how to properly change filaments, so instead of attempting that I stopped the print, and printed the contrast layer and top deck separately, and planned to glue them together. S3D's ability to start and stop at certain points is easier to use than MatterControl's, though I wish it were specified in layer numbers rather than measurements.

What a huge difference in print quality! I could see it right from the start, with great adhesion and smoothness in the first layer, and perfect smoothness all through the infill. The lettering was incredible. I spent maybe two minutes cleaning up a couple tiny globs with an Xacto knife, and NO Dremel work at all. I decided I did not need to sand the nameplates at all either, which would let them stain better. As one of the reviewers pointed out, the saving in post-processing time alone justifies switching to Simplify3D. I'm sold! (Though it does have a few quirks...)

The finished product

The first finished iteration was from MatterControl with a lot of cleanup. The customer loved it. "Just one thing... could you move this to there instead?" Um... sure... I'll just do another 6-hour print, stain, varnish...  The second iteration was done with Simplify3D, which required very little cleanup. It came out much smoother, with much sharper lettering, though slightly less woody-looking due to the poorer stain penetration. The customer loved the final result!

Replacement base for a smoke alarm

A smoke alarm in our house is held onto its base by two thin tabs of plastic that eventually broke. I found a design on Thingiverse by buwprinter (from Germany). It was obviously not made for my model - there are zillions out there - but I thought it might work. It was provided as an STL file, not a modifiable design. MatterControl has a scale feature, but it's an overall resize not intended for specific accurate needs. So I had to learn a couple of things in order to resize it accurately in Fusion 360:

• How to import a file.
• How to scale a mesh design.

The overall shape and appearance of the base is not that important. What matters is the spacing of the locking tabs that hold the alarm in place. I measured that carefully with calipers and then used the scale ratio feature and hoped for the best.

Also, this was the first time I was switching my printer from a high-temperature plastic (PETG) to a lower temp (PLA). I had heard that this could be an issue, so recently I bought some cleaning filament. It's an odd size, so you don't feed it through with the motor, you push it by hand. I was surprised how much I had to push through before the result was fully clear with no trace of green from the PETG.

I noticed that the PLA was not extruding straight out but rather curling up as if it were sticking on one side. I had to scrape the outsize of the nozzle to get rid of some scorched debris, and also tried some advice about pushing and pulling filament getting out a few times until getting a nice clean "cone" on the end. Seems to be printing OK now.

The diameter of the locking tabs came out perfect, but each tab was a bit too long for the slots. I ground off about 1/8" from each with my Dremel tool and then it locked on just fine. Here's the final result:

Jack-o-lanterns

Just for fun since I have orange and green PLA on hand. An LED tea light fits inside. I downloaded this from Thingiverse, provided by mb20music.

Lamp repair - again - with metal and PET-G

There was just too much stress on the plastic threaded tube, and the beefier version broke in the same place again. That vertical tube needs to be metal, so I shopped on line and found some 6" long nipples of the same diameter and thread as the original one. That meant that the "base" could be simplified. I decided to stop using a captive metal nut but to build threads right into it. That meant no more support to trim out!

About that time I saw an ad for PET-G filament, describing it as just a tough as ABS but without the fume problem. It is translucent, and comes in some nice rich colors. I ordered some red and green, thinking I might make some Christmas ornaments. PET-G requires hotter extruder and bed temperatures, and writers said it can be finicky.

I read up on how to reduce stringing and - I guess you could call it "globbing" - where oozing plastic goes where it's not supposed to. That led me to reading about calibrating my printer's feed speed. Huh? I didn't know I needed to do that. There's a process for marking a measured length of filament and telling the software to extrude that length, and then checking the accuracy. Mine was off quite a bit, feeding 92.5mm when 100mm was called for. I'm not sure what effects that may have had on my printing so far, but I went through the steps and corrected it through a steps-per-mm setting in the firmware. Test prints gave good results with the PET-G.

The part wasn't quite working, though. There was no good way to keep the top wedge in place in the tube while turning the screw to pull it down. Back to the electronic drawing board. I realized I needed a way for the base to keep the side wedges in place, and for them in turn to keep the top wedge in place. For that to work and still allow the side wedges to slide out and up/down, I designed a tab-and-slot arrangement:

Two wedges sit on the base with the tabs in the slots, free to move but not rotate. Then the top wedge fits between the side wedges, free to move down on the screw but not free to rotate. As long as I hold the base in place and tighten the screw, it should all stay aligned as it expands.

Only problem is, when I created threads of the right size with Fusion 360, the part was too tight on the screw. I fought this quite a while before figuring out I could expand the threads slightly. With the help of a video from Autodesk or someone, I learned to push back three parts of the four faces that make up threads. A little trial end error led me to expand by 0.6mm, which makes for a smooth-turning thread with no slop.

Here is the final assembly ready to insert into the lamp tube. The "top wedge" on the left side is threaded, and the "base" on the right is not, it sits against the bottom of the tube and the nipple pulls down through it. The wedges sit loosely between the two. The nut on the right is just to hold it all together temporarily. It worked great. Holding the base stationary and turning the nipple (with two nuts locked on the threads) locked it in place with no trouble at all. Then I removed the nuts, put the big lamp base and washer and nuts on the nipple, and tightened it all as much as I dared. It feels very secure.

I initially printed some of the parts at 99% infill to make them as tough as possible. But I needed to do a couple trial prints, and went to 10% for speed. Well, the PET-G is *very* tough. I bent and pushed on it and it's quite rigid. So I used the final test print at 10%.

Another great thing about PET-G: if I let it cool to room temperature, it self-detatches from the bed! It just pops right off. PLA never does that. Yet during the print it sticks really well even with a light, leftover amount of hairspray. No curling, no coming loose. Really nice.

So I've put the lamp back in service again - hopefully for the last time.

Second try at the pole lamp connector

Just as with software development, I can't always anticipate everything and turn out a perfect design the first time. Fortunately the low cost of 3D printing materials make it feasible to try several versions as I refine a design. I'll be honest on this blog about what works and what doesn't.

The first version of this repair insert didn't work because there was no good way to fasten the PVC pipe into the pole. Glue didn't set up around the shims. Because the first inch or so at the bottom of the pole is a smaller diameter than the rest, I can't just insert a solid pipe or something - anything that can get past that first constriction will slop around above it.

I was working on ideas based on a "toggle bolt" concept, when I found on Thingiverse someone's design for an expanding part kind of like what bicycle handlebars sometimes use to connect to their stem: wedges that move outward as a screw pulls them together. One problem with that idea is that it goes off center as it expands, which would not be good for a pole that needs to stand up straight. Also the center screw needs to be hollow to allow the lamp cord to pass through. So I got to work on my own design.

In this pic the black part is what sits at the bottom of the pole. I added a flange below the pole, sitting on the top of the base, to give it some more stability, and since that's going to be visible I printed it in black. It still has a place to hold the nut for the metal nipple that extends into the base. That's what takes a lot of the stress, so I didn't want to make that out of PLA, I'll continue to use the original metal nipple. Now the stem that goes upward is threaded so it can engage the wedge-shaped nut. As that is tightened, it will pull the two-sided wedge down between the two loose wedges, forcing them apart, gripping the inside of the tube.

The threads on the two plastic parts were quite tight and needed some cleaning out with the metal nipple and a nut, and soap to smooth the way. That's OK, I don't want it to slop around.

Not shown is a slot (kerf) in the bottom of the flange in case I needed to turn it with a tool, but I never used it.

Inserting the wedge into the pole.

Slipping the loose wedges in at the same time. I needed to expand the wedge a little at a time as it went in, because there was no way to hold the main wedge/nut once it was in. Carefully adding friction  seemed to work.

Unfortunately after I added the base (which is about 5 pounds) and stood it up, it soon broke as I tried to move it around on the floor. Back to the drawing board! The design seemed sound, but the parts must have had some weak spots.

The threaded tube broke right above where it connects to the main insert above the nut. I identified two aspects that I could improve:

1. Looking at it through a magnifying glass, I realized that the threaded tube was infilled, i.e. not solid plastic. That's how most 3D parts are printed by default, and I had set it for 60% infill (or 40% empty space). For the next iteration I made the whole black part 100% solid. I also added a chamfer around the base, to give it a little buttress in case it wanted to flex. That meant the side wedges needed a little more clearance, so I expanded their center cutout a little bit.

2. I speculated that the wedges were not seated down on the top of the black cylinder. If so, that would allow the leverage of the pole to flex the threaded tube from side to side. If the wedges were to seat down firmly on the cylinder, it should be rigid and resist that bending moment. If the point of the wedge-nut bottomed out before the wedges were tight, it would not be as strong as it could be. So I truncated the point of the wedge - it's noticeably shorter and rounder in this pic. By ensuring it would force the wedges outward, and by starting with it screwed down a little further, I hoped to ensure they would seat all the way down.

That all went really well. I inserted and tightened it by hand as much as I possibly could. It seemed to get really tight and never approached stripping the plastic threads - they're quite long and tight, so that's not really much of a problem.

Here's the repaired lamp standing upright. It wobbles just a little bit - that's nearly six feet of leverage on the bottom joint. I speculate that if someone were to drag it sideways by grabbing the top of the pole, it could still break the threaded part - it is hollow after all, to allow for the cord. But as long as we lift it up vertically if we need to move it, I think it will be OK.

Insert for repairing a pole lamp

We have a nice Tiffany-style pole lamp, but the bottom of the pole started to break, so it wobbled on the base. (Simple metal fatigue; it is probably 30 years old or more. I decided to make an insert for the base screw to fit into. The inside of the tube is an odd shape, smaller in diameter at the mouth, making it hard to use a single piece of pipe or something without it wobbling. My solution is a piece of PVC pipe wedged and glued in place up the tube, and a 3D printed piece that fits snugly in the mouth, slides 2.5 inches up the PVC pipe for stability, and captures the nut securely. Oh yeah, with a hole through the center for the cord to go through. Not a glamorous project, just a fix-it job that needs a custom part one that no one sells.

I printed it in PLA with 60% infill for strength, which made the upper tube essentially solid. The nut slides into a hole that is a hex shape on four sides.

The part with the captured nut and the base nipple. Why orange? 'Cuz that's what was in the printer.

Inserted snugly into the PVC - I needed to sand down the little PLA bumps to get it to fit.

Going into the pole. Actually I wedged some split dowels around the PVC to center it and stabilize it in the pole. I inserted Liquid Nails glue as I assembled it.

All assembled. I'll let the glue dry until tomorrow. When I put the base on we'll see how well it holds up.

Quilting machine carriage brakes (channel locks)

My wife recently acquired a quilting machine, which is basically a sewing machine head on a carriage which moves freely in two dimensions. The operator can move it around to sew in any imaginable quilting design. But there are times when one needs to "baste," which is stitching in a straight line to hold the quilt together before the fancy stitching starts. In that case it's desirable to restrict the carriage motion to the X dimension by preventing it from moving in the Y dimension. There are no brakes on the carriage, so the company sells what they call "channel locks" that clip over one or more wheels. That sounded like something I could print for far less than the $12 a set that they cost on line.

Here's the finished product, so you can see what I'm talking about.








This project took quite a bit of trial end error, on two fronts.

First, I thought that the "channel locks" worked by acting like chocks, wedging under the leading and trailing edges of the wheels. I had seen a pair in real life, and seen pics on line, so I had an idea of what they should look like but not exactly what the important characteristics were. We knew that "clingy" plastic was supposed to be better than slick plastic. So I figured I'd print them in Nylon, which is more resilient than PLA. As it turns out, they don't work as chocks, but rather as brakes grabbing onto the rims of the wheels, and the ends that rest on the track stop the wheels from turning. So the important aspect is to exert spring pressure inward onto the wheels. Nylon is too flexible and doesn't exert any pressure.

So it was back to PLA, which is more rigid. The inside diameter needs to be just right so it will touch at several points with sufficient pressure. That explains the little "bars" on the inside: drum brakes are hard to get to fit correctly, but "caliper" brakes touching at just a few points are easier to fit. The interplay of inside diameter and total arc are critical: when it's installed, the ends of the arc need to be just long enough to touch the track without any play.

The second aspect of trial and error was making the design fully parametric. This means having every dimension based on a parameter (variable) so you don't need to redraw anything to make changes:

Parametric design sounds easy, but I've found that the sequence of "what is built on what" can make or break such a design. In this case I needed to build the arcs onto each other, and make the arc dependent on the inside diameter which matches the inside points of the bars (the "caliper" touch points) etc. Working with Fusion 360, I found that I needed to add fillets at the 3D body level, not at the 2D sketch level, or any angle adjustment broke them. I don't fully understand that relationship, but it worked. I got in the habit of testing every minor design change by altering the basic inside diameter parameter up and down and checking whether the final diagram behaved correctly.

This process took about 10 cycles of measure-resize-print-test before I got it right, 5 in Nylon and 5 in PLA. That's a lot more than I expected, but at about 20 cents per part, it still cost only about $2 or so. Each iteration took about 20 minutes to print, so I could just do it in and around other stuff on this long weekend. And if they ever break or wear out I can just print more. With two wheels locked, I hope the carriage is held rigidly enough. If the brake is not grabby enough, I might put some Shoe Goo on the caliper touch points.

Squishy turtles

I saw these featured on Thingiverse and thought they were such a cool design I wanted to try them out. I really like clever designs that move or have hidden features. And I hadn't printed any multi-part objects, so I wanted to learn about fitting things together. (This one includes a little H-shaped clip which attaches the shells together.)











The head retracts, like any turtle should do, and you push on the tail to pop it back out again.

The clever parts of this design are the built-in springs that allow the legs to move, which is what makes these turtles "springy". And there's a nice little spring to put pressure on the head-tail part so it doesn't slide in and out too easily.













I also liked the idea of printing the upper shells (carapace) in different colors than the head, legs, and plastron. That was an excuse good reason to go buy some bright green and orange filament.

I printed one of each part in each color and then mixed them up. When I arranged them together to print a batch, the first layers looked like some exotic creature or alien holding an oar or weapon. I had some fun getting my FaceBook friends to guess what it was going to turn into in real life.

Ethernet cables and elephant feet

For a network project at my church, I printed up a bunch of these nifty Ethernet cable organizing clips designed by Murray Clark on Thingiverse. They come in a variety of sizes, with or without holes to fasten them down with cable ties or screws. You just squeeze one side to open the "jaw" and slip one or two cables in on the other side.





I didn't notice that they were designed for CAT5 cable, and our project used mostly CAT6 which has extra shielding. So when I tried to use them, they were too tight, and the cables didn't really fit in. That's OK, even though the files are compiled .STL and I can't really manipulate them. MatterControl has a Scale feature, so I figured out how to use that. I took some measurements, did some experiments, and eventually settled on scaling up by 8% in the two dimensions that affect the hole diameters. (No need to scale up in the third dimension, because thicker is not necessarily better.) I had printed the CAT5 clips in white, so I decided to print all the CAT6 clips in blue so I could tell them apart.

But when I removed the first clips from some test cables, they left deep slits in the insulation. What? Not good! Why was that happening? Well, I had noticed that many of my prints had a little "flange" on the first layer or two. I thought that was just the way things worked. It was annoying on my bottle cap project, because it was rather sharp when I twisted the cap on and off. Here's a pic in profile with a contrasting background. Look at the flange on the left side, and you can see how it could make a nice little razor knife inside each cable hole:

A little research showed me that this is called "elephant foot" and there are definitely ways to deal with it. It's caused by the first layer getting squashed by the upper layers. That can happen because of one or more of the following:

1. Bed is too hot, so the lower layer doesn't firm up and the weight of the next layers squashes it.
2. First layer is too thick.
3. The nozzle to bed distance is not accurate, so the calculations are off. That could foil efforts to adjust #2.

I tried varying the bed temp and it seemed to have little effect, but I left it lower. I tried varying both #2 and #3 and saw progressive improvement. I settled on making the first layer the same height as the rest (the default was 50% thicker... not sure why) and adjusting the Z offset. I also turned off a setting that was turning off the fan for the first two layers (double negative there).

As I reduced the "elephant foot" I found I could reduce the scaling as well: that flange was significantly intruding on the hole.

At this point I'll mention that I keep track of the settings for all my print jobs in an Excel spreadsheet. That's because there are so many variables in 3D printing that it would be really easy to lose track of what works and what doesn't. I'm a software specialist, and have done lots of systematic testing in my career, and I've found it's important to either vary only one thing at a time, or if that's not possible, keep good records so you can go back over them. Here's a sample showing the parameters I was varying:

I had some trouble with the Z offset, as the manual and software help didn't make it clear whether to go positive or negative. My first tries were the wrong direction, causing the nozzle to be right on the bed. That did a good job of fooling me into thinking I had a nozzle jam. Eventually I reversed that setting and it went much better.

The final settings resulted in nearly zero "elephant foot". I don't have a good picture of the final result... they're all down at the project site now. The pic below kind of shows it. But here's also a fun picture of how this can all go wrong. I printed a batch of 12 clips at once (of various sizes and shapes) and because I didn't refresh the hairspray on the bed (or didn't have enough in that corner), one of the clips came loose. Being in the corner, the printing direction caused it to kind of stay in the area, so the nozzle kept coming back to it and adding to the mess, instead of making a total mess of the whole job.

Network cable routing bracket

We're getting ready to install a network switch on a wall at my church. We'll have a few cables to run, and to make them nicely vertical and horizontal it's common to use what I used to call "U-brackets". Turns out they are called "Routing rings" or "Distribution rings". I found one such bracket on Thingiverse but I didn't like the design because the bracket is square, which would cause wear and friction on the cables. These should be round - they're usually made out of round stock with feet pressed into them or attached to them. So I designed my own.

Here's a shot of the design in Fusion 360. Obviously it can't print in this standing position, I'll print it lying on its back. Round things can be a problem, but I've found that round things lying down on the bed can work OK if they are not too big. Originally I had the feet oriented in alignment with the axis of the bridge, but then realized that would cause the bridge to not lay flat, but to print at an angle to the bed. So, duh, I turned them at an angle so the back of the leg will align with the back of the foot and lie flat.




The bridge printing horizontally will take advantage of the strongest direction of the plastic.

The feet sticking up will be printed in short layers and will be the weaker parts... in theory they could snap if a lot of stress was put across the screw hole. I printed it in PLA with 50% infill and the result feels plenty strong.