Useful Household Items – Drip irrigation connectors

One of the first things I did when I purchased my Up! printer was to think about how it could be used to produce little things around the house.  To wit, I designed things like the electrical outlet cover plates, and other things with the ‘athome‘ tag on Thingiverse.

although it is very interesting to design many things that can be used in the home, sometimes it is not practical to actually print them out.  For example, the light switch cover plate, in order to print it requires quite a lot of plastic.  Given that these can be purchased for relatively cheap, since they’re so common, it’s not particularly cost effective to print at home.

But, other items make more sense, either because they are scarce, or so unique that you could not get them otherwise.  I recently pursued creating such an item.  It is the Flanged Connector.

There are several uses for this connector.  The most basic is to use it as part of a drip irrigation system.  You would insert this into the end of a piece of drip irrigation tubing.  Since it is hollow, it will allow water to flow through with ease.

When I designed it, I wasn’t actually trying to create something for drip irrigation.  I was after being able to easily connect drinking straws together.  I had purchased this book: Messing Around With Drinking Straw Construction.  I wanted to construct some structures with my daughter.  The method of connecting the drinking straws was to insert paper clips into the ends of the straws.  Where multiple straws came together, there were multiple paper clips interlocked.  It was that or pin, or tape.

As a general mechanism, it has the advantage of ease, and low cost.  Paper clips are readily available by the thousands, at relative low cost.

But, we found the technique to be a bit cumbersome.  The straws were not stiff enough, and the paper clips could not hold shape at the vertex, so it required multiple hands, or support to keep the structure from simply collapsing until the thing was entirely finished.

I wanted a better way to connect the straws, and at the time (around 2004), I was dreaming of a simple connector that I could stick into the ends of the straws.  I contacted an injection molding outfit, but they wanted a few thousand dollars to develop the design, do the mold, before anything was actually created.  I pretty much left that idea behind and bought quite a few Zome Tools instead.  That construction set worked quite well, and was more than sufficient to meet our needs.

Recently, I have been cleaning out the house, in preparation for a move, and came across the bundle of about 1,000 straws I had purchased so many years ago.  That bundle reminded me of the little connector that I wanted to create at that time.  Now, 7 years later, I actually know how to use 3D design tools, at least OpenScad.  Now I realize that what I want to create is a simple matter of a few odd shaped cones and cylinders, attached at various angles.

After going back and forth on a few design iterations with Sjoerd de Jong, there now exists a ready made library of routines to construct just about any type of vertex you want.  The Vertex Generator allows you to create vertices for a few well known solids, as well as create vertices of your own.  It utilizes some vectors that you pass to a routine, and it does the rest.

One of the things that I wanted from that library was the ability to separate the printing of the arms from the vertex math itself.  The library goes far down this path, and you could imagine replacing the ‘rod connectors’ with these tube inserts instead.

But, not needing the full generality of that library, I decided to start from scratch and create this imple connectors.  My requirements were that I could stick them into straws, as well as vinyl tubing.  I also wanted there to be some ready made connectors for common tasks.

I start with a straight connector, which can be used to simply join two pieces together in a straight line

This comes from the print_connectors(num) module.  Basically, the ‘num’ parameter is the number of connectors you want to be connected.  In this case, it was a simple matter of calling it: print_connectors(2);

You can call it similarly with any number of connectors.  There is a global parameter ‘standoff’.  This is the amount the based of the flanged connector is offset from the origin.  In the case where you have a high connector count, like 8, you might want to increase this size to accomodate the multiple connectors.

In this case, I used print_connectors(8); and ‘standoff=10;’.  This leaves enough space for the tubing to slide over the connectors, as well as get pretty close to the hub.

The ‘print_connectors()’ module is fairly handy when it comes to creating a set of connectors that are spread evenly around the hub.  There are some cases where you might like to specialize though.  Elbows are acommon connection type, as are ‘T’s and risers.  The library currently includes a module to create elbows.


Here, there are two elbows.  The first is specified with ‘print_elbow(angle=90, $fn=24);’, the second is printed with ‘print_elbow(angle=120, $fn=24);’.  In this way, I have specialized for the case of printing two connectors with an angle between them.  Really, this could be generalized to specify any number of vectors in a list, and let the print_connectors() module do the right thing.  That may be an exercise for the next round of these routines.

The really nice thing about this design is the hollow tubing.  Meaning, these are like pipe connectors, in that they will allow liquid to flow through the connector itself.  That ‘liquid’ can be anything.  One example might be colored water that is placed inside the straws, just to make things look interesting.  But, it’s just an open space.  These connectors could easily be used to route cables, with attached conduit.  You could use vinyl tubing to route wiring in a device, and put a little bit of elwire in there as well to light up the path.

One other Idea I had, for forming rigid framing, is to use vinyl tubing to connect things, then fill the tubing with some hardening foam, or epoxy, or something else that can first flow as a liquid, then harden into something much more strong and rigid.  That might be a great way to ship some simple structure, and assemble it without having to worry about long strong members.

Lastly, printing these things, although relatively inexpensive, is quite challenging.  The amount of overhang, and the tiny proportions, will challenge most DIY 3D printers of today.  Ideally, this would be injection molded, which was my original intentions.  But who knows.  Over time, being able to render such a design, inexpensively, and quickly, at home may become a reality fairly soon.  When it is more feasible, I can imagine the joy children and adults will have when they want to create a new toy for themselves, they go to their insta-printer, and out comes the results they expect.



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