Laser Cut Helical Springs

I created the helical spring GIFified₁ above by using the Trotec rotary attachment in a Speedy 300 to laser cut a 3D printed PLA plastic tube.

It is one of many helical springs I've laser cut over the past three months₂. The springs vary in design and material - so far, I have used 3D printed PLA, clear acrylic, and cardboard shipping tubes. Take a look at the bottom picture for a sneak peak of the whole collection.

The 3D Printed / Laser Cut Spring concept is pretty cool, I think, and a decent lead in because it's recognizable, but definitely not what I'm most excited to show in this Instructable. So before I lose you, scroll down to Step 1 and check out the wave springs. Lots more pictures and videos after that. Eventually, I'll give an explanation of how they are made (starting at Step 7).


¹ _{Props to audreyobscura for her extremely helpful instructable on turning videos into GIFS.}

² _{What's the point? For a little while, I turned my attention to finding an application for these, but that proved to be way less fun than experimenting with the process and cutting new springs. So for now, they are what they are.}


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These acrylic springs were made by cutting each coil along sine wave or zig-zag paths. As you can see in the GIFS above, when you twist them, the waves and zig-zags line up and form helixes that wrap around the spring. The springs want to untwist themselves, but with just a little pressure from the ends they hold the pattern.

Check out the video below to see how they move in real time.

These springs are sort of a variation on the zig-zaggy wave spring. I've done the step thing with squares and circles. The blue one is spray painted. Other than that, not too much to say about them except I think they're nice to look at. 

They spin when you bounce them. Check out the video below to see them in motion.

Many of the wave springs change shape when put on their side, including the 2 shown in Step 1. When pushed, some of the springs will actually flatten out and look rectangular in cross section, or even lock into a flat shape. Sometimes this makes them look like snakes.

The video below shows the best examples I have of springs that change shapes fluidly, both cut from cardboard₁.




^{1 Cardboard has less springiness than plastic, making it more willing to do this shape change trick, but it is also less robust. The longer spring in the video broke after a few days of springing, splitting into the two individual springs shown in the pictures.}

I made these by accident. Halfway through this project I decided to organize and display the springs I'd cut. I laid some out on my desk, hung some from my window, and took a picture (see above). A month later, I took down the hanging springs and found that they held their stretched shape. Now they jump out of your hand when you press them down.

The whole gang, some odd balls that didn't fit in on earlier pages, and a few family pictures.

Next, how they're made.

Interested in making your own, just to do it? Or, maybe you've thought up some application for a custom spring. Hopefully you'll find everything you need to know here, and if not, let me know in the comments.

The how-to section of this Instructable will focus on laser cutting a regular helical spring from 3D printed PLA, with notes for cutting different designs in different materials given as asides along the way.

I'll start by showing the Illustrator file that contains the cut path read by the laser, because that's usually what people ask about first.
From there I'll cover...

- modeling and 3D printing a suitable plastic tube
- information on using acrylic tube or cardboard
- the jig used for cutting, and the rotary it fits into
- laser cutting, notes and settings
- post processing

Imagine you draw a single line that spirals around a can of soup. Then, remove the label and stretch it flat on your kitchen counter. Now instead of one line, you have a bunch of lines running diagonally across a rectangle, each ending on the right side of the label exactly where the line below it starts on the left. That diagonally striped rectangle is your cut file.

There are a lots of ways to achieve this in Illustrator or Corel Draw. I'll leave it up to you to either figure out your own method, or you can just download the Illustrator file i've attached to this step.

width = circumference of the spring
height = height of spring
# of diagonal lines = # of coils in the spring

Working from the basic Illustrator file in step 8, files for most of the springs shown in this Instructable can be made with just a few additional mouse clicks. I'll explain one such transformation and leave it up to you to extrapolate from there.

In Illustrator, to get from a straight spring to one with the wavy 3 cycle sine curve slinky shown above...

1) Select all of the diagonal lines
2) Effects -> Distort & Transform ->  Zig Zag
3) Play with the settings
              - size (.4 used here)
              - ridges per segment (5 here - this has to be an odd number in order for your lines to line up. the reason will be obvious if you                    try it yourself)
             - smooth/curve
4) Delete paths on the top and bottom to reduce the total height

Surprisingly simple, right?
      

3D printing a simple shape like a tube might seem like a waste of time (the print ran about 2 hours) and money, but it's the only way I could find of getting a PLA plastic tube. As far as I know, PLA is the only laser friendly plastic commonly available aside from acrylic. If you want to cut your own slinky, make sure you're printing in PLA and not ABS.

MODELING: There are many better Instructables for learning to use Autodesk Inventor and Makerware, so I'm uploading the .stl file I used to print my tube and leaving it at that.

PRINTING: The one special consideration when printing a tube for slinky cutting is to print enough shells that there is no infill. You can see my settings in the pictures above. I have a hunch that the grain in the plastic created by the 3D printing process (concentric circles around the tube) actually makes it especially good for being slinkified, but i'm no scientist.

Cardboard tubes are everywhere, especially once you start looking for them. They vary in quality, but I'm guessing a discussion of that is probably only of interest to the most hardcore of cardboard spring making nerd (which title I may be the sole holder of). For now I'll just say most any cardboard tube of about 1/8th inch wall thickness will do.

I bought my acrylic tube from tap plastics.  Specs are 1/8th in wall, 3 inch outside diameter.

I used a chop saw to cut tubes of both material down to length for each spring.

Ok, you have your 3D printed PLA tube and you've got your file. Time to cut! Well, not exactly.

There are two things that need to be considered when mounting the cylinder on the rotary for laser cutting...

1) Venting - Bad things will happen if smoke and heat can't escape the cylinder as it's being cut. With cardboard tube the solution is pretty simple - you just cut out gaps at ends of the tube (see pictures). Wasting a little bit of cardboard is not a big deal. If you're cutting relatively expensive plastic, on the other hand, you probably want to save as much material as possible.

2) Pressure - The rotary attachment is spring loaded to exert pressure from the ends of whatever is mounted in it (check out the note in the main picture). When cutting cardboard this is actually useful - as material is cut away and the cylinder being cut shortens, the rotary's spring¹ expands and prevents the cylinder from falling out from between centers. However, when cutting plastic the pressure from the rotary will deform the plastic as it's heated and cut, creating a big mass of plastic that doesn't act like a spring at all.

Result - When cutting cardboard springs, no jig is needed. When cutting plastic springs, you need a jig that will support the spring from the inside without putting pressure on it form the ends.

Unfortunately, the cut file for the jig pictured was lost along with a USB. This isn't really all that much of a tragedy because it barely functions and is in need of a redesign, but it does mean that if you want to cut a plastic slinky you'll have to do some work on this step. Sorry!



_{1 Sorry if you're getting confused by this explanation involving both a spring mounted in the rotary and a spring that is part of the rotary mechanism. It's confusing me too.}

I've been using the same power and speed settings for acrylic and PLA. As you might expect, cardboard cuts faster and at a lower power setting. Settings windows for both are pictured.

Watching these things cut can be downright  hypnotic. Video of some actual cutting below.

PLA and acrylic spring coils partially fuse back together as they're cut. To separate the coils I gently ran a razor along the cut line, doing a little sawing motion at any points of resistance.

This part is tedious. It's also extremely gratifying watching and feeling the spring become more spring-like with each pass of the box cutter. At the same time, there's an element of fear that you'll break the spring as you're separating the coils, and if you do, it's a real bummer. Lots going on during this step, emotions-wise. 

Pictures from the beginning.

That is all. Thanks for reading!

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