How can I cleanly cut thick plastic straws?

Question

I have drinking straws like this:

They are thicker, reusable straws, probably PVC. They're the thickness you generally find in tumblers that come with their own straw.

I thought it'd be neat and cute to cut them down and make a fun panflute for my kids!

The cut needs to be clean, without breaking, splitting or damaging the rest of the straw (which rules out my bolt cutters). I not only need to cut them to size, but also make the holes where the air comes out.

This will be purely decorative, and given to children, so it needs to have no sharp edges.

Answer 1

It's worth noting, if you feel like taking a trip to your local hardware store, that they make specialty blades that fit boxcutters. Some of these are designed for laminate. Most likely, the blades that came in your boxcutter are ok for opening boxes, plastic packagine etc. However, you can buy some designed for cutting laminate, PVC, etc. Look for blades that are thicker and may have a wavy pattern on the edge. These can be especially helpful in working with plastics. The sharper the blade, the less force needed to cut/saw. Like in the kitchen, this is safer than a dull knife that needs lots of force (that ends up slipping into your thumb - Ouch).

Similarly, rather than "homebrew" a solution, for under $10 you should be able to find a cutoff wheel for your dremel made for plastic. They often are serrated, and may have holes through the wheel that lighten in.

They are super helpful and will give a great, square cut (often without burrs).

Watch out for any sharp edges if these will be near a child's mouth. A good wash in soap and water should take care of any residual dust. Those would not be "Good Eats"

Answer 2

I did not tried it but that's how I would proceed:

For the cut: (to make a pan flute)

• Solution 1: My guess is that cutting the straw with a heated knife will be very messy and gives a bad result. So I'd simply use a serrated knife. Something like this one:
  
  and saw the straw with it. Pay attention to really use the sawing part of the knife (this is why the teeth are important), i.e. don't press the knife too firmly against the straw to make sure that you don't break it. You can then smooth the edges of your cut again by using some kind of heating process. In this case, I would even consider having a very hot surface and then simply press (as vertically as possible) the end points of your straw on the surface. Ideally, you have a pencil ready to put it in the straw when the plastic is soft and make sure that the hole is not obstructed by the plastic. I'm pretty sure this should work well. In fact, you could also use this knife to get third type of holes in straw (my guess is that different holes will lead to different sounds).
• Solution 2: This is based on a surprising experiment I made one evening by pure interest. And actually you could consider merging some ideas of this solution with Solution 1. The experiment was easy, take a plastic glass fill it with water and try to make a whole in the glass with a lighter to empty some water: impossible. The plastic above the water will melt exactly until the water level is reached and afterward, no way to go further... (maybe with a blowtorch it could work but this is not the goal here). Moreover, the melted plastic tends to curl outside the glass and does clearly not go where the water is. So you can use this phenomenon at your advantage: Indeed you could stuck one side of the straw (with a chewing gum or something similar), fill it with water at the level you wish and melt the remaining part. If you have to melt 2/3 of your straw this will eventually be long and smoky (and this are the kind of smokes your lungs really want to avoid). So, I would consider first cutting the main part with a knife and then make the last 3-5 millimeters in this way in order to get a very smooth result.

For the holes: (to make a regular flute)
Actually I misread the question at first (and forgot about the "pan" part of your flute), so these solutions can be useful if you want to build a regular flute with several holes in the same straw (which IMO could also be an interesting option to consider).

• Solution 1: Consider a tool like this one (an awl):
  

  Hold the extremity above a candle and then make your hole. The heat should (locally) soften the plastic and make a relatively neat hole. Just pay attention to retain your move in order to avoid piercing both sides of the straw :). Note that you could also put something in the straw to stop the awl on the midway.

• Solution 2: Another way could be to use sand paper rolled. I would wrap a pencil with sandpaper and use it to make the whole. The advantage is that the whole will be even more clean however you'll get a kind of ellipsoidal hole (which might change the sound of your instrument) and you can certainly not make as small holes as with Solution 1. Another relatively small drawback is that this is very sand paper consuming. Indeed, my experience, is that when rubbing with sandpaper, the plastic will melt a bit on your sandpaper which makes it quickly unusable (but at least sandpaper is quite cheap).

• Solution 3: Use the same knife as in the first part of this answer and cut some "V"'s in your straw, something like that (cut along the red lines):

  you will get a third type of holes. The problem however (as well as the solution with sandpaper but even worst) is that the different holes will likely be different from each other, so unless you have some other tools to make sure that the cut will be exactly at 45° and not pass the half of the straw, I would avoid this solution.

Answer 3

I have cut thick plastic tube using garden secateurs. Even easier is to use double action tin snips. Hardware shops may sell snips like the picture. They are great for cutting plastic, leather and trimming cat's claws.

Answer 4

You may want to consider a hot wire cutter. Professional models aren't cheap (although you can rig one up, or even rig up something useful w/ a soldering iron and chunk of flattened coat hanger) , but it works really well for the type of cuts you're looking to make.

If you know someone who works with polystyrene foam, they likely have one. (it's rather common in terrain modelling -- either miniature-based wargamers, or model train folks).

Answer 5

A safety letter opener would hold the straw open and the blade is hidden. Would be a safe way to slice the straws open.