If you’ve ever had the misfortune of breaking a bone then you might know how terrifying it is when it’s eventually time to have the medical cast removed.
The noisy cast saw drilling next to your skin might be enough to instil the fear that something out of Final Destination might happen to you, but in reality, it’s perfectly safe.
And there’s one incredible reason why a cast saw will never cut through human skin.
This has all been explained by a YouTuber named Steve Mould who took to the social media platform to lift the lid on how a cast saw really works.
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Don’t panic - despite its name, there is nothing gory to worry about when it comes to the practice.
In fact, Mould even hired a slo-mo camera in order to film a bunch of clips of the cast being used on various different materials, including his skin.
First of all, the blade of the cast saw doesn’t actually spin around, despite looking a lot like they do.
Instead, the blade oscillates back and forth a tiny amount incredibly quickly.
This makes a tiny sawing motion along the blade’s edge, although there is a specific safety component of its design.
The video touches on a huge number of really technical details, but the point effectively boils down to how rigid and elastic a material is. As the blade scrapes on the surface, whether it's a bit of rubber or the skin on your arm, a more elastic surface just adapts to the oscillations.
This means that your skin will just ripple and move with the saw, rather than being ripped by it, something determined by a combination of how fast the tool oscillates, and what your skin's elastic limit is.
This means, to be clear, and as explained by Mould, that other oscillating tools could well move faster or have different blade types that would mean they do break skin, so don't do any foolish experiments at home!
Medical casts, by contrast, are mostly dried fibreglass and plaster, so they're really rigid and have little to no elasticity - hence they're able to be easily cut off by a simple saw.
So, for all the technical details, it’s a pretty simple but fascinating explanation, and should help you to breathe a sigh of relief next time you unfortunately need a cast for any reason.
It turns out that it isn’t quite as scary as you might think!