Let's even take the classic (by now) example of a 9" wide board with 88 kg person standing in the middle.
What should be the thickness of the PLA deck so it won’t break with SF of 1.5?
You already know this, following the process from here, the thickness of the deck will be around 15 mm.
Sounds promising, isn't it? (although on the thick side)
You still don't know how flexible or stiff your deck is.
Luckily, there's a simple formula for simply supported structure with central force - just like the deck:
"The deflection in the middle (d) equals the force in the middle (F) multiplied by the length (L) to the third, divided by 48 times Young's modulus (E) times the moment of inertia (I)"
In other words, it suits the general deck case:
The best part is you're already familiar with all the terms inside, except Young's modulus.
Young's modulus indicates how stiff the material is and how it resists stressing.
Rubber has a very low Young's modulus, steel has a high one.
[The units are force divided by the area (like in stress)]
For the dimensions from above and the calculated thickness of 15 mm, the deflection is 36 mm.
To make it more interesting, let's see different materials with numbers:
With PLA we've got a chubby deck on the flexible side.
Going the classic wooden route will make your deck stiffer by more than twice (for the same thickness)
Or you can get creative and go with carbon or even aluminum (like here), both of which can make the structure thinner and much stiffer.
So, should you always 3d print?
As always, it depends.
How stiff do you want it, or what shape do you want it to have are important questions when deciding about materials.
Personally, I tend to combine materials and shapes to make it more efficient and interesting.
And we can talk about this in the next post.
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A short series of posts dedicated to designing your own, as strong as you want, structures.
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