Doe you mean this:

import("C:\Users\Eigenaar\Documents\Mijn 3D
design\basklarinetbocht_v2.stl", convexity = 5);

?

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The four sections overlap pretty well with the parameter values you are using
but it begins to fail as:

• rotatie increases - wall gets thin in upper bell region,

• as height increases,

• as mildfactor increases.
  However I don't think the white dots are symptons of this. They look like a
  display artifact.

• I can't simulate the gaping hole you're seeing in the side. Not sure
  what's causing that.

• The base of the inner horn doe snot penetrate the outer horn's shae so
  there is no hole in the base of my models.

• The model I exported as STL had nothing wrong with its mesh. So maybe
  your parameter space needs tweaking ?

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The dots tend to indicate two vertices close to each other, I think it is a
similar artefact to z-fighting. If they go away on render don 't worry to
much, but I do try to eliminate them by moving a face a smidgeon one way...

Re the hole, if higher convexity doesn't work, try
Edit/Preferences/Advanced/Force_Goldfeather, if that fixes it, it points to
your graphics drivers, try updating. (I always struggle not to type it as
Goldfinger... :)

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BTW unless you color()'ed it, that purple is a sign that your faces are
inside-out.

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oops - strike that. Metalic color scheme...

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Thanks Neon22 for checking.
The white dots dissappeared when i made the thickness of the cylinders that
enclose each hull minimal (d = 0.001). In fact each cylinder on top of each
pie coincide with the bottom one of the next pie.

But because of other problems (error checking in meshLab) i decided to
increased the space parameter by increasing the thickness.

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Thanks MichaelAtOZ. I will try what heappen with higher convexity, The
Goldfeather option was on.

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