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I came across this drawing of a "Finned Tube" (Google translate). Took me a while to make out why the horizontal fin was different from all the rest in the side view at first. It turns out they added the bottom bends which are cut off from sight in the remainder of the fins.

enter image description here

I was able to construct the end view eventually. It was like pulling teeth initially trying to get all the ends to connect in the array for some reason.

enter image description here

I then extruded the section view for the 260 length.

extrusion

And stopped at trimming the ends at a 15 degree angle. (Apparently I left a small sliver on the pointed tip.)

enter image description here

The reason I stopped here is I realized that the 10 mm dimension is actually showing the point where the "fins" start to deform. And this also made me realize what the faint lines were in the cross section/ end view.

What is an approach to model the transition to those pinched ends?

I am guessing loft, but really shaky on the details that would be involved.

(I had no clue what the 2 mm diameter radius would be when the pipe was formed, so I just kept that number to keep things simplified. I am making the assumption that the more important dimensions are the inside and outside dimeters when done along with the 15 degree end chamfer.)

I am using Inventor LT 2021. No access to sheet metal tools

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2 Answers 2

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The device to make this is called a sheet metal bender or brake.

The last point of the star is different because it would be hard to put a radius on it.

When looking at old German designs, when you consider how it will be made, the answer is probably "in a very complicated way."

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  • $\begingroup$ Its not the pointed bit I am worried about, it all the rounded bits that need to be crimped together on an angle. $\endgroup$
    – Forward Ed
    Nov 13, 2021 at 0:11
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    $\begingroup$ I think the question is about modelling, not manufacturing, right? $\endgroup$
    – Jpe61
    Nov 13, 2021 at 13:40
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    $\begingroup$ @Jpe61 Correct. Though knowing the manufacturing process can give good insight as to how things should be modelled sometimes. $\endgroup$
    – Forward Ed
    Nov 13, 2021 at 16:04
  • $\begingroup$ Absolutely, it is easy to fool oneself by becoming an expert in modelling, but at the same time produce parts that are extremely hard to manufacture due to some very minor detail. Every modeller should have solid knowledge on manufacturing above all! $\endgroup$
    – Jpe61
    Nov 13, 2021 at 17:47
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Presumably the fins are for improved heat transfer. A more practical method is use standard round tubes ( much easier fabrication) and wrap, in a spiral, with thin aluminum strip. The aluminum has a "L" cross-section and one leg is cut at about 1/8 " intervals. The assembled exchanger has a "furry" or porcupine look. The design I describe can only be used with air or gas on the OD but that is the normal application where more contact area is needed on the OD. These type tubes are used in fin / fan exchangers but I cold not find a good diagram; there are a few fin types.

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