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CNC

Steel bulb nr3


Jari made this steel bulb over the weekend. It has a slightly triangular cross section in the beginning which flattens out to a 'beaver-tail' at the end.

3 replies on “Steel bulb nr3”

If you were to make a steel bulb the same size as a lead bulb, how much differance would it weight? Or how much bigger would it have to be to weight the same as a lead buld. Maybe you could take a picture of a lead and steel bulb side by side.

Hi Andrew,

I don't have the CAD files for the two bulbs here right now. A quick calculation goes something like this.

We want the bulb to weigh say 2400 g.
If made from pure lead with a density of 11.34 kglitre then the volume should be 0.211 litres.
If from steel with 8 kg/litre the volume should be 0.3 litres
if from brass/bronze with 8.7 kg/litre the volume should be 0.276 litres.

If we imagine a very simple cylindrical bulb with a length of 350 mm and a constant circular cross-section (nobody would actually build a bulb like this...) then we can look at the differences in diameter:
350mm long 2400 g Lead-cylinder has a diameter of 27.7 mm
350mm long 2400 g Steel-cylinder has a diameter of 33.0 mm
350mm long 2400 g Brass-cylinder has a diameter of 31.7 mm

For a more reasonable NACA or other shape I would guess the differences in diameter are similar. I don't know how much of a performance effect this can have - probably very little.

We have been running a similar shape bulb for about 3 years now and seems to perform quiet well. Am curios to know what the reasoning was on the beaver tail shape you are making.

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