In your specific case, it sounds like the design thickness of the head is 3/8", so this was used as the minimum thickness during manufacture, maintained at the apex which is why the part is thicker at the base. This is typical of pressed or spun heads, and is the reason why spherical hulls are often fabricated from several smaller spherical sections welded together - the smaller the piece, the smaller the thickness variance, so you don't end up carrying a bunch of superfluous material.
Machining a formed head is a big undertaking for a hobbyist, and although this would be a superior way to do it since it would eliminate unnecessary weight, in your case I would suggest simply doing an appropriate bevel as a weld prep, welding, and then adding additional weld material at the joint to create your taper transition. This is easy to visualize if you imagine the two parts as being nothing more than shells with zero thickness, occurring at the middle of the material thickness. You need to join them in such a way as to have a smooth transition with no discontinuities, so if these theoretical parts don't align, add weld material to essentially create a cone to join the two different diameters.
-Sean Jon Wallace wrote:
James,Is the inside diameter of the heads equal to the inside diameter of the hull? Vice-versa? I'm trying to understand where the excess material is located geometrically. The end caps are not too heavy and I assume you ordered a minimum thickness of 3/8 inch which is why the sides are thicker. Kittredge used thicker heads on the K600 than the hull because the company he built it for insisted on it. As I recall, the ID of head and hull were identical and the excess material is on the outside of the hull, and he did not grind it down as the conning tower is. Looking at the head to hull connection on the outside, you can imagine there would be an obvious edge because of the two dissimilar thicknesses. However, some material was used to flair the transition from the head to the hull. Now, I have no idea what material was used but I'm sure it wasn't car body filler or anything like that. Without knowing, I suspect that area was built up with welding filler material and then ground down as smooth as they were able. Again, from recollection, the length of the flair, or transition from head to hull, appeared to be about a 2-3 inches. Also on the K600, the same approach was taken with the conning tower. Kittredge did not grind down the conning tower thru-hull as he shows in the K350 plans, but instead used build-up on the outside edge flaring it to the CT itself.Jon James Frankland wrote:Hi All, Ive been making some slow but steady progress on my sub.Im am at the stage where i am starting work on the endcaps. A few penetrations to go in and then i am ready to assemble the main parts of the hull together.But I have what i think is a problem with the endcaps. I specified the correct thickness as per the plans (3/8ths) but they are spun so while they are 3\8ths (10mm approx) at the centre, they are 13mm at the edge.I dont know the exact weight but they seem extremely heavy to me. Questions: 1. Are they to heavy?2. Do i need to machine a taper onto the inside diameter to take the 13mm down to 6mm (hull thickness) in a controlled manner or can i just bevel it for welding? If i do not machine it, there will be quite a step from 6 - 13mm. I have a feeling it should have a stress reducing taper like where the main tower shell joins the hull reinforcement ring.Endcaps link - http://www.guernseysubmarine.com/index_files/Page493.htmTaper Example link - http://www.guernseysubmarine.com/index_files/Page3975.htmWhat have other people done at this point?? Many thanks for your advice. James
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