Thank you very much Daniel.
To start with, the method that I used on the Haarlem was different to the one I used today. On the Haarlem, I had no intention of re-using the cut-out pieces, while I tried my utmost today to keep the cut-outs intact so that I could use re-use them as the gunport lids.
Unfortunately, when I do this, I always work alone so you will appreciate that I am not taking pictures as I use both hands all the time. However, on the Haarlem, the method that I followed was based on the same one
@pietsan Piet Sanders uses and he has documented it beautifully.
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After the outline of the gunport had been marked on the hull, draw an inner line - well clear of the outer one and mark out a few dots which will serve as guidelines where to drill.
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Start by drilling four holes - one in each corner. Obviously the drill bit size, must allow the hole to remain inside the outer-line.
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This picture though, shows multiple holes being drilled and then it is simply a case of using a very sharp knife (e.g. an X-Acto) to cut between the dots. You can drill as many holes as you are comfortable with, but I have found that four work well for me. I have found that if there are too many holes, it is difficult to cut in a straight line which requires quite a bit of filing or sanding afterwards.
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Lastly, it is just a case of filing the holes square and sanding the edges smooth.
So let me explain this picture then:
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Obviously when you are busy cutting out the port from hole to hole, you have to cut repeatedly before the blade makes a clean cut and the cut-out can be removed. Here, I scored the gunport once or twice and then placed the X-acto in a vertical position on the cutout-line so that the edge of the blade faces inwards. Then I just gently tapped the knife with a normal-sized hammer. The blade (provided that it is a new and sharp blade), will follow the scored lines beautifully. This way, it is much quicker - but obviously, there is also more risk involved.
Today though, I could not use the drill, because that would mean the four corners of the cut-out piece would be destroyed. So, it was simply a case of using an X-Acto knife (with a metal ruler as guide) and - as accurately as possible - making repeated cuts until a clean-cut was eventually achieved. Afterwards, the gunport was finished with an assortment of files and a sanding stick (see picture below):
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A: X-Acto knife (or rather a Chinese version of it): I used the same blade on two gunports and then changed - three blades used in total.
B: Coarse file with pointed tip: This was used to file away the interfering bulkheads until they were flush with the gunports. This file was not used in the finishing process (it is too coarse for that).
C: Triangular File with smooth sides. This was used to create sharp corners as it only has one filing surface.
D: Flat File (medium grit): Used to make sure the gunports were square.
E: Diamond File: Used when difficult to reach areas need to be filed (not used today).
F: Square sanding stich with 360 grit sandpaper only applied to one side - not all four!
There you go my friend. I trust that you find this helpful.