Mill files can be purchased in hardware and like stores. I've found these files to have courser teeth than required. Many years ago I purchased my mill files at a jewelers' supply company in Downtown Chicago. These files have finer teeth. I obtained mill files designated "00", "0", and I think "1". They are also of different sizes (lengths and widths).
This is not the time or place to go into a dissertation on filing. However, if you have filed enough "things", you know the thinner the piece to be filed, the finer the teeth have to be. Also, be aware trying to file something flat and square takes great skill. Over the years I've made patterns for parts to be cast out of brass. Some brass patterns had to be filed square. Now with age my skills are starting to wane.
Filing the hole square takes time. Often it comes down to 1 or 2 strokes of the file and then measurements are taken. If you are doing this take your time. Long strokes over the length of the piece or hole are best. Correct any dips or off-square edges and corners immediately.
An old white sock was placed inside the model to prevent brass filings from getting all over the interior. The sock also protected the glazing and wall opposite where the work was being done. The scratch in the left window post can painted using a small, fine brush. The gray line above the windows will be covered over with an aluminum stripe decal.
Remember my comments in the prior post about the soldering together of the 2 pieces of brass? This is where I ran into a minor problem. Near the edges of the hole, the 2 pieces of brass were not soldered together. In filing the hole square, I was filing 2 separate pieces of brass.
Filing tends to "pick" at the edge of the piece being filed. In one corner of the opening as the corner was being filed, the 2 pieces of brass separated a little.
The worst part of having the 2 pieces of brass separate, causing a gap, is the separation makes the window appear deeper than it actually is. Trying to clamp the 2 pieces of brass together is nearly impossible. The exterior brass is finished. Placing just any clamp will not do as it will probably mar or scratch the paint. Also, the clamp has to be small to fit into the hole due to the location of the brass separation in the model. There are small, plastic clamps available. I could not find mine.
I placed a small amount of slow curing ACC into the separation and held the 2 pieces of brass together with weights placed inside the model. To keep the weights from sticking to the model's interior wall wax paper was placed between the interior of the model and the weights. The model was placed on its side on soft material with the weights inside.
This photo was taken after the ACC had cured. The raised portion of the interior brass can be noticed.This is the same photo at the beginning of this post. What needs to be done is make a set of 2 windows to fill the opening in the side of the model. Also notice the unpainted brass in the sides of the opening. This brass has to be either covered-up or painted as part of the window construction or installation.
This will give you an idea as to the measurements for the replacement windows. On the left of the drawing are the measurements for the window post between the windows. All measurements were taken with a Vernier caliper.
I decided to make a drop-in set of pre-painted windows just like the ones you can get to replace the windows in your house. What will be done is to make the replacement windows in a metal housing having a hole the same size as the hole in the model.
First a 0.040" thick piece of styrene was cut to the exact dimensions as the hole in the model. The piece of styrene was made having a snug fit into the hole.
Notice the word "outside" written on the plastic "pattern". What you do not see, and there is no photo showing, are the tiny gaps around the edges of the hole and plastic "pattern" where light shows through. When the replacement window is installed, gap filling ACC will be used and then painted over.
By a stroke of luck I had a squared off, rectangular piece of 1/16" thick aluminum sheet of an appropriate size to make the styrene window for the model. You'll see it in the next post.