To paraphrase Vane Jones, "Knowledge is of little value until shared with others."

Monday, March 30, 2015

Finishing a CTM 4000 Baldie Kit Part 4: More Roof Vents, and Miscellenous Details

Intake Vents
Thinking of how to add the 2 small square vents built into the roof of the prototype took some time. First something already available was looked for.
Nothing could be found.

These vents were built into the roof. They are louvers which blocked objects falling from above from entering the duct. At this end (#1) of the car, an electric intake fan in the ceiling of the entrance/exit vestibule pulled air from the outside through the 2 vents and into the car. The 2 vents near the center of the car were passive exhaust vents.

After much thought a square vent 0.010" thick was built out of styrene. Styrene 0.010" thick is flexible enough to conform to the contours of the roof. This same type of vent could be made from etched 0.005" or 0.010" brass. I do not know of anyone who etches brass so the styrene vent was made.

Now that my roof is finished, I feel my measurements were a little bit off. Therefore as we go through this section, my comments about measurements will reflect this.

First a square had to be built from 0.010" x 0.020" styrene strips. Using my concept of if 2 opposite corners of a square or rectangle (1/2 of a larger square being made) are square then the shape is square. The photos go through the building process.

Eight pieces of 0.010" x 0.020" styrene were cut and glued together at 90 degree angles. Each piece of styrene was cut longer than required. A small machinist's square block was used to ensure each joint was square. Small amounts of styrene glue was used. Too much would warp and/or dissolve the styrene strips.

After each of the joints had completely dried, they were prepared to be glued into squares. Notice the penciled lines on 2 of the 1/2 squares. These are the final size of the complete square.

The red and green arrows point to the pencil marks. The blue area points to an area where too much styrene glue had been used. The styrene dissolved to provide the webbing effect.

The next steps were to make the squares. The photo taken below shows the process just after one of the sides was cut short. BTW - all cuts in the making of the squares is at 45 degrees to allow the square to lay flat. Small drops of styrene glue were used.
IMPORTANT - Leave one arm attached to the box (green arrow).
You need the one arm on the styrene square for the installation of the louvers. Four louvers need to be installed leaving 5 slots for the air to enter the car. The louvers are 0.015" x 0.020" styrene cut to the correct length to fit into the square.
The louvers are placed on their 0.015" side which means they will be sticking out of the square. After all the louvers are installed, they will be sanded down to 0.010" thickness.
Use the handle to hold the styrene square against the glass as each louver is installed and glued in place. Dentist scrappers and other picks are useful in cleaning up the vents.
This is a close-up of one of the vents after gluing and sanding. Notice how the glue has softened the styrene. At this point the styrene is stuck to the glass. It can be cleaned up plus the handle cut off. Gently use a new razor blade to remove the vent from the glass.

Handle the vents carefully. Now the vents have to be glued onto the roof. These vents are located at the #1 end of the car above the side door on each side. Glue the bottom of the vent 1st.

Then after the glue has set, continue gluing the vent around the curve of the roof. Be sure to glue each slat of the vent to the roof. The vent will be sanded and you do not want any of the slats to come loose.
The vent has been completely glued to the roof. The vent can be gently sanded to even out the vent plus reduce the slat size. Remember they were 0.015" sticking out (0.005" higher than the 0.010" thick vent material) from the roof.

Next comes the old auto body or if you prefer the old plasterers' trick. Many years ago we hired a pair of plasterers to repair some cracks etc. in a wall we had in our home. After the work was done I commented to one of them about how nice and flat the finished wall looked. He told me the wall really isn't flat but an allusion of looking flat. The trick was to make the wall look as smooth and finished as possible over the long flat plane of the wall.

I've repaired the body of an old car (1953 Porsche) with "bondo". The idea was not so much to match the curve of the other side of the car as much as to make the side being repaired look like a smooth and finish curve without holes or cracks. This was much the same as the plaster work in our home.

The intake vents on the roofs of the prototype 4000's were into the material of the roof. The vent did not stuck out from the roof. On the model the same thing has to be done. Squadron body filling putty is applied around the vent and allowed to dry. Do not use an old tube of Squadron putty. It will not flow well and will dry with cracks and small holes in it.

Apply the body putty up to the center of the roof, for 1/2" to 3/4" towards the center of the car, down to the bottom of the roof, and all the way towards the front of the car.

Squadron body putty actually dries to hardness. As the solvent evaporates the coating of putty with shrivel up. Thin coats will dry quickly and not crack. Thick coats with shrink in and crack!

It's best to wet sand (320 or finer grit) the vent and body putty until the area is smooth without cracks or holes. Clean out the slats in the vents. If the edges are not feathered and/or there are cracks or holes apply more body putty. When dry wet sand again. Clean out the slats in the vents.

Repeat the cycles of application and sanding until the area looks smooth and finished. At this time you'll notice the vent to appear as though it's into the material of the roof. The slight "bump" of the vent will be un-noticeable.
This is the vent during the sanding process. The rivet decal had been prematurely applied to the roof. Photos which are cropped and the size readjusted are great to show the imperfections in a model. The lines were drawn to be sure the slat holes were the same length.
More work of filling in the cracks etc. had to be done to the vent in the above photo before the rain gutter and rivets were re applied. Unfortunately I failed to take enough photos of the work.

This post is getting long and there's still the rain gutters, roof rivets, and something strange about the roof! The next post will have to cover them.


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