Scratchbuilding the Dove part 7

In closing out the privious section, I mentioned that the first attempt to make the cockpit master was a failure do to a miss-located access hatch outline. Identification of that problem manifested itself well into the parts fabrication. With so much work wasted, I swallowed hard, set it aside, and proceeded with Fabrication of a new unit.

BUILDING THE COCKPIT AND ACCESS HATCH MASTER

At variance with the procedural sketch, I made up the cockpit blank from just two pieces of modeling foam  not three as  illustrated.  Arrayed around the foam blanks are the marking and cutting templates used to guide me as I cut the assembled blank to plan and profile.

The Second Attempt To Fabricate The Cockpit Master   The photo shows how I made use of cutting and marking templates to plot out the plan and profile cuts to the light-weight modeling foam blanks that would take form to become the cockpit master. Note that I used two pieces to make up the blank; a left and a right hand pair, not the three pieces I was contemplating when I drew up the procedural sketch.

(The procedural sketches are guides, not stone tablets! Often, as the actual operation is initiated, it will be found that variances to the proposed technique  are a better way to go than the original conception).

I remind the reader that the term 'plan' as applied here refers to the overhead view (projection), and that the term 'profile' refers to the side view.

The three-view orthographic drawing at the bottom of the picture is the access hatch and cockpit working drawing and is a development of the Phil Rae plans, his work a resource that mysteriously seems to get better each time I examine it! Phil did one hell of a job 'getting it right'.

Marking templates are plastic forms that represent the profile and plan view. It is best to only make one half of the plan template (used to mark  off the cut line on to the left and right side of the cockpit blank) and to invert it to mark out the other side of the blank. This way you are assured of absolute symmetry to the left and right blank halves.

You'll note that on the plan and profile orthographic projections that there are doted lines near the bottom. These dotted lines represent the interface points between the curved upper hull and cockpit base. To simplify  fabrication of the master I terminated the bottom of the canopy master as a flat plane, therefore I had to extended the curvature of the plan and profile projections to terminate as a flat plan. Later, after all side, top, and section shaping had been done I would cut the bottom of the master to conform to the geometry of the hull. But, that's another story who's gory details will be revealed in a later installment.

Because  there were two different plan shapes (one where the hull interfaces with the canopy, the other where the piece terminates as a flat plane) I was compelled to make two plan templates. The larger of the two, the one marking off the outline to the flat plane, was used initially. Only after all shaping was done was the bottom of the master marked with the smaller of the two plan templates, and the master cut back and test fitted atop  the hull master.

Marking Out The Access Hatch Base   The three plastic cutting templates were attached to the two foam blank halves. One sandwiched between the two blanks, and the others attached to the outside of the assembled blank. These cutting templates assured that I cut only to the outline of these templates as I made the initial profile cut.

The only clue on Phil's drawing as to the sectional layout of  the cockpit was the outline of the access hatch. So, I elected to cut the cockpit master to represent the cockpit without the access hatch. This permitted me to mark off atop the cockpit master the base outline of the access hatch - an important 'landmark'.
 

One cutting template sandwiched between the two blank halves and two attached to the outside of the assembled blank controlled the profile cut of not only the cockpit proper, but also the cut-out at its top that would later receive a discrete access hatch piece.  Once an initial cut was made on a band saw, all work was brought even with the templates by the careful use of sandpaper and file.

The photo above shows the assembled blank after making the initial profile cut to the height of the access hatch base. The initial cut was done on a band saw, then finished off with hand tools, specifically course and second-cut files followed by a working over with course and medium grit sanding blocks.

A marking template was used to pen in the outline of the access hatch base atop the cockpit master. At that point I completed cutting the forward and after ends of the cockpit master to profile - right to the tops of the side and inboard cutting templates.

(The central template would remain as a clear indication of the masters longitudinal centerline. This center-cutting template would become the datum line, from which other measurements would be plotted onto the master).

The Cockpit Master Cut To Plan   Once I had cut the entire blank to profile I inverted the master, marked off the plan outline on its bottom and band sawed away the outer portions, loosing the two outboard cutting templates in the process - they had done their job during the cutting to profile operation.

The next step was to make and install a pre-formed access hatch, made from twenty-pound modeling foam.

However, before proceeding with work on the cockpit master further, lets take a closer look at the different densities of modeling foam employed for the creation of the cockpit and access hatch masters:

Here we see the different reactions between two different densities of model builder's foam to knife, scribe and sanding tools.  The  denser foam, the twenty pound stuff to the left, renders a clean scribe mark, but is harder to work with hand tools.  The light weight foam, the ten ten pound stuff to the right, has a rough surface and  gets sloppy when scribed or cut, but works very easily with hand tools.  Use the ten pound foam for big items of relatively simple shape,  Use the twenty pound foam for small detailed items.

The Medium And Light Density Modeling Foams   Photo #5 shows the different reactions between the different densities of model builder's foam  to common hand tools. Specifically, these mediums reaction to knife, scribe, and sanding tools.

(Density, as defined here, is expressed as pounds per cubic foot).

The denser foam - the twenty-pound stuff to the left, renders a clean scribe mark, but is harder to work with hand tools. The light weight foam - the ten-pound stuff to the right, has a rough surface and gets sloppy when scribed or cut, but works very easily  with hand tools.

Use the ten-pound foam for big items of relatively simple shape. Use the twenty-pound foam for small, detailed items.

The dense modeling foam will sand to a finish suitable for direct  application of primer. On the other hand, the light weight modeling foam will present a course, open cell surface no mater how carefully sanded with fine grit sandpaper. The lightweight modeling foam has to be 'filled' with some other substance before its surface can be readied for priming and painting.

For several installments of this DOVE article I have raved on about the many virtues of the modeling foam. Time to give you guy's some insight into where to buy it:

The trade name of the stuff I prefer is Poly-Shape. Its described as a Urethane Foam Tooling Board, each type comes in a minimum sized 'board' measuring 2"X18"X40".

It's been over five years since I have placed an order, so the price likely has gone up. Back then I paid about $400 for each type board. That price does not include shipping charges.

The ten-pound Poly-Shape catalog number is 077010, the number for the twenty-pound Poly-Shape is 077020. The source is the Freeman Manufacturing and Supply Co., 1246 W. 70th Street, Cleveland, OH 44102. Their phone number, 1-800-321-8511. Sorry, I don't know if they have a web site or not.

I'm sure that there are specialty supply houses out there that sell smaller quantities of these modeling foams, you'll have to  look around. Micro-Mart, maybe?

In part 8, we shape the cockpit....