Scratchbuilding the Dove part 4

BEGINNING WORK ON THE HULL MASTER

Fortunately, the maximum width of all hull structure (less the wings) occurred on the same horizontal plane. I took advantage of this observation as I drew up procedural sketches on how I would build the hull master.

The steps I worked out for upper and lower hull assembly. At the top is the assembly board upon which the armature (built of  thick plastic sheet) is temporarily mounted. Between the frames of the armature are fit blocks of modeling foam, illustrated in the lower drawing.

I elected to make the hull master in two halves, separated at the horizontal break line - the plane of maxim width. This permitted me to cut frames from  the sectional drawings as upper and lower units.

The Armature   A central keel piece (an upper and lower unit) was needed to give rigidity to the mounted frames and to produce longitudinal datum lines (a known point on an object from which other measurements are plotted), top and bottom. Each keel piece, of course, captured the profile shape (side-view) of the hull.

What I would produce would be two skeletal structures. Each comprising a vertical keel piece running the length of the hull. Attached to the keel are left and right frames. This keel-frame combination is better described as an armature.

The Hull Assembly  Board   On the band saw I cut out a piece of three-quarter inch thick shelf material  to the plan (top/bottom projections) of the hull. The shelving material I get from Lowe's is available in a number of widths and lengths. Shelving material is ideal for making true workbench tops as well.

To assure that I cut an exact shape to the assembly board I first lofted off the plan view onto a stout piece of plastic sheet the hull plan outlines and then cut the sheet to shape. This marking template was then used to mark off onto the assembly board with a cutting stylus (scribe) to minimize the sloppy with of a pencil or pen line.  Careful cutting and sanding to this engraved line resulted in a truly symmetrical assembly board, or construction jig.

(Jig: A device, often with metal surfaces, used as a guide for a tool or as a template.  That's out of my Webster New World dictionary, boy's and girl's. In this case I have built the assembly board to act as a jig, a means of assuring the correct orientation of a structure (the two armatures) built upon  it. This type of jig can also be described as a working template).

The assembly board was then marked with a longitudinal line at its center. Radiating from that line, perpendiculars to it were marked off the station locations from the working drawing. Those lines denoted where I would position the keel and frames as I built upon the assembly board the upper and lower armatures.

Not illustrated were four blocks,  mounted against the sides of each keel piece near the front and back. Through these blocks were drilled vertical holes which were tapped to receive 6-32 machine screws. Corresponding holes were drilled through the  assembly board. In practice retaining screws are passed through the bottom of the assembly board and into the armature, making the armature and assembly board one.

Before armature fabrication began, the all surfaces of the assembly board were coated with mold release wax (available at most marine/auto repair outlets) and the wax layer buffed to a high gloss. This wax layer would prevent any glue that later got away from me from permanently adhering the armature/foam blocks to the assembly board. I had to lift the armatures off the assembly board eventually for further work. The assembly board is a working jig, not an integral part of the hull master.

Building The Armature   The assembly board readied, I cut an upper keel piece from .060 inch thick styrene plastic sheet, checking it against the profile drawing - sanding until it was perfect of shape. After attaching the four foundation blocks and drilling them to accept the mounting bolts, I secured the keel atop the assembly board.

Using a copy of the section plan I punched a series of pinpricks through the paper onto the surface of another sheet of plastic. The pinpricks denote the outline of a specific half-frame. Removing the drawing, and 'connecting the dots' on the plastic with a knife, I then snapped the frame clear of the surrounding plastic sheet. The plastic frame was then checked atop the drawing and worked with file and sandpaper till perfect. After each half-frame was cleaned up, it was used as a template to mark out its opposite number.

Cutting out all the frame pieces was the most tedious portion of the hull master job.

Each quarter frame piece was held against the keel, super glue applied (only at the frame/keel union point), and I moved on with the next. By holding each frame piece over the correct station perpendicular line drawn atop the assembly board I was assured correct location on the keel and a truly perpendicular orientation of the frame to the keel.

 After the top armature had been assembled, I removed its securing bolts, and pulled it free of the assembly board. I then made and attached the bottom  keel piece to the assembly board and repeated the operation.

With two completed armatures in hand - one for the top half of the hull, the other for the bottom half - I moved on to the task of inserting carefully  cut blocks of model building foam between all frames.

The actual hull master elements in work. To the left is the upper hull half armature with blocks being trial fitted. To the right is the lower armature mounted atop the assembly board - its blocks are in the process of being glued permanently to the armature. Work with the band saw has eliminated much of the work of shaping the  foam blocks. Final shaping is done with file and sandpaper.

Working With Dense Foam   Modeling foam, as mentioned earlier, is available in a number of densities; the denser the material, the tougher it is to work with hand tools, but the better the surface finish. I elected to go with a relatively light type. This permitted me to work the material with files and sandpaper once all the spaces between armature frames  had been filled with blocks of foam.

I took care to shape the foam to the height of each adjacent frame without risking cutting into the frame or keel - such action would alter its shape and ruin the symmetry of  the hull master. The trick is to select a fill material (in this case soft foam) that is much easier to abrade and cut than the material that makes up the frames and keel. Fifteen years ago my armature would be built up of marine plywood or soldered brass sheet, and the fill blocks would have been Balsa or Sugar Pine. Times and material choices change.

With an armature remounted on the assembly board I began cutting slightly  oversized square foam blocks to fit between the frames. Before gluing each block in place, I temporarily inserted it between its frames and holding it with one hand I marked the outline of the frame ahead and the frame  behind, the outline of the keel, and the bottom of the block where it overhung the assembly board. Pulling the block out of the armature, it was worked on the band saw, refining its shape to about a sixteenth-of-an-inch over the marked lines.

Pre-shaping the foam blocks reduced the amount of filing once all the blocks for an armature were secured in place. The initial shaping went very fast, in no time at all I had the upper and  lower hull masters cut to shape. I started shaping with a course hand file, then a sanding block loaded with #100 and finally #240 grit sandpaper. I worked the foam to the tops of the keel and frames and to the edge of the assembly board, no farther - it is the shape of the frames, keel, and assembly board that drives the final shape of each hull half.

Greg Jein and his modeling staff at ILM employed this same foam-between-frames building technique to fabricate the masters needed to produce GRP parts for the huge 1701-D miniature used for the first couple of seasons of the STNG TV show.

Greg clued me onto the specifics of this technique and also sent a series of slides showing that work - information I shared during one of my 2000 Wonderfest talks.

In Part 5  I'll take you through the finishing of the hull master surfaces, creation of the cockpit master, and  use of a special marking jig.

Remember: model kits have their place. We all need stretched sprue every now and then.  Onto Part 5