Scratchbuilding the Dove part 10

COMPLETING THE COCKPIT-ACCESS HATCH MASTER

CHECKING THE CONTOURS

Last installment I took you as far as coating the rough surface of the cockpit master with Spot-Lite filler.

After the filler had cured hard I sanded the piece to a smooth finish - starting with #100 for the first few swipes, then shifting to a more careful rub down with #240 grit. On those few spots where this sanding cut through the filler, once again reveal the open cell structure of the modeling foam, I re-applied the filler and sanded again. The filling/sanding continuing until I had achieved a relatively smooth surface of Spot-Lite filler over the modeling foam substrate, at that point the cockpit master was protected and almost ready for priming.
 

The cockpit piece temporarily mounted on the marking fixture and marked off with a series of radial lines with the aid of a waterline-marking tool. These lines become visual cues used to help me finish off the shaping so one side is symmetrical with the other.

This initial 'smoothing' of the cockpit's surface done I mounted the piece, with the aid of carpet tape, to the marking fixture (made earlier to mark off the radial and longitudinal lines onto the two hull master halves). As illustrated in the accompanying photo, the cockpit was marked off with a series of radial lines with the aid of a waterline marking tool.

Removed from the marking fixture and holding the piece directly at one eye, dead on (front and back), the black radial lines aided me in determining the symmetry between one side of the cockpit master and the other. Gross problem areas were addressed with either file or filler. After these operations I took care to hand draw the radial lines back onto the piece. I continued to 'eyeball' and worked the piece to the point where I could not detect any imperfections without the aid of tools.

Using a contour gauge to check the right and left sides of the cockpit master for symmetry. Problem areas identified with the  gauge either receive filler or attention with file and sandpaper.

Looking over the second photo reveals a neat tool that should be at hand in any well-equipped Model Builder's shop, the contour gauge. You can purchase this tool at any of the larger hardware stores. The picture does a better job of describing how this gadget works than I can describe here, but I'll give it a shot:

Pressing the contour tool against one side of the master causes the pins of the tool to adapt to the curvature of the line being checked. Notice that the pins adopt a negative curve where they make contact. Of course it is our intent to get the other side to reflect that shape, to be a mirror representation of the opposite side.

Working one set (left and right of the central datum line) of radial lines at a time, I lofted off a curve from one side of the master and the contour gauge was shifted to the other side of the work, flipped (turned end to end to get the 'mirrored' curve line of the other side), positioned, and that side of the master checked.

If the outboard pins of the tool make contact and there are gaps between the inboard pins and the masters surface, the gaps are marked with pencil. These spots were filled and smoothed out with sandpaper and rechecked with the contour gauge.

However, if the outboard pins stand clear of the work that indicates that material has to be removed from the center of the radial line. This is done carefully with sanding block, constantly rechecking until nearly all the pins are observed to make contact with the radial line.

Using the contour gauge in this manner the process becomes one of filling or filing. This work continues until the gauge indicates near perfect symmetry between the right and left side of the master along all radial lines (of course, the more radial lines plotted onto the work, the more accurate the symmetry between the sides becomes).
 

Leveling off the demarcation line of the cockpit with that of the hull under which it will sit. This method is most useful in getting two items that have to share the same surface with a tight fit to conform to one another..

Sanding The Cockpit To Fit The Upper Hull 

At this point I transferring the dotted 'cut' line from the orthographic working drawings to the cockpit master. With razor saw and sanding block I trimmed the base of the master to the cut line as well as I could. This was the initial shaping of the cockpit masters base to fit the compound curve of the spot atop the upper hull master where the cockpit would fit. Ideally, this operation would have taken the bottom of the cockpit to fit tightly with the top of the hull master. But, this is not an ideal world and the achievement of a tight union between cockpit and hull became a bit more of a chore.

There was a slight miss-match between the base of the modeling foam cockpit base and top of the hull master where it would sit. I started to rectify this problem using a special sanding technique:

First, however, to make the work go faster I pencil marked a perimeter line one-sixteenth of an inch wide onto the bottom of the foam cockpit master. Using a round burr in a moto-tool I dug out a cavity of about one-eighth inch deep within the pencil boarder. Removing this base material greatly expedite the next operation.

Adhering some strips of #100 sandpaper to the top of the hull with the aid of  carpet tape I carefully slide the cockpit master fore and aft atop the abrasive. Since the geometry of the upper hull is not uniform I had to keep the back and forth strokes limited to about one-quarter inch. Using the very course sandpaper I quickly knocked down the cockpit base high points. Unfortunately, there were still noticeable gaps along the interface line and to continue the sanding would have lowered the cockpit piece below the height dictated in the plan. I was compelled to build up those gaps with filler.

Off came the sanding paper and carpet tape from atop the hull piece.

Next in part 11  Using Filler To Better Fit The Cockpit To The Hull