Scratchbuilding the Dove part 5

ESTABLISING DATUM LINES AND ASSEMBLY POINTS

The ability to mark off  model subassemblies with accurate points and lines lofted off the plan is vital to the process of model building (and, to a lesser degree, kit assembling). Misplaced location points and datum lines are the biggest reason that assembled model subassemblies fall out of symmetry.

For example, a recent attempt to build a master of the DOVE's canopy failed because I miss-located the access hatch outline. Using that line as a  datum line (from which other measurements were plotted) meant all other lines using the access hatch outline as reference too were in error. That resulted in eventual miss-shaping of the entire piece. The perfect  example of one error compounding into many errors.

A FEW THOUGHT S ON COMPETITION

This has everything to do with fine model building. So. swallow hard and read on.

Let me tell you why you guy's don't win anything above an 'honorable mention' at Wonderfest an the IPMS National's: Your kit was likely assembled out of alignment; you did not exercise care during joining of the subassemblies. You did not win a prize or any recognition to be proud of because you committed one  or more basic model assembly sins that worked to immediately drop your entry from any consideration for top honors.

All the poorly built resin and styrene ENTERPRISE kits I have seen at contests were slapped  together with little more effort on the assemblers part other than to check by eye if things looked even as the glue set. As a result, many models go to show with askew warp engines, primary hull out of alignment with  the secondary hull, even a sensor dish out of align with the secondary hulls longitudinal axis. And worse!

These and other errors of alignment are rarely the fault of the kit manufacturer. Those problems rest in the lap of the builder/assembler. You!

The reasons so many kits are built cockeyed are twofold: One is because the kit assembler did not make an effort to build an assembly jig to secure the work as everything was glued together. And, second, the kit assembler failed to come up with a means of accurately identifying the pre-existing datum lines on the model (seam lines between halves of hull sections is one example of a pre  existing datum line). And to use those 'land marks' to assure correct location and orientation of the subassemblies.

MARKING FIXTURE

I needed to come up with a means of accurately holding each of the DOVE half-hull masters vertically and horizontally as I marked radial and longitudinal  ink lines. These lines needed to denote frame locations (visual aids as I checked hull symmetry with a contour gauge), location for appendages, and position of the two 'wing fence' grooves on the upper hull master.

I built my marking fixture from a piece of shelving and two lengths of two-by-four bolted to two of the shelving edges. Clamping the marking fixture to the worktable stood it perpendicular to the table. With the  hull pointed vertically I could lay down radial lines. With the marking fixture rotated so the hull was oriented horizontal to the table, I could mark off longitudinal lines.

Using the waterline marking tool to lay down the horizontal 'section' lines to the face of the hull master marking fixture

In the first photo I'm marking the station/section lines onto the face of the DOVE marking fixture. Note that I'm using a home made surface gauge - in  this case more accurately described as a waterline marking tool - to mark off the marking fixture. Note that I can outfit this waterline marking tool with either a pen or pencil.

A hull half master mounted to the marking fixture.  I have already marked off onto the hull the radial lines denoting the specific station locations along its length.  These are used as datum points from which other item locations are plotted.

The same taped holes in the half hull masters used to secure them to the assembly board are used to secure the hull masters to the marking fixture.

Another type of marking fixture, suited for round subjects, is this unit I built to mark off a 1/48 master of the BIS (British Interplanetary Society) Moon Lander.

(I don't think I'll invoke too much reader wrath if I, from time to time, refer to a non-DOVE subject to amplify a technique or tool under discussion. you can look for more of these side-bar examples in future installments of this article).

A different type of marking fixture, this one for a round spaceship, a 1/48-scale master of the British Interplanetary Society's Moon Ship.  In this case an indexing disc is attached to the base of the subject, the disc marked with specific item locations around its edge.

(I don't think I'll invoke too much reader wrath if I, from time to time, refer to a non-DOVE subject to amplify a technique or tool under discussion. you can look for more of these side-bar examples in future installments of this article).

Note that with the round-of-section BIS Moon Lander, reference marks are denoted on a white plastic disc tack glued to the  base of the master itself. A waterline marking tool, its pen point set to the height of the objects center of rotation, is used to lay down the longitudinal and radial lines onto the hull master. This done by either moving the waterline marking tool left and right on the table surface for longitudinal lines, or holding the pen steady and rotating the hull under the pen, marking off a radial line.

Be the model subject complicated of shape like the DOVE, or a simple modified cone, like the BIS Moon Ship, you are always well served to devise a means (before fabrication begins) of working out how to accurately place radial and  longitudinal lines onto the surface of the model/master; a methodology of transferring orthographically projected lines to the three-dimensional construct being worked by your two hands.

Next:  FINISHING HULL MASTER SURFACES