Scratchbuilding the Dove part 15

OPENING THE COCKPIT WINDOWS

USE OF SCRIBING TEMPLATE

To open up the cockpit window areas I made a marking template, lofting its outline from the Phil Rae plan. To assure that the plastic scribing template would not shift off the work as I used it to guide the scribing tool I actually glued it in place on the cockpit master.

To open up the cockpit window areas I first made a marking template and then tack glued it to one side of the cockpit. Using a sharp scribing tool, I traced the templates outline onto the surface of the GRP part. Flipping the template and mounting it on the other side completed the window outline marking task.

Using a sharp scribing tool, I traced the glued templates outline onto the surface of the GRP master. The gray gel-coat is very responsive to this cutting action and is an excellent substrate; hard yet easily takes to cutting, filing, and sanding. One window outline scribed out, the template was popped off with a putty knife, inverted, and glued to the other side and used to mark off that window outline.

OPENING THE COCKPIT WINDOWS

I opened up the windows with the aid of a drill bit worked in a moto-tool. A long time ago I found that if you drilled a hole in GRP with a relatively small bit, and then applied a lateral force to the bits axis, I could, with practice, make clean quick cuts to an outline. Working the bit this way quickly opens up big round holes, square holes, or any other cutout shape needed, just using the drill bit. And that's just how I roughed out the rectangular holes of the cockpit windows.

I opened up the windows with the aid of a drill bit used as a free-hand router. After making the initial roughing out with this tool I shifted to flat and round files. There is a pronounced positive bevel to the window frames and great care was taken to represent these bevels as I worked the window opening to outline with jeweler's files.

After making the initial roughing (keeping the bit about one-thirty-second of an inch inside of the scribed boarders) with the laterally moving drill bit I shifted to flat and round files to enlarge the holes to their scribed outlines.

There is a pronounced positive bevel to the window frames and great care was taken to represent these bevels as I worked the files.

Well. I think that is quite enough talk about the cockpit for a while. I'll get back to it in a future installment, but for now, let's take a break and work on other aspects of the DOVE master.

NOW, FOR SOME METAL TURNING:

The two wings of the DOVE vehicle, located either side of the hulls stern, can rotate about their root axis, which is perpendicular to the hulls longitudinal axis. The wings, rotated from horizontal to near vertical, permit the DOVE to fit within the tight confines of the PHOENIX's (the DOVE' s parent craft) hangar. Facilitating this rotation at the root of each wing is a drum, or cylinder, set within the hull afterbody. These cylinders fair into the outboard perimeter of the after end of the hull and can rotate, without altering the hull geometry. It is the rotation of the cylinder through nearly ninety-degrees that positions the wing either horizontal for 'flight' or vertical for 'storage' within the PHOENIX.

Though the two wing cylinders are of constant diameter, each is 'ribbed' with a series of radial bands (I assume these to be bearing surfaces for internal rollers that assure structure rigidity against flight loads).

The DOVE wing cylinders present a special modeling challenge: how to capture the obvious relief between cylinder ribs and grooves.

The 'cylinder', to which each wing of the DOVE attached, though of constant diameter, was 'ribbed' with a series of radial bands. I elected to turn a mater of the cylinder from machine brass because of the relative ease of working this medium on the metal lathe.

TURNING THE WING CYLANDER MASTER

I elected to make a single cylinder master by turning it on my machine lathe. The material of choice here was 'machine brass' because of the relative ease with which one can machine this medium without overheating the cutting tool.

I use the Taig Micro Lathe, model number TA1001A. The basic machine and accessories will run you slightly over $500, but is well worth the price. I got mine, and great follow up service and parts support, through Hobby Lobby. You can get their free catalog and more information by calling, 615-373-1444. Their site is, www.hobby-lobby.com.

You can get machine brass and other raw materials suitable for turning from the McMaster-Carr Company. Get their catalog by dialing, 732-329-3200 or you can e-mail them at, nj.sales@mcmaster.com. The catalog is free, is over three thousand pages thick, and chock full of neat stuff of interest to the advanced model builder.

My choice of tool was made because of this lathes indexed X and Y slides that secure the cutting tool, permitting me to accurately measure along the length of the work as I cut in the grooves. The graduated scales on the slide operating handles made the work very precise and easy to accomplish.

I mounted the work, a piece of seven-eighth inch diameter machine brass rod with the aid of a four-jaw chuck. I also employed a tailstock steady bearing at the other end of the work to assure a secure low chatter set-up that would work well with the tools, brass, and speeds selected.

As the outside diameter of the ribs of the cylinder were equal to the size of the brass round stock being turned (sometimes fortune smiles!) all I had to do was cut the one-thirty-second of an inch deep grooves between the ribs. This work was completed (less set-up time) in only five minutes. At each end of the brass wing cylinder master were machined three-eighth inch diameter nubs. Each nub about one-quarter inch in length.

(The nubs at each end of the wing cylinder master later formed cavities within the production RTV tool, those cavities receiving a brass core piece. That core piece would substantially reduce the amount of resin needed to create the resin wing cylinder piece, thereby reducing shrinkage to this dimensionally critical item. This particular resin casting technique will be covered fully in a following installment of the article).

Coming up in part 16, making the wing and vertical stabilzer masters