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Main Rangefinders

July 21, 2008 / efoeth

This post was updated 16th of November 2008

These two objects are HMS Hood’s main rangefinders. One is situated on top of the conning tower, the other one on top of the spotting top. The parts are built up from simple circle segments.

The conning tower’s range finder still has its stereoscopic rangefinder which I built with the viewports open, just as is possible for the rangefinders of the main armament (which I kept close).

The top rangefinder houses the radar antenna for the Type 284 Gunnery Radar. There aren’t many good pictures of the frame of the radar which is a guestimate, but there is an excellent drawing in Campbell’s “Naval weapons of world war II” and a few pics of other ships carrying the same antenna. It’s much more solid than all the etched parts.

Note the configuration of the rear of the rangefinder, which doesn’t have the typical box shape added to it as found on all drawings and all but the latest models. Yours truly found out, from careful observation, that the roof of the rangefinder was locally heightened and that the box shape followed from an optical illusion, probably caused the small ladder. Having the latest photographic finds on the official HMS Hood site helped, of course. A few custom-etched parts were fitted later, a few hatches and so forth.

A small detail was added later to the forward rangefinder make from tube. The steel tube was first heated and then pressed into shape with a pointed object. Two of these tubes were trimmed to size and inserted into a plastic strip.

Main Mast, part II

May 7, 2008 / efoeth

The main crane derrick is operated from a platform at the base of the main mast. Two large winches are below the boat deck in the boat hoist compartment. Two cables run through pipes in the deck to a series of pulleys at the top of the tripod. One cable goes through the lower pulley and a pulley in the end of the main crane derrick, hoisting the boats on and off board, the other cable goes back and forth five times from the middle single pulley and two double pulleys—one at the top position on the main mast and one at the crane derrick’s end—setting the main derrick elevation.

The drawing in the Anatomy of the Ship series isn’t very accurately depicting the construction of the pulleys or the correct alignment along the main mast. The new position was determined using a series of pictures from this particular area. I started by adding the lower part of the frame of each pully, with a few difficult-to-cut parts. A series of supports are added to the frames, but as the wiring runs through these supports to the boat hoist compartment, and a double set of these supports is seen on the photographs.

The pulleys are an etched part plus the pulley themselves, made from 0.13mm Evergreen styrene. The pulleys rotate along an axis, but the wire as to be able to run downward with the derrick swayed to the side of the ship. I don’t know if the wiring runs through the pulley support, but it seems a logical approach. These supports were later replaced by steel tubing.

All pulleys in place. Note that the pulleys can swivel, following the position of the main derrick. The wiring, when the model is rigged, can still go around the pulley and through the supports. Not that I plan to have a fully operational 1/350 main crane, but it does allow for the use of only two wires to rig the entire crane (as in the real thing) and for alinging the lower pulleys toward the end of the main crane. In the outboard position, the pulleys are at an odd angle but that won’t be visible with the derrick in the stowed position.

mainmast_081

Chopper

April 13, 2008 / efoeth

The most important tool for my modeling is the chopper. I bought one from NorthWest Short Line a few years back. They say it is “one of the most useful tools ever, for model building, working in wood, or styrene strip materials”. For once, I agree with a manufacturer’s claim. As with many modeling tools, the quality is wanting (to be fair, it is cheap) and I made a few simple modifications. The base plate damages rather quickly, so I added a plastic ruler as a base plate. You can buy these in our local bookshops. I also added some plastic at the base of the lever to correct for the added thickness. I intend to replace it with a more rugged design later, perhaps. Or buy one of their more expensive variants. This chopper wouldn’t function properly without my trusted Mitutoya vernier caliper. They are expensive, but indispensable for accurate modeling. If you want to start with accurate scratchbuilding, consider them your most important tools.

In stead of measuring with the caliper, I use the depth probe to set the chopper. I purposely avoid the calipers with a digital readout. They are more precise, but I think I would spend too much time setting the depth probe to an exact setting! I changed the cutting miter so that it works with the depth probe of the caliper, but this does wear down the razor blade. So, I need to change razor blades frequently but they are inexpensive and come in a box of 100.

You can measure the result to see if the setting was satisfactory, in this case 10.0mm. Setting the depth probe to a certain depth usually doesn’t result in a cut of the same length, but with some trial and error you can change the setting (+ 0.1mm in my case) that usually gives a good cut. In fact, it is now so easy to set my chopper that I can have accurate and reproducable parts in seconds. If I need to replace a part (and I wrote down its dimensions somewhere), I know it will be of the same dimensions. Somehow I enjoy replacing or adding parts to a subconstruction years later, only to find out that the parts were made with high accuracy. It’s not just important that the part is made accurately to scale, but that the model is built consistently. Although a tenth of a millimeter doesn’t really matter to all but the smallest parts, in my opinion it can be the difference between a very sharp and a rather poor build; stacking a few decks which are all off by a few tenths of a millimeter will show up in the end.

The chopper itself cannot swivel, but you can make inclined cutting miters. Here you can see a part for one of Hood’s fast motor boats about to be cut to size. When cutting these very small parts, I add a small strip of plastic to the miter so that I can be sure that I reposition the parts consistently (when using inclined miters, the position along the miter influences the part’s final appearance, so you need to fix the part’s position along the miter). Using these cutting miters can require more trial and error with positioning when the dimensions of the part are absolutely critical. If you need simple parts with a slope, first add the slope and then use to straight miter to cut the part to size. You can also first cut strip to length and then cut a slope to one end but that is usually asking for mistakes.

Vacuum Forming

April 10, 2008 / efoeth

Vacuum forming is a very simple technique that can produce thin-skinned parts of various forms. I mainly used vacuum-forming for producing the gun shields for the twin 4″ mounts and the hulls of all the boats and launches.

This is it, basically. A small box with a connection for your vacuum cleaner and a series of holes in its top plate. Try keeping the box airtight at the seems. This is my small version with the basic forms of several small hulls awaiting to be copied.

Part two is a small double frame holding a sheet of plastic. I used a few simple clamps to keep the plastic sheet firmly in place. As you need to heat this part, not using metal might be a good idea.

Heat your oven to some predetermined level, whatever works, and start heating the plastic sheet. Once the plastic gets warm, you’ll notice it will droop down. When you think the plastic is soft enough, fire up the vacuum cleaner, take the plastic from the oven, and thrown the sheet on the vacuum former. The plastic will nicely form around the moulds. This will take some practice and sometimes a mould tips over or the plastic won’t form properly over the mould (folding around edges). This is also the part where I should warm you that you can burn your fingers. I use large plastic sheets, not the more expensive styrene by Evergreen. When an attempt fails, I usually throw the sheet back in the oven and start again.

Here is a series of copies of hulls. You still need to trim all the parts to size. The reproducibility is as good as the moulds (they might suffer a bit) but this is a very easy technique to use.