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Pompom director Mk I

August 11, 2009 / efoeth

The pom pom director Mk I is an elusive director. The Mk 1* was fitted to Rodney & Nelson, Hood, Furious (2), Royal Sovereign (2), Barham, and locations at Fort Cumberland, Devonport, and to Vickers-Armstrongs. The Mk I** was also fitted to Hood, as well as Barham, Ramillies (2), Repulse (2), Nelson, and locations at Porthmouth, Crayford, Chatman, and to Vickers-Armstrong. The differences between the versions consists of a cross wire foresight and some additional knobs although the older units were updated. The differences with the MkI** are unknown to me.

Knowing where these directors were fitted doesn’t really help in finding images. The location aboard HMS Hood is known but there are no photographs. Fortunately, Admiralty record Adm 186-316 in the UK’s National archives, entitled “Pamphlet on the director for the 2-PDR “M” Mark V Pom Pom” from 1932 contains a few pictures and diagrams. I ordered a copy for 30 pounds, just hoping the information would be there. Fortunately, it was! This pamphlet will be sent to the official HMS Hood site later.

From the material I gathered, it was clear that the directors Mk II to IV were smaller updates to the existing design while keeping a general family resemblance. The Mk I didn’t fit this pattern as the space located aboard HMS Hood for these directors was too small for the Mk IIs: the Mk I had to be smaller.

Here’s all the photographic material of the Mk I I could find. No measurements or general dimensions and no details of the lower part of the director.

The picture above shows something that does resemble the director greatly and is so far the only picture I have of the Mk I director “in the wild”. It also allows me to estimate the general dimensions, even though the dimensions of its emplacement are estimates as well.

Here’s the reconstruction in Autocad. The image at right is with the estimated tub dimensions of the spotting top emplacements.

This is the model of the Mk I together with the better-documented Mk II director. It’s not really much lower, but it does have a smaller footprint. I do not know if there are chairs and platforms fitted to the pedestal, as I do not have any more information. I do know there were more chairs fitted to the Mk II so that model will be updated later when my new etch set is completed. Of course, several etched parts for the foresight bars of this Mk I director will be included.

Here you can see the Mk I directors at their correct location. I copied an earlier picture with the Mk IIs. Note that the splinter shield now runs behind the directors, as is evident on photographs printed in Chesneau’s book. I changed the sponsons too: the radius of curvature is now equal to the radius of the circular emplacements on the spotting top when the directors where fitted aloft (AOTS Hood). The final locations were also fitted a bit lower than deck level to match the photographs better.

So, a lot of work and money spent on two puny directors that nobody knows what they look like… but one step closer to getting this model more correct than any other. I guess that matters.

Searchlights, part I

July 26, 2009 / efoeth

The large 44″ searchlights of HMS Hood were one of the last items of which I did not have good information except for a few pictures. Fortunately, John Lambert issued a series of drawings, L/O/162, although he mentions it’s the Mk VII of 1942-44, while Hood was sunk in 1941. I ordered them anyway and initially thought they were wrong as the frame didn’t match the photographs. However, I found out that nearly all pictures of the searchlights showed their port side and that I somehow thought the unit was symmetrical. On closer inspection it seems the drawing of the searchlights is as good a match as far as I can tell. This picture shows some of the best images of the searchlight. The images at left ware taken of HMS Onslow (top) and HMS Prince of Wales (bottom) with HMS Hood at right.

I intend to build the searchlights in two parts. The frame is mainly built in styrene (can’t see how to make a photoetch part that I can physically fold into the frame shape) and the projector itself mainly as a photoetched part.

I started with strips cut to shape for the frame and gluing them into the shape shown right. The front and rear should angle back about 8 degrees and this first attempt resulted in very uneven parts. It’s not so well visible in this particular picture but when continuing to add the rest of the frame, the part didn’t really work out. On to the Mk II miniature frame! This time, I spent some more time pondering and I eventually took a slightly different approach by cutting triangles first. At the bottom the mould for the chopper is shown. I use this approach a lot to cut angled parts to size. At right you can see a small template triangle in place to position the template. After a few sizes of triangle, you end up with the size you need (there’s always a slight difference in the template and copy size, usually about 0.1 mm.

Top left shows how to prepare large amounts of strip at an angle. Works pretty well, but right shows the easier approach; strips glued to the triangles. Now it’s just a matter of chopping the parts to size using another small mould. I always have large cheap styrene sheets laying nearby to spend on such actions. Two chops later and the front and rear base frames are cut to size much more consistently (and easier) than adding strips cut to size.

The next mould is a small plate angled forward 8 degrees and placeholder strips for the frame. The two blocks are for positioning what’s shown at right; two strips glued to a center block that acts as a spacer (and makes it easier to handle as well). Add a bit of glue and it’s fixed. Next, the part is cut to size and the same mould is used to glue the second frame. All parts were given some superglue in the corners. Now both the front and end plate are at the correct angle. Using a few moulds seems to be a lot of work but in the end the result was less work, resulted in less rejected parts and the parts more consistent in shape than when not using the moulds.

The top half of the frame was built from strip drilled in using my new drill press which I bought for the occasion. The side detail was built from a small ring, a small tube and some triangles.

This part was sanded to size and added to the frame. I made another ring for the searchlight bearing and checked if the part was nicely aligned. The hand wheel was then added, starting from a strip drilled in with a small 0.3 mm drill using the drill press. I start using thicker and slow-curing CA more frequently when bonding metals as the photoetch parts do not allow most of the other glues I have to stick.

The second hand wheel is being constructed from a small ring and strip. It barely survives the chopper! The end result is a small part to be added to the searchlight base.

Here’s the completed frame. The base part is made using my new lathe The lower base part has a conical shape and a 2mm gap so that it can be fitted easily on a disk on the model. The top part of the base is a small disk but with a very small 2mm extension so that it fits concentrically in the lower base part.

This is the design for the lantern which will be nearly all photoetch except for a small disk to close the part off. I couldn’t add all the required detail in a double-layer part, so I made three additional part to be glued onto the main part. The two parts for the side will be aligned using some rod, the top part will be aligned using the small square visible in the middle of the main part. Should be a nice folding exercise!

Go on to part II.

Proxxon Precission Lathe

July 1, 2009 / efoeth

After having bought the drill press, I bought a small lathe by Proxxon. I owned an older Emco Compact 8 for a while but only used it on occasion as it needed more space to operate than I had. I lost a few parts moving it to my new house and the live center was completely stuck in the tail stock. I damaged the lathe while trying to repair it (how typical) and decided I wanted a smaller, newer, and more compact lathe. Easy access to spare parts is a diminishing feature of the Elco, let alone access to affordable spare parts. Similar to their drill presses, Proxxon offers two lathes, the PD230/E (small) and the PD400 (large), but the differences between them are large enough to look more closely before deciding. The PD400 has twice the distance between the centers, weighs 45 kg, and has a spindle bore of 20.5 mm while the PD230 weights only 10 kg, but has a smaller spindle bore of 10.5 mm. This meets my needs perfectly for a small tool that I can easily store in my hobby room. The PD230 has the same range as accessories as the PD400—including milling and drilling equipment—(except a quick-change holder for a parting tool and the traversing steady). A disadvantage of the Proxxon lathes is that they each come with their own chucks, clamps and collets, and share few parts among them including the mill/drill upgrade. This shouldn’t be a problem as I do not want to have two lathes now, but the PD400 can also be bought as a CNC version. It is too expensive for me now (listed at €4400. The other list prices are €930 for the smaller and €2300 for the larger lathe) but might be a nice option in the future requiring me to possibly buy all these items once more. The lower cost, weight, and footprint of the PD230 made it the logical choice for now. I purchased the lathe on Ebay for €699 from a German reseller with an Ebay-nick of Briggebaecker.

Here’s the lathe including the “Splash guard and chip collecting tray” (24006). I decided to have a few accessories with the lathe. This first one is a collet set (24042) for better accuracy (centricity) and easy of use . As I intend to use styrene when possible, I want to minimize damage of the styrene of the three-way chuck leading to the part being off-center, but this is a very expensive accessory. However, it will be very easy to use with stock styrene and brass rod and the collets come in a range of 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 8.0, and 10.0 mm. (postscript July 2010: I never use the collet set. The three-jay chuck is just fine) The second accessory is a gear chuck (24020) for drilling. I expect this will really be an improvement over using tubing with a given inner diameter. Of course, without the cutters the lathe won’t work so I also threw in a set of cutters (24530). The last accessory is a quick-change holder for the easy change of cutters (24022). I’m not too sure I’ll be using it often but I’ve seen machinists use them and they looked very convenient as you do not need thin metal sheet to change the height of the tool. This part is fitted on the PD400 by default, but is again a different type and parts are not interchangeable. (postscript July 2010: the quick-change holder is a necessity, not an option!). The PD230 also doesn’t have the parting-tool holder and cutter for its quick-change holder according to the brochure of Proxxon. The last item is a center turning attachment (24070) which might be nice for longer parts.

The lathe comes with a a change gear set for wire cutting (left and right handed), live center (MT-1), three-way chuck and a set of hex keys, so no need to worry about different types of screws here. The PD230 can be used for thread cutting although I do not foresee I will be using that option. The lead screw, cross and top slide, tail stock, and tail stock sleeve position can all be fixed, though not too tight. The tail stock sleeve is fixed by a bolt and not by a hex screw. All the functions my old Emco had are present, although the Proxxon has less screws to properly calibrate all positions.

The quick-change holder is seen at left, the live center (included) and gear chuck at right.

Several items can be attached to the lathe. The top left picture shows both a triple and quadruple array of bolts to fix chucks to the headstock. The three-jaw chuck is shown at right. Proxxon does sell a four-way chuck (24030) but I don’t think I’ll even need it. The bottom-left image shows the center turning attachment. The free-hanging bit on the right is clamped on the work piece which is on its turn mounted on the center. The screw fits in the slot and will rotate the workpiece. Apparently more accurate to use, but also very nice to fix certain parts between the centers. At right the collet chuck is shown. The collet chuck of the Elco automatically pulls out the collet when the chuck is loosened, but not so for the Proxxon. You need to hit it with some stock rod through the spindle bore if the collet won’t come out easily.

I first spent a few hours taking the lathe apart, cleaning up the grease, oiling it, and putting it back together again. I started experimenting with 4.0 mm styrene rod. You have to be careful choosing a low rpm for the parting and drilling, as they quickly melt the styrene. The parting tool by Proxxon is just over 3 mm wide, which is a bit too much for the poor 4 mm rod to handle. I intend to make a very thin parting tool and have Micromark’s cut-off tool holder on order (82753), a small tool that holds a thin cut-off blade. I intend to grind one cut-off blade to a much tinner width and see if that works. Micromark sells many additional extras for the American variant of the Proxxon, called the Microlux minilathe. There are many more accessories for the Microlux than the Proxxon, even a digital readout.

Cutting tubing

May 3, 2009 / efoeth

A small how-to on cutting steel tubing at very small sizes accurately. I bought mine from Cammett Ltd (update 2021: I switched to Albion Alloys micro-tubes that is a much nicer material to work with). The tubing comes in a wide variety of inner and outer diameters and can be most useful for small detail work.

I start cutting of a bit of tubing and inserting it into the chuck of my drill. Both Proxxon (28941) and Dremel (4486) offer these chuck as a affordable accessory to their drills next to their range of collets. At this point I usually sand down the tube. I then use the depth probe of my caliper to insert the tube into the chuck with the to-be-cut tubing sticking out at the right distance. The drill is switched on and I use a sharp knife to cut off the tubing in a sawing movement. I do this carefully, as the part sometimes jettisons away. Don’t try to hold the part in place using a finger, you might inadvertently drill yourself. After the tube is cut, I use a precision reamer to clean the remaining tubing. I do this by hand, I lost a few reamers with the drill turned on. Positioning the reamer is probably the hardest part.

Now the small tube needs to be cleaned, but it can be very small and near-impossible to hold. I use the reamer to pick up the tube and reinsert into the chuck. I apply the reamer when the tube is again firmly in place and a drill to check if the outer diameter is larger enough after cleaning (and for drilling). Sanding down the part at this point is also possible. At the end you have small pieces of tiny tubing at a consistent size. Using the macro setting of my camera shows the edged are a bit rough, but it’s a 0.5 by 0.5 mm part.