Container Spaceship part 4

Once I had the major components for the spaceship laid out I designed up a truss in LibreCAD.

I needed some way to hold all the truss tubes in position while they get silver soldered (silver brazed). I considered small welding magnets but found they had a plastic part that would more than likely melt under the sustained heat of the propane torch I was going to use. In the end I decided a steel jig was required and I needed a milling machine to make it. Lucky for me I currently work in a machine shop and was allowed some time on the mill to knock something up.

Below you can see the result which is a slab of mild steel with 6mm wide slots 2mm deep machined into it. Then later at home I used a hole saw to cut away the area of the jig where the torch flame would need to heat the matimng surfaces of the tube. In the CAD drawing above you can see a small cross section where the 8mm tube locates in the 6mm slot and only touches on the edges, hopefully minimising heat transfer from the tube to the jig.

A clamping plate was made in the same way out of thinner material and without the slots. The slotted plate had four holes drilled and tapped for some clamping cap screws.

The tubes were cut to length in the mini lathe using a live centre as a length gauge. My high speed steel parting tool is 1mm thick and is mounted upside down so the lathe runs in reverse to part off. I used a little water soluble oil coolant squirted on from a spray bottle to ease the cutting.

 

The next problem to tackle was a mini tube notcher to "fishmouth" all the mating tubes some at 90 degrees and the others at 59 degrees. I figured I could use an 8mm end mill in the chuck of my mini lathe and make a tool post mounted jig to hold the tubes in position while the notch is cut. The jig had an adjustable end stop, with an 8mm diameter spigot which would align the previously fish-mouthed end of a tube with the cutting of the other end. I made up two of these end stops, one for the straight cuts and one for the angled cuts. The main body of the jig is a piece of 25mm square brass with a chunk of bronze bolted on that gets clamped in the tool post. The 8mm through hole was done by mounting the blank brass holder in the tool post and drilling through with the drill mounted in the chuck so the centre height would be correct for eventually cutting the fish-mouths.

Once the tube was locked into the jig by nipping up the cap screw, the carbide cutter was run up to around 2800 rpm and the carriage was then wound left towards the cutter .The mini lathe is not the most rigid of machines so I could only cut 1mm at a time so it took about 4 passes to cut to full depth.

The depth of the cut was adjusted with the cross slide and by setting the dial to zero at first touch. Each full rotation of the cross slide handwheel and the dial is 1mm depth and generally the full depth of cut required was 4mm. To make sure I didn't lose where I was with the depth and to make all the tubes the same I marked a line in white fine paint pen on the cross slide base.

The angled cuts where done in the same way using the same straight end stop for the first end swapping over to the angled end stop for the other end. The desired angle of 31 degrees was achieved by rotating the compound slide and locking it in position.

 

It took a couple of days to cut to length and fish-mouth all the tubes for the sides of the truss.

The silver soldering process could then begin by fitting the tubes into the jig and clamping it down. Liberal amounts of silver brazing flux was applied to the joints and just as the tubes were reaching  cherry red the silver solder was applied making sure the capillary action drew it along the joint. Then the clamping cap screws could be removed and the jig moved along to the next position locating on the previously brazed last vertical tube, repeating the process along the full length of the truss. Once I started I realised it would be better to have an even number of bays in the final truss so added some to the long tubes with a small insert of mild steel rod inserted to hold the extra bits in position.

Once the two sides were made I then had to join them together with cross members. The cross members needed an extra notch cut at 90 degrees to the main fish-mouth as they had to join at a junction of an existing upright tube. This notch also had to be slightly angled as the truss is trapezoid in cross section, angled in for the bottom cross member and out at the top. See the CAD drawing for what I mean. The picture below shows one of the bottom cross members receiving that secondary notch at 90 degrees to the main one.

I was worried that I would need another jig to hold the sides at the correct angle but found that I could clamp the sides together with four cross members temporarily in position using a protractor to set the correct angle. The clamps held sufficiently to solder a couple of cross members at each end and then the whole thing was locked into position. All I had to do was then snap the remaining cross member into position and solder them up.

As I was only using propane as a heating source I had to use the lowest melting point silver solder. Unfortunately that is the one that has the greatest silver content and is consequently rather expensive. I used 5 lengths of 1.6mm rod which when I purchased it some years ago was around $100 AUS dollars. It is now even more expensive than that. Conversely I also did the whole lot with a 1.25 KG gas bottle using a medium sized burner.

The hearth I used was just 4 lightweight autoclaved aerated concrete blocks known here in Australia as Hebel. I have found them very good for this job as they are very good insulators.

Before I started I was concerned that the truss may end up twisted once finished as I had no way of keeping the whole length aligned as I soldered. In the end It came out reasonably well with a slight banana curve in the vertical direction which probably wont be noticed when the model is complete.

A couple of steel plates were soldered to the ends for attaching the modules. M4 button head cap screws screw into an 8mm block of PVC glued to the top of the modules to secure them in place. I also added a couple of strips of steel either side of the centre cross member of the truss to attach a 15mm water pipe flange which will be part of the model support structure.

The next task which was to clean off all the flux and scale using water steel wool and assorted wire brushes. I then primed it with a zinc auto primer as it started showing signs of rust.

The picture above shows the model support made from water pipe fittings. There will be a bottom mount and a side mount in case I ever manage to build a motion control camera and want to film the underside of the model unobstructed. There will be a central styrene box built around the mounting which is still to come.

All in all it took a solid six days to complete this truss and it is incredibly strong. I can easily stand on it without any deflection what so ever.

Thanks for looking.

More soon...
 

Container spaceship part 3

I have been working on the Container ship project which I started in October 2016 and the last post on the project appeared in July 2017. Click on the links below to start at the beginning of the story.

Link to part 1 and part 2

The project stalled while I contemplated building a truss that ties the two ends together, the cockpit section at the front and an engine section at the rear with a number of containers hanging under the truss. I was considering brass tube at the time but some 8mm diameter, 1 metre long steel tubes, four to a package, appeared in my local ALDI supermarket at a cheap price which I thought would be ideal for making the truss. I purchased all they had in my store and at another nearby ALDI store to get enough for the project. That tube stock then sat around for some years as I needed a system of holding the tubes together at the right angles and at the right dimensions. I also needed a method to fishmouth the tube ends where they join to other tubes. More on that later.

Just recently I re-evaluated the project and decided that I didn't think the engine housing I had built was the right proportion for the front cockpit section I made. I decided to scrap the engine housing and build another. That scrapped engine housing will probably end up in some future project so all the work that went into it will not go to waste. 

The original concept art from Tomy Z-Knights that inspired the project. Thanks to a reader of the RcSciFi blog I was reminded that it appeared in a Hobby Japan magazine from August 1991.

Looking again at the original concept art that sparked the project I decided to mimic the three cylindrical engine arrangement that attaches to a truncated triangle shaped box. I had almost enough PVC plumbing parts already to hand to make the engines. Arranging the tri-layout of the engines  in LibreCAD a free open source 2D CAD program, then gave me the dimensions for the truncated triangle box section. 

 

Below you can see the Pvc engines roughly taped together and the rest of the raw components laid out to get an idea of the relative size of everything together. In the middle are the index card boxes I am going to use as containers. Two lengths of the 1 metre long tube are placed on top where the truss will go.

There will be space for six containers but I only have five so I am thinking of making a tank pod for some variation, an idea inspired by the Hunter Gratzner spaceship from the movie Pitch Black shown below.

 

The engines will have the usual MR16 12 volt Led downlights mounted in them which fit into a PVC pipe concrete slab repair fitting which in turn fit into a 90mm to 65mm down pipe adaptor with some strips of 2mm styrene glued to the inside. First a piece of masking tape was adhered to the inside surface and marked where it overlapped. This was then removed, measured and then divided into the number of strips required, marked out and returned to the inside surface. The marks from the tape where then transferred to the PVC adapter to guide the placement of the strips which are held in place with a drop or two of thin superglue.

The inner PVC fitting is a nice tight fit once pressed in from the back with the strips holding it firmly. The Led downlights will then get superglued into the interior. I beveled the inner edge of the fitting so the lamps will sit down flush.

Guide marks where also applied to the other end of the engines for future placement of panels. As an alternative to the masking tape method I have a small piece of chipboard marked out with circles and radiating divisions I can use to mark out cylindrical forms. To use it I draw a circle with a compass just slightly wider than the diameter of the object I want to mark out, then centre the object using the guide circle just drawn and then mark of the required divisions.

The truncated triangle shaped box was built from 2mm styrene and a series of three short lengths of PVC pipe glued to the back wall to locate the engines in the correct position.

Then the engines were detailed with kit parts, evergreen textured sheet and single solid core copper wiring for piping. I searched through my kit part stash for any parts that I had in multiples of three so each engine could be similarly detailed. There is still some paneling work to do. In the picture below you can see the ends of all the copper wire piping poking through drilled holes in the PVC parts. The  down pipe adapter which is the engine nozzle will remain removable to get access to the lighting connectors. Visible in the picture above is a toggle switch so the engines can be turned off separately from the cockpit lighting.

The truncated triangle box has also been detailed with kit parts and evergreen textured sheet. The picture below shows the bottom surface which is detailed differently to the two upper sides which are mirrored.

The inner face of the engine box has a panel with cutouts made from 2mm styrene and a central circular hatch to access the wiring. I first drew the shape for the panel in Librecad, printed it out full size and stuck it on the styrene for cutting out. All the radiuses were drilled out first with a step drill. I put a dot on my CAD drawing at the centre point of all the radiuses to guide the drilling step. The hatch is held in place with a kitchen cabinet magnet.

The old cockpit section now seemed too small for the new engine design so I made another truncated triangle box to join to the rear of the cockpit section. It was made in much the same way as the rear box. I also sprayed the old cockpit with primer as it is essentially finished bar the interior. In the photos below I have temporarily clamped a couple of the steel tubes in place to see how it is all coming together.

 Unfortunately I have only left a small hatch to get access to the cockpit which is going to make fitting out the interior extremely fiddly and frustrating. What a maroon.

The next part of the story concerns the making of the truss.

Thanks for looking.

More soon...