Wednesday, July 18, 2012

How I constructed a crane wagon

Preamble

I short while ago, I decided the railway needed a crane wagon. I reasoned that not only would it be useful for permanent way and engineering jobs on the line, it could be hitched to the occasional freight train to assist with loading and unloading heavy or awkward loads in the absence of yard cranes at stations.

Initially, I opted for a second-hand LGB ToyTrain crane wagon, but felt somewhat dissatisfied with it - apart from a few steam-powered cranes, to my mind it didn't resemble any prototypes which I had seen on UK light railways.
LGB ToyTrain crane wagon
After browsing the web and accumulating various images of likely candidates, I homed in on a design which cropped up quite often which seemed to comprise a manually operated yard crane mounted on a flat wagon.

Construction

The flat wagon was provided by Hartland - one of their budget wagons with holes suitable plugged with resin. The various slots and holes in the body were covered with masking tape, then the body was inverted and the holes filled with resin from the underside.
The underside of the Hartland wagon body - holes filled with resin
 Once set, the planking was then re-scribed and any excess resin filed off.
Upper side of the wagon body - holes filled and planking re-scribed

Gears

I decided the most significant part of the wagon would be the gear mechanism - the gear train needed to mesh and hence this would dictate the size and shape of the underlying wagon structure. The gears which seemed most appropriate in terms of size were found in my plastic bits-drawer (I've outgrown a bits-box). These were bought many years ago as part of a job-lot from Technology Teaching Supplies (TTS) which provide all sorts of interesting bits and pieces for use in primary school design and technology lessons. The design of these plastic gears has changed since I bought them, but I decided they needed modification anyway, to make them more prototypical. Similar gears can be bought from - Techbots
The two larger gears as purchased
The centres filed out into spokes
Additional spokes added
The larger gears in all the photos I had seen of manually operated crane wagons were spoked. To create spokes on my gears, I filed the internal webbing into spokes and added additional spokes from plasticard. As this model was created whilst on holiday, I had a very limited range of tools (a steel rule, craft knife, a couple of miniature files and some sand paper), and as a consequence the shaping was done largely by eye. Although they do not bear close scrutiny, the spoked gear wheels are sufficiently representative to give a feel for the prototype on which they are based.

Mounting plates

Using a couple of the prototype photos as inspiration, two mounting plates for the gears were shaped from 1.5mm thick plasticard. Again, the flowing curves were drawn by eye, roughly cut with a craft knife and then filed to shape.
One side plate cut out roughly
Edging strips were added to the side plates with two 2.5mm wide strips of 1mm thick plasticard. The rural French community in which we were holidaying was unforthcoming in terms of liquid solvent glues suppliers and so initially a bottle of cellulose thinners from the local Supermarch√© was used as a solvent. Although this was OK for bonding flat pieces of plasticard together it adversely affected the flexibility of the plastic when it was put under tension - such as when attempting to wrap the strip around the curves of the side plates. After a few frustrating tries I resorted to a solvent-based cyano-superglue. although this was substantially more expensive than the litre bottle of thinners, it was considerably more effective.
Side plate with edging stripe

Counterbalance weight

In the meantime, I fashioned the 30mm x 27mm x 35mm counterbalance weight from six pieces of 1.5mm thick plasticard as I decided this should determine the width of the crane - ie the space between the two side plates.
The counterbalance weight

Pivot plate

After considering various options for the pivot mounting for the crane, rather than using the top of a plastic milk bottle as a template, I slimmed the bottle-top down and glued this directly on the centre-line of the wagon body, slightly off-set from the absolute middle so it was towards one end of the body - again this was done by eye rather than careful measurement. I've found from experience that there are occasions when positioning things by eye gives a much more pleasing effect than fiddling about with a ruler! As the wagon body was cast in hard plastic and the bottle top in oily plastic I was unsure as to which adhesive to use. In the end I opted for my universal stop-gap - clear Bostik/UHU - which seems to have done the trick!
Milk bottle cap pivot plate

Crane arm

In some of the photos, crane arms are hexagonal in section, in others they are lattice and some are box section. For a while I considered using the barrel of a cheap biro pen as the basis for the arm but they seemed a tad under-scale, so in the end I opted for a box section. Rather than a plain tube, I went for one wit a double taper from the centre. This was made from four pieces of 1.5mm thick plasticard - 160mm long and 10mm wide (tapering down to 6mm on each side piece).
The main component pieces for the crane arm
The pieces assembled
The hinge pivot at the lower end of the arm was made from a 26mm x 10mm box section which was then slightly tapered towards each end with sand paper.
The pivot mount for the crane arm
 The mounting for the pulley wheel at the top end was shaped from a few 10mm wide strips of plasticard - a small bottle-top acting as the template for the rounded section.
The pulley-mount for the crane arm
The pulley-wheel itself was made from two 4mm scale plastic wagon wheels. Firstly they were sanded flat on their outside edges........

.......before being superglued together.

A 2mm hole was drilled in the mounting for the pulley-wheel and a short length of brass rod inserted to hold the pulley wheel in place.


Final construction

As I didn't want the completed model to be crushed in the suitcase on the return flight, the various pieces were packed away for final completion on home-ground.

After drilling 4.5mm holes for the gear shafts in the mounting plates........

....... a 28mm x 72mm piece of 1.5mm plasticard was attached between them as the base for the crane structure, with a 4mm hole drilled in the centre for the pivot.

A further piece of 28mm x 42mm was mounted above this with a 4mm hole drilled A further piece of 28mm wide plasticard were glued as a spacer between the gear mounting plates just beneath the uppermost hole for the gear shaft.

The counterbalance weight was also glued into place. The wheels were cut from some left-over bases of a 4mm station canopy plastic kit........
........ slimmed-down with a razor-saw.

The arm was pivoted between the mounting plates with a length of 2mm brass rod.

Having no suitable brass rod for the bracing ties, I cut some lengths of copper wire from some redundant earthing cable I had knocking around.

To straighten the wire...........

 ........... I rolled each length of wire between a piece of timber and the table.

The wires were then trimmed to length and slotted into holes drilled in the counter-balance support and the vertical mounting-plate..........

..... and the plate and the the end of the jib.

The crane assembly was then test-mounted on the base by glueing a piece of 4mm dowel into the hole in the bottom of the crane ................

.............and inserting this into a 4.5mm hole in the base. 

Finding the main pivot was a bit slack, I cut a short piece of redundant biro tube and glued this to the 4mm dowel, enlarging the hole in the base to make an interference fit.

After scrubbing everything clean in a bowl of warm water and dishwasher fluid, everything was  given a couple of coats of Halfords primer from a rattle can in my hi-tech spray-booth (made from an old cardboard carton) .........
......... and the paint left a couple of days to fully harden.

The gears (suitable blackened with acrylic paint) were push-fitted on to 4mm dia wooden dowels and then mounted in the mounting plates. A drum for the hoisting chain was fashioned from an old ball-point pen barrel and a suitable length of fine chain was glued into place - the hook made from three pieces of 1.5mm thick plasticard and a short piece of copper wire bent to shape.

The Hartland chassis was re-assembled, with metal wheels in place of the plastic ones supplied with the kit and then the superstructure was mounted on to the chassis ............


............ and then the wagon was given a test-run - or two ........
The next job is to lightly weather the crane as it looks a bit too pristine at the moment. I may also make a match-truck for it, maybe with some tool chests and general permanent way clutter.

 Update (10 August 2014)

 A match truck has now been provided for the crane - again constructed from a Hartland flat wagon.
The two loco jacks are whitemetal castings from GRS, as are the tools. The toolbox is a piece of balsa wood, suitably shaped with paper-clip handles. A couple of pieces of stained stripwood plus a coil of garden twine and some chain finish off the detailing. For more details of how I constructed this and other flat wagons see (How I constructed some flat wagons)

In response to a request for drawings of the wagon and also to show how it looks now it has been weathered, I hope the following photos are useful. The dimensions of the Hartland wagon body on which the crane is mounted are 140mm x 86mm. It should be possible to determine the dimensions of the crane from those two measurements. I determined the dimensions of the superstructure from the size of the gears which I was able to purchase. If you are considering making your own model, I would advise you to get the gears first and then adjust the dimensions to accommodate the gears.

In addition, you might find the following photos helpful. They were taken recently on the Isle of Man at what remains of Union Mills Station on the Douglas to Peel line. I wish I had seen this wagon before I had constructed my own. Maybe one day I will construct another model of a mobile crane based more closely on this prototype.

To provide a scale, the red book in the following pictures is 210mm x 143mm
 

3 comments:

Simeon said...

Would it be possible for you to make a set of drawings for this, even if they are only rough?

Ge Rik said...

I'll see what I can do. Unfortunately, I'm no draughtsman and haven't yet mastered a CAD package.

Ge Rik said...

Rather than making drawings, I've posted some more photos and given some key dimensions. From these you should be able to determine the other dimensions. The photos of a prototype crane on the IMR might help you to make a more realistic model than mine which was based on a couple of pictures of standard gauge cranes.