Wednesday, 27 January 2016

Follow the construction of this ultra-large model

June 2016.  Photo by Clint Bradfield of Foto First Grahamstown

After finishing the Meccano Krupp 288 bucket wheel excavator model I decided to build a model of the Marion 6360 stripping shovel in the same scale (1 in 18) also using self-made replica parts and with the help of the same laser-cutting facility in Port Elizabeth (Steelcut Services) to cut out the mild steel blanks. Once again I am also indebted to Mr. Screw of Port Elizabeth for supply of all the stainless steel fixers . A big thank you to Sally and Roxy respectively at these companies for their knowledge, efficiency and help in procuring all the requirements to build the model.

Background – stripping shovels

Stripping shovels were essentially an American development and were built with the purpose of removing the layer of overburden in mines (mainly coal mines).  The 1960’s saw competition between 2 companies, Bucyrus-Erie and Marion, to build the largest ever such machine, a race eventually won by Marion, with their mighty 6360 machine, a 21-storey high giant with a mass of 12,730 metric tons and a bucket capacity of 132 cubic metres.   A picture of the machine is shown here

Also have a look at this video : Discovery Channel's "Mega-Excavators" revisits "The Captain," a massive stripping shovel that suffered an untimely death when it was destroyed in a fire

Principal parts of 6360

An excellent line drawing by William E Oldani, shows the principal parts diagrammatically.  The business end of the machine is a single bucket which is fixed at the end of a dipper arm.  At the rear of the bucket is a door which can be opened to dump the load on the overburden pile by pulling on a cable.  (The 6360 had two doors – the only model to have these - side by side, to lessen the shock when they slammed shut). At the other end of the dipper arm was a pivot from which 2 arms pivoted.  One such unit was roughly vertical and in turn pivoted at the front-end of a huge machinery hall.  This was called the stiff leg.  The other unit was roughly horizontal and was driven back and forth by a very powerful thrusting mechanism called the crowd mechanism.  This was the source of the thrust action of the bucket against the work face, so powerful that the rock almost seemed to explode when the teeth of the bucket made contact.
There were 2 types of crowd mechanism used in the industry.  One employed a rope drive, the other a rack and pinion drive.  The latter type was use on the 6360.  A feature unique to the 6360 was that it had twin toothed rack booms, and not just one.
Inspection of the drawing will also show a main supporting boom which is fixed at 45° to the horizontal.  At the top end of this boom are a set of pulleys over which the hoist ropes ride.  This hoist mechanism is the other part of the digging story and allows the load to be hoisted out of the mine pit and deposited at a chosen level on the overburden pile.

On following the hoist ropes back one can see that they run over more pulleys at the top of a gantry which reaches nearly as high as the top of the main boom from where they go down into the large machinery hall.  There they wind onto the hoist winding-drums. It is also evident that the tall gantry is responsible for holding up the main boom via 12 strong steel cables. The 6360 was unique in that it had 2 gantries side by side.  This double gantry also gave support to the double crowd mechanism.
Working our way downward we see that the entire upper part of the machine (everything described so far) can slew through 360°on an enormous roller-race.  This action is also called “swing”. The roller-race is mounted on an extremely strong mainframe which is, in turn, supported by 8 crawler mechanisms (grouped in pairs), one pair at each corner.  These pairs can be steered by means of tillers which are moved by hydraulic rams anchored to the mainframe.
Several systems work together to allow the machine to move on uneven ground while maintaining maximum contact with the ground.  Firstly, each pair of crawlers can be moved vertically by means of huge hydraulic levelling pistons (of diameter 1.67 metres).  Secondly, each crawler is mounted on a rocker axle perpendicular to the direction of travel, and finally, each pair of crawlers can roll on an axis parallel to the direction of travel.  This could be called rock and roll suspension or we could say that the crawlers can rotate on 3 mutually perpendicular axes, the third axis being the vertical one involved in steering.


One would be struck, when watching this machine working, by the silence of the operation – except for the crash of the bucket into the rock face and the subsequent rumble of spoil as the bucket doors open.  This is because the machine is electrically powered.  Power is brought in through an armoured cable at 14,000 volts AC.  Inside the machinery hall are 4 motor generator units (MG units) which convert this to 220 or 440 volts DC to power all actions.  About 30,000 horse power is the maximum power requirement (about 22 megawatts). Mounted at the front and back of the lower mainframe are 2 large winding drums for the HT supply cable which allow the machine to change its digging direction without turning around.
The staff complement on the 6360 was three.  The digging controller sat in an air-conditioned cabin (with kitchen and toilet ) at the left front of the machinery hall; a ground man steered the machine remotely from the ground (he also had a substantial bulldozer on hand to move obstacles out of the way of the crawlers); finally, an oiler moved constantly around the machine checking its lubrication, etc.  An interesting feature was a small 3-man elevator which ran in the hollow swing kingpin and took staff from the lower works up to the driver’s cab or to the roof of the machinery hall, a vertical journey of 8 floors.

Tragic end of the 6360

Only one 6360 was built.  It was the largest fully mobile land-based machine in the world when it was commissioned in 1965. (The title was taken away when the German 240,000 cubic metre per day bucket wheel excavators were built in the 70s.) 
The 6360 had a sad end.  It caught fire in 1991 when an hydraulic line burst spraying onto electrical equipment.  Over the years a large amount of grease had built up in the swing roller race area and this burnt fiercely for nearly a day.  The crew escaped unhurt but a great deal of damage was done as fire teams had difficulty getting equipment to the machine due to the remote part of the mine and difficult terrain.  It was deemed uneconomical to repair and was scrapped in 1992.

My model - introduction

The model I am building (at a scale of 1 in 18) will have a height of 12 feet and width of 5 feet.  With dipper fully extended it will be about 17 feet long. Estimated mass is in excess of 1,100 kg which is not as much as my Krupp 288 model which comes in at 1,335 kg (making it the largest Meccano model in the world, I believe).  The Marion 6360 model could possibly be the second largest.  The 6360 is more compact and chunkier than the Krupp 288.  It will fit into a double garage which has a ceiling height of 13 feet.

My model – lower works

Much of the first year of construction on the 6360 has been taken up with drilling the parts, flatting down burring, phosphate treating and painting.  All girders and most plates have now been done (January 2016). As with the Krupp model, the most-used plate is the 5½" by 2½", with nearly 4000 being done in gauges 0.6, 1.0 and 2.0mm.  I still need to make about 400 in a 0.2 gauge – to be cut from used spray paint cans - used in the machinery hall roof. The heavy gauge plates are used mainly in the crawler system and some parts of the lower works (steering thrusters) and key parts of the mainframe.
 I view the construction of these giant models in terms of a series of boxes, supporting one on top of the other, as in Figure 1.
Fig 1

In the average Meccano model built from only genuine parts you would only find the top two boxes.  This is fine if your model weighs in at, for example 100 kg,  but to go to say, 500 kg, you need the third box (1.0 mm gauge) and for something around 1000 kg, the lowest box (2.0 mmm gauge) becomes necessary.

Having said so much about parts manufacture I am happy to report that I have also been able to work on the lower works of the machine.  The strength of the mainframe is provided by a toroidal frame consisting of 32 bulkheads, 10½" by 10½", with a plating of 1.0 mm plate around the perimeter.  These bulkheads have their positions in a circle defined by thirty two 5½" by 3½" plates at the centre in exactly the same way as the toroidal frames of the Krupp 288 were laid out.  The outer surface of the torus is created by two layers of 5½" by 2½" (0.6 gauge) plates, overlapped in the lateral sense.  The depth of the torus is 22 holes, with joiner flat girders keeping the two 11-hole deep curved surfaces together.  The resultant toroidal structure is shown in Figure 2.  The diameter of the outer curved surface is 41", so this will be the diameter of the main roller race which will be attached directly.  As with the Krupp model I will use a strap of 3mm flat mild steel to create a strong and smooth rail.

Fig 2:  Completed torus embedded in square frame

Next, because the lower works are square, this toroidal structure had to be developed into a square by attaching the correct size outer bulkheads to the outer girders of the torus and carrying out to a square frame, 22 holes deep and measuring 43" square.  Because of limited space between square and round members only 20 such outer bulkheads could be fitted, five in each corner – this was not an engineering train smash of any sort since it will be the corners of the square which come under the greatest stress.  In the extreme corner positions are also four closed box columns made of 2mm plates and with a 20mm hole at each end.  Through these hold will pass the four M20 stainless steel threaded rods which go down into the four roller axis frames which hold the eight crawlers on four rocker axis M20 rods (thus allowing two axis motion as well as the steering motion in a third, mutually perpendicular axis).
The completed lower frame torus to square development is shown in Figure 2, while Figure 3 shows the partially completed work with part of the square juxtaposed with the torus.

Fig 3:  Toroidal structure with square frame temporarily placed

Examination of Figure 2 shows twelve 5½" by 2½" plates with a “crucifix” pattern of holes reamed out to 8mm.  This is to connect inner and outer bulkheads, remembering that there are several thicknesses of plate which come between and make connection by standard parts impossible.  Also of note about the structure is the fact that the four corner outer bulkheads are made of 2mm plate for extra stiffness in these crucial positions.  

In Figure 4 are shown some cosmetic additions to the corners of the square structure formed out of several obtuse girders and plates.  These are meant to represent the four mighty hydraulic levelling cylinders in the corners.  Unfortunately my model will not have this vertical adjustment since hydraulics are not possible without considerable extra parts which are not in the spirit of Meccano. Also, at around 1200 kg, threaded rod type drives would be impractical.
I don’t think levelling will be necessary as the lower works frame is very stiff and should tolerate a bit of standing on three legs! (I don’t envisage doing much rough terrain work either!)

Fig 4: Cosmetic exterior representation of a corner levelling cylinder

Figure 5 shows the four roller axis devices.  I have used M20 stainless steel axles running in four bearings each.  This is a bit of an over-design since there will be two moment reversals within the length of the roller axle (only 250 mm) . However , as I already possessed the necessary plates with 20mm holes I used these rather than make new parts with smaller holes.  Also visible in Figure 5 are the four M20 rocker axles on which the eight crawlers can rock.  These are not over-designed as there are no moment reversals in these 500mm long axles (there are no outer bearings).  The moment which they have to support is obviously enormous.  Finally, the four vertical M20 threaded rods are also in the picture, fixed in with a nut on either side of the top 3½" by 3½" plate.

Fig 5:  Four rock and roll suspension units


Figure 6 shows aluminium representations of the four levelling pistons turned from some 102mm diameter stock. These have 20mm holes through as well as a larger cup at one end to accommodate the M20 nut alluded to above. To finish off the whole effect of the levelling pistons in their cylinders I have used a piece of 12mm thick aluminium sheet, laser-cut to an 8" diameter disk, as seen in Figure 7.  

Fig 6:  Aluminium representations of the four levelling pistons

Fig 7: 4 aluminium finishing flanges to hydraulic levelling pistons and 1 turned hoisting pulley made from the same blank

The whole structure is seen put together in Figure 8.  Unfortunately the threaded rods do not take up their proper positions in this picture as the structure is upside down.  I await some help from strong friends to turn it right side up and place it on a strong wooden structure where it will stay until the entire lower works are completed in a few months.
Fig 8:  The lower works so far (upside down)

Work has also begun on the crawler units.  All eight frames have been fabricated from 2mm plate and one has been fitted with its 2 motors, 2 gearboxes and 2 final drives. Figures 9, 10 and 11 show this as well as the eight aluminium rollers at the bottom (arranged in 4 pairs on sprung rocker axles).  5 rollers are also visible at the top – 2 pairs on sprung rocker axles at front and rear and a 5th fixed in the centre.  This springing gives tension to the crawler belt seen fitted in Figure 9 - where some cosmetic work on the outer side face of the crawler is also visible.  This cosmetic work replicates as best I could the look of the actual Marion crawlers. On the prototype this structure is anything but cosmetic, but because very strong structures in Meccano are easier to build employing only right angles (juxtaposed closed boxes) I chose to build the main strength into the internal members.  The side plates are assembled from 2mm gauge plates of various sizes as seen. 

Fig 9: Crawler unit showing some outer cosmetic work and aluminium rollers on sprung rockers

Fig 10: Crawler unit upside down

Fig 11: Similar, from the other side, showing motors
Spanning the space between the side plates are a total of thirteen 3½" by 2½" plates, as seen in Figure 12.  Appropriate large holes have been drilled from 8mm shafts in the reduction boxes and 10mm final drive shafts.

Fig 12: Thirteen cross-wise bulkheads
The crowd mechanism
I have also at the stage (January 2016) completed the double boom crowd mechanism – shown in Figure 13, upside-down on trestles.  The large-toothed racks are visible. There were also cut by Steelcut Services with great precision in 12½" sections.  The pinion drives are contained in the two boxes which can ride along the booms on a total of thirty-two 1" diameter flanged wheels.  On the prototype the booms are guided by friction pads which can be adjusted for wear.  I decided to depart from this design feature in the Meccano model due to the difficulty of creating such large units with no bolt heads in the way of the friction pads.  There are a total of eight rails installed on which the flanged wheels ride.  A first attempt at using Meccano-style parts to create these rails was bedevilled by a lot of annoying clickety-clack so instead I got my friendly hardware man to cut eight lengths of 32mm wide 1mm gauge galvanised hoop iron, being careful to avoid getting any kinks.  With appropriate mounting holes drilled these work extremely well and the operation is smooth and almost noiseless

Fig 13: Twin crowd booms and slide supports

Each of the two crowd drive guide boxes will have a drive motor driving onto the toothed rack via a 28-tooth pinion. The latter has a spring loaded slip clutch to ensure that no strain will occur in the drive train should an inexperienced operator not cut the crowd power in time.  I am also incorporating spring loaded override bumpers to prevent the boom crashing when they come to the end of their travel in either direction, as there is a lot of mass on the move in the digging part of the machine.

Fig 14: Hollow swing kingpin and 8 floor lift (elevator) shaft

In figure 14 is shown the hollow kingpin and its eight supporting bulkheads, looking rather like the guidance vanes on a SAM missile! The Kingpin is octagonal, formed from 135 degree obtuse girders with 2 ½ inch plate faces. Also shown in this figure is the 63 inch long lift (elevator) shaft for the three-person lift which will run in the hollow kingpin, described earlier. This will give about 57 inches of travel needed to get from the lower works to the roof of the machinery hall, with a stop for the digging operator halfway.

The steering arrangements

I have now (February 2016) started work on the massively strong anchorage arms for the “hydraulic” steering thrusters.  These are fabricated from a mixture of 2mm and 1mm gauge plate.  Because there is a non-standard angle involved I opted to ream 4 holes in the 2mm plates out to 8mm and use M8 bolts instead of drilling multiple non-standard position 4.2mm holes in order to get a strong join.  This work is visible figures 15 and 16.

Fig 15: Steering thruster anchorage at one end (note 19mm spanners on floor)

Fig 16:  An overall view showing steering thruster anchorages at both ends
Parallel with work on the anchorages is the creation of the thrust units themselves.  One of these is seen in Figure 17.  At one end is a motor, its output pinion driving a large toothed gear (27t). This gear is bolted to a 12t pinion which drives a 35t gear which is fixed directly onto a length of M12 threaded rod.  This rod created the sideways thrust to swing a pair of crawlers round by revolving in a large aluminium collar with an M12 thread, held in an aluminium fork piece which was machined from 70mm diameter stock.  These “half universals” are shown in Figure 18 along with some 70mm aluminium faceplates which bolt onto the ends of the steering tiller arms, which in turn are shown in Figure 19 (3 of them).  All of this allows the ram to move with two angular degrees of freedom at the tiller arm (the fork pieces revolve against the faceplates on M12 axles). The other end of the ram can also move with 2 angular degrees of freedom. Examination of Figure 17 which shows the ram motor and gear box reveals a very strongly built box behind the gear box which can rotate with respect to the gear box through a small angle.  This box in turn can rotate about a perpendicular axis with respect to the anchorage arm, thus achieving full movement in solid space.

Fig 17:  Steering thruster motor, gear box and swivelling device

Fig 18:  Aluminium fork pieces and faceplates
Fig 19:  Rock and roll suspension devices with steering tillers and parts from Fig 18

All the above work will allow steering action to take place no matter what height the jacking pistons have been set at in the case of the prototype.  My model, which has a fixed position for the levelling pistons, still needs these degrees of freedom due to the fact that the steering rams do not swing in one horizontal plane.  

March 2016:

Lower Works Righted

Figures 20 and 21 show the lower works turned right side up and placed on a special set of wooden supports which give support at the centres of the four straight sides.  The four rock and roll supports for the crawler system have also been bolted in place by passing the M20 bolts up through the corner boxes of the lower works frame and putting M20 nuts in place.  This required using an hydraulic car jack to life each corner so that the long bolts could be slid into place. 

Fig. 20: Lower works righted. Note - steering thruster anchorages and rock and roll devices with steering tillers in place

Fig. 21: Similar to Fig. 20

The support system has been designed so that the 8 crawlers can be slipped into place on their horizontal M20 rocker axles which go into the holes in the rock and roll devices without further lifting. At that stage the crawlers will be about an inch above floor level.  When all crawlers are securely in place the wooden structures will be dismantled in situ and the final one inch journey to the floor will be made, aided by the car jack.  The wooden supports have also been placed so that they will not interfere with the crawlers in a lateral sense.

Also visible in Figures 20 and 21 are the now completed anchorage systems for the steering thrusters.  These structures are very strong as they have to withstand enough lateral thrust to swing the crawler pairs round under the 1200 Kg machine.

It will also be noticed that the hollow swing kingpin has been bolted in place.  In Figure 22 one can see the temporary placement of the elevator shaft.  This shaft will eventually be fixed to the machinery hall above and will rotate inside the kingpin.  Personnel board the elevator at a station which is level with the lower works underside and can alight just above the top of the kingpin (to get to the digging controller’s cabin) or on the roof of the machinery hall.  

Fig. 22: Elevator shaft inside hollow swing kingpin

The elevator shaft does not extend to ground level as the machine was designed to have a height clearance of 16 feet between the crawler pairs so that the ground man could drive his bulldozer back and forth through the alleyway thus created.  This is enough clearance for a Caterpillar D10 bulldozer, for example (a D10 on this scale would be about 10 inches high. It was the largest production bulldozer available in 1973 when it was introduced).

May 2016:
The Crawler System

All eight crawler trucks have now been assembled and all belts installed.  All sixteen gear boxes have been completed and tested for adjustment.  This is crucial as clearances are about 1mm between the successive gear wheels in the reduction sequences and there must not be any touch.  Each gearbox has been fitted with a slipping clutch so that there can be some differentiation as the machine turns when steered.  (Ideally there should also be some voltage modulation taking the geometry of the trucks into account – feedback – but I will need some advice on that one).  The parts of a slipping clutch are shown in Figure 23.  There are two turned brass faceplates, 40mm in diameter, a leather friction plate between and a 4kg compression spring.  This clutch is placed at the top of the reduction cascade (fastest axle) so the torque available to the final drives is very large.
Fig. 23:  The parts of a slipping clutch

The crawler belts represent a great deal of work, some of it rather tedious.  There is a total of 6 fishplates per crawler tread, four 2-hole ones and two 3-hole ones.  There are also 6 lock nuttings per tread and a total of 40 fixers per tread.  There are 368 treads altogether so that is 14,720 fixers and 2,208 fishplates.

The 8 crawlers are now all installed on their M20 stainless steel rocker axles and secured in place by a total of 16 turned collars.  Figure 24 shows the installation of the last crawler about to happen (onto a M20 stub axle protruding from the rock and roll suspension unit).  

Fig. 24: Support to final crawler truck

Figures 25-27 show the Completed installation of 8 crawler trucks from different angles.

Fig. 25
Fig. 26
Fig. 27

               Figures 25-27 show the Completed installation of 8 crawler trucks from different angles.

The lower works are still supported by the wooden support structure in these pictures so the belts are hanging slacked onto the ground.  When the wooden support is removed they will ride properly on the 8 positioning bottom rollers on their sprung rocker axles.  Belt tension has been adjusted by means of the larger rollers at the top of each unit also on sprung rockers. 

Before lowering to the floor I will do a final check of the motor polarities and will also tidy up the wires bringing in power.

I will delay installation of the steering thrusters as there is quite a lot of work to do on the underside and the only way in is through the gap between crawlers.  With the thrusters in place there will be enough room to drive a scale caterpillar D10 through but then I’m not that compact!

Finally, the crowd motor gearboxes have been installed. Here is a short video clip of these crowd motor gearboxes (with slipping clutches) in operation

28th June 2016

Upper torroidal ring and machinery hall floor pan
The upper rotating toroidal ring has now been completed and rails have been installed on both upper and lower rings.  These rails were made from 40x3mm mild steel flat.  My friend Dixie Westcott used his homemade plate roller to roll the rails into 105cm diameter hoops.  Suitable holes were then drilled for mounting.  The lower rail also needed to have 165 eight mm holes drilled at a spacing of 21mm into which some 40mm M8 bolts were placed, with free ends facing outward.  These became the teeth for the large swing ring gear.  Another plate rolled flat was also made with 64 similar holes drilled and this would become the 64 wheel roller race with 32mm brass flanged wheels installed on M8 bolts.  These developments can be seen in Figures 28 and 29.

Fig 28: Torus, with 64 wheel race
Fig 29: Lower rail

The 4 swing motor/gearboxes have also been installed and wired up.  These provide immense torque for swinging what will be the 700kg upper part of the machine at a realistic speed.  This work can be seen in the following 2 photographs (Figures 30 and 31) taken by a professional photographer, Clint Bradfield of FotoFirst, Grahamstown.  I have decided to place the swing motor gear boxes on the outside of the swing ring.  This is different from the prototype but I took this step for 2 reasons. Firstly, I did not want to interfere with the frame of the upper toroidal ring, thus reducing its strength and secondly, had these units been inside it would become impossible to service them without dismantling much of the machine.

Fig 30

Fig 31

The upper swing bearing consisting of 8 smaller brass flanged wheels fixed to the hollow swing kingpin which in turn is fixed to the lower works can be seen in Figure 32.  These wheels roll on a rail installed on the inside of the upper toroidal frame.
Fig 32: Upper swing bearing
The 6" deep upper torus is of course part of the floor pan of the machinery hall and as such now needed to be developed into the said floor pan.  This has been done by attaching outer bulkheads to 24 of the 32 outer girders of the torus (the remaining 8 outer girders anchor the swing motor gearboxes).  The result can be seen in Figure 33.  Here we see that the floor pan is rectangular on three sides (the front and sides) while the rear is a segment of a circle, concentric with the kingpin. (There is also a slight bulge on the front)
Fig 33: Floor pan
The rear end of the floor pan can be seen to have 6 empty boxes.  These will house a total of 48 one litre concrete blocks with a total mass of about 125kgs.  This is the counterbalance weight needed to counter the overturn moment of the main boom, dipper arm, crowd arm and stiff leg.
The plating of the hall rear end is complicated as the lower part (below the colour change line) is in fact a segment of a frustum of a cone.  It is not possible to plate this with rectangular plates without doing considerable mutilation and landing up an untidy job.  I have therefore opted to cut and drill some custom shaped ones out of scrap galvanised plate kindly provided by Mr Bud Hare, a local plumber.  The lower 6 have been installed and the effect is seen in Figure 34.
Fig 34: Curved frustum of cone

The next major task will be the creation of the 2 double hoist winding drums driven by 4 motors.  The prototype had 8 motors of 1000hp each but 4 window winders will be sufficient on the model, especially since I do not plan to ever fill the 1½ cubic foot dipper with stone!  The main gears of the hoists are these beautifully made 12" ones cut by SteelCut Services – Figure 35.  I could not resist the temptation of having 12 cut even though only 2 are needed.  With laser cutting the most expensive unit is the first as the cost of design and storage in the machine’s CAD (computer aided design) system is incorporated.  Once the design is held further copies are only slightly more expensive than the cost of the material.
Fig 35: 12 inch main gears (12 of)

Other details are being filled in along the way.  One of the 2 electric supply cable winding drums can be seen in Clint Bradfield’s pictures (Figures 30 and 31 above).  The red rounded structure to one side of the winder would house a slip ring capable of handling the 14,000v three-phase incoming power at the rate of 22 megawatts on the prototype.  On the model these are just for show as the actuating power will come in via 2 multicore cable harnesses, one to the lower works and one to the upper works. (I do not plan to put a multidisc slip ring between upper and lower works as there are too many individual cores and should one lose contact the consequences could be serious with, for example, 3 swing motors trying to drive a stalled swing motor).

17th July 2016

The winding drums and some corrections to the rear end

Work on the winding drums has started and these can be seen mounted in Figure 36.  On each side is a double drum with a central divider so that the cables remain separate (4 cables altogether then).  The drums have 6" faceplates at each end and a 7½" divider.  Each is fixed to a 12" driving gear which will be driven directly by the output pinions from 2 motors.

Fig 36,: Winding drums

I also decided to change the rear end of the machine slightly. I have added 7 bulkhead framers of width 3½" each.  These will be the frame to the section of a frustum of a cone which is the lower part of the rear end.  This step achieves two aims.  One is that a slight scale error in the machinery hall versus the lower works has been corrected. Secondly, the rear end supports in the picture (Figure 37) support 4 motor-generator units (M-G) which are very heavy in the prototype as they convert 22Mw of high voltage AC 3-phase power into 440 and 220 volt DC. I shall build representations of these driven by Meccano 6 volt motors so the extra framing is all to the good.
Fig 37: New rear frames

Figure 38 shows the floor pan taken from above.  Compare the shape with the actual 6360 floor plan shown in Figure 39.
Fig 38: Aerial view of floor pan

Fig. 39: Diagram of floor pan

Finally, the plating of the two side extension “lugs”, 5½" outward has been effected using some purpose made plates recycled from my plumber’s scrap heap (Figure 40) rather than mutilate rectangular plates to achieve the rather complicated shape.
Fig 40: Bottom of the rear "side lugs"

3rd September 2016

The double gantry

I have now started work on the next main phase, the double gantry above the machinery hall floor, which supports all the upper parts of the machine, viz., main boom, crowd arm and by way of pinioned joints, part of the dipper and stiff leg.
Fig 41: 8 main uprights. Note scaffolding to work from.

Figure 41 shows the eights main struts in place.  Each of these is a closed box beam made from 2½" wide plates onto corner girders.  The rear four have girders facing inward and hence one plate face had to be fabricated entirely from 2½" x 2½" plates since fingers cannot get inside to hold nuts 5½" away.  The front four have girders facing outwards and hence resemble two I-beams bolted side by side.  This was necessitated by the fact that there is a considerable amount of cross-bracing between the front uprights as well as strong supports to the crowd drive mechanisms.  The outward facing girders were convenient to bolt all this on.

Fig 42: Some cross-bracing

The start of the cross-bracing can be seen in Figure 42.  Strong corner gussets have been installed with a high bolt density as can be seen in detail in Figure 43.  Plates of 1.0mm gauge have been used for most of the gantry.
Fig 43: Corner gussets

I have designed the gantry so that the top four feet or so can be removed in order to get the model through the garage door.  Each upright member of the gantry can be split in two at just above the hall roof line.  This will require about 300 nuts to be loosened.  The break in the lower X-brace can be seen in Figure 42.  Only the upper V part of the X has been assembled. The upper part of the gantry will have a mass of about 100Kg and so by attaching two wooden lifting battens it should be easily managed by four people.

2nd October 2016
The Stiff Leg, Hoist, Pulleys, etc
The stiff leg has now been fabricated and two views (front and back) are shown in Figures 44 and 45 respectively.  This unit is just over 6 feet long and is built from about 300 plates, most of which are 4½"x2½". Each of the two main stanchions is a closed box with butt-joined girders in the corners and lap-joined 4½"x2½" plates (0.6 gauge) spanning.  The cross join between these uses some 1.0 gauge plate as it must resist any torsional stress applied. It is also a totally enclosed box.  Visible at the upper end is a piece of 20mm aluminium rod which will act as a hinge to the twin crowd boom and the dipper handle. 

Fig 44: Stiff leg, front view
Fig 45: Stiff leg, rear view

Further work has been done on the gantry.  In Figure 46 some more bracing (in green) can be seen.  These braces are in planes perpendicular to the main  bracing.  As with the main bracing members these members can be split in two just above the machinery hall roof so that the top half of the gantry can be removed to exit the machine from garage.  
Fig 46: Gantry bracing

In Figure 47 four hoist pulleys at the gantry top are shown.  These are mounted on very strong bearing units and run on 8mm axles.  Figure 48 shows the two bearing boxes for the crowd mechanisms.  My crowd drives will rock on 8mm axles which are offset from the drive axles (also 8mm) by 1".  I did not want to let the weight of the crowd boom rest on these drive axles (this weight is magnified when the crowd boom is in the cantilevered full back position).  I am using two motors to drive the crowd through slipping clutches.  Since ©Meccano does not utilise ball bearings I was afraid that the drive shafts would experience too much clamping action if things were done as on the prototype (bearings rocking on the drive shafts).  This change has also necessitated a slight change in the geometry of the upper section of the gantry, but the spirit of the machine will not be lost, I feel.
Among other things I have also spent some time manufacturing another five hundred 5½"x2½" plates. Three hundred of these plates will be used in the machinery hall roof.  My original plan was to use flexible plates here (cut from empty spray paint tins, coffee tins, etc.).  I have, however, rethought this and realised that the roof needs to be stronger due to the strategy for transport (removal of the upper part of the gantry).
Fig 47: Four 8 inch hoist pulleys

Fig 48: Crowd drive rocker axles
3rd December 2016 : Some details, some gaps filled and the Dipper .

Some detail has now been installed. Fig 49 shows the present state of the main hoist winding drum area. The drive to these  drums is supplied by four window winder motors as explained before but now eight imitation representations of the eight  1000 hp electric motors on the prototype have been installed. These are seen to have six sided bodies ( employing some 110 degree and 135 degree obtuse angled parts) . On top of each motor is a small aluminium fitting made from 20mm and 30mm stock,  meant to represent the double impeller cooling blowers for the 1000hp motors needed since the latter run almost continuously and are too slow revving to run their own coolers. Also visible on each motor is a lifting hook. I used M6 eye bolts as M4 were not available. A bit clumsy but they give the idea.
Fig 49: Some detail in the winding drum area

Also in evidence around this area is a network of access platforms and stairs. As usual I use narrow strip for horizontal rails and long bolts for upright stanchions. This theme is continued in Fig 50 which shows some of the labyrinthine ladder network and servicing platforms near the top of the gantries.

Fig 50 : Servicing platforms and access ladders on gantry

In Fig 51 the large raised platform at the very rear of the machine is now shown completed. This will support the four large motor generator units , each consisting of a 14000V AC motor driving four or six generators putting  out 220 or 440 V DC on the prototype. Below this platform are six large boxes which will house about 125 kg ballast in the form of one litre concrete blocks .This is needed to counter the overturn moment of the main boom and the three moving arms. 
Fig 51 : Motor generator platform

Work has also begun on the dipper. In Fig 52 the handle to the dipper is shown. This is fabricated largely from 0.6 gauge plates overlapped with butt joined girders in the corners. The upper end of the handle is narrowed down to 2.5 inches square by means of four purpose cut plates. At this end an aluminium fork piece and collar can swivel. The 20mm axle on which all three moving arms pivot passes through this collar. The lower end of the handle is widened to 5.5 inches. This is where the digging bucket will join on.
Fig 52 : Dipper handle

The said bucket has been built too and two views are shown in Figs 53 and 54. The first is from the front offside and shows the digging teeth while the second is from the rear offside and shows the two doors which open on hinges at the top to release the load. I still need to install the locking latch system as well as a system to slow the closing of the doors (nubbers). Then the components can be mated to complete the dipper handle.
Fig 53 : Digger bucket front off-side view
Fig 54 : Digger bucket rear off-side view

It may be noticed that I have coloured several parts which are traditionally green in red instead. I felt that a uniform red for the main body of the bucket would be more pleasing to the eye. This part of the bucket employs a double skin with about an inch between in parts. This is done to give an idea of the massive steel casting which was the prototype bucket front.

Readers familiar with the 6360 will notice that my bucket has been modelled on the revised bucket seen on the machine after it was taken over by Arch Minerals. The earlier bucket seen on the machine in its time with South Western Illinois Coal Corp. was replaced by this design which was easy to recognise by its distinctive side ribbing. Perhaps the older bucket wore out? I would appreciate it if someone could tell me the story.

2nd January 2017 

Crowd arm, stiff leg, dipper and motor-generator sets

The crowd arm and stiff leg have now been installed with some help from two of my sons who were in town for Christmas holidays. This is seen in Figures 55 and 56. Tolerances were quite tight but nothing clashes and the motor drives can lift the units with ease. The crowd drive motor/gearboxes are shown close up in Figure 57. The original 40mm slipping clutches have been replaced by 110mm ones,u as I felt the 40 mm ones might not have sufficient pull. The solid brass face plates needed quite a bit of cutting in the lathe as I had to start with a blank which was big enough to grip securely in the chuck.
Fig 55: Proud arm and stiff leg now working

Fig 56: Similar, from the front

Fig 57: Close up of crowd drives

Figure 58 shows the dipper, which has now been put together, and the lifting hitch with four 8 inch aluminium pulleys installed. This unit can only be installed once the main boom is in place since most of its weight is borne by the main hoist winding drums through cables running over another four pulleys at the top end of the said main boom.
Fig 58: Dipper with attached pulleys

Figure 59 shows one of the four motor generator (M-G) sets assembled. The roughly cubic structure in the centre represents a high voltage motor (14000 volts three phase AC) which drives four generators with open frames. Ersatz windings in the stators were made using three hole strips and stacked washers while ersatz rotors were made using the tops of Rustoleum spray paint cans cut, pushed together and sprayed black. 
Fig 59: One of four motor generator units installed

In Figure 60 all four M-G sets can be seen installed on their raised platform at the rear of the machinery hall. Although these are cosmetic in the sense that they do not form part of the model’s power train, they all do actually revolve. The H.T. motors in the front two actually have motors inside driving through speed step up boxes (since the output pinions revolve too slowly) which drive the four larger open cage generators as well as the parallel sets with six smaller fully enclosed generators by means of Meccano sprockets and chain. (One of the few Binns Road parts used!)
Fig 60: Four motor generator units installed

The axle common to each M-G has been journalled in only four points due to inevitable alignment problems. On either side of every H.T. motor are flexible drive units to avoid these problems. These flexidrives were made from a central 3mm thick disk of insertion rubber and turned brass bush wheels on either side with bolts between as shown in an exploded view in Figure 61. I got this idea from a flexidrive unit in the prop shaft of a rear wheel drive Fiat motor car I once owned.
Fig 61: Parts of a flexidrive unit

An aerial view of the M-G sets is shown in Figure 62. Compare this with the floor plan of the prototype shown in Figure 39. The M-G layout was quite time consuming to build as many parts needed to be specially made. These included 44 bush wheels for flexidrives as well as for the frames of the open generators. Although most of the plates used were made from recycled coffee tins and spray paint cans, the whole structure is quite heavy. This is all to the good as it acts as a counterbalance. On the prototype the counterbalance effect was even greater as these were very heavy items. Once the enclosed cabin of the machinery hall is under way I will have to install some very substantial travelling cranes to enable these units to be lifted out for service etc.
Fig 62: Aerial view focused on rear of floorpan

Work on the main boom has now been started in another room. This will weigh about 80 kg but I am hoping to minimise the need for help to get it into place at an upward angle of 45 degrees in the same way as the builders of the prototype got the boom up. I shall install two smaller pulleys at the upper end of the boom and build a special highly geared down double winding drum to pull it up. I cannot use the hoist drums as they revolve quite fast and do not have the pull for this job. (The hoist process would be tedious to watch if it happens too slowly. Hoist and crowd speeds need to be matched for ease of operation too.)

1st March 2017  

Main boom

During the past 60 days substantial work has been done on the 12 foot 8 inch long ,6000 nuts and bolts main boom. The two halves were assembled in the study of my home and then taken up to the garage which is the Marion assembly site where they have been joined together and a lot of detail filled in. I have provided the best pictures I could get but this has been difficult due to the fact that the unit almost completely fills the space cleared in front of the model so far. Figures 63, 64 and 65 are the best overall views my wife Eileen could get. (She being a better photographer) 

Fig. 63

Fig. 64

Fig. 65

Figure 66 shows a tapered lower end at one side. This was assembled from some specially prepared 1.0mm plates with a bend just off diagonal which are shown in figure 67. I decided that this was the neatest way of creating the tapered end keeping the look close to prototype while maintaining great strength.

Fig. 66: One tapered lower end

Fig 67. : Four 1.0mm plates with an off-diagonal bend each

In figure 68 are shown some strong angle brackets made by bending 3.5 by 2.5 inch 2.0mm plate. These will be bolted onto the 2.0mm plate between the angled bent plates in figure 66. Also seen in figure 68 are two hinge parts (green) with 10mm holes . Their gauge is 3mm and the will bolt onto the red angle brackets and form one half of the hinge supporting the main boom . An M10 bolt will serve as a pin.
Fig. 68: Two angle brackets and two hinge plates

Figure 69 is a view of the bearing box for the four 8inch aluminium main hoist pulleys. Figure 70 is another view of this unit with details of some access stairs visible I am indebted to Classic Construction Models and photographs of their highly detailed brass model of the 6360 for information on these finer details.
Also visible in figure 69 is a turned aluminium 4 inch pulley mounted in a swinging yoke and running in a plane which stays perpendicular to the plane of the main hoist pulleys. This is the first of four such pulleys . I plan to  hoist the main boom up into position using a strong motor driven winding drum and another four sheaf pulley system .This is the way the boom was installed on the prototype. I calculate that tension in the cord should only be about 12kg, which is manageable.
Fig, 69: Bearing box for hoist pulleys

Fig. 70: Similar, showing access ladders

In figure 71 is shown a transfer stairway between two main stairways going up one side of the boom. I’m not sure why it was necessary to have four different routes for staff to get to the top of the main boom. Perhaps someone in the know could enlighten me?
Fig. 71: Transfer ladder between upper and lower main stairways
Finally figure 72 shows some cosmetic work at the front end of the bearing box. The strength of my version really lies in eight parallel bulkheads with cross bracing bulkheads between .Three different stresses have to be designed for: (1) The 8 inch load hoist pulleys (2) The 4 inch boom hoisting pulleys. (3) The twelve stay rods which will connect the top of the main boom to the top of the gantry.
Fig. 72: Cosmetic work at front of bearing box