Caprotti Black 5

Dave Holt
Posts: 29
Joined: Thu May 28, 2009 9:44 pm

Caprotti Black 5

Postby Dave Holt » Sun Jan 06, 2019 3:41 pm

Whilst I'm unable to do any physical modelling till my arm mends, I can still post stuff on here, so I thought I would show my Caprotti fitted Black 5. Unlike the BR Standard 2 tank, this is yet another loco with no real justification on my layout apart from imaginary use on a Wakes holiday special. Actually, one of the later, outside drive locos did visit the Delph branch when the Royal Train was stabled overnight, long after the passenger service had ceased.

The model was built from a Comet kit, with various modifications and additions to suit my preferences and interests. The Wild Swan Profile book covering these locos proved an invaluable source of information, including engineering drawings and a good selection of detailed photographs.

Following my now standard arrangement for 4-6-0 locos, the chassis has a fully compensated suspension with twin beams for the centre and rear coupled axles and a single beam linking the front coupled axle and a load transfer pin inside a tubular bogie pivot. The bottom of the pin rests on a transverse tube which carries the external bogie compensating beams. This arrangement includes the bogie axles in the suspension, but not the bogie frame. This frame can pivot and slide sideways but does not move up or down and is held up against side bearing pads by light springs. Thus replicating the real thing. This arrangement of compensation also results in the ideal beam pivot points for both weight distribution and stability. I learnt this the hard way when an early effort with a fixed driven rear axle and a single beam between the centre and leading coupled axles [with the bogie just along for the ride] was seen to lift the inside rear wheel off the track when taking curves at speed. It seems the loco CoG was too near the apex of the three point suspension so that the effect of the centrifugal force move the effective CoG outside the triangle formed by the three fixed point and the loco was actually tipping up - a bit like a kiddy's tricycle cornering too fast.

Here are a few photos of various stages of construction.

First, we have the chassis showing the compensation arrangement and keeper plate and a shot showing the separate components primer painted.

IMG_1362.JPG
chassis top


IMG_1363.JPG
chassis underside


IMG_1549.JPG
chassis parts primed


Next, we have the footplate assembly and some closer shots of the chassis and footplate assembled. I deviated from the kit intent by attaching the cylinders and slide bars to the footplate rather than the chassis. This was to try to avoid the visible line through the cylinders seen on other examples of this kit resulting from the cylinders being on the chassis and the cam boxes on the footplate.
I tried to represent all the lubrication and lubricator steam heating pipes on top of the footplate and splashers.

IMG_1370.JPG
chassis/foot plate front rhs


IMG_1371.JPG
chassis/foot plate top


IMG_1372.JPG
chassis/foot plate front lhs


IMG_1373.JPG
rhs cylinder close up


Now the loco is starting to come together. I kept it in basic sub-units till final assembly to allow access for detailing. It proved quite an interesting puzzle to work out how best to split details which cross from one sub-unit to another. This was especially tricky under the cab, due to the open steps not providing any cover to hide joints and gaps!
The main sub-units,

IMG_1544.JPG
loco main sub units


and more detailed shots and the assembled loco.

IMG_1488.JPG
lhs complete


IMG_1489.JPG
lhs cab close up


IMG_1497.JPG
rear rhs


IMG_1547.JPG
foot plate unit


This is a separate unit which fits below the cab and carries part of the brake gear, the exhaust steam injector and bits of various pipes, including the hose connections to the tender.

IMG_1546.JPG
piping sub unit


When the loco went for painting, David Clarke observed that the RHS of the tender body was badly cockled. The Comet etched sides are very thin and I was aware I might have done some damage, but it didn't look too bad in the raw, but once painted black it looked terrible. A replacement body was purchased to obtain a new side and, luckily as it turned out, I hadn't done a particularly good job of soldering the side on, so I was able to remove the damaged side and fix a new one in its place [mainly glued].

IMG_1553_1.JPG
damaged tender side highlighted


IMG_1557.JPG
damaged tender side removed


IMG_1562.JPG
replacement tender side


The loco was painted, lined and weathered for me by David Clarke, as seen below. In the shot of the RHS, the tender is not connected and is slightly too far from the loco.

Revised weathering 5.JPG
weathered rhs, tender separate


Revised with boiler bands and more weathering  1.JPG
weathered lhs


And finally, a rather cruel close up.
IMG_1644.JPG
weathered rhs front close up


Dave.

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Le Corbusier
Posts: 1149
Joined: Wed Feb 11, 2015 3:39 pm

Re: Caprotti Black 5

Postby Le Corbusier » Sun Jan 06, 2019 3:57 pm

Again ... lovely work Dave :thumb

Can I as what the suspension arrangement is on the bogie? I can see that the unit itself is compensated along with the leading driver ... but what is the arrangement for the individual axles/wheels?
Tim Lee

Dave Holt
Posts: 29
Joined: Thu May 28, 2009 9:44 pm

Re: Caprotti Black 5

Postby Dave Holt » Sun Jan 06, 2019 9:34 pm

Can I as what the suspension arrangement is on the bogie? I can see that the unit itself is compensated along with the leading driver ... but what is the arrangement for the individual axles/wheels?[/quote]

Tim,

I'll try to explain with reference to the photo of the primed chassis parts.

Bogie compensation detail.JPG


You will see the bogie frame, compensating beams and the top rubbing plate along the top of the photo. In this case, the axles have axle boxes [square brass tube with round tube inside] which engage in the external horn guides on the frames. The axles pass through slots to allow vertical movement and the cross shaft linking the compensating beams also locates in a slot. One of these beams has a 1,6 mm tube fitted, which has the open end tapped 14 BA. The other beam has a 14 BA screw attached, so the the two beams can be screwed together but allowing the beams to twist relative to each other. The compensating beam cross shaft is retained in the bogie frames by fixing the top rubbing plate [which also carries the side control springs] to the top of the bogie frames. The degree of twist is limited by the ends of the beams resting on top of the axle boxes. Thus, the wheel sets and compensating beam assembly can move up and down within the bogie frame and also the axles can rock relative to each other.
On fitting under the loco, the compensating assembly cross tube rests against the bottom of a pin [which can slide inside a hollow bogie pivot] which, in turn, bears against the front compensating beam of the loco.
Obviously, in order to function properly, it is necessary to determine the pin length and the ride heights of the loco chassis, bogie frame/rubbing plate and the compensating beams, etc., not a straight forward exercise involving measurement of parts, various sketches and calculations - but I enjoy that aspect of modelling as much as the actual building.
Sorry if this explanation is over complicated but I can't explain the arrangement any easier.

Dave.

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TonyMont
Posts: 84
Joined: Mon Jul 28, 2008 2:19 pm

Re: Caprotti Black 5

Postby TonyMont » Mon Jan 07, 2019 1:01 pm

Hi Dave,

I have admired your work on many occasions and it is a pleasure to now be able to take time to study the construction in detail.

I have been experimenting with the removable keeper plate system, with sander pipes etc. I try to include the pickups, are these included in yours? I can see some helical wound wires but they do not seem to be insulated, do these have another purpose?

Regards, Tony.

Dave Holt
Posts: 29
Joined: Thu May 28, 2009 9:44 pm

Re: Caprotti Black 5

Postby Dave Holt » Mon Jan 07, 2019 2:00 pm

Tony,

It's quite some time since I built this loco and, to be honest, I was struggling to remember quite how the pick-ups were arranged - I don't always follow the same arrangement on every model, varying it to suit the particular chassis layout. However, looking at an enlarged view of the keeper plate, I can make out enough detail to refresh my memory.

Caprotti_Blk5_keeper_001.JPG


Although not absolutely clear from this shot, there are copper clad pads attached to the underside of the keeper plate at three locations. The 0,33 mm brass wire pick-ups are attached to these [actually, the centre driver pick-ups are attached direct to the bus bars], passing inboard of the dummy springs and then curving round through 180 degrees to bear on the rear of the coupled wheel rims, hidden from external view behind the brake blocks. The pads are linked by bare brass bus bars and then up to the upper rear area of the chassis by the two "prongs" on which the keeper is resting, in its upside-down orientation. As you note, all these parts are un-insulated brass wire and are routed so as not to touch any other part of the keeper or chassis.

Dave.

Julian Roberts
Posts: 610
Joined: Sat Jan 09, 2010 11:33 pm

Re: Caprotti Black 5

Postby Julian Roberts » Thu Jan 10, 2019 1:09 pm

Dave

I'm sure Tim Lee spoke for all us readers. "Fearfully wonderful" is an expression that occurs to me contemplating the Everest-like heights of modelling wonder you have presented to us. I'm especially in awe of your standard compensation arrangements of the 4-6-0 bogie. (Would a 4-6-2 merit any difference in approach I wonder? - I surmise, not.) Partly, I have to admit (despite your explanation), because I'm still not quite clear how the beam from the front driver connects with the bogie compensation transverse tube. From the photo of the chassis top view the beam from the front driver seems to end on top of a frame stretcher.

Is this concealing what you describe here? -

"the compensating assembly cross tube rests against the bottom of a pin [which can slide inside a hollow bogie pivot] which, in turn, bears against the front compensating beam of the loco."

I hope that Tim V will be seeking an article about this for the Snooze too! While the driving wheels compensation is quite standard, the bogie and its connection through the pivot, and your thinking regarding the overall system as it works on the whole loco, merits a very detailed description surely - seemingly to me taking Sharman ideas to a still more sophisticated level.

While writing (on a long journey) could I ask you two rather more banal questions? First, how do you make so realistically the joints on Walschaerts valve gear? If you use pin and solder what is your technique to avoid the joint going solid? - and is the pinhead outside or inside? I am so disappointed in the appearance of my efforts using rivets (on my Crab)!

Second, do you make your locos for a minimum radius that's less than prototypical for each type? Or are sharper curves on Delph restricted to suitable traction as on the real thing?

Any time you want to tell more about Delph the layout I for one would be all ears and eyes. Very best wishes for a most speedy recovery but in the meantime your posts have brought, along with Mike's NE locos thread, a great deal of new inspiration.

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Le Corbusier
Posts: 1149
Joined: Wed Feb 11, 2015 3:39 pm

Re: Caprotti Black 5

Postby Le Corbusier » Thu Jan 10, 2019 2:16 pm

Julian Roberts wrote:Any time you want to tell more about Delph the layout I for one would be all ears and eyes. Very best wishes for a most speedy recovery but in the meantime your posts have brought, along with Mike's NE locos thread, a great deal of new inspiration.

:thumb :thumb :thumb :thumb :thumb :thumb :thumb
Tim Lee

Dave Holt
Posts: 29
Joined: Thu May 28, 2009 9:44 pm

Re: Caprotti Black 5

Postby Dave Holt » Thu Jan 10, 2019 4:22 pm

Thanks to everyone for the kind comments. All rather embarrassing, really, as I have never set out to impress anyone, just satisfied my own interests and obsessions. There's loads of models out there to a better standard than my efforts but I do try to capture the essence of the prototype and incorporate some semblance of the detail, including the underneath, which I think improves the silhouette when viewed from a low angle. Nothing spoils the illusion for me more than seeing daylight between bogies or pony trucks and the loco chassis, lack of ash pans or major pipework below cabs. Of course, I do perhaps have an advantage over many modellers, stemming from my professional mechanical engineering career (not railway related) and many years of full sized loco restoration and maintenance, which gives me almost unfettered access in, on and under various steam locos and enables me to well understand what is there that we are trying to replicate in miniature. Except for a small vertical drill, all my modelling is done using normal hand tools, so I think others can do the same, given some prototype knowledge, basic skill and by taking care and attention to detail.

Regarding the specific questions raised:
I have one pacific and two 2-6-4 tanks in which the suspension of the bogie and coupled axles is as per the 4-6-0 and the pony truck has a sprung axle within the truck. My 2-6-2 tanks are compensated as 0-6-0's (front axle on a centre rocker and twin beams for the centre and rear coupled axles, with both pony trucks having a sprung axle.

I don't have any better photos of the bogie compensating arrangement, but the following sketch is an attempt to explain the arrangement.

Bogie_comp_sketch_001.jpg


The frame stretcher at the bogie centre, to which the hollow pivot tube is attached, is usually a double thickness, with the lower one extending beyond the main frames and carrying the side bearing pads mentioned in the original description. Omitted for clarity in the bogie frame, which has stretchers that slide against each side of the pivot tube, holding the bogie in place and preventing it from tipping in the longitudinal plane.

Where possible, I put the head of the valve gear pivot pins on the back side, even though I reduce the pin head in both diameter and thickness. I try to make the pin shaft a tighter fit in the part it attached to and a slacker fit (0.054 mm bigger drill) in the pivoting part. I always use a thickness of cigarette paper, to act as a spacer and a barrier to solder bunging the whole thing up. I have used a dab of oil on the paper, which improves the effectiveness of the barrier but if done to excess or left too long before making the joint, I've experienced the oil wicking into the joint and preventing soldering to the fixed part, so I usually do it dry. Others may well have different experience and approaches.

Regarding minimum radius curves, my approach has changed over time. Early on, I made the basic chassis capable of negotiating a 900 mm reverse curve test rack and calculated side play and bogie side throw accordingly. However, I found that other features, such as front steps and loco/tender clearances, also came into play and so in practice, my models tend to be limited to 1000 to 1200 mm minimum radius. Even then, some locos have had to have their front steps moved out slightly to achieve this. Before I start any new loco, I do try to determine the side throw needed for any trucks and bogies, just to get an idea. As far as the coupled axles are concerned, I restrict the front to a mere running clearance, a little more at the rear and I just leave the centre axle to follow the track without particularly limiting the side play. Generally it seems to work when using Society or Alan Gibson frame spacers.

Hope that helps and I haven't rambled on too much.

Dave.


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