G-Train Locomotive Works / Graeme King Joint Venture - GCR/LNER 4-6-0s - B3/1 & B7 available; B3/2 in progress

[Horsetan]

Caprotti B3/2 showing early promise there. Hopefully we might see a kit next year.

[iainkirk]

Wonderful. Simply wonderful.
Worth waiting to see this coming together.
All power to your solder and resin...

[LNER4479]

A quick update, at risk of raising the excitement levels too far too fast...

The feedback from the B7 has been sent to Nick (Easton), who has duly updated the design. Given the relatively low number of changes required and the similarity with the B3 design, we've 'gone for it' and placed an initial order for 20 etches.

As if that wasn't enough...

PPD, who had earlier suspended etching due to Coronavirus, appear to have restarted as I've had word that the updated self trimming tender etch is ready.

More soon!

[Horsetan]

....PPD, who had earlier suspended etching due to Coronavirus, appear to have restarted as I've had word that the updated self trimming tender etch is ready....

Encouraging. Might we see a B3/2 next year

Meanwhile I have secured some more GC-type inside motion parts (ex-Rod Neep/Peter K/Exactoscale, actually designed with the D11 in mind) for the B3, so some mathematics may have to be involved.....

[john coffin]

be glad to see that my modifications are exactly as GK asked for, and tender looks and goes together in the way that both
he and I agreed in January.

I look forward to your comments Graham.

Best wishes to all, stay safe

Paul

[Woodcock29]

Great news Graham on the progress with the B7. Maybe I'll have it later this year?

Andrew

[iainkirk]

Splendid news!
We wait calmly for things to come together...

[Horsetan]

...We wait calmly ...

[LNER4479]

Encouraging. Might we see a B3/2 next year

Well, you and anyone else on here, might actually be able to help us out here!

I have all the feed back ready to send but I'm 'stuck' on one aspect - the configuration of the Caprotti drive (or the visible parts of it). Here are a few piccies which might prompt the grey matter.

6166 Caprotti1.jpg (30.05 KiB) Viewed 12918 times

6168 Caprotti.jpg (34.31 KiB) Viewed 12918 times

The etch currently has a part (reverser support bracket) to support the reversing shaft from the cab. However, this was based solely on a 2D side-on drawing; the moment you see it at an angle then it clearly has more to it. I'm assuming this is part of the gearing to get the drive across to the other side of the loco (where there appears to be an equal and opposite bracket - where I've fitted it on the test build). If anyone can shed any more light on this (a drawing would be great!) then I'll suggest a more accurate part accordingly.

In passing:

As you may already know, the casing round the cam boxes was pretty quickly removed and the locos spent most of their time running around without the covers, as depicted in the photos, so would be good to include some parts for maximum appeal. I'm going to suggest that the etch includes a part for the full exhaust pipe at the front as that shouldn't be too difficult but the cam box would be little better than a wild guess. It looks to be full of curves, which doesn't lend itself to a etched part in any case. Once again, a drawing would help?

The pic of 6167 (1498) shows a revised configuration for the reversing shaft, and what looks like a different shaped support bracket. Was this a later mod or were some of the rebuilds fitted thus?

Any info or comments gratefully received

[Horsetan]

....The etch currently has a part (reverser support bracket) to support the reversing shaft from the cab. However, this was based solely on a 2D side-on drawing; the moment you see it at an angle then it clearly has more to it. I'm assuming this is part of the gearing to get the drive across to the other side of the loco (where there appears to be an equal and opposite bracket - where I've fitted it on the test build). If anyone can shed any more light on this (a drawing would be great!) then I'll suggest a more accurate part accordingly.

I don't have many photos of B3/2s, but I think I may have spotted one - and only one - offside view which might help. I will have to dig out my smartphone and use its camera as a magnifying glass.

..... casing round the cam boxes was pretty quickly removed and the locos spent most of their time running around without the covers, as depicted in the photos, so would be good to include some parts for maximum appeal. I'm going to suggest that the etch includes a part for the full exhaust pipe at the front as that shouldn't be too difficult but the cam box would be little better than a wild guess. It looks to be full of curves, which doesn't lend itself to a etched part in any case. Once again, a drawing would help?

The closest cam box shape I can find is that fitted to the LMS Caprotti Black Fives in the 1940s, by which time the gear had evolved. Although there is a Comet kit for that class available via Wizard Models, I'm not sure that the cam box casting is available as a spare.

The pic of 6167 (1498) shows a revised configuration for the reversing shaft, and what looks like a different shaped support bracket. Was this a later mod or were some of the rebuilds fitted thus?

Presumably you are catering for both one- and two-piece reversing rods? The 1929 conversions 6166 and 6168 had single-piece, whilst the 1938/39 conversions 6164 and 6167 had a two-piece rod with a support bracket to hold what looks like a universal joint between the two lengths.

[Horsetan]

Using the smartphone as a magnifying glass, I have zoomed into the photos published in Vol.2 of the Johnson book on GCR Locomotives. It looks like there was some sort of step-down / reduction box to take the drive from the reversing rod down to the cams.

The close-up of 6168's offside cambox is probably the best view I've been able to render, and shows the cambox shape to be similar to that carried on the Ivatt Caprotti Black 5s (except for the last two). The strakes in the front and rear casing are either vents or reinforcements.

There must be some better broadside views of the B3/2s somewhere, but I don't have them. I'm not sure the NRM or MoSI have any drawings that would shed light on how these arrangements were meant to look.

[Horsetan]

Update: a search of the Doncaster drawings catalogue has turned up nothing except some drawings for the B3 chimney.

Will check Darlington catalogue next. Expect to be disappointed.

[Seagull]

The strakes in the front and rear casing are either vents or reinforcements.

Page 56 of the said Locomotives of the GCR Vol.2 the middle picture shows the originally solid front of the outer casing now with several round holes in suggesting strongly that the cooling was not good. That to me infers that the 'ribs' are indeed cooling louvres and in any case the design of the cover is such that strengthening ribs would be of little or no value.

Regarding the reversing rod arrangements might I suggest a look at this video - Distribuzione Caprotti in funzione https://www.youtube.com/watch?v=pIK5mnd_h_U

In the opening shot the large diameter shaft running from 11 o'clock to 5 o'clock is the valve drive.
This runs athwartships - side to side - across the engine and is placed above the cylinders.
In the lower picture on page 57 of Locos of the GCR you can see the end 'pimple' of it sticking out above the righthand cylinder.

At the 21-22 second time in the video the upper shaft running from 9 o'clock to 3 o'clock is the reversing shaft which runs fore & aft on the engine.
Again the picture on page 57 you can see the end of the shaft sticking out of the forward side of the casing adjacent to the steam pipe into the smokebox.

At the 29-32 second time you can see the reversing shaft turned through about 90 degrees to change the gear from one direction to the other.
I cannot work out myself exactly how the cut-off is varied unless it is by only partly rotating the rod which.


There is another set of videos which show a computer simulation of the operation However the attached text is not helpful and is nearly the same for all the clips:- Caprotti scroll nut.... https://www.youtube.com/watch?v=c_HMXJF ... BZ&index=1
(The author thought it was a good idea to auto-run the clips - I have my own opinion!)

While I'm dubious about the value of the clips it does show more clearly the shafts and gearing and I belive suggests that the cut off is varied by varying the degree of rotation of the shaft.


There is mention of a booklet - '71000 Caprotti Valve Gear Booklet' - https://www.theduke.uk.com/product/booklet/

25 page PDF booklet describing the Caprotti Valve Gear of BR Class 8P 4-6-2 Steam Locomotive No 71000 Duke of Gloucester – How it Works. Written by Peter Scarborough and 2004 updates by Dr Gary Shannon.

This item is available as a PDF download £6

I believe the shaft from the cab would only require to rotate through about 90 degrees so to transfer the travel to the other side of the locomotive would require either a simple linkage or a set of bevel gears and shaft across under the boiler.

I'm pretty sure that the bottom picture on page 56 shows a casing which lowers the drive down to a line below the boiler.
The corresponding picture at the top of page 56 shows the casing raising the drive up to the reversing spindle on the left side of the engine.
To me that picture shows a plain flat rod and a bell-crank arrangement rather than bevel gears.

Alan

[Seagull]

Just had a look at the Ian Allan Locomotives illustrated 49 - The Robinson GCR 4-6-0s

There are only three pictures of Caprotti fitted engines and all three are poor for detail so no help there!

Alan

[Seagull]

Found something a little more useful in the Geoffrey Huges book LNER 4-6-0s At Work.

Page 50 the top picture shows a 3/4 front view of 6166.

I have taken a closeup of the photo in the book - acknowledgements to the original authors

The reversing rod runs into a casing which fairly obviously contains gearing.
Out of the forward side one shaft runs to the right hand cylinder valve gear box.
Beside/below that another shaft comes out with a crank arm on it.
It is not clear exactly what is attached, but the arm is the mirror image of the one on the left side of the loco adjacent to the lefthand gear box.

I'm 95% sure that there is a simple flat connecting rod running under the boiler from one side to the other.

I believe this arrangement may only apply to the first two conversions though.
So far I have not found anything to show what they did on the second two.

Alan