4 hours ago, magmouse said:

I have used just the etched ratchet part and made the rest from NS strip, but you method correctly represents the twist where they meet - very nice.

I did get some of those from Ambis and they are very nice but, as you say, rather delicate and not up to the twist necessary to turn the rack perpendicular to the vehicle side.  I didn't think I could make one - until I tried! Amusingly, it works a bit like a safety pin once the extended bit is cut to length, it can be pinged into a slot in the little stub that holds the lever when parked 'off'. Referring to photos of the real thing, it looks pretty chunky so I thought I could get away with a reasonably heavy material - 0.4mm n/s. Thanks for your kind comment (and for pointing out the anomaly in the initial post: I'm not sure what happened there so I deleted the post and re-did it).

4 hours ago, Dave John said:

I think the brake gear was worth the effort with so much being visible around the wheels. 

It was an effort! - I wondered what I'd got myself into but, on the other hand, I couldn't quite see what I could leave out to simplify things!  It became an exploration of the Dean outside link brake which is a bit counter-intuitive in its operation as, on first inspection, it looks as if it couldn't possibly work.  Musing on this a while ago, I realised that it works just like an old nutcracker we have which has an "outside link" and cracks nuts very nicely (I included a picture in an earlier post). Once you've seen it, you can't see how it wasn't obvious in the first place: it's a clever piece of engineering and I think unique to the GWR.  There were clearly developments in the design either as retro fit or perhaps just on newer vehicles but I think the equipment on the model is a reasonable guess at its date of building. To quote from Monty Python "...and now for something completely different" - perhaps some further building devlopment on the layout.

Wonderful model, that brake gear looks terribly complex.  I also like to model the brake gear and other details of the nether regions of wagons and coaches.  It does take quite a lot of research but is hugely satisfying when done.  For myself, I am very grateful to RMweb members who provided me with much valued information.

John

3 hours ago, brossard said:

I am very grateful to RMweb members who provided me with much valued information.

Thanks brossard - yes complex, and yes, RMweb is an amazing rescource (and full marks to those who restored pictures after the great disappearance).  In this instance - the Dean era brakes - it was Western Thunder which helped as well. My last post on RMweb about No 88 produced some comments and more photos of 'boxes which sent me off in several very useful direcitons:  the comments are always welcome!

14 hours ago, Compound2632 said:

Early Clayton Midland carriages have a similar arrangement

Thanks Stephen and for comment about early Clayton carriages (and presumably NPCS). I'd be interested to see what Clayton produced - I did look for other companies' similar dated braking apparatus and there are plenty of diagrams for the general arrangement but with underframes represented by wheels and not much else - no detaill of brakes (mea culpa - most of my library is GWR so I was relying on the web!). 

It looks like the closest relative in the bicycle world is the 'cantilever brake' with a right angled crank arm each side of the wheel. The "outside link" is provided by the wheel forks. It's an interesting comparison because the brake works across the wheel, not on the circumference, and therefore the blocks tends to rise on the coned rim where Dean's outer brake shoe would tend to move outwards, reducing its efficiency.  The coach at Diccot that I referred to above appears (from one photo) to have a bar linking opposite brake shoes on the outer ends of the vehicle which I assume is to counter that tendency.  The inner brake shoes are held more firmly in place because their lever arms are anchored to the stub pillars which are themselves linked together. 

Another interesting thing I noticed with the Dean system on a 6 wheel coach is that the very long pull rods running from the central brake cross shaft to at least as far as the buffer beam show self weight deflection: I haven't seen that with with the shorter pull rods offered by the later system of triangular yokes/tumblers and a single pull rod.

4 hours ago, Mikkel said:

And thanks for explaining how the brake works in detail. I have been wondering about it when running my 4mm one.

Mikkel, thanks.  I hope I've got it right!