brake pull rods on North British 0-4-0 shunter

nigelcliffe
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brake pull rods on North British 0-4-0 shunter

Postby nigelcliffe » Thu Jul 30, 2020 8:02 am

I'm putting together a North British 0-4-0 shunter, BR 11706. I'm having trouble working out how the brake rods should be arranged.

I can see the brake cylinder (behind RH front step), and a cross shaft at the front. The brake shoes and hangers mean the shoes move in opposite directions to apply the brakes. So, how do various rods connect the cross shaft at the front to the brakes ?

Does anyone have a diagram ? Or experience crawling under similar locos ?


- Nigel

Daddyman
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Re: brake pull rods on North British 0-4-0 shunter

Postby Daddyman » Thu Jul 30, 2020 4:52 pm

Can anything been worked out from these?

P1370128.JPG


P1370138.JPG


P1370126.JPG

nigelcliffe
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Re: brake pull rods on North British 0-4-0 shunter

Postby nigelcliffe » Thu Jul 30, 2020 5:06 pm

Daddyman wrote:Can anything been worked out from these?


Unfortunately, that's the wrong loco.

D11700-11707 are different to the later NB locos, specifically the brakes which are between the wheels on the earlier locos. One brake shoe moves forwards the other backwards when apply braking forces.


- Nigel

bécasse
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Re: brake pull rods on North British 0-4-0 shunter

Postby bécasse » Thu Jul 30, 2020 7:22 pm

This sort of loco:
NB0-4-0BRDieselShunter.jpg
NB0-4-0BRDieselShunter.jpg (353.32 KiB) Viewed 488 times

Apart from the rod going back from a crank under the brake cylinder at the front of the loco which you already mention, I can't find any photos which show details of the operating mechanism but that seems to be because it is hidden between the frames. There is probably a T-shaped crank which forces the blocks on to the wheels when the brake cylinder operates, and quite possibly a spring which causes the brake blocks to "relax" when the brakes are released, but, as I said, all hidden.
I am sure that I have seen a similar arrangement on an industrial steam engine but have been unable to find a reference.

Daddyman
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Re: brake pull rods on North British 0-4-0 shunter

Postby Daddyman » Thu Jul 30, 2020 7:25 pm

nigelcliffe wrote:
Daddyman wrote:Can anything been worked out from these?


Unfortunately, that's the wrong loco.

D11700-11707 are different to the later NB locos, specifically the brakes which are between the wheels on the earlier locos. One brake shoe moves forwards the other backwards when apply braking forces.


- Nigel


Ooops! Sorry!

nigelcliffe
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Re: brake pull rods on North British 0-4-0 shunter

Postby nigelcliffe » Fri Jul 31, 2020 10:19 am

bécasse wrote:This sort of loco:
…..


Yes, one of those. Specifically the next one in the build sequence (11706), but they're going to be the same on this detail.
I know there is an industrial version at the Bo'ness museum, but that's shut at present.

I agree the brake linkages are likely to be similar to steam locos carrying the same brake arrangement.

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Noel
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Re: brake pull rods on North British 0-4-0 shunter

Postby Noel » Fri Jul 31, 2020 10:39 am

I've been looking at the drawings in Modern Locomotives Illustrated 195; they are basically weight diagrams, with some extra detail. How reliable it is, I don't know, but it appears to show a direct link from the crank to the bottom of the front brake hanger, plus a rigid link between the top of the brake hangers. The implication seems to be that as the brakes are applied the front shoe makes contact with the wheel, and the brake hanger then pivots on the shoe attachment point, and the link at the top pushes the top of the rear hanger back applying the rear wheel shoe. The net result would be equalisation of the brake force between the wheels.

The rear hanger would have to have a fixed pivot at the bottom, with the shoe again free to pivot on its attachment to the hanger. The drawing for the earlier version is different, but that for 11703-7 has a dotted oval around the top of the hangers, longer than the distance between the hangers, so possibly a slot in the frames to allow connections across the loco? The rigid link at the top of the hangers is partly obscured by the under-footplate tank but is partially visible in photographs.

Quite a bit of guesswork on inadequate data, but I hope it helps.
Regards
Noel

nigelcliffe
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Re: brake pull rods on North British 0-4-0 shunter

Postby nigelcliffe » Fri Jul 31, 2020 11:38 am

Noel wrote:I've been looking at the drawings in Modern Locomotives Illustrated 195; …..
Quite a bit of guesswork on inadequate data, but I hope it helps.


Thanks Noel, yes, piecing that lot together I can see how it might work. Its not sophisticated, but not expecting sophisticated on a low-speed shunting loco of the period. Photos with those tanks obscuring the links do make it hard to determine what's going on.

Just got to work out how the cab brake lever relates to all that as well !

I can feel a Meccano simulation is needed. Or a CAD simulation, but the CAD would take me longer to do.

- Nigel

bécasse
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Re: brake pull rods on North British 0-4-0 shunter

Postby bécasse » Fri Jul 31, 2020 12:30 pm

If you look at various photos of members of the class (although they are rare on the web), it seems that the brake hangers and blocks are at differing different heights relative to rail level. I suspect that the top "lozenge" is in fact a floating (but fixed length) link pinned to each of the two hangers at that point and that the rear hanger is then fixed relative to the frames at the bottom. For both brakes the blocks rotate about a central pin in their respective hangers (as normal).
This arrangement wouldn't need a spring. When the brakes are applied the rod pulls the front brakes on from the base, causing the top of the hanger to move to the back, which in turn causes the top of the rear brake hanger to move back in turn applying that brake. Crude but workable - and easy to maintain.
The in-service braking would be via a hydraulic (and probably vertically mounted) cylinder behind the front buffer beam, so just a handle in the cab. There must have been a hand (parking) brake in the cab as well, probably linked to a rearward extension of the operating rod by a slotted connection so that the hydraulic brake could be operated even with the hand-brake off, but that the hand-brake would override the hydraulic one at any time for parking.

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Noel
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Re: brake pull rods on North British 0-4-0 shunter

Postby Noel » Fri Jul 31, 2020 2:05 pm

bécasse wrote:The in-service braking would be via a hydraulic (and probably vertically mounted) cylinder behind the front buffer beam, so just a handle in the cab


This class, like, I think, all BR diesels, had automatic air brakes, with air pressure maintained by compressor; opening the brake valve released air from the system and applied the brake [i.e.failsafe]. The operating cylinder is behind the front bufferbeam, RHS looking forward, outside the frames [unusually]. The early batch had no train brake, the later one had a vacuum exhauster, and hence a train brake as well as the loco brake.
Regards
Noel

nigelcliffe
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Re: brake pull rods on North British 0-4-0 shunter

Postby nigelcliffe » Fri Jul 31, 2020 3:24 pm

I'm following all this so far. Just one more detail - the front linkage from the cross-rod...

The cylinder is fine (RHS behind step), which has a lever to the cross-rod. Then what ? I'm guessing a lever in the centre of the rod, to a pull rod running along the centre line, splitting into a Y-shape, the two ends of the Y's connecting to the rigid link which goes between the bottom of the front brake arms. That would be simple, and have a single point of adjustment. Whereas any twin-rod arrangement has two points of adjustment and much more complicated to keep aligned correctly. Thoughts on this ?

Yes, no train brakes on the version I'm building - late 1950's 11706, pre-"D" numbering. Some of the 11703-7 batch had train brakes retro-fitted in the 1960's in green livery: at least one photo I've found with an example with green livery and wasp-stripe ends shows train brakes added.

- Nigel

bécasse
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Re: brake pull rods on North British 0-4-0 shunter

Postby bécasse » Fri Jul 31, 2020 7:35 pm

Mike Edge (in the name of his wife Judith) does a kit for the earlier three 11700-2 which had the same brake arrangement. He is usually very knowledgeable in respect of the prototypes of his kits, so have you tried asking him?

nigelcliffe
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Re: brake pull rods on North British 0-4-0 shunter

Postby nigelcliffe » Fri Jul 31, 2020 8:05 pm

bécasse wrote:Mike Edge (in the name of his wife Judith) does a kit for the earlier three 11700-2 which had the same brake arrangement. He is usually very knowledgeable in respect of the prototypes of his kits, so have you tried asking him?


Yes, in part because I'm building one of his kits for 11706 (a different kit to that for 11700-2). He isn't sure, though has said if he finds the drawing he thinks he has, he'll let me know what is found.
There is a preserved industrial version at the Bo'ness museum. But that's shut at present.

- Nigel

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Noel
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Re: brake pull rods on North British 0-4-0 shunter

Postby Noel » Sat Aug 01, 2020 10:09 am

nigelcliffe wrote:The cylinder is fine (RHS behind step), which has a lever to the cross-rod. Then what ? I'm guessing a lever in the centre of the rod, to a pull rod running along the centre line, splitting into a Y-shape, the two ends of the Y's connecting to the rigid link which goes between the bottom of the front brake arms. That would be simple, and have a single point of adjustment. Whereas any twin-rod arrangement has two points of adjustment and much more complicated to keep aligned correctly. Thoughts on this ?


Photographs show that the lower part of the crank on the cylinder side is replicated on the non-cylinder side, together with the pull rod behind the front wheel, so the central arrangement you propose seems to be ruled out.

As well as the 6 cylinder diesel engine under the bonnet, plus its auxiliaries, there was a hydraulic transmission, including a torque converter, plus a set of bevel gears, a set of reduction gears, and a reversing dog clutch [according to contemporary Ian Allan ABCs] to fit in between the engine and the cross shaft for the jackshaft drive. I suspect that there wasn't a lot of spare room between the frames.
Regards
Noel

nigelcliffe
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Re: brake pull rods on North British 0-4-0 shunter

Postby nigelcliffe » Sun Aug 02, 2020 3:43 pm

Ignoring the centre-pull idea, where I was incoorect, this photo seems to confirm the linkage arrangement discussed in the thread.

https://transportsofdelight.smugmug.com ... /i-763vLLx

Zooming well in, I think the upper linkage is visible, and there is a substantial strengthening bracket at the bottom pivot of the rear brake arm. That strength would be needed to take the brake forces from both shoes and not twist against the frames.

I think I'm near enough for 4mm model making purposes now.


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