Loco bogies

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zebedeesknees
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Loco bogies

Postby zebedeesknees » Mon Aug 03, 2020 3:38 pm

Interesting article in the August BR Ill by Allan C. Baker on the history of the 'bogies used on Stanier's LMS engines', including drawings, pictures and explanations. The primary compensation principle is one well known, but the lateral spring control was an education - to me at least.

Now that Mitchell Castle bogie...

Ted.
(A purists' purist)

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johndarch
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Re: Loco bogies

Postby johndarch » Mon Aug 03, 2020 7:19 pm

If it's any help, this is what I did with my MM Castle bogie.
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zebedeesknees
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Re: Loco bogies

Postby zebedeesknees » Tue Aug 04, 2020 2:59 pm

Thanks John, that answers a few of my questions about where things go. That drawing in Brill is very helpful too, but there are still some things I am wondering about. No doubt they will be answered when Nick continues the build, P.C... (Post Covid). I would like to complete the bogie as close to the prototype as possible, not sure how tight a curve it will need to negotiate!

Meantime, some shots of the LRM 'Spinner' bogie I modified some time ago.
Bogie dismantled2.jpg
Handrail knobs in the equalisation, or compensation beams as written in the Brill article. Ball race bearings as I figured that with a single driver I needed all the help I could get to minimise friction.


Bogie frame.jpg
Bogie frame the right way up, the handrail knob in the centre of the bogie frame is the fixed anchor and the pivot for the beam.


Bogie underside.jpg
The underneath showing the centering arrangement. Not obvious, but the pivot hole is a slot, allowing 1mm movement either side of centre. As near as I can scale from the drawing in Brill, the sideplay allowed is 3" each side, so that wouldn't be far out. This is the way we've always done it! But Stanier when he was at Swindon and later for the LMS used a design that he had learned from what we now call 'reverse engineering' the bogie in the De Glehn (mis-spelled in the article) compound atlantics, subsequently called the 'French bogie'. In this the pivot was circular, the sideplay taken up by a sliding channel against the chassis bolster with coil springs. The drawing really helps, but I'm not sure if copyright would allow me to include it here.


Chassis fixing.jpg



The big difference in the Stanier LMS bogie, used in the Princess, Duchess, and Royal Scot classes, and later in the Britannia, is that the weight is not borne by the bogie frames as you and I have done, but by the chassis bolster bearing directly onto the fixed anchor which is attached to the bolster rather than the bogie side frames.
Can it be modelled? Will it be worth it? As one of those who complicates for the sake of it, I'll give it a go. Y'all may never hear of it from me again!

Ted.
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(A purists' purist)

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PeteT
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Re: Loco bogies

Postby PeteT » Tue Aug 04, 2020 6:53 pm

That looks brilliant. I'm probably over thinking this, but does the spring only having 1 handrail knob on the main frame not potentially allow the sprung sideframes to try and twist laterally, especially which entering curves? Or is the idea that there isn't much sideplay allowed, and so it all has to sit where it should?

Dave Holt
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Re: Loco bogies

Postby Dave Holt » Tue Aug 04, 2020 7:11 pm

The compensated bogies under my Stanier and BR Standards, transmit the load direct from the external equalising beams to the loco compensation system. As with the real thing, the bogie frames carry no weight and simply keep the axles in the right place and allow pivoting and side movement. Very light subsidiary springs, bearing on top of the axles, hold the bogie frame up against the side bearing pads.
My latest Brassmasters Black 5 uses coil springs between the external compensating beams and the bearing plate on the loco mainframes so, again, the bogie frames carry no weight.
So, yes it can be modelled.
I'm fairly sure I've posted photos and sketches of these arrangements on here at some time or other.
Best of luck with yours.
Dave.

davebradwell
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Re: Loco bogies

Postby davebradwell » Tue Aug 04, 2020 7:29 pm

Just to add my experience that putting a spring each side, as in your Spinner bogie, Ted, is a far better arrangement than the single centre spring used in the Castle bogie which we find prone to derailment at speed.

Your arrangement of the spring within the equalising beams follows the spirit of the prototype and had you soldered a plate across the top and put your centre handrail knob vertically into it you would have reached your Nirvana and avoided the dreaded twisting moment on the frames which means nothing to us but represented the success of the GW/Stanier layout. Thompson borrowed this feature for his development of the Gresley bogie which is a much easier type to represent correctly.

As I understand the drgs in the Wild Swan Black 5 books, the stretcher that bears on the springs is fixed to the bogie frames and so supports them. If there was no connection here there would be nothing to support the frames and they would just rattle up and down with the tops of the horn cutouts resting on the axleboxes - clearly not desirable and not how they are drawn. Surely there is no vertical movement between the bogie and loco frames. There certainly isn't on the Thompson version.

DaveB

Dave Holt
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Re: Loco bogies

Postby Dave Holt » Wed Aug 05, 2020 9:28 am

DaveB, you're absolutely right.
On Stanier and BR Std bogies, the inverted leaf spring buckle bears on the underside of the bogie top stretcher casting. This, in turn, bears against the underside of the loco main frames, via a pair of cup and hemispherical bearing pads. As you say, the springs hold the bogie frame firmly in contact with the loco frames. The spherical bearing cups do permit the bogie frame to pitch in the fore/aft plane.
Excellent as the bogie design was, it did throw up various problems which resulted in trials of various friction materials between the bearing pads and the bogie stretcher casting, both with and without lubrication. Side control pre-load was also an issue and the whole thing was quite sensitive to differential wear of the wheels between bogie and locomotive, which caused weight transfer problems.
Thank goodness our models are not so sensitive, once set up properly.
Dave.

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zebedeesknees
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Re: Loco bogies

Postby zebedeesknees » Wed Aug 05, 2020 1:27 pm

PeteT wrote:That looks brilliant. I'm probably over thinking this, but does the spring only having 1 handrail knob on the main frame not potentially allow the sprung sideframes to try and twist laterally, especially which entering curves? Or is the idea that there isn't much sideplay allowed, and so it all has to sit where it should?


Thanks Pete, if I understand what you mean by twist laterally, then potentially yes.. but. Notice that the axles are sleeved with tube, and the spacers between the wheels and the bearings are of the same. There is minimal sideplay on each axle relative to the beam, just enough to allow sufficient roll freedom of each axle with the inner race of the bearing.

The arrangement of the ball heads, the outer spring anchors on the beams, coincides with the space taken by the fixed anchor on the frames, so each beam can rotate about the fixed anchor in the yaw plane only by the clearance needed for the beams to move freely in the vertical. Note they are in line with the axle centres, so the effect is the same as if the wheelsets were guiding the bogie as in usual frame mounted bearings.

Ted.
(A purists' purist)


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