CSB Fulcrums

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Le Corbusier
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CSB Fulcrums

Postby Le Corbusier » Sat Dec 01, 2018 7:17 am

I thought I would pick up this discussion here as it is separate to the Crab discussion on Julian's thread

Will L wrote:
Le Corbusier wrote:.. I can't help feeling that there must be a way to mount the bogie itself so that it is sprung off the main CSB? ....Hopefully in such a way that it can be calculated as a simple 0-6-0 with the percentage of weight allocated to the Bogie truck via the spread sheet in line with the loading requirement? Presumably the bogie itself could then be simply compensated as the loco would be isolated from the compensation by the CSB? Couldn't what I think you are calling the rubbing plate (still not fully up to speed on the nomenclature to make deciphering the more abstruse threads fruitful :? ) ride on a version of hornblocks attached to the CSB in a similar manner to the drivers?


This sort of idea makes logical sense, I may even have suggested something similar myself see here However I have yet to see it done. By the by, that post also covers a CSB version of the fake front bogie used by the Bachmann Baldwin

I have a concern by the fact that that the effective height from the rail head to the CSB fulcrum needs to be the same for the bogie to rubbing plate assembly as for the driving wheel axle bearing block assembly. Basic CSB are amenable to kitchen table modelling techniques and accuracies but do rely on all the wheels and axle blocks being the same size, as a difference of only one or two tenths of a millimetre in rail head to fulcrum height would be significant in terms of the CSB calculations. Achieving this degree of accuracy for the bogie assembly seems to be to be altogether more tricky. For this reason I have tended not to suggest supporting bogies on the main CSB but went in steed for methods that rely on something you can measure accurately enough, i.e that the running plate is parallel with the track. See the very next post to the one referred to above or here which extends the whole idea to locos with more than 2 driving axles.


Will L wrote:"Le Corbusier" PMed me querying me exactly what I meant by
Will L wrote:... I have a concern by the fact that that the effective height from the rail head to the CSB fulcrum needs to be the same for the bogie to rubbing plate assembly as for the driving wheel axle bearing block assembly. ...
and asked for a diagram. I hope this one will elucidate
CSB C12 draw opt 1 hight.jpg

The diagram as drawn seems to suggest that all the attachment points of the wheels to the CSB should be at an identical height above the rail height? ... Maybe I am getting confused about this?

Anyway here goes ...If there is no weight acting on the CSB then surely this height will relate directly to the heights of the anchor points in the frames ...and the deflection which you have drawn relates to the spread sheet calculations ...... dependent upon the C of G and the relative positions of the anchor points?

If this is the case, then surely so long as the height from the wheel tread at the contact point with the rail to csb attachment point is the same for both the drivers and bogie truck, then what you have drawn will have been achieved? ...and the spread sheet will do the rest as far as deflections and relative weight distribution is concerned? If this is the case and I haven't misunderstood, then it seems to me that so long as there is a built in method of adjustment on the the bogie (which can be locked off permanently once set) you can initially set up the chassis 'rigidly'* and unloaded allowing it to be adjusted to horizontal relative to the track?

By rigid I mean with a stiff wire substituted for the csb so that there is no deflection when just the chassis is involved. This should allow the bogie to be adjusted so that everything lies level to the track. Then the correct CSB and body weight can be added and the loco will function as an 0-6-0 ?
Last edited by Le Corbusier on Sat Dec 01, 2018 10:49 pm, edited 1 time in total.
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Will L
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Re: CSB Fulcrums

Postby Will L » Sat Dec 01, 2018 7:40 pm

Le Corbusier wrote:...If there is no weight acting on the CSB then surely this height will relate directly to the heights of the anchor points in the frames ...and the deflection which you have drawn relates to the spread sheet calculations ...... dependent upon the C of G and the relative positions of the anchor points?
Correct
If this is the case, then surely so long as the height from the wheel tread at the contact point with the rail to csb attachment point is the same for both the drivers and bogie truck, then what you have drawn will have been achieved? ...and the spread sheet will do the rest as far as deflections and relative weight distribution is concerned?
Correct
If this is the case and I haven't misunderstood, then it seems to me that so long as there is a built in method of adjustment on the the bogie (which can be locked off permanently once set) you can initially set up the chassis 'rigidly'* and unloaded allowing it to be adjusted to horizontal relative to the track?

Its a reasonable approach.
By rigid I mean with a stiff substituted for the csb so that there is no deflection when just the chassis is involved. This should allow the bogie to be adjusted so that everything lies level to the track. Then the correct CSB and body weight can be added and the loco will function as an 0-6-0 ?

I always build my CSB with the thickest wire I can get in so that, given the bare chassis is very light you get little or no deflection and so you can check that you have actulay managed to build the chassis flat and square and you are not requiring the suspension to make up for any defect in the build. The chassis is then expected to run reliably in this form on a track which is flat and level

My concern with doing what you suggest if that constructing the bogies, its rubbing plate and what ever constrains it so it can only move up and down and the suspension from the wires, can be done so the height is achieved accurtaly enough. This being a critical dimension if the CSB is to distribute weight as designed. In the end I reckoned it was easier to separate the bogies from the CSB wire as documented here.

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Le Corbusier
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Re: CSB Fulcrums

Postby Le Corbusier » Sat Dec 01, 2018 8:23 pm

Will L wrote:My concern with doing what you suggest is that of constructing the bogies, its rubbing plate and what ever constrains it so it can only move up and down and the suspension from the wires, can be done so the height is achieved accurately enough. This being a critical dimension if the CSB is to distribute weight as designed. In the end I reckoned it was easier to separate the bogies from the CSB wire as documented here.


Will,

I have read your solution carefully and it self-evidently works well .... ingenious.

However, I am still keen to pursue this thought experiment a little further ... so returning to the 0-6-0 problem ....

I am assuming that it is the horn blocks which ensure the vertical movement you are describing as far as the driven axles are concerned? The axles themselves have the ability to pivot giving independent springing action to each wheel?

Presumably therefore, so long as the method of attaching the bogie carrier to the CSB on either side is similarly constrained then this will also work?

I would look to separate this constrained attachment from any method of height adjustment.

Presumably, so long as the bogie can then be adjusted to ensure that the chassis sits level - perhaps using the stiff set up wires in the CSB anchors which could be left extended a few mm beyond the ends of the frames to get an accurate measure to the rail head - we should be in business? I assume a vernier calliper measurement of this would suffice?

I am trying to make sure I understand the principles (the theory), so I can then see if I can come up with a suitable design ;) before most likely failing :( and then copying your solution :D

Nothing ventured nothing gained as they say :thumb
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Will L
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Re: CSB Fulcrums

Postby Will L » Sat Dec 01, 2018 10:08 pm

Le Corbusier wrote:...I am assuming that it is the horn blocks which ensure the vertical movement you are describing as far as the driven axles are concerned? The axles themselves have the ability to pivot giving independent springing action to each wheel?
In theory, though quite how independent opposite ends of a 1/8 axle can be is an interesting question
Presumably therefore, so long as the method of attaching the bogie carrier to the CSB on either side is similarly constrained then this will also work?
Yes I think so. I have had this discussion with at least one other modeller as to workable ways of doing it and I look forward to somebody showing a workable solution
---Presumably, so long as the bogie can then be adjusted to ensure that the chassis sits level -

On most (but not all) locos the foot plate is supposed to be level. Put a 300mm rule alone it and you can measure the two ends are the same distance from the rail head well enough with a six inch steel rule.
I am trying to make sure I understand the principles (the theory), so I can then see if I can come up with a suitable design ;) before most likely failing :( and then copying your solution :D

Nothing ventured nothing gained as they say :thumb

Absolutely correct, get to it and have fun,

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Le Corbusier
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Re: CSB Fulcrums

Postby Le Corbusier » Sun Dec 02, 2018 10:07 am

Will L wrote: ...... get to it and have fun,


Sounds like Mr Darcy talking to Bingley in The 1990s Pride an Prejudice :D
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Re: CSB Fulcrums

Postby billbedford » Sun Dec 02, 2018 10:59 am

It's always amusing to watch people overthinking stuff and making things more complicated than they need to be.
Bogies on steam locos had only one freedom of motion relative to the frames and that was rotation about the central pivot. Track unevenness was allowed for by either having sprung axleboxes or, more commonly, having a sprung compensation beam between the axleboxes.
Occam's razor would suggest that the most beneficial way of springing a loco with a bogie would be to follow the prototype and not attempt to introduce springing between the bogie and frame. For a four-coupled loco, this also has the advantage of more or less ensuring that the driving axles take equal weights.
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Guy Rixon
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Re: CSB Fulcrums

Postby Guy Rixon » Sun Dec 02, 2018 11:24 am

So, on a full-size, locomotive, with the front-end weight resting on the bearing pads of the bogie, how does one tune the weight balance between bogie and coupled wheels?

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Re: CSB Fulcrums

Postby billbedford » Sun Dec 02, 2018 11:34 am

Using the same method used for adjusting the weights on the drivers, ie by adjusting the lengths of the spring shackles.
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Le Corbusier
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Re: CSB Fulcrums

Postby Le Corbusier » Sun Dec 02, 2018 1:34 pm

billbedford wrote:It's always amusing to watch people overthinking stuff and making things more complicated than they need to be.


:shock: ouch! :D
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Le Corbusier
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Re: CSB Fulcrums

Postby Le Corbusier » Sun Dec 02, 2018 1:39 pm

Guy Rixon wrote:So, on a full-size, locomotive, with the front-end weight resting on the bearing pads of the bogie, how does one tune the weight balance between bogie and coupled wheels?

Hoping that ... if I can make it work (big if ;) ) .... the weight tuning and ride level will all be taken care of by the spread sheet. It would be fun to see if the distribution could be made to match the real thing. However ... whatever the complexity of the 'over thinking' ;) it will need to be a simple build otherwise forget it. :thumb
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Will L
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Re: CSB Fulcrums

Postby Will L » Sun Dec 02, 2018 6:57 pm

billbedford wrote:...For a four-coupled loco, this also has the advantage of more or less ensuring that the driving axles take equal weights.


Yes but only if and when the loco is sitting level.

I do agree that we are most unlikely to have any greater need for secondary springing on a bogie than the prototype and the simple solutions are always the best. Two things though

1. Yes I have recommended a bogie design which effectively looks like it does have secondary springing. However this is to do with finding the simplest way to provide electrical pick up from the bogie than to provide any form of functional suspension and may well run with the springs fully compressed.
2. A CSB on the driving wheel definitely isn't secondary suspension so should we consider it secondary if we also use it to support the bogie.

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Re: CSB Fulcrums

Postby billbedford » Sun Dec 02, 2018 8:46 pm

Primary suspensions link the axleboxes to the frames, secondary suspensions link sub-frame, eg bogies, to the main frames.
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