Advice re 1/8" bearings and coupling hook springs

[davebradwell]

Actually in the original context of the phrase, it's the fire and combustion that were usually referred to but it can be conveniently stretched to cover anything inconvenient like behaviour of pendulums or things that act like them.

DaveB

[Noel]

I think the prime purpose was to prevent poor driving technique causing damage to wagons (i.e. pull the headstock off)

From the grouping RCH regulations required continuous drawgear on new 4 wheel wagons, so that the pull was applied to the trailing buffer plank, which does support that suggestion. However, the link was not actually continuous, being by means of a central cradle containing a spring which was compressed when a pull was applied to either drawbar, presumably to reduce shock?

[Noel]

It's weight you can't scale not mass. That is to say you can't scale time within the context of what we do i.e. a dimensionally scaled model railway.

You can scale weight in a constant gravity field, as the force applied by gravity varies directly with variations in mass. Cut a piece of paper in half, and the two pieces will each weigh half the weight of the original, and that relationship is as true on the moon as here, although the force applied by gravity is different, so that the actual weights are less. The problems mostly arise because dimensions scale linearly, and mass by cubic measure, so that a homogeneous cube 2 x 2 x 2 is 8 times heavier than one of the same material 1 x 1 x 1 [linear scale 2:1], and one 76 x 76 x 76 [linear scale 76:1] is 438,976 times heavier.

[Will L]

...Unfortunately by only scaling dimensions you distort the dynamic response of the system...

Are... back to the scale time discussion. If you can scale time (and I'm not convinced) then all sorts of other things, like apparent speed, become distorted. You can't win.

If smooth operation is a primary aim, and as you can't prevent un-prototypical movements due to the none scalability of Mass (or Time) all you can do is try an eliminate their causes#. So not springing your coupling hooks and applying springing to you suspensions are among the best ways of doing that.

[Will L]

It's weight you can't scale not mass. That is to say you can't scale time within the context of what we do i.e. a dimensionally scaled model railway.

You can scale weight in a constant gravity field...

But if you scaled weight (ok Mass) by 1:72 the liner dimensions to achieve that would be nothing like the 1:72 of the original. You can't win.

[Tony Wilkins]

As Justin comments I think the prime purpose was to prevent poor driving technique causing damage to wagons (i.e. pull the headstock off) and the relative strengths of our stock makes this generally superfluous, except when using white metal coupling hocks apparently.

Will's comment reminds me of an incident that happened long ago with Heckmondwike. During one of our running sessions, a coal train departed from the fiddle yard accompanied by an unusual noise. When we went to investigate, we discovered that the entire end of a Slaters coal wagon had parted company with the rest of the wagon and was bumping along the track.
Regards
Tony.

[billb]

Ted,I think you know I would certainly agree with the general sentiment/approach you suggest, but as Justin comments I think the prime purpose was to prevent poor driving technique causing damage to wagons (i.e. pull the headstock off) and the relative strengths of our stock makes this generally superfluous, except when using white metal coupling hocks apparently.

Well, sort of. Someone in the late nineteenth century invented continuous drawbars which moved all the tractive force on the wagon to the trailing end of the wagon and made detached headstocks a thing of the past. The LMS society has just uploaded some RCH drawings. Drawing 18A is of the buffers and drawgear and gives the parameters for the drawgear spring:

7 3/8" free
7 1/16" fitted 2 tons on
5 1/2" on stop, 12 tons on

Therefore there was 1 9/16" possible deflection in these springs per wagon. That's just over 0.5mm in 4mm scale.

To put these loads into context, the tractive effort, ie the maximum force at starting, for a 4F was about 10.25 tons.

[zebedeesknees]

. Someone in the late nineteenth century invented continuous drawbars which moved all the tractive force on the wagon to the trailing end of the wagon and made detached headstocks a thing of the past.

Like this:-

Couplng1999_1214_192338AA.JPG

Made up like this:-

Couplng1999_1214_192646AA.JPG

Since 1999...

Ted.

[Will L]

Ted,I think you know I would certainly agree with the general sentiment/approach you suggest, but as Justin comments I think the prime purpose was to prevent poor driving technique causing damage to wagons (i.e. pull the headstock off) and the relative strengths of our stock makes this generally superfluous, except when using white metal coupling hocks apparently.

Well, sort of. Someone in the late nineteenth century invented continuous drawbars which moved all the tractive force on the wagon to the trailing end of the wagon and made detached headstocks a thing of the past. ...

I am well aware that for many wagons the draw gear was arranged as you described. I've even built a few wagons that implemented it. However the point I was trying to make was, given that the forces which cause the prototype to install such springs are not significant at our scale, the decision whether to model them functional or otherwise, becomes more one of modelling philosophy (because its there) than actual function.

[Tim V]

In my experience, and when I was running 30 wagon trains, sprung buffers/couplings were a waste of time.

Too many times I saw sprung buffers that were stuck in. Very unprototypical.

I wanted reliability.

KISS principles or RAM-D was used.