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On the start line

Posted by Kenton , 14 October 2009 · 458 views

kitbuilding suspension
Instructions read and re-read, yet I cannot get over the fact that they remain incomplete as a whole, making too many assumptions of the kitbuilder's knowledge of the prototype, kit locomotives and building this type of kit. A good description of the process in text referring to numbered parts in a list and on the fret does not give the builder any real idea where a part happens to be used on the prototype or on the model. Not all parts are clearly identifiable as a locomotive part. The drawings are detailed but suffer from reproduction on paper and at being to scale. This is where a larger diagram with annotated parts would help immensely, even more so if it was an exploded view. For example, it is quite difficult to identify which parts have rivet requirements.

Nevertheless, the instructions are of a much better standard that some I have seen, often having no parts list and obscure, unnumbered parts on the fret.

In terms of possible problem areas for the kit builder I have identified:
1. This is an 0-4-0 with a coupled jackshaft, therefore must be treated as a 0-6-0. The instructions give clarification on how to proceed with this.
2. The suspension system description is vague to the point of not of any help.
3. There are many parts that require overlays - nothing wrong with that in design terms but they can present a problem for some.
4. There are a number of parts (e.g. bonnet, cab roof, ) that require bending. Sometimes more than once.
5. A few parts will present alignment difficulties (engine doors) as visually it can be very obvious if they are even slightly out of alignment/spacing.
6. There are quite a number of screws and nuts used in the construction - so alignment of these may present issues.

Other than that most of the parts look quite straightforward once you have figured out where and which way round they go.

So there is a big decision to be made before we make a start:

Suspension: (if any, and if so what type?)
This web article on the subject is very technical, written from a P4 perspective and not IMO that helpful with the basics, but is worth a read anyway.

I have to repeat here that the model is for OO and so will not in this case have to endure the rigours and tolerances of fine scale track. I would with most kits happily go ahead with a rigid chassis construction. But with an 0-4-0 this is generally frowned upon.
Firstly, the kit instructions on building the frames rigid are very clear and the axle bearings are among the parts supplied with the kit. But there are alternatives suggested.
The second option is the use of springing (hornblocks) is only just hinted at in the instructions with no more advice than the fact that the frames have "cut outs" half-etched on them. There is no advice given on fully independent, complete or single rigid single axle convention, or indeed on the impact that the rigid jackshaft would have on this arrangement. I should add, that I have attended a lecture given by Mike Edge and am aware of his opinions expressed there on springing. Which will inevitably influence his kit designs.
Thirdly there is the option for a type of beam compensation on the rear (non-driving) axle. The components to do this again are in the kit and are clearly the way this kit was intended to be built. However, we are back to the thorny issue of understanding how the parts go together and how it actually works.

So which is it to be ? ... perhaps a question for wider forum discussion

.





I have to agree on the instruction front as so often I think that both an A4 sheet clearly indicating whats what and an exploded diagram of the kit should be included as unless you have reference material available the orientation and placement of some components is a complete mystery.

What have you opted for in the way of suspension at this stage?

Darren.

What have you opted for in the way of suspension at this stage?

Still very much "suspended" :D

My normal approach to kitbuilding is to build as the kit maker intended - not generally wishing to add what wasn't designed in.

But I'll wait a day or so to gauge forum opinion
... now where is that option to add a forum poll ?

I'm fairly comfortable building it any way.
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Miss Prism
Oct 14 2009 13:40
This 0-4-0 with a coupled jackshaft should be treated, in suspension terms, as an 0-4-0. Not an 0-6-0. The only way it would have to be treated as an 0-6-0 is if the coupling rod and jackshaft rod are a single rigid item, which I hope they are not! If the coupling rod and jackshaft rod are a single rigid item, you will have little alternative to building it all with rigid axles.

This 0-4-0 with a coupled jackshaft should be treated, in suspension terms, as an 0-4-0. Not an 0-6-0. The only way it would have to be treated as an 0-6-0 is if the coupling rod and jackshaft rod are a single rigid item, which I hope they are not! If the coupling rod and jackshaft rod are a single rigid item, you will have little alternative to building it all with rigid axles.


From the way I am reading the instructions and observing the parts (so I may be wrong) :(

The jackshaft is a supplied as a separate turned 1/8" axle with 2.65mm steps at each end. The axle is mounted in its own fixed bearings in the frames and eventually the cranks (made up of layered etches) are a inference push fit on the steps. Their rods being connected to the wheel crank pins in the usual way (16BA screws and nuts). The jackshaft itself is therefore fixed in its own vertical and longitudinal axis but the rods enable some potential semi-vertical movement through the rods. The compensation design is such that the swinging arms of the compensation have large cut-outs to clear the jackshaft axle. These arms are designed to take bearings for the rear axle and the rear axle frame bearings are left out. In this way the compensation is provided by the swinging arms that are pivoted on a rod at the back of the frame (2 points) and on the "knife edge" (third point)

I hope that is a bit clearer :shrug:
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Miss Prism
Oct 14 2009 17:14
I've seen one of these Judith Edge chassis horrors on a friend's workbench, but it wasn't the same kit, so I don't know exactly what is going on from your description of your particular kit. To clarify:

1 Is the rod coupling the coupled axles and the jackshaft a single piece etch or not?

2 If it is a single piece etch, which hole in the rod allows the 'semi-vertical movement'?

3 Is the single-point ("knife edge") compensator on the front axle?

4 Is the kit intended to be driven on the rear wheel?

5 From which transverse axis on the chassis are the (I assume two) 'swinging arms' pivoted? (And why do they need large cut outs to clear the jackshaft axle?)
Miss Prism - thanks for your interest.

1 Is the rod coupling the coupled axles and the jackshaft a single piece etch or not?

constructed as separate overlays - will be mounted on same rear wheel crank pin.
Posted Image

3 Is the single-point ("knife edge") compensator on the front axle?

No, from what I can make out from the scale CAD drawing (with a strong magnifying glass) the "knife edge" rests on the frame spacer above the rear axle and a "pivot pin" presumably central to the "knife edge"/frame (but here a diagram would help the kitbuilder ;)

4 Is the kit intended to be driven on the rear wheel?

Sorry thought i had stated that it is front axle driven - though that is only deduced from the drawings - I have not yet decided on the gearbox/motor combination - but do not expect it will change that fact.

5 From which transverse axis on the chassis are the (I assume two) 'swinging arms' pivoted? (And why do they need large cut outs to clear the jackshaft axle?)

Correct two (made up of 2 overlays each to give bearing purchase) pivot on a bar across the back of the frames. if there were no cut outs to freely clear the jackshaft axle the would interfere with the axle.
Posted Image

The following image should give you the idea of the jackshaft cranks/weights (note - probably not the correct term) that are made up from 4 overlays each and are push fit on the stepped end of the jackshaft axle. (correct quartering will be needed)
Posted Image
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Miss Prism
Oct 14 2009 21:46
Glad to hear that the rods can articulate. That at least is a good start.

Notwithstanding the difficulty of understanding the drawing in the instructions, I wasn't sure of the precise constitution of the single point from your description, but would you agree that the principle of the suspension intended by the kit for the wheel axles is:

http://www.clag.org....41-0/fig34a.gif
Yes Miss Prism,
Having battered this one about in my head and on here, I think I agree with you - the principle is just that. Made more complicated somewhat by the way that the swing arms operate.

I hope I have not confused things by describing the jackshaft axles. They are most definitely NOT part of the suspension system they are in fixed bearings in the frame and are only connected to it by the rods articulated on the rear axle crankpin. The problem with the drawings is not so much understanding them as their total practical absence in terms of construction detail.

The beam in your diagram is in the kit as a flat "knife edge" and is not horizontal across the chassis but in the longitudinal plane. It is, however, fixed to the frames by being soldered on the underside of one of the frame spacers. The "pin point" in the description is left up to the kitbuilder to interpret and may mean the addition of an actual pin soldered to this "knife edge" to correspond to the actual longitudinal axis of the knife, thereby minimizing the contact area with the axle. But I would have thought that the knife could have been designed to the exact dimension (height) to be sufficient. We shall see, if I take the decision to follow this mode of suspension.

I probably will defer my decision until Monday as modelling time is restricted over the next few days.
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Miss Prism
Oct 15 2009 14:29

Having battered this one about in my head and on here, I think I agree with you - the principle is just that. Made more complicated somewhat by the way that the swing arms operate.

If the principle is just that, then what on earth is the intended function of those swing arms? Are they not superfluous, over-complicated, and a reflection of the strange mind of a designer who is uncomfortable in this whole area?

If the principle is just that, then what on earth is the intended function of those swing arms? Are they not superfluous, over-complicated, and a reflection of the strange mind of a designer who is uncomfortable in this whole area?


I think the intention is that you put the bearings in the swing arms, so that the axle passes through the larger hole in the frames and so is allowed limited movement. The swing arms then constrain this movement to the near vertical and prevent any forward/backward movement. Seems to be a way of avoiding hornblocks.

Nick
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Captain Kernow
Oct 22 2009 14:48
I built the Judith Edge North British/Paxman 0-4-0 a few years ago - this has a jackshaft as well, with articulated rods. I don't recall a swinging beam system being an option, but this might just be my memory. The loco was built to OO gauge and I decided just to take loads of care and build the chassis uncompensated or sprung but exactly square and ensure all wheels were on the track. It generally runs pretty well, provided the wheels and track are kept clean.

If I was building it now, however, or doing one in P4, I'd probably opt for the basic 3 point compensation system, with one fixed axle and the other gently pivoting with minimal vertical movement in the hornguides. If you want to install something more complex, then fine, but the simpler version suits my purposes at the moment.

I built the Judith Edge North British/Paxman 0-4-0 a few years ago - this has a jackshaft as well, with articulated rods.

Another very good choice ... and I must say I was/will be tempted ... but hardly S&DJR running :D ... in fact very difficult prototype with only 3 built. A much older kit though so probably the swing arm compensation is a new addition to these new NBL-MAN kits.

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