Crab Comet conversion

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Will L
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Re: Crab Comet conversion

Postby Will L » Mon Nov 26, 2018 10:59 am

Le Corbusier wrote:...For Clarification purposes .... could someone define the difference between a 'pony' and a bogie truck ... and where each is used on a locomotive? and why the difference? - both I assume are there primarily for weight distribution. :thumb


A pony truck has 1 axle and a bogie (normally) 2. The use of either was primarily and originally driven by the need to stay within a given weight per axle. So as locos got bigger they needed extra carrying axles to carry the additional weight and to avoid the complexity of additional coupled driving axles. To start with these extra carrying axle(s) were in the same rigid frame as the driver(s) but the limitation in flexibility of a long fixed wheel base lead to the development of radial trucks (mounted in the frames but with additional side play and which turned slightly as they slid side to side), pony trucks and bogies. Only when they had such things did they also develop a role in providing more stability on the resulting long locos with relatively short fixed wheelbases travelling at speed.

A bit of an over simplification but gives you the general idea. The differences in stability issues at speed beteewn our models and the real thing (resulting from implications of physics on scaled models), and the fact that we don't have the axle weight constraint leads to us being able to do things differently, depending on how much we are being driven by a wish to build exact scale models.

Julian Roberts wrote:... I think the problem is, as always, with our less than prototypical curves, and (I think) the necessity to make a loco be able to cope with track irregularities that are more challenging than the real thing. The real Crab minimum radius I'll bet is more than the 5 chains that is our 4ft - and many of us want sharper than that. I wanted to preserve the real clearance between pony and frame which is 1mm or less and I think that in order for it never to have any chance of fouling there needs to be some means of preventing the wheel rising any closer. ..a backstop!!! :o

Which is the point about modelling in P4 isn't it, as it reduces, but does not eliminate, the need for modelling compromises. If we model scale flanges and the carrying wheels cleared the frames on the original then we should be able to do it on the model. If they didn't then either you don't use small curves or you start making the compromises. I'm not sure arraging for for your loco to lift its front drivers will prove operationally satisfying,
Last edited by grovenor-2685 on Mon Nov 26, 2018 12:04 pm, edited 1 time in total.
Reason: Corrected first quote

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Will L
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Re: Crab Comet conversion

Postby Will L » Mon Nov 26, 2018 12:37 pm

Continued post household chores.

Of course once you had bogies in play, our American fiends discovered that the 4-4-0 configuration gave considerable advantages when trying to deal with less than perfect track as well as allowing a much larger boiler to be mounted over two coupled axles which provided quite sufficient pulling power. The resulting huge overhang cannot adequately be modelled without taking some weight on the bogie. The same is true of British examples of the form, 4-4-0 Tender locos and 0-4-4 tanks spring to mind. It is just about possible to model these with no weight carried on the bogie but the result isn't pretty. Whether there are examples of pony truck fitted locos of which the same is true is an interesting qusetion. The long overhangs on 2-4-2 are likely to mean putting a bit of weight on one or both carrying wheels. (Many locos of this form use radial trucks.) Whether any model of a 2-6-0 (or even 4-6-0) really needs weight on the carrying wheels for performance reason is open to question and I rather doubt if any 4-6-2 or 4-4-2 ever really needs weight on the trailing axle.

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Le Corbusier
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Re: Crab Comet conversion

Postby Le Corbusier » Mon Nov 26, 2018 1:19 pm

Will L wrote:Continued post household chores.

The same is true of British examples of the form, 4-4-0 Tender locos and 0-4-4 tanks spring to mind. It is just about possible to model these with no weight carried on the bogie but the result isn't pretty.


As I am sure you know ... my question was prompted by not just the need to understand the criteria for modelling the Johnson 4-4-0s but also the 0-4-4 tanks as well - so I assume perhaps a properly balanced weighting across the bogies in either case will be in order? ... and also I shall I think be asking on my own thread for thoughts about possible csb springing of the said bogies - apologies Julian for the hijack :thumb
Tim Lee

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Re: Crab Comet conversion

Postby Julian Roberts » Mon Nov 26, 2018 5:59 pm

Will L wrote:... I'm not sure arraging for for your loco to lift its front drivers will prove operationally satisfying,


Quite. So the logical conclusion for me at least is that the suspension on the driving wheels only, that we hoped would be adequate (with trailing wheels just going for the ride), has to be rethought. The only satisfactory solution is for the front driver to be sprung, which could be a CSB type spring or as on this Crab the coil spring supplied. The spring force needs to be adjusted so that there is also adequate weight on the backstop so maybe a 50/50 split.

I'll come back to this.

No problem Tim: the explanations you have received from Noel and Will have filled in some gaps in my knowledge and are useful for forthcoming explanation of my dissatisfaction with "model" clearances round carrying wheels.

I wonder if anyone can fill me in on Cartazzi trucks and how they function?

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Noel
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Re: Crab Comet conversion

Postby Noel » Mon Nov 26, 2018 8:29 pm

[quote="Will L"] our American fiends[/quote]
!!

[quote="Will L"] The use of either was primarily and originally driven by the need to stay within a given weight per axle. So as locos got bigger they needed extra carrying axles to carry the additional weight and to avoid the complexity of additional coupled driving axles. [/quote]
Some designs undoubtedly gained carrying axles for this reason, but I am not convinced that this is the primary reason. In the 20th Century, Fowler built 0-8-0 freight engines, the Hughes designed 2-6-0 mixed traffic loco, and 4-4-0 express passenger locos. Stanier built 2-8-0 freight engines, intended to cope with express freights, and 4-6-0 and 4-6-2 mixed traffic and express passenger locos. Churchward built 2-8-0 freight engines, 2-6-0 and 2-8-0 mixed traffic engines and 4-6-0 express passenger locos; Collett moved up to 4-6-0 mixed traffic engines. In Europe 0-8-0, 0-10-0 and even 0-12-0 freight engines were built. There are many other examples of similar patterns. Designers were clearly capable of designing locos with more than 3 coupled axles, but nevertheless there seems to have been a general consensus that the faster an engine was intended to work, the more leading axles it needed, the inference being that they were seen as helping stability and track holding at speed.

[quote="Le Corbusier"]so I assume perhaps a properly balanced weighting across the bogies in either case will be in order?[/quote]
The prototype generally had bogie and pony truck wheels with an axle loading of very roughly 50% of the load on the driving wheels. Presumably this was regarded as a reasonable minimum, since designers would want to put as much weight as possible [subject to the Civil Engineer's limitations] on driving axles to maximise adhesion. This is not necessary relevant to a model as the physics mostly doesn't scale.

[quote="Julian Roberts"]I wonder if anyone can fill me in on Cartazzi trucks and how they function?[/quote]
A Cartazzi truck isn't really a truck. It's a fixed axle with additional sideplay limited by inclined slides. Just to confuse the issue, you can get pony trucks controlled by Cartazzi slides rather than springs.
Last edited by grovenor-2685 on Tue Nov 27, 2018 12:13 am, edited 1 time in total.
Reason: the [quotes] mysteriously not working, and I've failed to fix it
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Noel

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Re: Crab Comet conversion

Postby Julian Roberts » Wed Nov 28, 2018 5:16 am

Will L wrote:Which is the point about modelling in P4 isn't it, as it reduces, but does not eliminate, the need for modelling compromises. If we model scale flanges and the carrying wheels cleared the frames on the original then we should be able to do it on the model. If they didn't then either you don't use small curves or you start making the compromises.


Will (and Tim too, this may be useful?!) - my first P4 loco was quite a learning curve. An 0-4-4. At the time the issue was how to get it round even a 4ft curve as I'd used "P4" frame spacers, and as I've often said the cure was to bring the pivot back towards the driving wheels.

But subsequently the issue has been, rather, the bogie clearance. There were two things I did not know when I made it. First, that on the real loco the frames would be likely to narrow between the drivers and the bogie area.

Second, that the cutouts on the frames were meant to be smaller than the bogie wheels, and that is how they are on the real thing. I had been misled by the typical 00 loco, and the DJH kit, which I had originally made for 00. The DJH kit came with the bogie frame area an integral part of the footplate casting, with cutouts bigger than the wheels, and the bogie wheels clearly were meant to swivel inside the cutouts. So when I converted it to P4 and used the milled frames from Alan Gibson, I assumed the rather small cutouts were just one of the many things that need to be fettled to fit, and I filed them to be clear of the wheels as they swivel.

What I have found in practice is that the amount of clearance needed is more than I thought, as even if the wheels clear a short circuit can occur unless there is that little bit more.

Subsequently I took on a semi completed in P4 4-4-0 Compound. Here was the same setup already made. It was only as I looked hard at photos that I realised the frames look as though they have no cutouts at all, certainly there is not one around the outer circumference on the wheel. Only on drawings or very close photos can I see that there is a cut out there, about two thirds of the size of the wheel, and that this clears the bogie internal framing.

Understanding that was liberating. Although I have not worked on any since I now know not to enlarge frame cutouts of such locos, and to narrow the frames probably more than the real thing depending on minimum radius required. Or the other approach is as on my Don Rowlands 4-4-0 where the "loco frame" becomes actually part of the bogie, a trompe d'oeil. I think I'm correct to say that the real things have some sideways movement on the bogies as well as swivel. I think I will stick to replicating that movement by having the pivot moved towards the driving wheels as is the case with all three of my models.

So this is a story of a mishmash of all the compromises, misunderstandings and modelling bodges that can happen. The fun bit, I think, is working out how to make it look like the real thing yet actually work even on modellers curves. :P

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Re: Crab Comet conversion

Postby mikemeg » Wed Nov 28, 2018 5:53 am

Le Corbusier wrote:
Will L wrote:Continued post household chores.

The same is true of British examples of the form, 4-4-0 Tender locos and 0-4-4 tanks spring to mind. It is just about possible to model these with no weight carried on the bogie but the result isn't pretty.


As I am sure you know ... my question was prompted by not just the need to understand the criteria for modelling the Johnson 4-4-0s but also the 0-4-4 tanks as well - so I assume perhaps a properly balanced weighting across the bogies in either case will be in order? ... and also I shall I think be asking on my own thread for thoughts about possible csb springing of the said bogies - apologies Julian for the hijack :thumb


Having made a number of equalised bogies, though always using compensating beams, I would imagine that using csb's on bogies might be difficult. Most locomotive bogies have a wheelbase of 6' 0 - 7' 3" so 24 - 29 mm in 4 mm scale. In that distance and especially as there is very little space, beyond the axleboxes, it would be extremely difficult to accommodate the end fulcrums. So using even the thinnest wire, I don't think there is enough distance to allow the CSB's to spring.

I think the advantage of an equalised arrangement is that the bogie wheels will stay in contact with the rails, even with only a very small amount of weight on them, provided that the equalising mechanism moves freely.

But I could be proved wrong!

Cheers

Mike

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Le Corbusier
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Re: Crab Comet conversion

Postby Le Corbusier » Wed Nov 28, 2018 7:12 am

Thanks Mike ... still pondering options :thumb

Some interesting thoughts on this here ...https://www.scalefour.org/forum/viewtopic.php?f=19&t=3637&p=31002&hilit=csb+bogies#p31002
Tim Lee

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Mike Garwood
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Re: Crab Comet conversion

Postby Mike Garwood » Wed Nov 28, 2018 7:59 pm

I'd agree CSB on a bogie would be a bit of an ask! But that doesn't mean springing can't be used on a bogie. This is the arrangement I have on my Scot. Those who've seen it run will attest to the quality of the chassis - not all my own work admittedly. The bogie is a typical Garwood bodge! :D

P1010006-4.JPG
Scot bogie


You do need a rubbing plate to get this type of spring to work, as it's under tension all the time, but with enough height to allow the wheels to move up within the bogie. It takes a bit of measuring that's all.

P1010003-4.JPG
Rubbing plate


Just something else to add to your choices. I did etch some other bogies (Britannia and a Hall) using the High Level mini bearings fitting inside the etch which were sprung on a similar idea as this. But I can't find the flippin' photo's on my PC, may be just as well.

Mike

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Will L
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Re: Crab Comet conversion

Postby Will L » Thu Nov 29, 2018 12:19 am

mikemeg wrote:Having made a number of equalised bogies, though always using compensating beams, I would imagine that using csb's on bogies might be difficult. Most locomotive bogies have a wheelbase of 6' 0 - 7' 3" so 24 - 29 mm in 4 mm scale. In that distance and especially as there is very little space, beyond the axleboxes, it would be extremely difficult to accommodate the end fulcrums. So using even the thinnest wire, I don't think there is enough distance to allow the CSB's to spring.


I'm with Mike Meg on this one and I'm not convinced that CSB are applicable to (some) loco bogies. I have written up the issue on bogies and CSBs on this thread CSBs and the Single Bogie which describes the application to a 4-4-2 C12 which also has relevance to the to carry weight or not discussion. It also covers a loco bogie with pickups design which works well for me see here.

Given their ride characteristics, whether there is any real practical need for suspension on loco bogies I'm unsure. If you do decide that you would like springing, the solution shown by Mike G with a spring wire fixed centrally on the bogie and cantilevered over the wheel axle block, is the accepted wisdom. But beware, unlike a rigid, compensated or dubious CSB fitted bogie, (which can be allowed to rock freely about their pivot point), as Mike G says, a rubbing plate betwixt bogie and main frames is necessary keep the bogie frame level under the main frame. Of course this does give more better control over the interaction between the wheel rims and frame cut-outs which may be of interest to Julian.

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Re: Crab Comet conversion

Postby Julian Roberts » Thu Nov 29, 2018 9:47 am

Will L wrote: Of course this does give more better control over the interaction between the wheel rims and frame cut-outs which may be of interest to Julian.


Yes! Is this the Scot you mean, Mike G? If so, again, in relation to the present discussion what I'd be concerned about if making it (and I have been rash enough to buy a kit!) is that very small clearance of the front bogie wheel.... Whereas what happens around the rear bogie wheel doesn't look so much of a visual concern though is maybe more of a practical one, cylinder etc....
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Re: Crab Comet conversion

Postby Armchair Modeller » Thu Nov 29, 2018 10:01 am

The arrangement of the Bachmann narrow gauge Baldwin 4-6-0 may be of interest. Whilst it should have a bogie at the front, they have made the rear bogie wheel part of the rigid frame. The front axle is a kind of pony truck - all neatly disguised. It works very well. The front axle has a large degree of play whilst the rear is only allowed to move within the limits of the frames and the slide bars

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Re: Crab Comet conversion

Postby steamraiser » Thu Nov 29, 2018 10:23 am

Mike G, what is your rubbing plate made of?

Gordon A

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Mike Garwood
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Re: Crab Comet conversion

Postby Mike Garwood » Thu Nov 29, 2018 8:59 pm

Gordon

That's a Comet rubbing plate for coaches - still available separately - which I had milled down to the correct thickness (Comet part C59). Fortunately Newport MRS has it's own milling machine. Took about 1mm off the thickness.

Mike

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Re: Crab Comet conversion

Postby Mike Garwood » Thu Nov 29, 2018 9:19 pm

Julian

There is a slight compromise in where the bogie is positioned. The layouts that this runs on don't have the scaled bends. I think you can just see the compromise in this photo.
Dive in with the build. This is a Comet Scot kit and was great fun to build. The photo was by Bernie Baker, taken on his layout.

IMG_1145.JPG
Side Scot


Good luck

Mike

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Re: Crab Comet conversion

Postby Julian Roberts » Fri Nov 30, 2018 9:54 am

Mike G - Thank you! Really nice! The photo of course puts into perspective how much these things matter...or not! Another aspect of how visible any compromise is, is how it is painted. The blacker the framing the less noticeable, but if it's weathered to an almost orange as in the real A1 photo I put up earlier, the eyes are drawn to the detail.

The Scot is a vanity "one day" project which my friends will hardly welcome at least on a regular basis onto our rural backwaters, Calderside (ex CR) and Kettlewell (exLMS), for a humdrum passenger service. More relevant to the first layout is the Wemyss Bay tank loco. This'll be from a DJH kit and Gibson milled frames so basically make it up as I go along. No cut outs for the carrying wheels, hurrah! It looks as though I'll be able to cheat with narrow frames behind them.

More of a challenge may be the splasher over the trailing bogie wheel. The Baldwin idea that you posted, AM, is exactly the kind of lateral thinking that I like! - and may come in useful for any of these issues. On idle reflection so far I can't see how to make my backstop idea work on a bogie but acting on the front wheels only, but that Baldwin idea could be the answer. I'll edit this to include a photo.
Screenshot_2018-11-30-10-02-15.png
https://youtu.be/LJKrm44Bbvo

Will I assume you'd agree that springing of the bogie as in Mike's Scot means some weight is being taken. Although my original intention was to have the carrying wheels just going along for the ride, and while certainly they aren't necessary to support the loco weight as on the prototypes, my feeling is that it's difficult to get them heavy enough to be certain (i.e. 100% certain) that they won't jump the rails, without some kind of springing to increase the downward force. Taking for example a wagon, we weight it to 25g per axle for reasonably assured running. I weighted the pony on the Crab as much as I could, while preserving prototypical daylight below the cylinder. Some of the weight is taken at the pivot. The actual weight of the wheel pair on the kitchen scales is 15g, obviously holding the loco just clear of the backstop.
20171124_215324-1.jpg
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Le Corbusier
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Re: Crab Comet conversion

Postby Le Corbusier » Fri Nov 30, 2018 11:52 am

Will L wrote:
mikemeg wrote:Having made a number of equalised bogies, though always using compensating beams, I would imagine that using csb's on bogies might be difficult. Most locomotive bogies have a wheelbase of 6' 0 - 7' 3" so 24 - 29 mm in 4 mm scale. In that distance and especially as there is very little space, beyond the axleboxes, it would be extremely difficult to accommodate the end fulcrums. So using even the thinnest wire, I don't think there is enough distance to allow the CSB's to spring.


I'm with Mike Meg on this one and I'm not convinced that CSB are applicable to (some) loco bogies. I have written up the issue on bogies and CSBs on this thread CSBs and the Single Bogie which describes the application to a 4-4-2 C12 which also has relevance to the to carry weight or not discussion. It also covers a loco bogie with pickups design which works well for me see here.

Given their ride characteristics, whether there is any real practical need for suspension on loco bogies I'm unsure. If you do decide that you would like springing, the solution shown by Mike G with a spring wire fixed centrally on the bogie and cantilevered over the wheel axle block, is the accepted wisdom. But beware, unlike a rigid, compensated or dubious CSB fitted bogie, (which can be allowed to rock freely about their pivot point), as Mike G says, a rubbing plate betwixt bogie and main frames is necessary keep the bogie frame level under the main frame. Of course this does give more better control over the interaction between the wheel rims and frame cut-outs which may be of interest to Julian.


Sorry Julian ..another interruption

I have been spending a little time ploughing through the various threads etc an CSBs ... particularly in reference to bogies with the Johnson 0-4-4s and 4-4-0s in mind. Now i'm not sure I fully understand all the complexities that I have read and suspect that it will take practical experimentation in due course to properly arrange things in my mind.

I do have one question/thought on this though. With the above Johnson locos in mind and particularly the balance of the weight 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?
Tim Lee

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Will L
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Re: Crab Comet conversion

Postby Will L » Fri Nov 30, 2018 4:19 pm

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.

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Re: Crab Comet conversion

Postby Will L » Fri Nov 30, 2018 4:36 pm

Julian Roberts wrote:...Will I assume you'd agree that springing of the bogie as in Mike's Scot means some weight is being taken. Although my original intention was to have the carrying wheels just going along for the ride, and while certainly they aren't necessary to support the loco weight as on the prototypes, my feeling is that it's difficult to get them heavy enough to be certain (i.e. 100% certain) that they won't jump the rails, without some kind of springing to increase the downward force...


I would have said that there is lost of evidence that free running bogies are not particularly prone to jumping ship, and a little lead between the bogie frames is the easiest way to ensure the reliability you seek, but yes arranging a spring to load the bogie a bit is an option so long as it doesn't hinder the free movement of the bogie. (100% certainty? I think even the real things comes off occasional)

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Will L
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Re: Crab Comet conversion

Postby Will L » Sat Dec 01, 2018 12:22 am

"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

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Re: Crab Comet conversion

Postby Julian Roberts » Mon Feb 25, 2019 3:27 pm

At last I have some time to get on with the Crab. The tender now runs as an independent vehicle. The front wheel suspension was modified to give the correct ride height, with no upward travel possible. Two springs exert downward force. The sideplay was taken up with fibre washers, slotted so that they could be inserted without taking a wheel off. The centre axle is sprung with one spring and needs no modification. The coupling was modified so that it acts in a normal way. The weight is all glued in the coal space and is more or less irremoveable so it'll have to stay that way unless there are problems. Maybe it'll act as a kind of momentum device.

The RHS valve gear is now attached for trial. While the temporary glueing of the return crank sets (nail varnish) thoughts hover again on the best way to attach the valve gear at its other two fixing points, the reverser and the dieblock, yet in such a way that the valve gear remains detachable. I had visions of using a neat 16BA screw. However there are practical problems associated with tapping the material or fixing on a 16BA nut. In due time I will post what solution I come to but here is a close up (on the LHS) of the two places, the red lines showing where they are and the termporary present arrangement - a Peco pin and bent over piece of 0.6 wire.
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Dave Holt
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Re: Crab Comet conversion

Postby Dave Holt » Mon Feb 25, 2019 4:38 pm

Julian.
At least for the expansion link, could you not use a headed pin. inserted from the back and retained with more of your nail varnish (don't wear it myself, but...), or similar?
Dave.

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Re: Crab Comet conversion

Postby Julian Roberts » Fri Mar 01, 2019 4:06 pm

Dave, thanks for the useful idea. (Clear nail varnish is a very useful substance. Needed for lacquering the binding of bassoon reeds ;) and I find holds on crankpin nuts very satisfactorily. )

While I'm thinking about it I'm also thinking about, but rather more hazily, the only bit of wholly cosmetic modelling on the project, the cylinder drain cocks. I'm not terribly acquainted with them visually, and photos don't exactly home in on those details. An impression is all that's really needed, yet I always find it's hopeless trying to create an impression (as one would if making a painting). I wonder if you or anyone else has any close up photos...

The Bachmann model has some nicely detailed bits to manually attach to underneath the cylinders. If I use them it would mean removing the equivalent rather more crude bits of the Comet W/M casting. In either case it's a practical matter of attaching convincingly the pipes that are the prominent feature.

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Re: Crab Comet conversion

Postby Knuckles » Fri Mar 01, 2019 5:29 pm

Ignoring the fact it's 00 and the chipped paint.

This post 1939 version of a Gordon I bashed up has its drain cocks scratch built from 0.45mm brass rod with little 0.7mm bits. Just a quick soldier bash.

A bit rough around the edges but I'm happy with the result even a decade or so later.

Maybe try similar?

Image
Image
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Re: Crab Comet conversion

Postby Dave Holt » Fri Mar 01, 2019 6:36 pm

Julian.
The Crabs had very prominent and distinctive drain cocks which were, I believe, a Midland design. There are some good photos and drawings showing them in some detail in the Wild Swan profile book. For my model, i used some castings which were a good representation. Can't remember their origin but Comet, Alan Gibson or Brassmasters are all possibilities.
An awkward feature of Crabs in BR days is that the drain cock exhaust pipes on some locos were very long and the outer ends were clipped to the front steps. I did this on mine by making "U" shaped clips from thin phosphor bronze strip, attached under the bottom step. The main problem is remembering to ease the pipes out of the clips before separating the body and chassis. No need to ask how I know this is a potential problem!
Crab_drain_cocks_002.JPG


Crab_drain_cocks_001.JPG


Dave.


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