Radius Testing - Practical Experiments.

Discuss the prototype and how to model it.
Julian Roberts
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Re: Radius Testing - Practical Experiments.

Postby Julian Roberts » Sat Nov 10, 2018 5:50 pm

Knuckles I've been thinking why my 782 is happy going round much sharper curves than I designed. I think it
proves what Will L says on this page:


viewtopic.php?f=96&t=5030

You'll find useful and helpful stuff there. Particularly this conclusion

"This goes along with my experience that suggests that most of the problems people have getting locos round corners are much more to do with insufficient clearance between the wheels and the bodywork than any issue gauge widening. Having a test curve of your minimum radius on the work bench and building so that your locos go round it should see you home and clear."

And

"This is telling us that with 0.5mm end float on its middle axle our Black 5 is in only need of Gauge Widening on curves below 850mm (2’9”), and only if we are run monsters like a J19* should we to need to worry about gauge widening."


I didn't factor into my calculations on any of my loco builds either the Running Clearance or slop of 0.28mm nor the gauge widening given by the triangular tool. So he's right, P4 slop plus 0.5 sideplay on middle axle is going to get most locos round most likely modellers curves. The issue is much more to do with bogie and pony wheel (or Cartazzi truck) clearance from the chassis/bodywork.

Whether articulated frames and widened cylinders are needed you will have to find out but I would have thought they would add to the difficulties...no means of knowing except practical experience.

And by the way, yes regarding Check Rail gauged from the crossing. The 2ft test track incorporates the crossings of points (i.e. dummy points) to prove the point :o . The running reliability of switches of turnouts on 34" radius I would have thought could be more problematic.

PS obviously this was part of a discussion about gauge widening, and how much is needed. I think we're all agreed that the triangular tool works just fine.

Knuckles
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Re: Radius Testing - Practical Experiments.

Postby Knuckles » Tue Nov 13, 2018 9:29 am

Hi Julian, now I'm the one apologising for the delay.

I've read your two posts. Regarding EM spacers I'll consider that as a possibility. Overly large gaps between the frame edges and wheel backs are not ideal but I can live with them. The Bachmann Pannier I converted the easy way with Ultrascale wheels (boy, what a wait for dellivery) still has its 00 frames so you could easily fit a baby elephant in the gap.

My 3D printed P4 chassis are nominally 16mm diameter width and so far no issues with the running there on these overly tight curves.

The ruling 34 & 36" radius curves I have managed to redesign to be a minimum of 35.5" but that really is pushing it and cutting into scenery space. However in the redesign I also managed to replace some of the 36" curved with 38, 40.5 & 43" radii so that is a bit better. The bigger locomotives would still have to traverse the minimums though.

The compromises such as cutting into the insided of the cylinders I can live with, heck, with 00 modelling you are used to such fudges. As long as I can manage to get the horses around I'll be happy as further refinements can always be made later on.

What I find confusing and worrying is you said in a different thread you got a Black 5 around (I think) a 30" curve yet Mr Whittle said on a thread regarding Barrow Road his black 5 bogie was falling of 1400mm curves which a quick online calculator reveals is around 55" radius. It was a converted Hornby Black 5 so maybe if it has more tweaking or was built from a kit the problem will or would vanish.

I plan to use the Exactoscale 0.2mm gauge widened Fast track as in one of the crude tests on page 1 as it made a lot of difference.

Also the idea of having curved diamonds and double junctions on the 34 (now 35.5") curves can be scrapped in favour of some purpose built P4 'set track' fixed mechanically and electrically with small hinges as they would be outside the scenic sections and then, to my mind at least, providing sound joints, should provide easier running. This area doesn't have to be a fixed layout and route set based on the plans anyway.

All last night and a bit of this morning I took it upon myself to read your entire Crab thread in order. I was following the thread initially but didn't keep up with it.

Anyway, a most enlightening and entertaining read. Creates hope and fear all at once!

I'm not sure Amature would be an accurate way to describe your abilities even if you are feeling your away aroound things. If I was at your current modelling level regarding valve gear there would be nothing to worry me.

Current logic tells me some small 0-4-0's or something with cross head and slide bars would be a worthy first forray into anything more complex than articulated 0-6-0 rods with basic compensation which is my current and latest two feathers for the collection.
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Julian Roberts
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Re: Radius Testing - Practical Experiments.

Postby Julian Roberts » Wed Nov 14, 2018 1:17 pm

Hi Knuckles , glad the radius is slightly easing and diamond simplifying.

Just quickly to say, there is some mistake, I haven't made any Black 5, Will Litchfield was saying in his thread that in THEORY(!) a Black 5 would get round that curve. The problem of the bogie in the Barrow thread illustrates the issue that it's the other wheels that will be the problem. My friend Allan Goodwillie made an A4 years ago that goes round his layout perfectly, and plenty of other locos too. It's a question of junking the idea that a model has to work like the prototype in every way as well as look like it, and rather, deciding how to make it simply function! - likely to mean totally non prototypical suspension arrangements, though no less unprototypical than the electric motor and gearbox....especially for non prototypical curves.

My principle is perfectly simple and the same as the prototype. If the sideways forces on the flange are stronger than the downward ones the wheel will jump off the rails. It's blindingly obvious. Models are light. E.g. a buffer lock or malfunctioning gangway conection will probably derail us where on the real thing it's more likely the buffer or gangway will break. So I think out, on every wheel, what is happening? But I've yet to tackle something that big. A Wemyss Bay 4-6-2T will be my testing ground.

Please ask anything about the Crab you don't follow. Here or on that thread. See if I can even understand it myself! I'm travelling about working so this is the only modelling I can do just now but happy to help if I can.

Issue behind slide bars is perfectly simple...no side play on that wheel. A good kit like High Level will make it a doddle for getting the clearance needed

Julian Roberts
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Re: Radius Testing - Practical Experiments.

Postby Julian Roberts » Thu Nov 15, 2018 9:55 am

Knuckles, regarding the mention of an articulated chassis previously, I don't understand without reading the MRJ article what that can mean with an 0-6-0. But to in a sense articulate the chassis is the way to make bogie etc wheels able to swing far more than the real thing. If you look at this page

viewtopic.php?f=19&t=5277&p=51178&hilit=113+class#p51178

you can see it done in this simple case, a 4-4-0 without outside cylinders. The Class 113 bogie takes the loco framing with it as it swings - but the loco framing isn't fixed to the loco on the model, it has become part of the bogie. It is a trick, a modelling bodge, a trompe d'oeil but completely invisible to all intents and purposes. By doing it this way there is no issue of the bogie wheels hitting the frames as they swing. Often on models the cutouts in the chassis frames [which in real life (on this loco and in many cases) are not as big as the wheels but just big enough for the internal mostly hidden bogie frame] are made bigger than the wheels so that they can swing further. The problem then is that the clearance is never enough without there being a very visible and unprototypical gap, if sufficient allowance is made for uneven track - always a little more is needed than looks right.

The question would be how to do something like this with an outside cylinder loco in a similarly concealed yet effective manner.

DSC02309.JPG
Class 113 loco. Nothing unprototypical about bogie frame appearance
DSC02309.JPG (88.87 KiB) Viewed 1467 times
Attachments
2016-05-08 22.28.23.jpg
Bogie with loco frames and prototypical cutouts. Bogie has its own internal compensation.
2016-05-08 22.28.23.jpg (75.06 KiB) Viewed 1467 times

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Andy W
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Re: Radius Testing - Practical Experiments.

Postby Andy W » Thu Nov 15, 2018 11:17 am

I’m not knocking anyone’s efforts at experimenting with minimum radii etc. but one of finescale’s aims is usually to model the prototype and trying to get large locomotives around small curves is going to necessitate some pretty stern compromises. I can understand why these tests are valid, however I would be worried that if applied to a P4 layout the results could be somewhat incongruous.
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Noel
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Re: Radius Testing - Practical Experiments.

Postby Noel » Thu Nov 15, 2018 12:07 pm

Julian Roberts wrote:regarding the mention of an articulated chassis previously, I don't understand without reading the MRJ article what that can mean with an 0-6-0


It involved a joint in the frames behind the centre axle, effectively turning the loco into an 0-4-2-0. The joint itself is hidden behind the centre wheel tyre. The rear pair of rods are slotted for the centre wheel crankpins, and the drive is to centre and rear axles, via a ball and socket joint between the motor [which is mounted in the forward part of the frame] and the rear axle.
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Knuckles
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Re: Radius Testing - Practical Experiments.

Postby Knuckles » Thu Nov 15, 2018 12:17 pm

Julian Roberts wrote:Hi Knuckles , glad the radius is slightly easing and diamond simplifying.

Just quickly to say, there is some mistake, I haven't made any Black 5, Will Litchfield was saying in his thread that in THEORY(!) a Black 5 would get round that curve….


I think I made the mistake mentioning you, I think it was actually in this thread I gleaned the information from the following link with two quotes from previous conversations…
viewtopic.php?f=5&t=3488
Philip Hall wrote:I have converted a few 4-6-0s and 2-8-0s to P4 and all have been quite happy at 2'6"radius although I wouldn't expect to hurtle around at that speed. 3'0" to 3'6" is quite practicable, and indeed was going to be my own ruling radius until the possibility of a larger space came up. As Martin says, build for the layout the engines are going to run on. With a 4-6-0, I tend to allow sideplay on the middle axle, hardly any on the front behind the slidebars, and a little bit on the rear axle.

John Donnelly wrote:
Knuckles wrote:I just fear building 3' or 3'6" curves then finding out getting a pacific or black 5 around it is next to impossible.

Dave Bradwell's 9F chassis will go round a 3' radius curve so you should be in with a good chance with a Pacific...
John

Re-reading these threads and others was what gave me the impetus to reconsider P4 for this layout and so far I am feeling a bit more confidant it can be done…because evidently it has been done (unless they are lying!) so in theory in due time when I may tackle the ‘biggies’ there is hope.


…..The problem of the bogie in the Barrow thread illustrates the issue that it's the other wheels that will be the problem. My friend Allan Goodwillie made an A4 years ago that goes round his layout perfectly, and plenty of other locos too. It's a question of junking the idea that a model has to work like the prototype in every way as well as look like it, and rather, deciding how to make it simply function! - likely to mean totally non prototypical suspension arrangements, though no less unprototypical than the electric motor and gearbox....especially for non prototypical curves.

Aye, function over looks for me. Your articulated frame thingigummy is something I’m hoping I’ll never have to do, although it is good to see it as an option. Knowledge is power as they say.
Andy W wrote:I’m not knocking anyone’s efforts at experimenting with minimum radii etc. but one of finescale’s aims is usually to model the prototype and trying to get large locomotives around small curves is going to necessitate some pretty stern compromises. I can understand why these tests are valid, however I would be worried that if applied to a P4 layout the results could be somewhat incongruous.


Breaking established moulds is what I do best.
I either have tight P4 curves for the plan or I have NO P4 layout at all. It’s as simple as that. The cultural party line ethos goes out the window when you are bound between tight walls, alright for some… :cry:

Where there's a will there's a way as they say.

I fear this thread may be morphing into a subject already covered. (See above link somewhere)
Last edited by Knuckles on Fri Nov 16, 2018 1:40 pm, edited 2 times in total.
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Will L
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Re: Radius Testing - Practical Experiments.

Postby Will L » Thu Nov 15, 2018 4:10 pm

Julian Roberts wrote: The Class 113 bogie takes the loco framing with it as it swings - but the loco framing isn't fixed to the loco on the model, it has become part of the bogie. It is a trick, a modelling bodge, a trompe d'oeil but completely invisible to all intents and purposes. By doing it this way there is no issue of the bogie wheels hitting the frames as they swing. Often on models the cutouts in the chassis frames [which in real life (on this loco and in many cases) are not as big as the wheels but just big enough for the internal mostly hidden bogie frame] are made bigger than the wheels so that they can swing further. The problem then is that the clearance is never enough without there being a very visible and unprototypical gap, if sufficient allowance is made for uneven track - always a little more is needed than looks right.


Another simpler(?) solution to the same problem is to fix the bogie pivot central under the chimney and provide lateral freedom for the front driving wheels. Given sufficient body clearance, a loco so fitted will go round surprisingly sharp curves and is less inclined to suffer from excessive front buffer overhang. To ensure enough body clearance may require over wide splashes on the front driving axle and the whole idea may well not suit anything with outside cylinders and slide bars out side of the front driver.

Julian Roberts
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Re: Radius Testing - Practical Experiments.

Postby Julian Roberts » Fri Nov 16, 2018 12:20 pm

Absolutely, Will, regarding the pivot etc. As a matter of disclosure (!) the model was made by Don Rowlands so I shouldn't claim the bogie idea is mine.

What I'm thinking about is Knuckles' A1 and how the bogie will swing without excessive clearance. Here are some pix that show the difference between RTR model and reality. For me the model bogie wheel cutouts are really unsatisfactory. But I don't get wound up about the loco frames, if using EM spacers, being say 1mm further behind the driving wheels than they ought to be!...we all have different ideas of what bothers us I suppose! From a typical skyscraper viewing perspective which maximises the view of the track, which is what emphasizes how P4 looks so much better, this bogie wheel gap is just not an issue.

Much of my Crab thread is about how to get the pony wheel a prototypical distance from the cutout yet run reliably, and I would want to do the same with an A1.

Yes Knuckles I hope this isn't a famous morph. Another issue is, how reliably does a RTR loco run even in 00? My son's Bachmann N class could not be guaranteed to run reliably round 3rd radius curves on a hidden inaccessible fiddleyard...a real pain. The pony wheel derailed regularly.

Screenshot_2018-11-16-11-08-44-1.png
Hornby

Screenshot_2018-11-16-11-10-01-1.png
Hornby

Screenshot_2018-11-16-11-17-09-1.png
Bachmann

Screenshot_2018-11-16-11-19-37-1.png
Real thing

Screenshot_2018-11-17-12-59-23-1.png
Dave Bradwell chassis. More like it! "The kit provides working solutions to the problems inherent in building reliable models of Pacifics."


I have edited this to include the Dave Bradwell chassis kit which is something more like it :thumb :thumb :P

Knuckles
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Re: Radius Testing - Practical Experiments.

Postby Knuckles » Sun Nov 18, 2018 6:18 pm

Well, will just add a wee post here. Converted my 1st 00 coach to P4 today. In the past I tackled a variety of wagons and they needed different methods. I model with the mindset that if a simple wheel swap does it and it doesn't fall off then it's done - leave it. If it likes to divide ballst then think about compo or springs or whatever. Taking the same view with the coach I now have my 1st P4 coach that I think is ok. There is a bit of jiggle slop but that was there in the 00 wheels too. Unsure if this will help or not, a teeny bit seems to with some things but too much and it proves useless.

I rolled it through the Exactoscale C10 turnout I built with no issues, then rolled it down my 00 test track with P4 rail added, complete with 00 elephant gaps and no problem. Then I rolled it on some C&L flexi track into what looked like a 10-15" radius reverse curve, tighter than a....

No issue.

Now whether it will run through loads of P&C at speed in formation is something I currently cannot test.

An old Hornby Gresley teak from the 60's or 70's was the donor and the method was to shave about 1mm from the inside of each axle box, a bit off the bogey roof to aid wheel insertion and pop (ok force and jam with springing sides) the wheels in.

20181118_151518.jpg


The wheels are actually a larger diameter than the originals so likely will need changing one day. For a first coach conversion learning exercise good enough for now. The moulded brake pads don't line up! Just using what I had as the wagon wheels looked too small.....oooh, .. wagon wheels. Hhmm. Nom nom.
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Noel
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Re: Radius Testing - Practical Experiments.

Postby Noel » Sun Nov 18, 2018 8:41 pm

Knuckles wrote:Just using what I had as the wagon wheels looked too small...


Standard post-grouping wagon wheels were a nominal 3ft 1in - 3ft 2in, with Lowmac, etc wheels at 2ft 8ins. Post-grouping company coach designs used 3ft 7.5 ins wheels, and BR Mark 1 designs used 3ft 6ins. Before roller bearings, designers were concerned about the effect of high rotational speeds on axle bearings. Some post-grouping NPCCS designs did use wagon wheels, however.
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