Accepted side play in long wheelbase locos

[Lancastrian]

Just to resurrect this thread, I'm looking at S7 for a few locos I'm currently working on in QCAD, so what advice from the genius-pool on minimum clearance measured from frame face to rear of wheel ? For example, is 1mm just about enough, or more than enough ?



The red line is 1.2375 mm.
Blue lines are the frames as currently designed.
Pink lines are frames at prototypical width.
Green line indicates rear face of wheel.

Ian

Ian

 

[paulc]

Mick

If you want to use battery power, there is no need for ball races for any of the axles. I have 12 locos fitted with red arrow control, none of which have ball races and all will run for several hours on one charge using AAA batteries, 8 in the smaller locos ten in the larger ones, including 2 DJH V2s. The only down side of red arrow is that there is no sound which is why I have swapped back to DCC for my diesels.

There are of course other good reasons for using ball races, you can get some real momentum effects if you do, but they are not necessary for battery operation.

Richard

Hi Richard if you want the best of both worlds , DCC sound with radio control then look at the Fosworks site .
Developed using Zimo decoders but other brands work fine . I will be converting my Heljan 37 soon , cant wait.
Cheers Paul

 

[simond]

I have used CAD to work out sideplay since I built my fourth (I think) loco which was a Warren Shepherd 52xx. My second loco (and first brass one) was a Finney 47xx which was an unmitigated pain to get to cross a Peco crossover, this being the gold standard for Finescale locos that will run on other modellers’ layouts, so I determined to design out the pain early on...

I’ve used the approach since, notably my Dukedog, and a couple in S7 for Graham (@DogStar) on here.

I used 2D CAD originally, as that’s what I had, 3D will be simpler. I prepare a frame layout for the axle spacings in side view, and put the tyre and flange diameters on it. I project the intersections of the tyre and flange with the railhead giving me 4 parallel lines per axle (plus centrelines, I guess) into a plan view.

I then draw in the wheel backs at appropriate b-t-b and add wheel faces - you can decide how much effort you put onto generating the flange face (can cut true sections in 3D) but I simply plotted the flange thickness at the axle centreline. This then gives you a point per wheel.

I then construct a circle of desired minimum radius through the two outer points on one side, with the centre on the other side, and a concentric circle at the appropriate gauge, inside, of course. If the point(s) on the other axle(s) are inside gauge, you’re good to go.

iteratively adjust gauge and radius as desired.

moving bogies around is also iterative, and a PITA,

picture on work computer, can post Monday.

hth
Simon

 

[Eastsidepilot]

Just to resurrect this thread, I'm looking at S7 for a few locos I'm currently working on in QCAD, so what advice from the genius-pool on minimum clearance measured from frame face to rear of wheel ? For example, is 1mm just about enough, or more than enough ?

View attachment 134365

The red line is 1.2375 mm.
Blue lines are the frames as currently designed.
Pink lines are frames at prototypical width.
Green line indicates rear face of wheel.

Ian

Ian

A lot depends on the wheel base dimension, the shorter the wheel base the less side play needed. Number of axles makes a difference also.
Most if not all the S7 loco's I've built have been steam prototypes and I've found that 29-29.5mm o/a frame dimension works well as this is pretty much prototype dimension anyway.
At 1mm side play on the axles should work but again depends on what your building ?
I have reduced centre axle tyre flange width on loco's such as 0-8-0's etc. which all helps in S7 plus gauge widening is important on tight radii .

Col.

 

[Lancastrian]

Morning,
Col: At the moment it's a LYR Baltic tank with a wheelbase of 6'9 + 6'10 for the driving wheels.

Ian

 

[richard carr]

Ian

For steam locos, it is rarely the main driving wheels wheelbase that will determine the minimum radius, it is far more likely to be the movement of a bogie or pony truck. Front bogies in particular are the problem as they tend run into cylinders etc when you don't want them to.

How tight a radius do you want your locos to go round ? If its 8 feet/2.5 meters, just about anything with 29mm frames will go round, if it's 6 feet or less then you will struggle with anything much larger than a tank loco. For your baltic tank, the bogies will be the issue the frames just need 0.75mm each side to work.

Richard

 

[Ian@StEnochs]

Ian,

I am building a G&SWR Baltic in S7 at the moment. I am having problems getting it round anything less than 9’. The problem is not the driving wheels, with the frames set at 29.5 they go round 5’6” curves, it’s the bogies. The prototype permitted 5” sideplay on the bogie but getting more is limited on the model by the bogie splashers which are fixed to the mainframes.

With the thinnest material for the splasher fronts, pushed out a bit, but constrained by the cylinders and tail rods, and the wheels turned to minimum thickness they still rub and derail! I expect that the originals straightened out the track and racked the frames on shed curves anyway but they had mass which our models lack. Even with as much weight as I can cram into the bogie it still won’t bend either the track or the frames.

My model might just end up as a glass case example.

Ian.

 

[simond]

Ian,

I doubt it will help, but I’ll happily do the CAD construction if you want to send me the relevant dimensions - I’ll need to know the wheelbase, wheel diameters, and where the bogie pivots are. Presuming it’s S7, I think I have the relevant wheel thickness data, but you can include that too if it’s to hand.

It becomes an interesting mind game over lunchtimes at work, much better than reading the news, anyway.

atb
Simon

 

[Lancastrian]

Thankfully there are no bogie splashers.
There should be enough swing in the front bogie without the cylinders impeding movement.
The frames are currently set at 28.825 mm over the outside faces.

Ian

 

[Yorkshire Dave]

I am building a G&SWR Baltic in S7 at the moment. I am having problems getting it round anything less than 9’. The problem is not the driving wheels, with the frames set at 29.5 they go round 5’6” curves, it’s the bogies. The prototype permitted 5” sideplay on the bogie but getting more is limited on the model by the bogie splashers which are fixed to the mainframes.

With the thinnest material for the splasher fronts, pushed out a bit, but constrained by the cylinders and tail rods, and the wheels turned to minimum thickness they still rub and derail! I expect that the originals straightened out the track and racked the frames on shed curves anyway but they had mass which our models lack. Even with as much weight as I can cram into the bogie it still won’t bend either the track or the frames.

Hi Ian

Depending on how much you want to compromise* to achieve the running on tighter radii could the idea below work to increase the flexibility of the bogies and splashers to accomodate this? *Apologies (or not) in advance for using compromise in the S7 world....

It uses half tubes with one fixed to the frames and the other snugly free floating inside this. Rather than describe in words, and in true Blue Peter fashion, here's one I made earlier from scrap card to show the concept.

The inside of the bogie splasher on the free floating tube can be insulated with superglue and tissue paper. As the loco traverses the curve the outer rim of the bogie wheels can move the tube slightly. A piece of fine spingy wire can be utilised to centralise the bogie splasher tube once on straight track to maintain the illusion.

 

[Lancastrian]

Hi Dave,

I like your Blue Peter example.

I'm currently at this stage:


In theory, I should have enough side-play there, or maybe even open out to 29mm. I'll likely leave as is as it would mean adjusting the drawings.

Ian

 

[Ian@StEnochs]

Hi Ian

Depending on how much you want to compromise* to achieve the running on tighter radii could the idea below work to increase the flexibility of the bogies and splashers to accomodate this? *Apologies (or not) in advance for using compromise in the S7 world....

It uses half tubes with one fixed to the frames and the other snugly free floating inside this. Rather than describe in words, and in true Blue Peter fashion, here's one I made earlier from scrap card to show the concept.

The inside of the bogie splasher on the free floating tube can be insulated with superglue and tissue paper. As the loco traverses the curve the outer rim of the bogie wheels can move the tube slightly. A piece of fine spingy wire can be utilised to centralise the bogie splasher tube once on straight track to maintain the illusion.

View attachment 134401

View attachment 134402

Hi Dave,

I like your thinking, your visual aid makes it very clear. However the splashers are as far out as the cylinders permit, this photo shows just how little space there is. You may see that the front splasher is tapered, wider at the front, as it was on the prototype. Sorry for the quality of the picture but not easy getting light yet not too much reflection.



Your idea is worth trying on the rear bogie, nothing to restrict movement except the balance pipes and they are quite far out. I could also let the rear drivers have some more sideplay which along with stiffer side control on the front bogie may get the beast round.

For my sins I am also building a fine standard O version alongside my S7 one. I have got this to go round a peco points crossover and a 5’6” curve. To do that I have made the frames under the bunker hinge, just behind the sandbox, and the bogie moves the frames sideways The side control on the front bogie pulls the drivers into curves helped by the slop between the flange and rail in fine standard.

I could do the same on the S7 model but I don’t want to.

Ian.

 

[Yorkshire Dave]

Your idea is worth trying on the rear bogie, nothing to restrict movement except the balance pipes and they are quite far out. I could also let the rear drivers have some more sideplay which along with stiffer side control on the front bogie may get the beast round.

I was thinking of the rear bogie when conceiving the idea. It's almost trying to get the 4-6-4 configuration to behave like a 4-4-2-4 or 4-4-2-2-2! Looking at the photos below I believe it would work as the 'gap' between the two halves of tube would be hidden by the balance pipes and in shadow to boot. Especially as the GSWR baltic appears to have larger diameter bogie wheels than the LTSR baltic.

I managed to find some photos on t'interweb of the Whitelegg baltics to see the rear bogie splashers. The GSWR one was harder to find and I've cropped both for the detail.

GSWR baltic detail


Shame I couldn't find this view for the GSWR baltic. This is the LTSR Whitelegg baltic and the rearmost bogie splasher looks a lot wider. Would it be the same for the GSWR baltic?

 

[Tim Watson]

Ian,

I am building a G&SWR Baltic in S7 at the moment. I am having problems getting it round anything less than 9’. The problem is not the driving wheels, with the frames set at 29.5 they go round 5’6” curves, it’s the bogies. The prototype permitted 5” sideplay on the bogie but getting more is limited on the model by the bogie splashers which are fixed to the mainframes.

With the thinnest material for the splasher fronts, pushed out a bit, but constrained by the cylinders and tail rods, and the wheels turned to minimum thickness they still rub and derail! I expect that the originals straightened out the track and racked the frames on shed curves anyway but they had mass which our models lack. Even with as much weight as I can cram into the bogie it still won’t bend either the track or the frames.

My model might just end up as a glass case example.

Ian.

View attachment 134397

In 2mm scale, I would pivot the rear frames with the opening and closing joint just behind the rear driving wheel rims, out of sight, so the splashers follow the wheels. At the front end I would run the rear bogie wheels independently of the front ones - a sort of floating radial arrangement on the rear wheels; the front would effectively be made as a pony truck, but with a long pivot arm. These were the arrangements broadly used on my MR Kirtley back tank and Stirling 8’ single.

Tim

 

[Ian@StEnochs]

I was thinking of the rear bogie when conceiving the idea. It's almost trying to get the 4-6-4 configuration to behave like a 4-4-2-4 or 4-4-2-2-2! Looking at the photos below I believe it would work as the 'gap' between the two halves of tube would be hidden by the balance pipes and in shadow to boot. Especially as the GSWR baltic appears to have larger diameter bogie wheels than the LTSR baltic.

I managed to find some photos on t'interweb of the Whitelegg baltics to see the rear bogie splashers. The GSWR one was harder to find and I've cropped both for the detail.

GSWR baltic detail
View attachment 134444

Shame I couldn't find this view for the GSWR baltic. This is the LTSR Whitelegg baltic and the rearmost bogie splasher looks a lot wider. Would it be the same for the GSWR baltic?
View attachment 134445

Dave,

Yes, I wish I could find a photo of the rear too. Plenty of pictures but all 3/4 front or side on but with the underframes in shadow! However here is a scan of the GA which shows just how little clearance they had.

I am going to work on getting the basic 4-6-0 round curves. I can get some sideplay on the centre and rear drivers and also thin the centre flange slightly. Once, If, that is satisfactory, then I will try your idea on the rear. There is plenty of space for sliding splashers, perhaps on a common mount and moved by the bogie centre

There are models with the splashers mounted on the bogie but I long ago dismissed that as being too difficult to make look like the real thing.

Ian

 

[Ian@StEnochs]

In 2mm scale, I would pivot the rear frames with the opening and closing joint just behind the rear driving wheel rims, out of sight, so the splashers follow the wheels. At the front end I would run the rear bogie wheels independently of the front ones - a sort of floating radial arrangement on the rear wheels; the front would effectively be made as a pony truck, but with a long pivot arm. These were the arrangements broadly used on my MR Kirtley back tank and Stirling 8’ single.

Tim

Hi Tim,

I have learned a lot from your builds. Turning bogies into poney trucks certainly works and I use a version on 0-4-4 tanks. However concealing them in 7 mm scale is quite tricky sometimes, especially where the prototype had air tanks or balance pipes in the way.

On the finestandard O model I made the rear end of the frames bend just behind the sandbox. There is lots of slop between rail and the wheels so not such a problem at the front end. S7 is just a wee bit more taxing!

Ian,

 

[isambardme]

Hi Dave,

I like your thinking, your visual aid makes it very clear. However the splashers are as far out as the cylinders permit, this photo shows just how little space there is. You may see that the front splasher is tapered, wider at the front, as it was on the prototype. Sorry for the quality of the picture but not easy getting light yet not too much reflection.

View attachment 134435

Your idea is worth trying on the rear bogie, nothing to restrict movement except the balance pipes and they are quite far out. I could also let the rear drivers have some more sideplay which along with stiffer side control on the front bogie may get the beast round.

For my sins I am also building a fine standard O version alongside my S7 one. I have got this to go round a peco points crossover and a 5’6” curve. To do that I have made the frames under the bunker hinge, just behind the sandbox, and the bogie moves the frames sideways The side control on the front bogie pulls the drivers into curves helped by the slop between the flange and rail in fine standard.

I could do the same on the S7 model but I don’t want to.

Ian.

I can see why you are building a fine scale O gauge version too. At the end of the day it's up to the individual to decide what compromises they are prepared to make to have models that run well on their own and perhaps other people's tracks. Some time ago a group of us decided to make our exhibition standard layout to fine scale O gauge standards to enable as many people as possible to run their locos, should they want to. It is a decision that has not been regretted.
I would also say, from testing and running a wide variety of O gauge locos over the years, it often helps to have the motor/gearbox driving the rear axle if at all possible, this allows more sideplay on the centre drivers.
Anyway, good luck with the S7 model, I shall follow the thread with interest.
It is also interesting to note that as time went on, the full scale railway companies moved towards conventional bogies and pony trucks, no doubt for good reason!
Steve

 

[Lancastrian]

No splashers to worry about. Although I have the works drawing for the splashers, I have yet to find a photo of one of the locos sporting them.
I will probably have the frames at scale width at the front and rear, and find a suitable break point to hide/mask the frames being narrow for where the driving wheels are.

Ian

 

[Yorkshire Dave]

However here is a scan of the GA which shows just how little clearance they had.

Seems strange RH Whitelegg did not incorporate the wider rear bogie splashers when he moved from the LTSR to the GSWR, especially when he designed both of their baltic tanks. As as you've alluded to earlier I suspect there was alot of metal clanging twixt bogies wheels and splashers.

No splashers to worry about. Although I have the works drawing for the splashers, I have yet to find a photo of one of the locos sporting them.
I will probably have the frames at scale width at the front and rear, and find a suitable break point to hide/mask the frames being narrow for where the driving wheels are.

Looking at photograhs you're quite fortunate as the L&Y also appeard to have used smaller diameter bogie wheels which would be able the bogie to swing under the frames.

Out of curiousity I downloaded these photos of the UK baltic tanks for comparison.

Furness



GSWR


L&Y


LBSCR


LTSR

 

[Lancastrian]

After watching the F1 the frames have been modified as below:



Scale width over frames at front and rear with both joints behind sandboxes