S7 loco frame spacer recommendations ?

[Michael D]

I'm planning my first S7 chassis,ive been reading theres more than one frame spacer width ??
Ill be using standard kit thickness frames, springing which I understand , its just what to allow for when cutting new frames spacers.
Is the philosophy for as wide as is practical,28 or 29mm?

For a 4-4-0 would it work to have the leading driving wheel axle sprung the other fixed, the design of the loco and depth of frame make it tricky to fit sprung hornblocks to the rear axle.

thanks in advance
Michael

 

[Dog Star]

This question has many answers and which suits you may be different to that which suits me.

I note that you are a GWR enthusiast and that means that the answer from a prototypical and scale point of view is dependent upon class... the GWR mostly used 4'1" between frame plates with the frame plates between 0.875" and 1.25" in thickness. So choose your class, look for a frame plan in GRWJ, measure the thickness of the frame plates in the kit and get busy with a calculator.

Now this answer is only going to work if your layout has curves that are comparable with the scale equivalent of the curves on which the prototype could have run and if every other part of the model corresponds to how Swindon built their kit.

S7 modellers often have to accept some element of compromise in order that their models can be seen running on S7 track which is probably close, in some part, to the minimum radius for the prototype. Adjusting the separation of the frame plates to give clearance / side-play / "slop" between wheels and frames / cylinders / motion is such a compromise. If modelling track with minimal (prototype) curves then one needs to consider including gauge widening as would have been required for the prototype (see Permanent Way Institute handbook for values).

Taking a loco with frame plates of 1" with a separation of 4'1" then a scale width over frame is 29.75mm... that is likely to be too wide for satisfactory operation given the considerations of the previous paragraph. Starting with 29.00mm is a reasonable value for distance over frame plates... 28.5mm may be required if using tight curves or pony /bogie wheels or a long wheelbase.

Graham

 

[Steph Dale]

Michael,

Turning to the other aspects of your question as I'm not an S7 modeller routinely:

Yes, it's possible to set up a 4-4-0 chassis with a fixed back axle and springing on the main drivers. It may help to find a way to adjust spring tension though as you'll want to get a fair bit of the loco's weight going through that sprung axle, for traction, pick-up and road holding. I tend to use compensation for my 4-4-0s as it's better at the weight distribution, for those built from from most manufacturers kits I tend to use a 'bearing in beam' for the back axle, the main drivers being in conventional hornblocks. So saying; the Ex-Martin Finney kits have full height frames which go up into the cab so have conventional hornblocks on all axles and are provided with compensation beams; conversion to springing is simple.

It's worth thinking about sideplay early on in the development of your chassis solution. Graham's picked some good points about frame spacing. I'd note that if you're making a model with inside motion you'll have to cut sideplay on the crankaxle and that the Finney kits achieve this by being designed effectively as 2-4-2 locos in terms of sideplay; i.e. with sideplay on the leading axle of the bogie and the back axle of the coupled wheelbase. This approach works well and allows the frames behind the bogie wheels to be modelled.

In the case of inside motion and outside frames it's also worth noting that you'll find clearances around the motion much easier to obtain if you build the front bogie as an outside-framed unit. Many kits have an inside-bearing bogie which impacts the space required over the back axle of the bogie.

Steph

Finney7 LLP

 

[Dog Star]

Michael, now that you have comments from two WTers, how about telling us what loco you are contemplating building and from which kit?

 

[Michael D]

Thats not a bad idea is it.
We have a NLR Class 51 4-4-0,the inside cylindered one. I have made some frames from scratch and I'm using some etches blown up from the old Peter K 4mm,but the frames on that etch are very shallow,no provision or depth in the frame for horn-blocks,unless I custom make some and build them into the frames themselves opening up the axle hole with some oval shaped holes perhaps? and of course the frame spacers are only 24mm. Theres plenty of problems to solve as I go along let alone with the outside frame bogie, me thinks.
Hence the scratching of head how to bounce it along using the original chassis etch.....
The other is the Gladiator NLR Park Tank, thats very straightforward with the horn blocks etched in, very civilised, just slotted the first for the slaters horn block very straightforward.

Thanks for the comments thus far by the way.....
best
Michael

 

[Steph Dale]

Michael,

If you need to muck about with frame profiles, this post might help. Hopefully you've got some scrap material of the same thickness..
Steph's Southern workbench - Another from Mr Adams

Steph

 

[Dog Star]

We have a NLR Class 51 4-4-0,the inside cylindered one.

Now that is new to me, a quick internet bash suggests outside frame bogie, how about a photo?

The other is the Gladiator NLR Park Tank

Now this is not likely to cause problems with the frame plates and frame stretchers... you are going to need to check that the cylinders are at the correct (scale) centres. Where you are going to have to be careful is with the clearance between the front crankpins and the slidebars / crossheads... probably holding the front axle to minimal side-play.

 

[demu1037]

Michael,
One other consideration is what other components are you going to use, for instance, if using *unmodified* Slaters hornblocks, the maximum width between the frames is 28.1mm, this usually slightly under scale (but not always) and if using plunger pickups gives just enough room for them, you can of course increase this by reversing the bearing and cutting off the circular portion etc, but as mentioned above, other issues then raise their heads

Andy

 

[Michael D]

Thanks for all the very useful info, its much appreciated, heres a pic of the loco in question as well, it really does sit on its frames!
best wishes
Michael

 

[Ian@StEnochs]

Michael,

I have built 6 x 4-4-0,s and 4 x 0-4-4t,s in S7.

All the 4-4-0,s and two of the tanks are fully sprung with individual coil springs on each axlebox. The bogies are either sprung or compensated but have a sprung centre pivot such that each wheel can rise and fall about the datum. Frames are spaced at 28 mm minimum with my most recent loco being wider at 28.5 spacing.

Bogies have sideplay with side control and there is some play on the rear driving axle where I have a crank axle and on both if I have been lazy and fitted dummy motion! I have found that the bogies need a bit of weight on their own plus that provided by the sprung centre to ensure they stay in line. At speed the locos glide over track bumps with the wheels noticeably moving while the body stays steady.

The other two tanks are compensated with the leading drivers running in plain fixed bearings and the rear end carried on the centre of the bogie. The bogies have a fixed axle and the other supported at its midpoint to give 3 point suspension. On one engine, quite a short loco, the bogie is supported at its midpoint. The other is much longer so the bogie is pivoted above the front axle but the weight is carried at the midpoint. On both locos the 2nd driver is sprung and has the gearbox fitted. Both locos work well enough but at speed any bump is noticeable by clunks and lurches!

Where sideplay is required it is important that the pickups do not interfere so I use a homespun low force plunger described here on post 16 or springy wire scratchers hidden inside the tanks.
Simple loco to fill a space!

I will have some of these locos at the S7 meeting at Mark this Saturday and will be happy to let you have a look.

Ian.

 

[Ian@StEnochs]

Thanks for all the very useful info, its much appreciated, heres a pic of the loco in question as well, it really does sit on its frames!
best wishes
MichaelView attachment 80100

Michael,

I have a similar loco on my build list, quite far down but there, see the quick photo from David Smiths book on the Little Railways of SW Scotland.

Ian.

 

[Michael D]

Hi Ian, yes thats the original, Bow Works born and bred, built around 1855, and some of them were sold on to various lucky people, bet the crews loved the cabs, one thing on the NLR another in a Scottish winter!
Various rebuilds went on in the 1880's and early 1900's and they lasted until the mid 1920's, quite an elegant
An excellent reference source is Locomotives Illustrated No 129 ,and I've collected material so if you need anything just let me know...
best wishes
Michael

 

[Ian@StEnochs]

Hi Ian, yes thats the original, Bow Works born and bred, built around 1855, and some of them were sold on to various lucky people, bet the crews loved the cabs, one thing on the NLR another in a Scottish winter!
Various rebuilds went on in the 1880's and early 1900's and they lasted until the mid 1920's, quite an elegant
An excellent reference source is Locomotives Illustrated No 129 ,and I've collected material so if you need anything just let me know...
best wishes
Michael

Michael,

I am looking for a photo of the loco, preferably one of the ones bought by the G&P,33,36,37, and a drawing near the end of its NLR life. There are no surviving photos of one in G&P service. I will have a search for the Locos Illustrated but any other help would be gratefully received.

Ian.