Bogie Basics

[petermeyer]

Postby davebradwell » Sat Jan 29, 2022 5:03 pm

...Finney kits build into a highly detailed model that has probably never been equalled in terms of appearance. However, in the years since they were introduced we have new components and techniques so hornblocks can be improved (Roy Jackson saw the point contact provided by the Flexichas bearings as the Achilles heel of P4), a single rigid axle gives a bumpier ride than other options and there are better designs of bogie and pony that are less prone to derailment...

DaveB

Whilst I am currently on with the Finney bogie for a Duke and a City, can I ask what is the current best practice for bogie design? How do I apply this and improve the Finney bogie? The digest pages on this subject are dated 2003, the same date as the Finney Duke.

[petermeyer]

For reference, here is a Finney City bogie. Not my build as I have held off getting this far to see if I can improve upon it. There is a 10ba bolt pivot from the chassis:

post-5096-0-06158700-1417821849.jpg

[davebradwell]

Favourite is a weight bearing bogie supporting body on a flat slide on top, like the prototype, with a spring each side outside the wheels and inside the frames which would be slotted to give the bearings some vertical movement. Just a single centre support for each spring. Try Jackson coupling wire for a first try - 11thou'. It seems it's the wider the better for the springs.

The single spring may not be suitable for your outside frames so it may need springing like a wagon - unless you move the springs inboard of the wheels which is no worse than my inside framed LNER bogies.

Side control has been discussed recently and I think I posted a bogie drg there. I can clarify if required.

DaveB

[LMS10640]

It would be worth looking at Dave Holt's Royal Scot topic. There is also a specific one on loco bogies by Zebedeesknees August 2020

best wishes,

David

[davebradwell]

I recall a thread discussing them and they're the same basic principles adapted to a bogie with equalising beams on the outside.

DaveB

[petermeyer]

It would be worth looking at Dave Holt's Royal Scot topic. There is also a specific one on loco bogies by Zebedeesknees August 2020

best wishes,

David

Thanks David, I've had a look at these and have picked up some clues. One thing that prompted me has been the recent discussion elsewhere on here on 4-4-0's and I have built a "Lycett-Smith" 4-4-0 chassis which seems to work, because I had the parts. That system of attaching the bogie would seem outmoded. It is how the bogie is attached to the chassis that occupies me at the moment.

[davebradwell]

It's worth looking at the prototype as bits of the bogie slide are sometimes visible outside the frames above the centre of the bogie. It's visible on City of Truro as the inner frames are visible here.

DaveB

[johndarch]

While we are on the subject of bogies, I have been doing a little experimenting myself. I am currently building a Martin Finney chassis to go under a Bachmann Hall. Why, because the MF kit only covers the earlier locos. I have been converted to CSBs so proposed using them on this chassis, dispensing with the compensation beams. However the body is very front heavy and although this can be remedied to a certain extent with lead in the firebox, the CoG is still forward of the centre drivers. I have never been entirely happy with the springing on my other MF Hall so looked into a solution that would kill two birds with one stone. I have a lot of Alan Gibson sprung pickups in my spares box and decided to see if I could use these to bear on the bogie. A styrene packer was cut to fit between, and level with, the bottom of the frame and both frame spacer and packer were drilled to take the nylon sleeves of the pickups. The springs were too strong, so I reduced their length by just under a half. The spacing and vertical location of the CSB pivots were calculated on the default position of the CoG just behind the centre drivers. The bogie was built as per the instructions except that the pivot slot was opened up to take the thin walled brass tube around the 10BA pivot bolt. It all went together for the first time today and I am pleased to say that it sits level, at the correct height and all ten wheels are firmly in contact with the track. It also glides though turnouts. Any minor adjustments to weight distribution once the model is complete can be made by adding lead as and where required to the chassis. I see from the photo I took today, that the height of the tender needs adjusting - a little spacing between the Brassmasters inner chassis and the Bachmann body will sort that.

Loco 13.jpg

Loco 12.jpg

[petermeyer]

John

A rather interesting solution. I am in the middle of a number of bogie locos including a MF City. I’m also about to take the plunge into CSB. I was wondering how to spring a MF bogie. Food for thought. Thanks

Peter

[Will L]

One of the interesting little consequences that comes out of fitting CSBs is that, if the CSB chassis is sitting level, (i.e. because the front of the loco is being supported on a bogie) then the proprtion of the loco weight carried by the CSB chassis will be distibute across the drivers as if that weight was situated on the CSB design point for the CofG for the chassis. The remaining weight is carried by the bogie. Given you know where the real CofG is located its a simple calculation to work out what percentage of the weight is actually on the bogie and how much is on the driving wheels.

For an explanation of how this all happen see CSBs a question of Gravity. The relevant explanation starts about half way trough the first post. The implication is that a CSB fitted locos with a weigh carrying bogie is not the logical conundrum that may have thought it might be.

[davebradwell]

The only snag I can see with this is that you can still see through the slide, rather like the floppy bogie that doesn't have one. Perhaps the cylinders block this view on a Hall. On the plus side, however, it's probably easier than fitting springs bearing on the axleboxes in the bogie in the photo. I just like copying the prototype slide and there must be something missing to make space.

DaveB

[Phil O]

You could add a bit of weight at the rear, by using whitemetal crew to the cab.

Cheers

Phil

[johndarch]

In light of another current topic re springs. I shortened the springs so that they needed to be compressed less to get the bogie sitting at the correct height not to make them weaker. Apologies for misleading wording!

[petermeyer]

No this is all good information. I was thinking of putting a coil spring on one of my bogies and cutting it down which now does not seem such a good idea. Despite initially looking promising, the bogie on my Experiment is a bit wayward so I need an alternative fixture. As a 4-6-0 it runs fine without the bogie so that isn’t carrying much weightif any. One idea to tame it is to fix a coil spring over a pivot to hold it down. The build is in the workbench section.

[johndarch]

The only snag I can see with this is that you can still see through the slide, rather like the floppy bogie that doesn't have one. Perhaps the cylinders block this view on a Hall.

DaveB

This is what it looks like without the cylinders

Loco 10a.jpg

[davebradwell]

You probably won't be able to see what a real Hall looks like down there because of the cylinders so it doesn't really matter and it's saved you the job of re-designing the bogie, John. I expect you are very pleased with the smooth and quiet running of the loco, especially with the front end properly supported.

The advantage of a proper slide is it enables this part of the prototype to be modelled correctly - if it matters.

I would warn that I believe putting a single spring over the bogie pivot gives less reliable trackholding than a spring or springs at each side, wherever placed.


It's intriguing to consider what might have happened to the rest of the Hall kit - is there a Finney body going around on a Hornby Chassis?

DaveB

[petermeyer]

Excuse my naivety as I am not such an accomplished modeler as those that have posted on here, and sorry to persevere with this, but getting back to basics, I alluded previously to the fact that I'd built one chassis with the Lycett-Smith system. This uses a swing arm support which is presumably frowned upon as an outdated way to attach the bogie. I cannot find a reference in the digest as how to best attach the bogie. From what I've seen, and in kits I have, there is either a pivot coming down from the chassis or screwing up into the chassis. Just attaching the bogie with a nut/washer is probably inadequate. Do I take that is best to have a slide interface between the upper part of the bogie and the chassis.

Taking the prompt to check the prototype, I was passing by the NRM today as you do, and popped in. City of Truro is at Shildon, but I had a good look round Lode Star. Unfortunately the barrier prevents a clear view, but I could not see any space between the bogie and frames to show the form of the slide.

IMG_0927.jpg

This is the underneath which shows a central pivot and springs fore and aft. I could not see any springs outside the wheels nor attached to the frames.

IMG_0933.jpg

IMG_0911.jpg

This is a close-up of JP Richards' excellent 7mm LNWR Experiment in a display cabinet. There is clearly a pivot on the bogie into the frames but plenty of daylight too. Presumably this is missing a slide.

JPR_Experiment_bogie.jpg

I'm still not sure even with the help of all these photos that I clearly understand...

[davebradwell]

That's just it - with a proper slide there is no obvious gap. The large triangular casting bolted to the outside of Lode Star's frames with 5 bolts is the top part of the slide. There is a corresponding casting fitted to the bogie frame and the polished circular things are the bearing pads or more likely the casings for the pads that fit between and transfer the weight of the front of the loco to the bogie frame. This suggests there will be a small gap according to the thickness of the pads but it's probably obstructed by casting details. In the underneath view the centre pin engages in a casting that slides. The horizontal coil springs are the side control. I expect each axlebox will have its own spring inside the frame.

The gist of this should be correct but I'm not familiar with the subtleties of GW bogies over the years.

There's a common form of bogie with outside central springs and equalising beams - I think it's called an Adams bogie - where the bracket on the frames engages directly with the top of the leaf spring. Ted S has one of these on the CLAG site. Here I recall the slide is simplified to 2 wires or some such.

DaveB