4mm On Heather's workbench - on a Holden to…Yarmouth?

[Mike Trice]

Use tapered/waisted bearings and countersink back of casting? I originally came up with the idea for tapered bearings to suit the Scalefour Sociaty's CCUs which featured a slotted "hornguide" and needed cast axleboxes to be opened up to allow movement. The tapered bearings made this much easier. Markits, Gibson, Maygib etc all do them.

Bearing and axle interfaces for coaches and wagons

Bearing and axle interfaces for coaches and wagons

www.clag.org.uk

 

[Simon]

But hang on a mo, surely there is enough "meat" in those casting to simply enlarge the hole with a drill bit held in a pin vice to give you the "slop" you require.

A whole lot easier than fretting, slotting, 3D printing or otherwise reinventing wheels - but what am I talking about, this is Western Thunder, so to paraphrase Mr Valentine "Roll on my beauties...."

 

[Heather Kay]

Use tapered/waisted bearings and countersink back of casting?

Rumney/Miscellany do recommend waisted bearings. I have pretty much the entire UK supply here! The suggestion to grind out the back of the axlebox casting is to give just a bit more headroom.

To be honest, there’s probably plenty of room as the castings are now. How much deflection of the springing should I expect on well-laid track? The bigger issue is the length of the cast spring.

 

[Heather Kay]

A whole lot easier than fretting, slotting, 3D printing or otherwise reinventing wheels

Quite. It’s the moulded leaf spring that’s concerning me most, though.

I have sought alternatives, as mentioned by the instructions. I need to check the leaf springs are the correct length on such alternatives before committing to a hefty investment, which is in hand. There is a drawing heading my way which will mean I have a much better handle on the scale of the prototype setup, and that may lead down some interesting avenues that may well be better than a lot of whitemetal bits of indifferent quality.

We shall see what transpires.

 

[Simon]

Well that wasn't the question you asked Heather was it? But no worries, instead of simply acknowledging what might be a good and simple idea you instead make a dismissive comment and then go off and start waffling and fretting about the next thing.

Now that isn't called "imposter syndrome" is it?

To be completely honest I find this sort of endless pontification and prevarication pretty tedious, but you lot obviously love it, so as Mr Valentine said....

Thankfully, other more interesting threads are available.

Sorry if that sounds a bit rude, but I have an aversion to "ENCS" (Emperors new clothes syndrome) and am currently suffering quite badly from EBF (endless bollocks fatigue)

 

[Heather Kay]

Simon, I’m trying to explain what’s going on without giving too much away about things that aren’t confirmed yet. I’m sorry you don’t like my waffle.

Besides, I am an Olympic standard prevaricator.

 

[Heather Kay]

The suspension is quite simple. A length of guitar string (Ernie Ball Custom Gauge 9, if you must know) is fitted to the folded bearing holder. The bearing holder is not held in place by anything else until a wheelset is fitted.



My first effort followed the kit instructions, where the top hat bearing is soldered into a rebate. This is designed for Exactscale bearings, but I’m using Gibson's, which are a little deeper. Consequently, the wheelset had quite a bit of side play with the Gibson P4 wheelset in place. I expected this, but wanted to confirm it. The instructions go into this, and the fix is to solder the top hat on the inside face of the bearing holder so the latter acts as a shim. Happily, on the second go round, the wheelset fitted with almost no sideplay.



As Simon noted, the axlebox casting won’t need a lot of grinding out to allow for bearing movement. If the leaf spring casting was the right length, I’d have done that already. A little tweaking of the brake shoes so they aligned with the tyres and didn't cause binding was required, so it was as well I decided not to solder the yokes in place in the hangers.



Like most other suspension systems, this is designed to mostly let the wheel drop into irregularities in track, rather than ride up. Once I have the other bogie rolling I can work out how to attach them to a coach underframe. Then I can play with extra weight and so on to get the best running qualities.

 

[Mark Tatlow]

Hi Heather

They are coming together well and by the time you have built all of them you will take the world record for the total number built!!

In respect to how the bearings are fitted in their carriers, I have found several depths of bearings and, to a much lesser degree, axle lengths and this does create issues. It sounds as if you have arrived at a conclusion to this.

With regard to the castings, I have not used the D&S GN castings and they do look short in your pictures. Oddly, I have used their NER ones and they are fine. I did manage to melt the end of one spring a while back and I dealt with this by turning the wire that holds the discs that make up the dampers (you haven't done this yet) of and then using epoxy putty but that is not a sensible to do this to all of them.

If you find a way around this, then making the slots in the white metal versions can be simply done with a scalpel. You can quite easily carve a little away at the top and bottom to ensure that the bearing slides unfettered. The cast brass ones are much harder and you will need a burr in a mini drill to do this but I quite accept it is hard work!


Mark

 

[Mark Tatlow]

One other thing Heather, I think the bearings are likely to be sitting a bit low (so the bogie is a bit high). If you feel this to be the case then you can flex the ends of the guitar wire a bit. So long as you do so consistently, then this works fine.



Mark

 

[Dave Holt]

Presumably they'll squat down a bit with the weight of the body? It might be advisable to leave the axlebox castings off till the first body is on before making spring adjustments?
Dave.

 

[Heather Kay]

Thanks Mark and Dave!

Leaving the cosmetic castings off is probably a good plan. Seeing where the ends of the bearings sit will be helpful as I adjust things. I need to work out how to mount the things to the D&S floor. Once I have a rolling chassis I can work out if the coaches might need extra weight, with the aim of getting the ride height so the bearings are sitting just off the top of the hornguides.

It looks like it’s going to be a hot one today. Doors and windows are wide open already, and fans are on standby. Whether I feel like working with a soldering iron remains to be seen.

 

[Ian@StEnochs]

It looks like it’s going to be a hot one today. Doors and windows are wide open already, and fans are on standby. Whether I feel like working with a soldering iron remains to be seen.
[/QUOTE]


It’s grey, murky with rain forecast here! Not a bad day for some workshop action but I’m giving it a miss in favour of a visit to the Glasgow real ale festival.

 

[simond]

mmm, difficult. Nice weather or Real Ale.

I'm in the office, so, I guess, neither, still all being well, a running session this evening, followed by a pint of something.

 

[Daddyman]

My tuppence worth: leave the castings off, yes. Open them out by twizzling a 2.4mm drill (to ensure clearance on the bearings) from the downward and upward direction. Springs can be bent with a simple jig (lines scored with a Vernier locked at 1mm intervals), though if you're using 9-gauge they may not need it. These are my 10-gauge ones (9-gauge on the bolsters):

 

[Dave Holt]

I would think the correct ride height of the bogies is with the bearings roughly half way up the narrow part of the slots, although someone with prior experience of these bogies might advise otherwise.
For mounting, it looks like an 8, 10 or 12 BA screw (whichever fits through the hole in the bolster) should protrude from the coach floor. The top of the bolster rubs on the underside of the floor or some packing piece and the buffer ride height can be adjusted by tightening/loosening of the retaining nut which also preloads the bolster springs (I assume the bolsters are sprung relative to the bogie frame?)? You may need to file the top faces of the bolsters smooth to allow easy sliding and rotation.
Dave.

 

[Daddyman]

I would think the correct ride height of the bogies is with the bearings roughly half way up the narrow part of the slots

Agreed.

the buffer ride height can be adjusted by tightening/loosening of the retaining nut which also preloads the bolster springs (I assume the bolsters are sprung relative to the bogie frame?)? .

The bolsters are sprung too, yes. But the retaining nut goes through the top of the bolster, so has no impact on ride height. It (the nut) needs to be just tight enough to allow rotation and to prevent waggle.

The ride height can only be adjusted by (a) packing under the carriage floor, and/or (b) bending the axlebox springs once the weight of the carriage is known (including seats, passengers, roof, roof fittings, floor fittings, etc).

 

[Daddyman]

The bolsters are sprung too, yes. But the retaining nut goes through the top of the bolster, so has no impact on ride height. It (the nut) needs to be just tight enough to allow rotation and to prevent waggle.

The ride height can only be adjusted by (a) packing under the carriage floor, and/or (b) bending the axlebox springs once the weight of the carriage is known (including seats, passengers, roof, roof fittings, floor fittings, etc).

Sorry - this is wrong: the retaining nut can compress the bolster springs. But I think it's bad engineering practice to let it do so - isn't it? - as it alters the tension in the bolster springs.

 

[Dave Holt]

I have no knowledge of these particular bogies, but the Dave Bradwell type, which also have sprung bolsters, specifically need pre-tension on the bolster springs to give lateral stability. Otherwise, the coach body can wobble from side to side in a most un-prototypical manner. Dave's instructions are quite specific about this. If I recall correctly, the method is to adjust the height of a bearer plate above the bolster, held between two nuts, not by tightening the bogie retaining nut underneath. It's a rather fiddly procedure but does give a super ride.
Dave.

 

[OzzyO]

Sorry - this is wrong: the retaining nut can compress the bolster springs. But I think it's bad engineering practice to let it do so - isn't it? - as it alters the tension in the bolster springs.

It's called pre-loading the spring. After that the spring should carry the weight.

OzzyO.

 

[simond]

I wouldn’t call it “bad engineering practice”. It’s only bad if it doesn’t get the result that you’re trying to achieve.

Pre-loading is achieved by pre-compressing a spring. This means that it won’t compress more, until a load exceeding the preload is applied. That might be a good thing in some applications, but, I doubt it’s what you’d want on a model, unless you’re using the preload to set a ride height, and you’re not too bothered about the smoothness of the ride.

(I‘ve never heard any of my passengers complain, but then at my age & mileage, high frequency hearing ain’t a strong suit).

I‘ve never “designed” springs for models, I’ve always tried the springs I could find in my bits boxes that fitted, and changed them about to see what worked best.

But if I were designing something, I guess I’d try to arrange the spring stiffness to be enough to keep them compressed a bit when you lift it off the track and the axleboxes go to the full droop position, and about twice the vehicle weight at the axlebox fully up position (ie suspension fully compressed), and with a bit of luck, they’d sit, static, at about half travel. Getting springs of this rate, which would be one eighth of the coach weight plus say 10%, divided by the travel (1-2mm?), might be a challenge, but sounds like a target.

Adjusting the ride height, having got the right spring rate (rate=stiffness units are N/mm or lbsf/inch), might involve some shimming, and a great deal of faffing about. Probably even more faffing in smaller scales. Or you can simply use what fits and try it. Add weight, or stretch the springs a bit.

But don’t cut coils off. That makes the spring shorter, but stiffer.

Thinner wire or bigger diameter or more coils = softer (lower rate)

the opposite is obviously true!

atb
Simon