CSB for a Class 14 Diesel?

[Triode]

Hi all,

I have one of Judith Edge Kits' new chassis kits for the Heljan Class 14 on order. The chassis kit comes with compensation, but I'm considering attempting a CSB solution. What I'm unsure of however is how to handle the fourth axle on this loco which carries the crank pins. Can this be left rigid to the chassis because it doesn't have any wheels fitted, or does it need to be sprung?

Also, I'd appreciate your thoughts on whether this project is too ambitious for a first effort at CSB, and also the first chassis I've built in a long while? Would the performance with CSB be much better than just building it with compensation?

Thanks,

Liam

[nigelcliffe]

On the prototype, the jackshaft isn't sprung (that's why it was done that way - no springing/flexibility between motor and jackshaft). Therefore don't spring your model and follow the prototype.

(Obviously?), the link from jackshaft to wheels needs to flex at two pivot points to allow the wheels to move on their springs.

[Tim V]

The performance isn't just down to how the wheels are suspended, the main effect on performance is the quality of the wheels and how they are assembled. Then it's down to the quality of the power train (!). A good compensated loco will outperform a poor CSB loco.

As for the gap in time between now and the last one, there has to be a first time for everyone! So long as you built locos that satisfied you then, no reason a CSB project should fail.

[Hardwicke]

Ooh this might solve my long term Constructeon class 14 problems.

[Will L]

... A good compensated loco will outperform a poor CSB loco...

Or visa versa. A well fitted CSB loc will, like any sprung loco, will run more smoothly than a compensated loco with a fixed axle.

[davebradwell]

How about just "a good loco will outperform a bad one" - it's all completely meaningless but whatever, the sprung one will be quieter.....unless it's a bad one, of course.

DaveB

[Triode]

As for the gap in time between now and the last one, there has to be a first time for everyone! So long as you built locos that satisfied you then, no reason a CSB project should fail.

The only comparable chassis I've built before was a rigid Branchlines 0-6-0 in 00. It did work, but I never finished the project and wouldn't say I made a very good job of it!

That said, it was 10+ years ago and I had zero experience of soldering or etched kit construction at the time. Since then I've built plenty of etched and sprung wagons and a couple of High Level gearboxes. I think I'm confident enough that I could build a rigid chassis well enough nowadays, but springing something with a motor on board is still a bit daunting!

[Tim V]

... A good compensated loco will outperform a poor CSB loco...

Or visa versa. A well fitted CSB loc will, like any sprung loco, will run more smoothly than a compensated loco with a fixed axle.

Sorry my bad English!

A well constructed compensated loco will out perform a poorly constructed CSB loco. CSB is not a panacea to good running, you still have to put a lot of work into making sure your wheels are round, concentric, the crankpin throws are consistent.

[davebradwell]

It still doesn't say anything - a well constructed loco will always out perform a poorly built one. If you think compensation is great and springing rubbish just say so and we'll know where you stand.

DaveB

[davebradwell]

To be more helpful, the jackshaft should be rigid and carry the gearbox like the prototype. Normal jointed rods will transfer the drive to the other wheels - I know a Dreary built like this. The really clever bit is getting the throw of the jackshaft crank exactly the same as that on the wheels so you would want to base the crank on a wheel centre for simplicity.

To avoid further controversy over suspension I'll just say that the sprung loco will always be quieter than the compensated, especially if the latter has the dreaded fixed single axle. This is probably the most obvious benefit of using springs and is frequently lost in the trivia. I doubt if an all rigid chassis would be a success - the rtr people rely on just the right amount of clearance to keep it on the track and this would be difficult to replicate while still getting it perfectly level and square. Anyway, the model came out of its box rigid so why make another one?

As for gearbox mounting, a rigid axle is rigid in name only as there is some clearance in the brgs. Therefore it should be dealt with in exactly the same way as you would on a moving axle so that it can take up its own alignment. It will want to move as the axle shifts slightly in the brgs.

DaveB

[Philip Hall]

I would agree that a sprung engine will be quieter than a rigid or compensated one. But as Tim says, truly concentric wheels are often not thought about; I even heard it said once that springing or compensation was to help out with non-concentric wheels!

But what has always amused me is that I have spent half a lifetime learning to build quiet mechanisms (of whatever persuasion) and now we have DCC sound which will completely drown out something that sounds like a concrete mixer full of granite boulders!

Philip

[Will L]

... CSB is not a panacea to good running, you still have to put a lot of work into making sure your wheels are round, concentric, the crankpin throws are consistent.

CSBs certainly don't grantee a good running chassis, its building them well that does that. And frankly the skills necessary to do that are much the same for Compensated or sprung chassis.

... But as Tim says, truly concentric wheels are often not thought about; I even heard it said once that springing or compensation was to help out with non-concentric wheels!

A Sprung chassis will certainly hide the effects of a none concentric wheel better than any other system, as the spring decouples the body from the wheels in a way compensation can't. So any up or down movement of the wheel is not immediately transferred to the body.
The basic truth is that any wheeled vehicle will ride more smoothly when sprung and for this reasons most wheel transport ends up being sprung. From horse and carts upwards. Why should the same not apply to out trains?

I agree one would rather not have the non-concentric wheel and hiding the effect is definitely second best to not having one, but just assuming you have one that's degree of non concentricity is only just visible..,.?

Anyway, wont DaveBs fancy measuring facilities tell us that truly concentric wheels are a rare beast?

As for the crankpin throw not being consistent, that will prevent any chassis type working well, so leaning to deal with that is a basis skill we all need.

[Triode]

Regarding concentric wheels and crankpin throws, aren't these purely dependant on the quality of the wheels from the manufacturer (Gibson, Ultrascale, etc.)? I didn't think there was much the end-user could do other than make sure they get the wheels square on the axles?

[davebradwell]

Don't forget all wheels need to be the same diameter, that is from the same batch. Even wagons need both wheels on an axle to be the same and if you have a rogue vehicle it's worth checking.

As for investing in equipment to check these components, this is a matter of whether you want to verify the critical dimensions first or wait until problems reveal themselves later. You'll see an eccentric wheel when it's mounted on the chassis but it's more work to take the thing apart to fix it.

Crankpin throws are usually ok but older stock might be suspect. Original Sharman's could be found with leaning crankpins where they had been removed from the mould too quickly. Just because you have a good wheel doesn't mean you can't mess it up by fitting the crankpin badly.

Returning to the thread, can you find fulcrum points for the asymmetric wheelbase, Will? Surely there's a limit but perhaps not this time.

DaveB

[Philip Hall]

Eccentric wheels can be fixed but require a lathe. It’s usually a matter of taking the tyre off, skimming the plastic centre true and gluing the tyre back on. I find I can judge the degree of truth by eye.

This can only be done of course if the tyres (like Alan Gibson) are a press fit on the centres. Others like Sharman need a form tool and more skill. Ultrascale are invariably dead true.

Philip

[davebradwell]

If you're lucky and your wheels are Gibson old stock, popping the tyre off will reveal the moulding pip which is causing the eccentricity. Easily sorted without a lathe but Colin has been much more careful about such things on later stock.

DaveB

[Triode]

Ultrascale are invariably dead true.

I do have a set of Ultrascales for the Class 14 that I was thinking of using, but they are on 2mm axles (as per the Heljan model) whereas the Juith Edge chassis is designed for 1/8" axles and Gibson wheels. I suppose it might be possible to put sleeves around the axles though.

Another issue is that the Ultrascale wheels for the Class 14 have protruding bosses on the backs to reduce sideplay in the Heljan chassis, but these would foul the Judith Edge chassis. It might be possible to cut or file the bosses away, but I’m hesitant to try this as the Ultrascale wheels aren’t cheap! Even attempting to take them off the axles to fit hornblocks etc. makes me nervous!

I also don't know whether the crank throws are the same for the Gibson and Ultrascale wheels.

[davebradwell]

Because Gibson and Ultrascale wheels come out of different moulds you have to assume the crank throws are not the same.

Reducing bosses on the back of wheels is a standard procedure when building chassis but with these already mounted for you I understand your reluctance, especially as there's a basic incompatibility of axle sizes. You need someone to turn you some stepped axles while sorting out the bosses or buy new wheels.

The drop-in wheels option is sounding more attractive!

DaveB

[Hardwicke]

Hi all,

I have one of Judith Edge Kits' new chassis kits for the Heljan Class 14 on order.

Liam

Can't see it on their website

[Will L]

... can you find fulcrum points for the asymmetric wheelbase, Will? Surely there's a limit ...

Yes but not one that needs to bother us. As I'm enjoying a restful afternoon in the India sun shine you can have the full answer now.

Asymmetric wheel bases are what the spread sheet is all about. 2 axle chassis are trivial, any symmetric setup with the middle fulcrum at the wheel base centre will do. The only use for the spreadsheet is to work out what size wire you need for a given vehicle weight. For more axle than 2 axles, once you’ve got a bit of experience, you can guestimate an answer for a symmetrical chassis. The answer will be symmetrical, with fulcrum point central between axles and the outer ones about 0.56 the distance from the axle as the inner ones. (there are other answers but that one works)

The asymmetric answers really aren’t guessable, the spread sheet allows you to ensure that each spring segment will be deflected by the same amount for a given applied weight. So given you have the vehicle CofG in the right place you will get a horizontal chassis with equal weight carried on each wheel. There are many potential quite close enough answers but none that are absolutely perfect. The good enough answers will fall in a sweet spot. I haven’t yet met a chassis which is so asymmetrical this isn’t true. You can tell if you are outside the sweet spot if very small changes in fulcrum position produce big changes in the displacement (Experience will also be alerted if there is either too long or too short a distance between the outside fulcrum points and the adjacent axle).

Russ and I argue about how far the end fulcrums should be from the end axle. A longer gap will result in the use of a slightly thicker wire and possibly a bigger sweet spot. I find shorter gaps work perfectly well and but in the end I am generally driven by where I would like the chassis spacers to be and incorporate the fulcrum point into them. Off course you must always take account of what fits a chassis and what you might want to avoid.

If you badly want an asymmetrical weight distribution too, i.e. the Loco's CofG resolutely wont fall centrally over the driving wheels, the spreadsheet will deal with that too, but now its getting complicated.

[Triode]

Can't see it on their website

I found out about it here: https://www.rmweb.co.uk/topic/45248-jud ... s/page/73/

[Daddyman]

I suppose it might be possible to put sleeves around the axles though.

Gibson does such sleeves. Product 4M68:
http://www.alangibsonworkshop.com/catalogue.pdf

And also, if you're going down the CSB route, presumably with High Level hornblocks, Chris at HL does 2mm-bore hornblocks, and all/most (?) of the gearboxes are available for 2mm axles.

[Triode]

I suppose it might be possible to put sleeves around the axles though.

Gibson does such sleeves. Product 4M68:
http://www.alangibsonworkshop.com/catalogue.pdf

Thanks. I bought a pack of those when trying to adapt Gibson wheens to the 2mm axles for the Heljan chassis. Unfortunately the majority of them weren't accurate in terms of having the 2mm bore dead centre to the sleeve. Not sure if I just had bad luck.

[zebedeesknees]

I suppose it might be possible to put sleeves around the axles though.

Gibson does such sleeves. Product 4M68:
http://www.alangibsonworkshop.com/catalogue.pdf

Page 12..

And also, if you're going down the CSB route, presumably with High Level hornblocks, Chris at HL does 2mm-bore hornblocks, and all/most (?) of the gearboxes are available for 2mm axles.

And the bosses will still need to be removed from the backs of the wheels. I have done several of these, fitting Ultrascale wheels to Penbits bogies on Cl.24/5s, it's dead easy, just find a washer that fits over the boss, steel preferably, and saw then file back to that.

On the subject of compensation versus springing, my motivation towards springs was inspired by the Deputy Chairman's Cup Competition decades ago, and the measurement of drawbar pull. One competitor, before my time at CLAG when they were using a cord over a wheel at the end of the track with a tray for weights on the end, produced a loco that couldn't lift the empty tray. That was compensated. Springs and the position of the centre of mass, balance, maximises the traction for a given weight. Whether individual springs or CSBs, that to me is the most important, ride quality and stability are collateral benefits in a locomotive.

http://www.clag.org.uk/41-0rev.html#figure42 explains.

Ted.

[Hardwicke]

Can't see it on their website

I found out about it here: https://www.rmweb.co.uk/topic/45248-jud ... s/page/73/

Ah, last year. I wonder why it's not mentioned anywhere else?