4-4-0T - A question of balance

hughesp87
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Joined: Tue Aug 05, 2008 8:25 pm

4-4-0T - A question of balance

Postby hughesp87 » Fri May 07, 2021 11:55 pm

Can anyone more experienced in the art of loco building give me some pointers as to how to achieve a suitable balance across the chassis of a 4-4-0 tank locomotive?

Common sense dictates that the bogie will have to carry a fair proportion of the weight, and the question therefore is how that can be most easily achieved with a sprung chassis.

Screenshot 2016-01-18 20.48.50 (2).png


Here is the beast to be tackled, with the complexities compounded by the fact that it's a 3foot gauge prototype from across the Irish Sea. Drivers will be sprung, with the gearbox mounted on the rear axle and the motor and flywheel projecting forwards along the boiler. Drivers are 14mm in diameter with a 24mm wheelbase. The bogie wheels are 8mm diameter with a 20mm wheelbase.

Is there any essential reading on this particular type of build for a 4-4-0, or can anyone give me the benefit of their practical experience please?

Thanks in advance.

Geraint
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Geraint Hughes
Cromford & High Peak in P4
Danish Railways in P87

Philip Hall
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Re: 4-4-0T - A question of balance

Postby Philip Hall » Sat May 08, 2021 9:07 am

I was about to reply as to how I'd done my NBR 'R' class 4-4-0T when I noticed that you wanted to spring the drivers. So that's where my experience walked out of the door! Just in case any part of it proves to be useful, though, I used a fixed axle at the rear, and a compensation beam between the front drivers and the bogie, with the bogie actually pivoted on the end of the front of the beam beam rather than having a rubbing plate on top. It works a dream and slides along silkily. Apart from the outside cylinders, it looks not unlike your little engine.

Philip

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Will L
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Re: 4-4-0T - A question of balance

Postby Will L » Sat May 08, 2021 9:43 am

hughesp87 wrote:Can anyone more experienced in the art of loco building give me some pointers as to how to achieve a suitable balance across the chassis of a 4-4-0 tank locomotive? ---

...Is there any essential reading on this particular type of build for a 4-4-0, or can anyone give me the benefit of their practical experience please?

Geraint

I have been this way before, and while I'm a little hesitant to decsribe my ramblings as "essential" I have covered CSB (sprung) locos including those with leading bogies in some detail.

If you follow this link to my
CSB Source book you will find an index of all my post in fitting CSB. which allows you to find the relevant posts and gives you links forward.
For your purposes the links onward that will be of most interest will be
CSBs and the Single Bogie cover my first try at doing what you want to do
CSBs a question of Gravitygeneralises the solutions to any loco with a leading bogie that you want to carry weight.

Sorry I'm not given to short punchy posts so there is a fair bit to read but I think the answers you want are there. Dont hesitate to get in touch if you need further assistance.

hughesp87
Posts: 137
Joined: Tue Aug 05, 2008 8:25 pm

Re: 4-4-0T - A question of balance

Postby hughesp87 » Sat May 08, 2021 10:07 am

Philip / Will,

Thanks for your replies. Much food for thought there - and some interesting reading!

Regards,

Geraint
Geraint Hughes
Cromford & High Peak in P4
Danish Railways in P87

timlewis
Posts: 51
Joined: Wed Jul 23, 2008 6:13 pm

Re: 4-4-0T - A question of balance

Postby timlewis » Sat May 08, 2021 10:36 am

There's an article by Roger Bird on scratchbuilding a Cavan and Leitrim 4-4-0 in MRJ 240, but no idea whether it was sprung or not - my MRJs are difficult to access at the moment so I can't easily check. (Come to think of it, it might not even be a tank engine (!) but from memory I think it was, though I'm not very familiar with the prototype).
Cheers.
Tim

davebradwell
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Re: 4-4-0T - A question of balance

Postby davebradwell » Sat May 08, 2021 10:45 am

I would just pretend it's an 0-6-0 with the bogie replacing the front axle, although it might benefit from a little more weight. Flat plate on bottom of frames sits on flat plate on top of bogie frame, bogie axle holes slotted and single spring each side of bogie sitting on axles at ends and something like single csb pivot in centre. Springs to be as far apart as possible. However you spring the loco, with such a small prototype your biggest enemy will be stiction in hornblocks/axleboxes so take great care smoothing and duburring all parts. Finding a narrow gearbox might be a issue.

DaveB

hughesp87
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Joined: Tue Aug 05, 2008 8:25 pm

Re: 4-4-0T - A question of balance

Postby hughesp87 » Sat May 08, 2021 10:59 am

Thanks Dave. The model is very much at the design stage at the moment, and the design will be transferred to artwork for etching in due course, including a tailored gearbox.

Although I've done a fair amount of design for other etched locos, this wheel arrangement I have no experience of, hence the plea for help.

Doubtless a fair amount of head scratching to go before the etchers receive my artwork!
Geraint Hughes
Cromford & High Peak in P4
Danish Railways in P87

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Will L
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Re: 4-4-0T - A question of balance

Postby Will L » Sat May 08, 2021 11:55 am

davebradwell wrote:I would just pretend it's an 0-6-0 with the bogie replacing the front axle, although it might benefit from a little more weight.

Certainly a valid approach, but as the height from rail top to fulcrum is one of the more critical dimensions and needs to be the same for driving wheels and bogie, it isn't that easy to ensure this is true. We are talking trying to be accurate to within 0.1 mm. Nor is it that simple to arrange how the bogie fulcrum point interface with the wire. Of course it can be done, and designing a bespoke etch is probably the best way to achieve it, but I find that once you've got your head round the implications of having a bogie separate from the CSB, that turns out to be simpler to do.
However you spring the loco, with such a small prototype your biggest enemy will be stiction in hornblocks/axleboxes so take great care smoothing and duburring all parts.

That is good advice.

davebradwell
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Re: 4-4-0T - A question of balance

Postby davebradwell » Sat May 08, 2021 12:06 pm

I was attempting to complement your advice, Will, with separate spring in bogie and drivers treated as a unit - we'd both previously expressed a wariness of trying to transfer csb to carrying wheels. It was a suggestion for % of weight on bogie and suitable mechanical arrgt. Actually for a 4 cpld unit you only need a single centre support for the spring (which might be adjustable) but that would, presumably, be outside the considerable help that your site provides.

DaveB


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