0-4-2 compensation

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steve howe
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0-4-2 compensation

Postby steve howe » Sun Jul 05, 2020 12:39 pm

I wonder if anyone has a view on this one: its a 0-4-2 GWR 517 class from an ancient Mallard kit. I built one of these when they first came out in the late 1970s in P4 using Mallard's method of compensation which has an inner cradle holding the motor, gear set and driven axle all pivoting on inner bearings on the front axle, the driven axle goes up and down in slots in the outer mainframes, the rear wheels are centre-sprung. 45 years on and with her original Anchoridge motor and 80-1 gears she still runs very sweetly indeed, unfortunately the motor does intrude in the cab a bit.

I want to do better with the other two I've got to make, and following the example of the brilliant High Level 14xx chassis kit I made a while ago. Here all axles are compensated: the leading one independently centre-pivotted; the driven and trailing axles controlled by compensation beams resting on the bearings. I am planning to do the same with this example for the driven and trailing axles, but I wonder if there is any real advantage in compensating the front one or leaving it rigid? Before the CSB brigade spring into action I should mention I don't really get on with springs and have generally had good results with compensation beams, matter of 'what you know' I guess. I plan to use High Level hornblocks and gearset in this build.

DSCF2954.JPG


Any thoughts welcome,

Steve

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Tim V
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Re: 0-4-2 compensation

Postby Tim V » Sun Jul 05, 2020 12:47 pm

Full compensation as the High Level version. The fixed axle, though easier to build, does result in the engine lurching on poor joints.

CSBs have their fans, I am not one of them.
Tim V
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garethashenden
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Re: 0-4-2 compensation

Postby garethashenden » Sun Jul 05, 2020 4:14 pm

I would be inclined to put compensation beams between the driven axles. You'll need a pair to clear the gearbox. Then put a central pivot for the trailing axle to rock on. Or you could do it the other way around, pivot the first axle and compensate the other two, but the geometry and construction would be harder.

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steve howe
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Re: 0-4-2 compensation

Postby steve howe » Sun Jul 05, 2020 4:43 pm

garethashenden wrote:I would be inclined to put compensation beams between the driven axles. You'll need a pair to clear the gearbox. Then put a central pivot for the trailing axle to rock on. Or you could do it the other way around, pivot the first axle and compensate the other two, but the geometry and construction would be harder.


Yes I was wondering that, the beams would be simpler with both axles being the same height.

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Will L
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Re: 0-4-2 compensation

Postby Will L » Sun Jul 05, 2020 6:36 pm

Tim V wrote:Full compensation as the High Level version. The fixed axle, though easier to build, does result in the engine lurching on poor joints.

CSBs have their fans, I am not one of them.

Tim is entirely right about not having a fixed axle, even if he is mistaken about CSBs.

You should have a careful think about how the weight will get distributed. Consider where the locos centre of gravity (CofG) is likely to be and what percentage of the weight you want on the carrying axle. There is a lot of appropriate stuff on the CLAG website on compensating 0-4-2s which will let you work out what the weight distribution will be like.

Put the two beams on the driving axles and your can guarantee you will get the adhesive weight equally distributed between them, but you have to watch you get an appropriate distribution of weight between the driving and carrying axles, which will depend entirely on the location of the CofG. You won't need to use horn blocks on these axles as plain bearings in the beams is a perfectly sound way if doing it..

Put the beam between the second driving axle and the carrying axle and you can use the potion of the pivot points to control the amount of weight on the carrying axle, but you need to check with the CogG that you're going to get reasonably consistent weight distribution across the driving axles. Horn blocks are necessary of this one.

Either is a possible but do think it through, good workable results are not guaranteed if you just guess.

If you're going to use horn blocks all round then you're already most of the way to doing a CSB chassis and CSB avoids all that faffing about with individual springs. That said an 0-4-2 probably isn't the easiest chassis for a first go.

Also on the CLAG website is a suggestion from Ted Scannel for an entertaining combination of beams and CSB but that may be a bit over the top.

davebradwell
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Re: 0-4-2 compensation

Postby davebradwell » Sun Jul 05, 2020 7:01 pm

You might modernise the drive by dropping the ratio to 30 or 40:1 and, with a more modern motor, relying on a good controller or DCC for low speed control. A further reduction in noise could be made by separating motor and gearbox and connecting them with a Cardan shaft, motor mounted in bunker on rubber. Although this won't give the clear cab you crave it would produce a very nice mover.

If you used even thickish piano wire for the beams it would just take the harshness out of the ride. Not quite springing but it keeps you on familiar ground.

DaveB

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steve howe
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Re: 0-4-2 compensation

Postby steve howe » Sun Jul 05, 2020 9:56 pm

Thanks Will for an excellent steer via the CLAG website, plenty of pitfalls to look out for!

and Dave thanks for the heads up on wire beams, I might give that a go, what thickness would you recommend?

I'm using a High Level gearbox in the 517 having had great results with them on previous projects, I might one day replace the gear/motor set on the old 517 to get the clear cab, but I have two more to build so I won't be short of 517's! noise does not seem to be much of a problem with the HL gearboxes other than a distinctive 'whine' which immediately identifies them in locos at shows!

Thanks for the useful feedback,

steve

petermeyer
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Re: 0-4-2 compensation

Postby petermeyer » Wed Jul 08, 2020 6:31 pm

I have used a High Level 14xx chassis with a Mallard 517 which required shortening the frames and swapping out the axleboxes for those in the Mallard kit but worked out fine.

IMG_1425.jpg


I understood that the Mallard kit is too wide for anything but a later 517 so I narrowed both the footplate and side tanks and built the earlier armchair bunker for my preWW1 variant.

petermeyer
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Re: 0-4-2 compensation

Postby petermeyer » Wed Jul 08, 2020 6:57 pm

I also updated an old M&L chassis to produce a shorter wheelbase 517 (15' without trailing axleboxes). In the pic you can make out my compensation beams for all 3 axles similar to the High Level arrangement. Again this is on a Mallard footplate:

IMG_1637.jpg

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Captain Kernow
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Re: 0-4-2 compensation

Postby Captain Kernow » Wed Jul 08, 2020 7:06 pm

Tim V wrote:Full compensation as the High Level version. The fixed axle, though easier to build, does result in the engine lurching on poor joints.

CSBs have their fans, I am not one of them.

I agree with Tim. I am planning a second compensated chassis to go under another DJM 14XX in due course and this one will replicate the High Level arrangement, as the chassis that I have is by Comet, so the compensation parts will have to be scratchbuilt.

If there are concerns about the centre of gravity, then you may also be able to alter this by the amount of weight in the loco body and where it is put, of course.
Tim M
Member of the Devon Riviera Area Group.

Stuart Firth
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Re: 0-4-2 compensation

Postby Stuart Firth » Thu Oct 22, 2020 7:57 am

Late to the party as always but I wanted to be sure this worked before posting..
I've recently finished rebuilding one of my oldest EM loco's, an M&L LNWR Bissel tank. It now has twin beams between the driving axles and a pivoted trailing axle, and the running is very good. It does put a lot of weight on the trailing axle at the expense of the drivers but haulage is not a big issue for me:

WP_20200802_11_36_54_Pro.jpg


WP_20201018_11_05_39_Pro.jpg


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