track holding

[Ian Austin]

Hi all. I have one section of track where the loco, in reverse, always comes off. The gauge here is a bit tight so this appears to be the problem. However the chassis by itself runs everywhere without fault. Compensation method employed is flex-chas. Is it the track or is it the chassis? I have tweaked the beam this way and that and but haven't found the correct spot. My other loco runs perfectly over this 'problem' area.

[Will L]

Hi all. I have one section of track where the loco, in reverse, always comes off. The gauge here is a bit tight so this appears to be the problem. However the chassis by itself runs everywhere without fault. Compensation method employed is flex-chas. Is it the track or is it the chassis? I have tweaked the beam this way and that and but haven't found the correct spot. My other loco runs perfectly over this 'problem' area.

It hard to say without seeing the loco and watching it run. Without direct access to the loco we would need to know at least body type, the wheel arrangement and the form of the flexi chassis, before would could start thinking seriously about it. One though thought, the locos centre of gravity needs to fall reasonably centrally into to the triangle formed by the three fixed point of the flexi chassis suspension. If it doesn't then it will be unstable and inclined to falling off in unexpected places. Those of you who think that the need to know where the centre of gravity of your loco is, is an unnecessary complication confined to CSB fitted loco's should bare this in mind.

[Ian Austin]

Hi Will,

The 'problem' loco is an 0-6-0, the 'good one' is a 4-4-0

Ian

[Tim V]

Check the back to back.

Is there side play on the middle axle? An 0-6-0 is stiffer than a 4-4-0.

[Ian Austin]

Hi Tim,

Checked back-to-back on S4 tapered gauge and all was well. Side play on middle axle is 1mm either side, so 2mm overall.

Ian

[Russ Elliott]

Is the suspect bit of track curved?
Does the loco derail when going backwards in both directions on the suspect bit of track?
Is the compensating beam on the front two axles or the rear two axles?

[Ian Austin]

Hi Russ,

Yes the track is curved and the loco comes off in one direction only. Other curves are correctly negotiated. It is this curved section that has a 'stiff'' area when pushing the gauge along making me think its the track and not the loco, \\\\\\\\\\but my expereince is limited.

Ian.

[Ian Austin]

Hi Russ,

Forgot to add that the fixed axle is the cab end and it is this end that comes off first.

Ian

[Will L]

Hi Russ,

Forgot to add that the fixed axle is the cab end and it is this end that comes off first.

Ian

If the loco centre of gravity (the point of balance) is ahead of the middle axle and close to the pivot of the flexi chassis beam, remarkably little weight will be carried on the fixed axle and that axle will be inclined to lift easily if, say, it meets a tight section. You may improve things by correcting the track gauge but that will leave you with a loco that will chose it's moment then misbehave else where. Pulling performance wont be good either.

To find out, pick up the loco by holding the running plate, lightly , between your fingers above the centre axle, if it tends to fall forward towards the front axle then you may have an unstable set up. The cure is to add weight to the body so that the balance point is a little behind the centre axle.

[Ian Austin]

Hi Russ,

Thanks for advice. Will pursue tomorrow.

Ian

[JFS]

Hi Ian,

I would definitely support the contributions from Will and Russ. It sounds like you have a coincidence of a number of small issues - each too small to be significant on its own but which just happen to come together.

And just to add one point for future reference.

In my experience, "fixed" axles are always MUCH more prone to derailment than others. For me, the traditional flexichas approach to an 0-6-0 (one fixed axle, one beam), whilst seductively simple, is always a problem waiting to happen - not least because - as Will implies - it is really difficult to put the weight where it is needed (BETWEEN the fixed axle and the beam pivot) because that is where the motor goes. Meanwhile, ahead of the pivot, there is all that empty boiler asking to be filled with concrete / lead / depleted uranium...

For your next loco, could I suggest that all axles are able to move - either using CSBs (Will will show you how) or, using two beams between the middle and trailing axles with a single fixed pivot in the middle of the leading axle - this is a much more stable method of compensation - not only because all axles can move but also because it eases the C of G issue described by Will.

Good Luck!,

[Ian Austin]

Hi Howard.

Thans for contribution. Certainly added weight over the fixed axle reduced the problem by about 50%. But still 50 % to go. In any case there is nowhere for the extra weight to be fitted. Doesn't look right stuck on top with blue tack!!

Ian

[Ian Austin]

Hi all,

With the angle back-to-back gauge stuck on the roof the loco performs beautifully. Now the impossible task of adding this weight out of sight. Don't think I can do it. Appears to be a new chassis incorporating your advice. Sad as excellent back-to-back and quartering currently achieved. Such a shame not to be able to benefit from this.

Ian

[JFS]

Now the impossible task of adding this weight out of sight.

Hi Ian - exactly my point! But all is not lost! As Will said, the issue might be where the weight is rather than there being not enough of it - so can you remove some from the smokebox end? that, combined with lead in the drag box (where it has most effect) might be enough.

Otherwise its down to making your floor plate crew from depleted uranium..

EDIT:- FLOOR Plate? What was in that last drink anyway?

Best wishes,

[Mike Garwood]

Ian

Howard raises a really good point. A whitemetal crew will add much needed weight to you engine. Will has had experience of a weighty crew throwing a curve ball to one of his engines - admittedly this was using CSB's.

MIke

[Tim V]

Tender engine? Thought of a weighted tender?

[Ian Austin]

Hi all, specifically Will, Tim , Russ, Howard and Mike,

Got there in the end. As you said getting the added weight in the right place was the task. With blue tack and trial bits ended up with a bar, 23mm x 10mm x 2.5mm under the cab extending across and under the tender. Works like a dream at creepy crawly speeds or mallard record speeds. Other than the gap between the tender and cab, which the platform (if that's the correct word) covers, it is virtually 'invisible'.
Thanks very much to you all. I have learned a lot.

Ian

[Philip Hall]

Have just spotted this post, and it occurs to me that the problem might also be that usually our wheels are not completely wobble free, however hard we try. Thus the B-B can vary a trifle between one side of a wheel and the other. Ths is more often the case with the more flexible wheels, such as AG; it doesn't tend to happen with Ultrascale, which are more rigid.

This tiny variation, in combination with the slightly tight gauge you mention, could be the reason for your problem. And I would always look first to the track gauge and B-B. I agree, though, that the fixed axle compensated chassis is the more likely to come off in these cases, to say nothing of a rigid one!

Philip