recommended sideplay on loco wheels

[billbedford]

I don't really get why Bill Bedford suggests you minimize the centre wheel sideplay.

It's a coarse scale cludge to a 00 problem, i.e. track with a fixed gauge.
It needs under-scale frame widths
It requires either sloppy coupling rod bearings or bendy coupling rods

It seems to me that setting a generous gauge widening when planning a layout would not save a whole lot of procrastination and displacement activity, but would make loco building a lot simpler.

[billbedford]

The two yard locos (no7 and no9), and the visiting colliery loco (Watkinson No2) will be 0-4-0Ts , The "mainline" loco (no8) will be a Sharp Stewart 0-6-0T with a similar wheelbase to No14. The first GCR locos sent to this section were Pollitt Class 5s (LNER J62). The A4 turnouts will only really be visited by No 14 and these locos, and realistically only the 0-4-0s and the Class 5 will be in the A4 section.

A class 5 will go round your 529mm curves with just 0.2mm gauge widening.

[Winander]

But I am interested in my v question because I'd like to know, for a given amount of sideplay (say0.5mm) how much longer the wheelbase can be of an 8-coupled than a 6-coupled to cope with a given radius curve - while keeping the sideplay to the intermediate axles.

You could either draw it, or use Templot as described by Martin Wynne earlier in the thread (viewtopic.php?f=20&t=5156#p49379) and measure using the measuring tool.

regards

[Will L]

It's a coarse scale cludge to a 00 problem, i.e. track with a fixed gauge.
It needs under-scale frame widths
It requires either sloppy coupling rod bearings or bendy coupling rods

Actually its a result of the fact that our curves are seriously too tight, OO of P4, its practical because unlike the prototype we use plain parallel axles. Because we don't have massive horn block casting bolted to our frames, it doesn't require under scale frames, any more than you need more sloppy coupling rod bearings than normal or bendy coupling rods, which I'm sorry to say I've been failing to fit to my loco's.

[Julian Roberts]

I hadn't wanted to reopen the gauge widening can of worms!
Son in NZ tells me that sideplay requirement of wheels half way between v and c will be 75% of the requirement at v
Here is his working in case anyone is interested and understands maths better than I do.

IMG-20161127-WA0001 (1).jpg

This was to work out the sideplay requirement on wheels half way between "v" and "c". A formula to work out sideplay at any point between them is promised...

[Julian Roberts]

Philip I'm sure you could do as follows on your mobile phone no less than I can!

So to take an Austerity 2-10-0 going round (or not) a 3 foot curve, ignoring its pony truck's problems: (I can't find the figures for a 9F just now)

The wheels are each 5'3" apart, (21mm), wheelbase is 21' (84mm). Like the 9F the centre pair are flangeless, the 2nd and 4th have thinned flanges. Just for this example I'm seeing how it works with all the sideplay on the second and fourth axles, outer axles no sideplay:

84x84=7056.
3 feet is 914.4mm. Multiply by 8 = 7315.2. Divide 7056 by 7315.2 =
0.96mm would be the sideplay required each side for a flanged centre driving wheel. 75% of that is
0.96 multiply by .75 =

0.72mm each side.

Frames would need to be 1.5mm narrower than distance between wheels inside bosses (leaving a full 0.06 margin of error!....so that's when the fun starts, getting that in actuality - but at least we would know what we were aiming for).

**************************************************************************************************************************************************************************

We could reduce the requirement by taking into account the slop in P4 and any gauge widening, which I think is what Bill is advocating. (Worth mentioning the 9F had a minimum radius of 400 feet - 5 foot 3 inches for us...!)

If we have a 17.67BB the slop each side is 17.67 + two flanges (0.8) = 18.47. Take that away from 18.83 = 0.36 total slop,

0.18 each side.

A spreadsheet also from my son shows that the P4 triangular gauge in theory gives 0.13mm gauge widening at 3 foot. (As per prototype we would have 0.25mm ). Can't quite work out in my head whether that would apply each side or whether we'd have to halve it, but I think it would apply in full.

0.18 + 0.13 = 0.31mm.

So take that from 0.72, our sideplay requirement is down to 0.41, or frames 0.82 narrow - i.e. making them 1mm narrow would give nearly 20% margin of error.

That's taken me around half an hour, but probably, if I were making the thing which I'm not, saved hours of experimentation, and given me a certainty of what should or should not be possible.

I wrote all this down here so that it can be corrected if it's wrong

[Philip Hall]

Thanks Julian, interesting to see how you worked it out. But I'm afraid I'm still going to stick to my old fashioned method because it works very easily for me! I also do not like to whittle such clearances down to a minimum because I have always found that a little extra play helps. Once completed, wheelsets will often move a fraction here and there and if clearances are tight to start with that could create a problem later on.

But if you have a feeling for the maths (and I don't, even with a calculator!) I can see that being able to make the calulation is useful.

Phil

[Russ Elliott]

So the second and fourth drivers will each come half way between the points c and v. So that will be the sideplay we need, but what is it? Is it half v? I doubt it, as between c and v it is, as it were, a curve sided triangle.

At an intermediate point:

versine-aleatory.gif

[Julian Roberts]

Thanks Russ!

I completely agree Philip that the numbers are one thing, practice another. What was interesting from my worked example (which I expected one of the Brains Trust on this Forum to say was all wrong) was first how amazingly little sideplay seemed to be needed in this rather extreme case, and second that the slop in P4, plus the gauge widening that should be there if we have used our triangular tool, gives plenty of margin of error if we don't factor them into the sideplay calculation (with all due respect to Bill).

To make spacers to an accuracy of 0.5mm is beyond me, but I have found "P4" or "EM" spacers are not a standard width as I try different sources, nor is frame material one thickness; to make the frames width to an accuracy of 0.5mm is also a task beyond me and clearly any error must be in the narrower rather than wider direction.

[billbedford]

It's a coarse scale cludge to a 00 problem, i.e. track with a fixed gauge.
It needs under-scale frame widths
It requires either sloppy coupling rod bearings or bendy coupling rods

Actually its a result of the fact that our curves are seriously too tight, OO of P4, its practical because unlike the prototype we use plain parallel axles. Because we don't have massive horn block casting bolted to our frames, it doesn't require under scale frames, any more than you need more sloppy coupling rod bearings than normal or bendy coupling rods, which I'm sorry to say I've been failing to fit to my loco's.

The scale width of frames is of the order of 17 - 17.5 mm which hardly leaves room for flanges on the bearing never mind side play on the axles.

If you take four rods e.g. pencil with three representing crank pins and the other a coupling rod, it become obvious that side play can only be accommodated by either extending the crank pins by an amount equal to the side play and/or having the coupling rods bend or that the side play is an illusion.

[Will L]

It's a coarse scale cludge to a 00 problem, i.e. track with a fixed gauge.
It needs under-scale frame widths
It requires either sloppy coupling rod bearings or bendy coupling rods

Actually its a result of the fact that our curves are seriously too tight, OO of P4, its practical because unlike the prototype we use plain parallel axles. Because we don't have massive horn block casting bolted to our frames, it doesn't require under scale frames, any more than you need more sloppy coupling rod bearings than normal or bendy coupling rods, which I'm sorry to say I've been failing to fit to my loco's.

The scale width of frames is of the order of 17 - 17.5 mm which hardly leaves room for flanges on the bearing never mind side play on the axles.

If you take four rod e.g. pencil with three representing crank pins and the other a coupling rod, it become obvious that side play can only be accommodated by either extending the crank pins by an amount equal to the side play and/or having the coupling rods bend or that the side play is an illusion.

Actually frame width varies from prototype to prototype. The GER tanks I'm modelling at the moment are nothing like that wide. I agree in theory the rods might seem to need to be fractionally longer, but the additional length is small compared with all the other variable factors that dictate the difference between rods that bind and rods that don't. If it was true in practice, loco's which run OK on strait track would bind on a curve. Never observed that in real life.

[billbedford]

Actually frame width varies from prototype to prototype. The GER tanks I'm modelling at the moment are nothing like that wide.

No? They were 4'1" between the frames plus 1" for each frame which makes 17mm in total.

[billbedford]

So to take an Austerity 2-10-0 going round (or not) a 3 foot curve, ignoring its pony truck's problems: (I can't find the figures for a 9F just now)

Which begs questions like 'why would anyone want to do that?'

The wheels are each 5'3" apart, (21mm), wheelbase is 21' (84mm). Like the 9F the centre pair are flangeless, the 2nd and 4th have thinned flanges. Just for this example I'm seeing how it works with all the sideplay on the second and fourth axles, outer axles no sideplay:

84x84=7056.
3 feet is 914.4mm. Multiply by 8 = 7315.2. Divide 7056 by 7315.2 =
0.96mm would be the sideplay required each side for a flanged centre driving wheel. 75% of that is
0.96 multiply by .75 =

0.72mm each side.

Maybe, but any sideplay in the outer axles needs to be taken from that figure.

We could reduce the requirement by taking into account the slop in P4 and any gauge widening, which I think is what Bill is advocating.

That's not what I'm saying.

The calculated versine less a proportion of the 'slop' represents the gauge widening needed to get a particular loco around a stated curve without any sideplay. So when planning a model people set their gauge widening to accommodate the longest loco they envisioned using then they would never have to worry about providing axial sideplay.

For example, the ten-coupled loco would need a gauge widening of at least 0.72 mm on 36" curves without sideplay, or it would be limited to 1838 radius curves without gauge widening but it would be quite happy negotiating 36" curves on SMP P4 track because the track gauge is around 19.1mm.

[Julian Roberts]

I am coming to grips with Russ' last formula. Hopefully only one more versine question remains in my head - working out the sideplay needed on some rear axles.

Take the 2-10-0 Austerity with 21mm between each axle for this (daft) 3ft curve. This time we fix the 1st and 4th axles as per Philip's post, so sideplay on 2nd (and 3rd but this is flangeless) axles is now

a is 21; b is 42. 21 x 42 = 882. The radius is 914.4mm, so 2r is 1828.8. 882 divided by 1828.8 is

0.48. (Compared with 0.72 for the outside axles fixed).

So what is it on the 5th? - I imagine it will have the same sideplay requirement as the others as the gap is the same.

But what about where the gap is not the same?

Going back to the 72xx (which is symmetrical - my mistake earlier on) - the three gaps between the four axles are 28, 24, and 28mm

Taking the first and third as fixed the second pair of wheels require

28 x 24 = 672. Divide by 1828.8: 0.37mm sideplay

But how to work out the 4th axle sideplay?

I assume it wouldn't be as much as the requirement of the 2nd and 3rd axles where the 4th one is fixed:

28 x 52 = 1456 divided by 1828.8 = 0.79

Bill I will reply in a separate post.

[Russ Elliott]

[2-10-0 Austerity] So what is it on the 5th? - I imagine it will have the same sideplay requirement as the others as the gap is the same.

Yes.

[72xx] But how to work out the 4th axle sideplay?

It's about the same as that on the 2nd axle, i.e. about 0.4mm.

Don't forget the natural sideplay of wheelsets on the track, which at that radius is going to be approx 0.4mm.

[Julian Roberts]

Russ I suppose if you, the fount of all knowledge, say "about" (0.4mm) I should be content!

I assume by the 0.4mm "natural sideplay" at this radius you mean the P4 slop plus the track gauge widening?

As I wrote in the last Snooze, my aim is to get a disproportionate amount of the weight on the outside driving wheels. I aim also to have no reliance on them for any sideplay (except sufficient clearance that they are able to revolve).

Will and Phil both say an 8-coupler (or 10) should have sideplay on alternate axles. My 0-8-0T was made without these figures to help, has sideplay on the intermediate axles and works fine.

The formulas that have appeared on this thread mean that in future I can know what should work before I start building, and the numbers show that both are correct in saying that the sideplay needed is less if on alternate wheels.

However they show - if I am correct!? - that a 72xx in theory could manage a 3ft curve on (about!) 0.4mm sideplay each side on the 2nd and 4th axles, and that the sideplay required is 0.8mm each side on both intermediate axles if building it my way, with fixed outer axles. The challenge for me, if I were making it able to take such a sharp curve, would be to see if I could make it actually work with approx maximum 1mm sideplay each side on axles 2 and 3.

[Will L]

... Will and Phil both say an 8-coupler (or 10) should have side play on alternate axles...

Not should, other ways work, but it is a good workable scheme which minimises the side play required on the second axle which in, most locos, can still get involved with the connecting rod and where too much side play would be an embarrassment. The is often little to worry about either side of the 4th axle.

[Russ Elliott]

I assume by the 0.4mm "natural sideplay" at this radius you mean the P4 slop plus the track gauge widening?

Yes.

My "about" attempts to convey that we're only looking for approximate values, to get a feel of what might be needed in a chassis. (In that respect, I'm actually sympathetic to Philip's view.)

As I wrote in the last Snooze, my aim is to get a disproportionate amount of the weight on the outside driving wheels.

Ok, but your inner wheels will be lightly loaded as a consequence - asking for lightly-loaded wheels to slide laterally through their bearings could make them restless, because those axles will move in the direction of least resistance. Sideplay in action is actually flanges graunching against railheads, with lots of nasty friction. To make matters worse, as the radius decreases, each side of an outer wheelset wants to revolve at a different rate.

[Julian Roberts]

My "about" attempts to convey that we're only looking for approximate values, to get a feel of what might be needed in a chassis. (In that respect, I'm actually sympathetic to Philip's view.)

I was surprised Russ at your 0.4mm for the 4th axle of the 72xx. Intuitively it seemed to me it would be more than that, having worked out the second axle needs 0.4 with the 3rd axle fixed. I don't know how to work it out, but Phil suggests up to twice as much for the 4th axle as for the second.

If the Q1 has had any of the problems you mention for lightly loaded wheels it has not resulted in anything visible. I see those issues could well be problematic at full size but it had not occurred to me to worry about the inner wheels behaviour at 4mm size. I have seen from these formulas it has much more sideplay than necessary for 4ft curves

The Barclay 0-6-0 I mentioned earlier is tested to its maximum on a 600mm curve test track, though the slop and gauge widening give extra room. The inner wheel is sometimes riding up and over the rail at one rail joint on the inside of the curve. But knowing in theory it should work, I ascribe this to it having only a temporary pick up arrangement which is acting in an upward and outward direction on the middle wheels, reducing the necessary downward force and freedom of movement. Rail joints on the inside of the curve will have to be fettled to give a smooth path for flanges just as they do on the outside, but that might be necessary also for wagons being pulled. When the loco is finished properly and is in operation on the layout (yet to be built) I will know how reliable the approach is.

Will - yes, and the Q1 has the crankpins on its 2nd pair of wheels reversed as for behind a crosshead. Additionally I filed a smooth curved path behind the connecting rod for the crankpin to prevent jamming. If both wheels are on the rails they will be moving sideways together and fouling should not happen, but it could happen when the loco is being tested off the rails.

Bill - am I right this time if I understand you to be saying we should ideally make our locos without sideplay (except those types that did have some like the SR Z class), and instead widen the track as necessary on curves for the longest one we expect to run? Presumably that restricts us to what the prototype could actually do if we take the maximum widening to be 0.25mm (or strictly speaking the 0.22mm P4 standard as we have reduced BB). Such a restriction would save us a whole load of problems as well as being realistic, but might put some people off!