recommended sideplay on loco wheels

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jon price
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recommended sideplay on loco wheels

Postby jon price » Tue Nov 22, 2016 11:51 am

As I wrestle with the CSB istallation I'm thinking ahead to the wheels and axles. I will be using Alan Gibson wheels so they have to fitted correctly the first time. The chassis, with EM spacers has a width of 15.3mm. My back to back guage is 17.7mm (I have two but I just measured them and one appears to be 17.8mm which is no good). This gives me 2.3mm of slacxk on the axle. The loco is an 0-6-0 with inside cylinders and a 40mm wheelbase.

This all gives me 1.15mm of slack at each side. I could put 1mm of washers on each end giving me .15mm of slack each side, .3mm total, but I'm slightly concerned that with minimum radius A4 turnouts of 529mm radius I might need more slack on the middle axle. Any suggestions as to how much slack I should leave?
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Re: recommended sideplay on loco wheels

Postby grovenor-2685 » Tue Nov 22, 2016 12:06 pm

Templot should be able to tell you this if you have it.
Draw a chord of the loco wheelbase onto the turnout and measure the offset. I would suggest trying at several places especially with the centre axle at the switch tips so you get the effect of the switch deflection angle.
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jon price
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Re: recommended sideplay on loco wheels

Postby jon price » Tue Nov 22, 2016 12:20 pm

Thanks for this suggestion Keith, but I don't have Templot. I tried it a long time ago and it was beyond me. Presumably I could use a standard society printed turnout template though.
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Russ Elliott
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Re: recommended sideplay on loco wheels

Postby Russ Elliott » Tue Nov 22, 2016 12:26 pm

versine.gif
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Winander
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Re: recommended sideplay on loco wheels

Postby Winander » Tue Nov 22, 2016 2:23 pm

The chord is the wheelbase, or is a little added to account for the wheel flanges?

V = 40x40 / 8x529 = 0.38

So 0.3 is insufficient.

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Will L
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Re: recommended sideplay on loco wheels

Postby Will L » Tue Nov 22, 2016 3:07 pm

In simple rule of thumb terns, next to none on the first and last axles and 0.5mm either side on the middle on (I, e. 1mm in total) should see you round all but the tightest curves. If you really do have tight curves apply the versign calculation to be sure. And just use the wheel base as the cord length.

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jon price
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Re: recommended sideplay on loco wheels

Postby jon price » Tue Nov 22, 2016 3:31 pm

Thanks for all this input. I knew there would be expert input, without which I would be lost.
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Russ Elliott
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Re: recommended sideplay on loco wheels

Postby Russ Elliott » Tue Nov 22, 2016 6:14 pm

Winander wrote:The chord is the wheelbase, or is a little added to account for the wheel flanges?

It's sensible to add a little to account for the wheel flanges.

flange-on-rail.png

(snaffled from the redrawn Malcolm Cross original)
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Russ Elliott
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Re: recommended sideplay on loco wheels

Postby Russ Elliott » Tue Nov 22, 2016 6:18 pm

jon price wrote:I have two but I just measured them and one appears to be 17.8mm which is no good.

17.8 is fine, Jon. Use it for the outer axles, and use the 17.7 one on the middle axle.

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Martin Wynne
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Re: recommended sideplay on loco wheels

Postby Martin Wynne » Tue Nov 22, 2016 8:31 pm

The dummy vehicle clearance mouse action in Templot can be used to measure the centre axle sideplay needed on 6-wheel vehicles at different radii. Set the required track gauge and radius. Set the body length to match the wheelbase. Set the body width to match the track gauge. The clearance marker can then be adjusted by mouse action to align with the outer rail. If there is significant gauge slop on the wheels (e.g. 00 gauge), the available slop can be subtracted from the indicated sideplay (which is in prototype inches).

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Re: recommended sideplay on loco wheels

Postby billbedford » Wed Nov 23, 2016 11:44 am

Winander wrote:The chord is the wheelbase, or is a little added to account for the wheel flanges?

V = 40x40 / 8x529 = 0.38

So 0.3 is insufficient.



No so, The back to back plus twice the effective flange width is less than the gauge by at least 0.65, so there is no reason at all to put any sideplay on the middle axle. There is probably no reason either to use under width frame spacers.

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Will L
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Re: recommended sideplay on loco wheels

Postby Will L » Wed Nov 23, 2016 3:30 pm

Actual the whole topic was done you death recently, in the context of the need or otherwise for gauge widenning. The thread Track Gauge Widening, All You’ll Ever Need to Know and specifically this post covers it. Some where in there there is also a copy of a spreadsheet that will, with a little effort, a do the sums for you.

Bill is quite right that until the critical curvature is reached no side play is required, the trick is knowing when that will be.

Russ Elliott wrote:
Winander wrote:The chord is the wheelbase, or is a little added to account for the wheel flanges?

It's sensible to add a little to account for the wheel flanges.


Just for once I would beg to differ Russ. Given the angle of the flange face (see your diagram), the flange doesn't enter into this until a significantly shape curves is met. The thread above gives chapter and verse (and jot and title as well)

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Julian Roberts
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Re: recommended sideplay on loco wheels

Postby Julian Roberts » Wed Nov 23, 2016 11:38 pm

I already sent this to Jon as a PM but realise I ought to submit it to public scrutiny from you folks with a lot more experience than me so that Jon can know if my thoughts are rubbish.

Hi Jon - you said:

"As I wrestle with the CSB istallation I'm thinking ahead to the wheels and axles. I will be using Alan Gibson wheels so they have to fitted correctly the first time. The chassis, with EM spacers has a width of 15.3mm. My back to back guage is 17.7mm (I have two but I just measured them and one appears to be 17.8mm which is no good). This gives me 2.3mm of slacxk on the axle. The loco is an 0-6-0 with inside cylinders and a 40mm wheelbase.

This all gives me 1.15mm of slack at each side."

Jon:

I am wondering if you are remembering to include the wheels inside boss. Mine have been 0.5mm or so if I remember correctly, though my current project with 3'6" wheels has an approx 0.25mm boss.

So surely your slack is 0.65mm each side without any washers (if your bosses are 0.5 each)?

I seem to remember from my Gauge Widening Tool thread you are making a pretty sharp curved layout but it wasn't 529mm minimum radius, more around 700 wasn't it? I am wondering if you are obliged to have this A4 point.

Anyway the versine shows you need 0.38 each side on the centre axle, so you're fine, you've got plenty. You just need the sideplay on the middle axle, you don't need any on the outside two axles.

There's no problem with a bit too much sideplay on the centre axle. The only problem with sideplay is lining up the brake blocks and the pickups. If you wanted to you could put in a minimum washer 0.25mm each side, and that would take you down to 0.4mm sideplay each side.

" I could put 1mm of washers on each end giving me .15mm of slack each side, .3mm total, but I'm slightly concerned that with minimum radius A4 turnouts of 529mm radius I might need more slack on the middle axle. Any suggestions as to how much slack I should leave?"

I think the difficult bit is getting the correct washering on axles where you don't need sideplay when you can only put the wheels on once. Any unnecessary sideplay on outside axles gives problems with buffers and couplings (especially AJs). But you need the wheels to go round freely. I reckon your 0.15 each side may be about right. I learnt quite a lot from the thread Getting the Wheels on Square
viewtopic.php?f=19&t=4911&start=25

I don't really get why Bill Bedford suggests you minimize the centre wheel sideplay. There's no problem with having it now that you've made your EM width frames (which I also do mostly). The P4 standards give plenty of slop for all wheels, and any AGGHHH Gauge Widening will give you some more, but I reckon leave both those out of the calculation, and you will have a loco that is guaranteed to go sweetly round the curve helped by those factors. I just did the same sort of calculations with my Hi Level Barclay for a 600mm curve and it works a treat. In fact I had thought it only needed to go round a 4ft curve, but left the more than adequate sideplay resulting from using the kit's P4 spacers. Finding a 600mm curve was required, fortunately the loco had enough.

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Russ Elliott
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Re: recommended sideplay on loco wheels

Postby Russ Elliott » Thu Nov 24, 2016 2:25 am

Will L wrote:Just for once I would beg to differ Russ. Given the angle of the flange face (see your diagram), the flange doesn't enter into this until a significantly sharp curve is met.

Yes, accepted, Will, and I was being over-safe, because in many cases (although not in this one), people who ask the 'sideplay question' are sometimes dreaming of getting their 9Fs through 'a significantly sharp curve'.

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Re: recommended sideplay on loco wheels

Postby Julian Roberts » Fri Nov 25, 2016 8:40 am

CALCULATING SIDEPLAY (versine).gif


Something I have wondered is how you work out the v on this formula above where your v is not half way between the two points c.

Lots of 0-6-0s have assymetrically placed centre axles. 8-coupled locos obviously don't have a wheel where v is, 10-coupled don't have flanges on the middle one.
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Will L
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Re: recommended sideplay on loco wheels

Postby Will L » Fri Nov 25, 2016 9:08 am

Julian Roberts wrote:CALCULATING SIDEPLAY (versine).gif

Something I have wondered is how you work out the v on this formula above where your v is not half way between the two points c.

Lots of 0-6-0s have assymetrically placed centre axles. 8-coupled locos obviously don't have a wheel where v is, 10-coupled don't have flanges on the middle one.


For 0-6_0s unless you are feeling really picky, then I would have thought that knowing it will be a little bit less than v ought to do, given the numbers are quite small anyway and usually less than the 0.5mm a side rule of thumb. Ditto for a 0-8-0 with fixed axles front and rear. However there are more option about where you can put the flexibility, I find 1st and 3rd axle fixed, flexibility on 2 and 4 has some advantages, particularly if you have outside cylinders but you will need to do some maths for your self.on the 4th axles which will be a bit (but not a lot) bigger than the v calculated as if the first 3 were an 0-6-0.

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Re: recommended sideplay on loco wheels

Postby Julian Roberts » Fri Nov 25, 2016 10:04 am

Yes Will the numbers are small. However if Jon has locos with any significantly longer wheelbase than his tiny 40mm to go round this A4 529mm radius point he's going to need every bit of help he can get.

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Re: recommended sideplay on loco wheels

Postby jon price » Fri Nov 25, 2016 10:21 am

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. A5 is the tightest elsewhere.There will be a different (more sensible) ruling B6 radius on the sections which accommodate the traffic coming in from the Chester and Hawarden direction (and potentially from the main LNWR line from Chester to Holyhead) where anything will be possible ( Pollitt 0-6-2T No17, and probably a GCR Tiny first of all).
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Re: recommended sideplay on loco wheels

Postby Julian Roberts » Fri Nov 25, 2016 10:52 am

Right so Jon you won't need any more SP than already worked out.

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.

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Re: recommended sideplay on loco wheels

Postby Philip Hall » Fri Nov 25, 2016 11:38 am

I'm frightened by all these calculations, and if I did try and work it out this way I'd probably be tempted to give it all up and try flower arranging instead. I have never needed to go to this extent to work out the sideplay. What I do (and I'm with Will on this one) is to have a little sideplay on the front and back axles, and a bit more on the middle one. Measuring potential sideplay, when I tried it, got me into all sorts of places I'd rather not have gone to. The Law Of Murphy says that when you've fitted the wheels into the chassis they invariably do not seem to have the same relationship with the chassis they had when you measured it.

So I use (apologies because I've mentioned this in another thread) is to have a wooden axle on which the wheels are an interference fit, put it into the chassis, add the wheels and see how much slop you've got. Then add washers to taste to get it about right. Then you fit the wheels properly on the axles, with all the washers you've just tried; either in the chassis on separately with 'drop out' bearings. If it's a bit loose then a fibre washer with a cut out in it can be slipped over the axle to take up a bit. You can thin the fibre washers as well, which you may need to do.

What is important is not measuring and calculating, but fitting. SIdeplay is only critical if you haven't got enough. Too much is easily taken care of. If trying (and I do mean trying, it's not an exact science) to calculate all this is your way of enjoying things, then great, but it's not really needed.

I suspect I might need to duck now...

Philip

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Russ Elliott
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Re: recommended sideplay on loco wheels

Postby Russ Elliott » Fri Nov 25, 2016 8:15 pm

Philip Hall wrote:SIdeplay is only critical if you haven't got enough.

Ah, there's the rub.

No one is criticising an empirical washers method, Philip. The sums are there in case anyone wants to know what might be entailed in the difference between "a little bit" and "a little bit more". Some kits have near-zero sideplay allowance - a Finney Dean Goods is 16.5mm over frames, and somewhere between 16.6 and 16.9 when the bearings are fitted (depending on how the blocks are sliding in the guides). The distance between inside faces of Ultrascale wheel bosses is 16.9mm (for a 17.7mm BB). Ouch. Ain't no chance of getting any washers into that little lot. In that particular case, the sums were actually quite useful in indicating what needed to be shaved off wheelbosses and bearingfronts (or, in extremis, squeezing the middle of the frame), the strategy being to gain a degree of confidence that the thing might actually work well around curves.

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Re: recommended sideplay on loco wheels

Postby Julian Roberts » Fri Nov 25, 2016 9:33 pm

What I am after is a bit more knowledge when deciding how wide to make the frames in the first place. I agree with all you said Philip except I find doing that versine calculation ever so much easier before than experimentation after. Yes getting it to work in practice is quite another thing from knowing it should work, but it is helpful to know the darned thing Should work!

So its easy to work out what I need for symmetrical 6-couplers and I would have thought there must be a not too difficult modification to the calculation for assymetrical ones and 8-couplers.

For example a 72xx. Known as point splitters I believe. Very long wheelbase assymetrically
arranged middle axles. I wanted to build one before restricting myself to Scottish locos.

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Re: recommended sideplay on loco wheels

Postby Philip Hall » Sat Nov 26, 2016 1:42 am

Russ, I take your point here but it's just that my brain hurts with all that maths! Your figures remind me of another,reason why there can be difficulty with not enough sideplay: the width over frames (and bearings). 16.9 is way too wide in the context of getting an engine around a reasonable curve. I would take at least a millimetre off that for a big engine. Martin Finney's chassis were often like that, and in those cases I would use the EM spacers.

Julian, if it helps, I have actually built a 72xx from the PDK kit and it is one of the difficult ones. I fitted twin beam compensation on the rear two axles, single beam on the front. No sideplay to speak of on the front axle, about 1mm on the second, hardly any on the third, and 1.5 - 2mm on the rear. With plenty of weight it just about squeezes around a 3ft radius curve.

Philip

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Julian Roberts
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Re: recommended sideplay on loco wheels

Postby Julian Roberts » Sat Nov 26, 2016 6:32 am

Interesting Philip! I too take fright at numbers, but doing that versine calculation is very easy with a calculator readily at hand on any mobile phone.

The 72xx is a difficult example. How about a 9F? Ignoring the pony truck, the centre wheels are flangeless, and there is even spacing between all the drivers, so it's symmetrical. 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.

CALCULATING SIDEPLAY (versine).gif


I will ask my son in NZ but I'm sure the Brains Trust on this Forum has the answer!
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Re: recommended sideplay on loco wheels

Postby Philip Hall » Sat Nov 26, 2016 9:56 am

Julian, I've never built a 9F, it being one of my life's ambitions not to have to; the nearest I might get is having to convert a Bachmann one if I was asked. Still trembling, though. Despite the flangeless centre drivers, I think the 'sideplay on alternate axles' would be the way to go. More sideplay can often put on the rear axle as to some extent any wag on straight track can be controlled by the tender.

Philip


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