Waddling 0-4-0

hollybeau
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Waddling 0-4-0

Postby hollybeau » Sun Oct 17, 2021 6:34 pm

I am looking for some help, advice or comment please.
Some years ago I built an 0-4-0T based on a High Level chassis and a Pug (Kitmaster/Dapol) body. It has Gibson wheels and a High Level gearbox with Mashima motor. It runs well enough but has always had a "waddle" - i.e. a side to side motion. This afternoon I was particularly annoyed with its gait and set out to find out what was causing it and from there devise a remedy, if possible.
First of all I noticed that in addition to moving sideways it can also be seen bobbing up and down at the rear end.
I have run the loco upside down in a cradle with a dial test indicator rubbing on the wheel treads. One rear wheel shows a displacement (?) in concentricity of 0.07mm, the other of over double that at 0.16mm. (I have done videos of this but it seems that the mp4 format cannot be used on here).
Sod's law being what it is it may be that the "high point" of one wheel coincides with the "low point" of its partner. If so then the maximum combined effect would be 0.23 mm or nearly a quarter of a millimetre. I suspect this is what is causing the wobbly running.
I suppose my questions are - what is an acceptable degree of concentricity? , and if these measurements are deemed to be outside the normal parameters then what can be done about it, short of buying new wheels from Gibsons that is? I have a lathe so I suppose I could bush the centres of the wheels but that assumes my 3 jaw chuck is accurate enough to allow for a new centre to be devised.
Thanks in anticipation.

Bryan

Philip Hall
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Re: Waddling 0-4-0

Postby Philip Hall » Sun Oct 17, 2021 7:40 pm

My view of an acceptable level of eccentricity is basically zero. This is of course unobtainable! Ultrascale are usually as near as dammit 'bang on', and in many cases so are Alan Gibson, but a simple method of truing, if you have a lathe, is to spring the tyres off whilst the wheel is mounted on a trued mandrel, and then skim the plastic centre before remounting the tyres with epoxy adhesive - I use Devcon 5 minute. I prefer to spin the lathe by hand but I guess it can be done under power. I think that only in extreme cases should bushing the centre be necessary and if they are that bad I would get replacements, not least because bushing is a bit beyond my abilities and machinery.

I have always found that trying to measure eccentricity with a gauge is problematic, in that if the wheel should wobble even a tiny amount the stylus will ride up and down the coning giving a false reading. Hence my preference for spinning the lathe by hand and viewing the centre against a piece of white card. I glue the tyre on in the lathe as well, so I can see it runs true and without wobble before it sets. It only comes off the mandrel once the glue has gone off.

Philip
Last edited by Philip Hall on Sun Oct 17, 2021 11:04 pm, edited 1 time in total.

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grovenor-2685
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Re: Waddling 0-4-0

Postby grovenor-2685 » Sun Oct 17, 2021 8:10 pm

hollybeau wrote: (I have done videos of this but it seems that the mp4 format cannot be used on here).

The wao put the videos on here is to upload them to Youtube, then to link to the video using the 'Youtube' button at the top of the post composition window.
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Keith
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Jeremy Suter
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Re: Waddling 0-4-0

Postby Jeremy Suter » Sun Oct 17, 2021 8:12 pm

Hi Bryan
If the tyres are out of concentricity so are your crank pins which may also be helping the chassis to waddle.
Buy a new set of wheels and start again. Round the end of your axles slightly so they don't scrap out any of the plastic in the wheel centres when you push them on.
Don't try resetting the wheel in a self centring chuck. Use a collet. Self centring does not mean they are centred just the jaws all go in at the same time when you close them and meet very close to the centre.
You could use the lathe to check the concentricity of the new wheels. but use a collet or as Philip has already said.
Tips and tricks in machine tool practice viewtopic.php?f=132&t=6350

davebradwell
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Re: Waddling 0-4-0

Postby davebradwell » Mon Oct 18, 2021 8:34 am

I've rescued wheels using similar technique to Philip. I turned a mandrel with a slight taper and pushed the plastic wheel centre onto that then skimmed the outer. Removed from mandrel and glued 5 thou' Plastikard around rim and when thoroughly dry skimmed this to give original press fit. Obviously don't take mandrel out of lathe while waiting for solvent to set. Tried it without the 5 thou' and Loctited tyre back on with loose fit but it didn't run true - perhaps epoxy is better but I stopped taking chances.

Usually problem is just the moulding pip and flash which can be cut off and wheel re-assembled with no turning. Whatever you do don't try and move the hole or crank throw is changed, as Jeremy suggests. If you replace just 1 wheelset, you'll probably find they're a slightly different diameter from the originals. The tolerance on wheel diameters is a whole new question but they kept them all quite close on the prototype - I always check this before using a set.

DaveB

Philip Hall
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Re: Waddling 0-4-0

Postby Philip Hall » Mon Oct 18, 2021 8:45 am

I usually aim for a sliding fit when the tyre goes back on and take up this slight slack with the Devcon. If it’s a bit too loose I use superglue to glue small pieces of cigarette paper in four places around the rim to take up the slack and then use plenty of Devcon on reassembly.

I did once use superglue to fix a tyre but it fell off easily, so I went back to Devcon.

Philip

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steve howe
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Re: Waddling 0-4-0

Postby steve howe » Mon Oct 18, 2021 10:36 am

I built two of these using the HL chassis kits with the Hornby body. Both have a bit of a waddle when running anything faster than a scale walking pace which I put down to Gibson wheels not being quite true. The chassis kit however is exemplary.

I was once told at a show by an ex-Liverpool shed driver that the real thing did too, due to the short wheelbase and outside cylinders 'punching' along. He recalled being rostered to take one from Liverpool to Warrington with the instruction to "get a move on". By the time they arrived he and his fireman were distinctly seasick!

Steve

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zebedeesknees
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Re: Waddling 0-4-0

Postby zebedeesknees » Mon Oct 18, 2021 3:20 pm

steve howe wrote:I was once told at a show by an ex-Liverpool shed driver that the real thing did too, due to the short wheelbase and outside cylinders 'punching' along. He recalled being rostered to take one from Liverpool to Warrington with the instruction to "get a move on". By the time they arrived he and his fireman were distinctly seasick!

Steve

Agreed, I recall seeing a film of a real 0-4-0ST working hard up a gradient and thinking that I could never get away with a model that waddled like that.
There is also, somewhere, film of a rebuilt Merchant Navy Class loco 'porpoising' far more violently than any model that I have witnessed!
Ted.
(A purists' purist)

hollybeau
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Re: Waddling 0-4-0

Postby hollybeau » Mon Oct 18, 2021 6:06 pm

My thanks to you all for your very helpful and informative replies.
I have made a start by taking the wheels off, removing the crankpins and the tyres. I have then made a mandrel from brass using my collet rather than the 3 jaw chuck (thanks Jeremy) and with a slight taper on the mandrel (thanks Dave). One wheel has been pushed onto this and then the diameter turned down until it is running true (or as true as I can get it (thanks Philip). I don't have any "Devcon 5" (sounds like a state of national emergency!) so have used the original Araldite. The tyre is no longer a tight fit of course but not so loose it needs anything to pack it out. I have turned the lathe by hand and it looks OK. Tomorrow will tell when I hope to do the other wheel.
As for the videos I have uploaded these to Youtube and attach them hopefully below (thanks Keith, although can I suggest that this be made clear in the FAQ's so that other people are aware of how to do this). I take your point Philip about the dial indicator riding up the coning but at least it gives some idea of the scale of the problem. I may rerun the test afterwards to see what improvement I have managed to make.


hollybeau
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Re: Waddling 0-4-0

Postby hollybeau » Tue Oct 19, 2021 5:52 pm

Here's the first wheel ; quite pleased. Its probably more luck than skill


davebradwell
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Re: Waddling 0-4-0

Postby davebradwell » Tue Oct 19, 2021 6:12 pm

Youtube has thrown a strop there but I'll take your word for it and offer congratulations. I'll stay with my press-fit tyres, however, so I can get them off again if something has gone wrong.

Would make the general point here that a lever type indicator is more versatile for our purposes as it can be dangled into horn openings to set up frames square or used as here to check axlebox concentricity. Cheaper makes are available and finer stylus tips than my standard 2mm type. Mag base is cheaper too.


IMG_5883.JPG



No, I'm not expecting you to buy a new one!

DaveB
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hollybeau
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Re: Waddling 0-4-0

Postby hollybeau » Tue Oct 19, 2021 6:20 pm

Dave,

If you paste the bit between the Youtube square brackets into a browser it takes you to the Youtube video showing the outcome of my efforts.
Never heard of a lever type indicator and certainly would not know how to use one: I am no engineer!

Bryan

I suspect that I have not posted the Youtube video correctly but that someone - probably Keith - has been in and corrected my fumblings about in the dark - hence the fact that the earlier videos show correctly but not the one I have just posted

Philip Hall
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Re: Waddling 0-4-0

Postby Philip Hall » Tue Oct 19, 2021 8:03 pm

Devcon 5 minute epoxy is commonly available - it goes off in 5 minutes - (I get mine from the local model shop) and I like it because it seems to stick quite well to the plastic that AG use for the wheel centres. Stuff like Araldite Rapid is very brittle, and I've never had much luck with it. Old fashioned Araldite, like you have used, should do the trick nicely though, and shouldn't ever shift! Your video shows a very good result!

Another dodge I use for truing a centre I pinched from Brian Harrap, and saves turning a mandrel: I simply put a length of axle steel, say about 2 inches, in the three jaw chuck, push the wheel centre on it, right through the wheel, and run the protruding end in a brass bearing (a lump of round brass bar with a hole in it!) in the tailstock chuck. Any eccentricity in the three jaw chuck is effectively taken out by running the end of the 'turning axle' with the wheel centre on it in a bearing held rigidly. This is probably best done, as I do, by turning the lathe by hand, which might not be available to everyone.

Philip

nigelcliffe
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Re: Waddling 0-4-0

Postby nigelcliffe » Tue Oct 19, 2021 8:34 pm

davebradwell wrote:
Would make the general point here that a lever type indicator is more versatile for our purposes as it can be dangled into horn openings to set up frames square or used as here to check axlebox concentricity. Cheaper makes are available and finer stylus tips than my standard 2mm type. Mag base is cheaper too.
....


I'd second that - lever indicators are much easier to use for the purpose, the tip can be angled so things fit for almost all situations. I have a Verdict example, with interchangeable stylus tips, bought many years ago at a model engineering show. I rarely remove the "fine" one from it. Its been used for a lot of 2mm Scale wheel assessments, as well as 4mm stuff.

The other simple way is bar pointer with an off-set pivot. If the pivot is 1-unit from the wheel, and 10-units from the free end, then the wheel movement is amplified by a factor of 10, so much more visible. Could make one with an axle running in bearings and a bit of scrap fixed to the axle.


- Nigel

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grovenor-2685
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Re: Waddling 0-4-0

Postby grovenor-2685 » Tue Oct 19, 2021 8:49 pm

hollybeau wrote:I suspect that I have not posted the Youtube video correctly but that someone - probably Keith - has been in and corrected my fumblings about in the dark - hence the fact that the earlier videos show correctly but not the one I have just posted

OK, edited the other one now.
If you hover the cursor over the 'youtube' button when composing your post it shows you the correct syntax to use.
Also just click on the edit pencil on one of the posts and you can see what I did. Essentially you only need the last section of the youtube url, ie the identifier that is after the last/ or after the v=.
Regards
Keith
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Daddyman
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Re: Waddling 0-4-0

Postby Daddyman » Wed Oct 20, 2021 7:41 am


davebradwell
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Re: Waddling 0-4-0

Postby davebradwell » Wed Oct 20, 2021 9:10 am

That's the right kind of thing, David, but much more sensitive than we need. Mine's quite a small device with a 1" diameter dial having a range of 0-030" or 0.75mm. Graduations are down to half-thous' (12.7 microns). It's the small travel makes it more compact than the big dial gauge. In use the lever moves to and fro rather than being a plunger and, as it's small, can be poked down holes to check concentricity, or whatever. Can't see how you get milling m/c vice parallel to axis without one. The direction of action is reversible by a lever on the side.

Last used for setting a piece of square bar in 4 jaw - stick base on convenient bit of saddle and check deflection on each side of bar. Probably quicker to get it right than fiddle with feeler gauges or kid yourself you can put a punch mark in the middle. Has also been used to check boiler is level!

DaveB

Terry Bendall
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Re: Waddling 0-4-0

Postby Terry Bendall » Wed Oct 20, 2021 7:56 pm

Daddyman wrote:Is this kind of thing any use?


The device is known as a dial test indicator, and I described how it is used to check a bar is concentric in the lathe in part six of the series that I wrote some years back on using machine tools. Scalefour News 160 is the relevant issue. My version is shown below on the stand that I made about 60 years ago as a school metalwork project. This stand is a bit on the large size for the smaller sort of lathes that some of us will use but it works for me.

DTI.jpg


The diameter of the face of the gauge is about 28mm and this is an ideal size for our work. The business end is the small lever with the ball end at the bottom and this can be rotated against a ratchet to get it in the position needed.

Terry Bendall
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