Wheels, curing eccentricity and wobble.

Philip Hall
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Philip Hall » Tue Jan 02, 2018 9:47 pm

Tim,

You can mount a wheel on a turned mandrel in the lathe, spin the lathe by hand and look at the wheel against a white background. I also usually bring a lathe tool almost up to the tyre surface and see how the gap between the tool and the tyre varies. You can use a dial gauge or similar to check but I have found the problem with that is that if the wheel wobbles ever so slightly, the reading on the gauge will as well, even if the wheel is true, as the stylus on the gauge runs up and down the coning. However, I now prefer not to use a turned mandrel, instead I use a long (100mm) ‘axle’ mounted in the lathe chuck with the other end (with the wheel pushed on it) running in a bearing in the tailstock chuck. Any run out of the lathe chuck (mine is about 1 thou) is removed by the ‘axle’ running in the bearing at the other end.

All this is no use at all If you don’t have a lathe, of course! Another method is to mount the wheels on an axle and roll the wheelset up and down a sheet of plate glass, or even a flat board like Contiboard. To hold the axle whilst you roll it just cut a square strip of timber and put a slot in it to take the axle, you can then hold the axle down as it rolls up and down. With practice, you will feel the eccentricity as it rolls along.

The third way is to mount the wheelset in a little jig with two bearings in it so you can spin the wheel (as with the lathe) and look at the wheels as they go around. Again, looking against a white card or having (say) a scriber in a clamp held up against the wheel is useful.

Once you've established that there is a problem, you have various ways of fixing it, the easiest being to replace the wheelset. With AG wheels and a lathe, it is possible to check, and usually correct, any eccentricity of the moulded centre, which does sometimes occur. Often slipping the tyre off and cleaning off the remains of the moulding pip will help. Wheels with locked on tyres, like Sharman, cannot be treated this way.

Philip

John Palmer
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby John Palmer » Wed Jan 03, 2018 12:27 pm

Philip Hall wrote:You can use a dial gauge or similar to check but I have found the problem with that is that if the wheel wobbles ever so slightly, the reading on the gauge will as well, even if the wheel is true, as the stylus on the gauge runs up and down the coning.
...
The third way is to mount the wheelset in a little jig with two bearings in it so you can spin the wheel (as with the lathe) and look at the wheels as they go around. Again, looking against a white card or having (say) a scriber in a clamp held up against the wheel is useful.
...
Wheels with locked on tyres, like Sharman, cannot be treated this way.

Philip
If you set your dial gauge plunger against the wheel face rather than on the tread, the coning won't affect the read-out.

It should be easy enough to improvise a wobble detector using similar principles to those of a dial gauge - my attached sketch
attempts to show the approach I would adopt. Any 'gainstroke' arrangement should magnify the extent of any wobble; in my sketch, the long arm of the pointer should magnify the extent of any wobble by a factor of two.
Improvised wobble gauge.jpg
Improvised wobble gauge.jpg (27.43 KiB) Viewed 1571 times

One of the nice things about Mike Sharman's wheels is that gentle sideways pressure against the wheel at the 'point of maximum wobble' will correct it, as the plastic spokes will 'give' slightly so that the wheel takes up a new position.

Philip Hall
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Philip Hall » Wed Jan 03, 2018 12:33 pm

Tim,

Another ‘kitchen table’ method has occurred to me: cut a short length of 2mm i/d tube, or take a 2mm top hat bearing, and hold it gently in a vice. Put the wheel in the axle, slip into the bearing and spin it, again viewing against some white card. Should be fairly easy to see the eccentricity. Again, something like a screwdriver or a scriber held up to the wheel as you spin will help.

Philip

PS: John, just seen your post. However, the test is for eccentricity rather than wobble, so surely a dial indicator stylus has to bear on the tread? Or somehow on the flange edge?

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Le Corbusier
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Le Corbusier » Wed Jan 03, 2018 12:41 pm

Philip Hall wrote:Tim,

Another ‘kitchen table’ method has occurred to me: cut a short length of 2mm i/d tube, or take a 2mm top hat bearing, and hold it gently in a vice. Put the wheel in the axle, slip into the bearing and spin it, again viewing against some white card. Should be fairly easy to see the eccentricity. Again, something like a screwdriver or a scriber held up to the wheel as you spin will help.

Philip

PS: John, just seen your post. However, the test is for eccentricity rather than wobble, so surely a dial indicator stylus has to bear on the tread? Or somehow on the flange edge?


Thanks Philip and John ... much appreciated.

I am assuming at present that the issue is eccentricity .... but will also try and check for wobble. :thumb

Presumably the flange edge is the best position to see the eccentricity - assuming the machining of the tyre is accurate?

I have to admit I am currently hoping that there is an obvious pip on the moulding as the tender movement does seem quite extensive. :?

The good news is that it still holds the track so something must be working right :D
Tim Lee

John Palmer
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby John Palmer » Wed Jan 03, 2018 1:05 pm

Philip Hall wrote:PS: John, just seen your post. However, the test is for eccentricity rather than wobble, so surely a dial indicator stylus has to bear on the tread? Or somehow on the flange edge?

Sorry, Philip, you're quite right; I should have been paying more attention! Getting any kind of consistency in readings if the dial gauge stylus has to bear directly on the cone or flange is problematic, so I think one might need to arange for some kind of bar to bear against the flange tip to measure for eccentricity. Whether that's done by attaching a bar to the stylus or improvising one's own detetctor, I think similar principles apply. I've done a further sketch suggesting how this might be done, again using a 'gainstroke' arrangement.
Improvised eccentricity gauge.jpg
Improvised eccentricity gauge.jpg (32.75 KiB) Viewed 1556 times

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Le Corbusier
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Le Corbusier » Wed Jan 03, 2018 1:12 pm

John Palmer wrote:
Philip Hall wrote:PS: John, just seen your post. However, the test is for eccentricity rather than wobble, so surely a dial indicator stylus has to bear on the tread? Or somehow on the flange edge?

Sorry, Philip, you're quite right; I should have been paying more attention! Getting any kind of consistency in readings if the dial gauge stylus has to bear directly on the cone or flange is problematic, so I think one might need to arange for some kind of bar to bear against the flange tip to measure for eccentricity. Whether that's done by attaching a bar to the stylus or improvising one's own detetctor, I think similar principles apply. I've done a further sketch suggesting how this might be done, again using a 'gainstroke' arrangement.Improvised eccentricity gauge.jpg

The problem of course will be when I find all the wheels are eccentric, and then we can debate how eccentric is too eccentric. :shock:
Tim Lee

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Jol Wilkinson
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Jol Wilkinson » Wed Jan 03, 2018 2:12 pm

It will also depend on whether the wheel is singly eccentric or its opposite number is "mirror" eccentric too. I.e. the B2B is consistent at opposite positions. That would mean the wheels will probably run through your trackwork but may create a lateral movement as they rotate. I have several locos with this eccentric wheelset issue, but where the locos run well.

As for how much eccentricity is too much, I am sure someone will be along with a calculator soon to find a number.

Philip Hall
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Philip Hall » Wed Jan 03, 2018 3:10 pm

Tim, aah... there’s the rub! I have a rule of thumb, depending on how the engine is suspended (or not). If the engine is rigid - ie a RTR conversion - I try to aim for zero tolerance, an unreachable utopia of course. I try to aim for about 1 thou, but I must emphasise I don’t measure this, I just look at the wheel as I have mentioned above, and aim to see no movement. Generally if I can have the outer wheels of an 0-6-0 as close to ‘bang on’ as possible, then I think that the middle axle, which often has a little up and down movement, can wander a bit. Ditto for a six wheeled tender. Sounds very non engineering like, but it works. As in so many such things, the eye is very much the best. I tend to look at the tyre surface, but if you are measuring (as per John’s post) the the flange edge would be better perhaps. I think we can happily assume that the relationship between tyre and flange is accurate and consistent, but I have (on occasion) skimmed off high spots on a tyre surface on a Sharman wheel and not altered the flange and it has worked!

For a suspended chassis (I can only speak for compensation) the fixed axle (if you have one) hopefully will be close to perfect, within 1 thou again. The moving axles, well I will allow up to about 2-3 thou, as this movement will be visibly lost within the compensation arrangements. As an example the GWR 72XX that I posted a picture of in Julian’s Crab thread a little while ago, probably had some eccentricity but because the engine had a twin beam/single beam arrangement, it simply glided along. So when you have a fully compensated twin beam 0-6-0, the moving axle criteria apply, 2-3thou. I check by eye mostly again. Some time ago I had some correspondence with Chris Pendlenton who seems to have the same idea of tolerances, and he, of course, is dealing with sprung chassis. If he is happy with such figures, I can only demur...

Everyone has their own ideas of what is acceptable, and I freely admit (and my modelling friends will tell you so!) that I am mildly nuts about wheels being round. Having done a lot of RTR conversions, it just seems to me to be perverse to take a beautifully smooth running 00 engine and converting it to P4 or EM and having it bouncing up and down the track in a way it never did in 00. So I have ended up checking and correcting where necessary. Most of the time our wheelrights do a great job, but occasionally, if you are like me, it is possible to improve things a bit.


Hope this helps!

John, thanks for the suggestion, that looks like a good solution to being able to check and measure eccentricity. I will look at making something up when the workshop is back up and running. I usually find that checking by eye is a pretty good way, though, but having some parameters could be useful.

Philip

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Le Corbusier
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Le Corbusier » Wed Jan 03, 2018 3:23 pm

Jol Wilkinson wrote:It will also depend on whether the wheel is singly eccentric or its opposite number is "mirror" eccentric too. I.e. the B2B is consistent at opposite positions. That would mean the wheels will probably run through your trackwork but may create a lateral movement as they rotate. I have several locos with this eccentric wheelset issue, but where the locos run well.

As for how much eccentricity is too much, I am sure someone will be along with a calculator soon to find a number.

Ah Jol ... but I always understood that eccentricity was one of the great attributes of the British :P are such things really quantifiable :?:
Tim Lee

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grovenor-2685
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby grovenor-2685 » Wed Jan 03, 2018 4:14 pm

As for how much eccentricity is too much, I am sure someone will be along with a calculator soon to find a number.

Nework Rail has a spec for it.
Regards

Terry Bendall
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Terry Bendall » Thu Jan 04, 2018 8:02 am

John Palmer wrote:so I think one might need to arange for some kind of bar to bear against the flange tip


A neat idea but this would test if the flange is concentric and not the tread which is probably the most important thing. The flange and the tread may well be on the same centre and both could be out of true but it may not always apply.

Terry Bendall

John Palmer
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby John Palmer » Thu Jan 04, 2018 11:34 am

Terry Bendall wrote:
John Palmer wrote:so I think one might need to arange for some kind of bar to bear against the flange tip


A neat idea but this would test if the flange is concentric and not the tread which is probably the most important thing. The flange and the tread may well be on the same centre and both could be out of true but it may not always apply.

Terry Bendall

Indeed, Terry, just that thought occurred to me after I posted the suggestion. However, I was inclined to discount the possibility of the flange tip and the tread being on different axes because that would imply that some shift of one or other axis had taken place whilst the profile was being generated. If both flange and tread profile have been simultaneously generated by the same form tool (which I take to be the usual manufacturing method) then the problem should not arise. If machining one's own wheels then woe betide the turner who fails to plan the operation in such a way as to avoid the need to remount the wheel, possibly on a different axis!

As it happens, I have some Sharman wheels of the coarse profile (was that his 'B' profile wheels?) which I shall be attempting to re-profile, so I may shortly be finding out whether practice bears out theory!

Philip Hall
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Philip Hall » Thu Jan 04, 2018 5:40 pm

John, re Sharman wheels:

Some time time ago, I sorted some old Sharman bogie wheels which were not (unusually) very round. I have an old (very old!) Unimat SL fitted with a Sherline chuck. The SL simply does not have the guts to handle a reprofiling tool, so I made a tool which just related to the tyre surface and flange edge. I reasoned that as long as the the tyre surface was true, a few thou out on the flange wouldn’t matter. The tool was basically a tool with a 20° angle and a rounded point, approximately the root radius for P4, which I could bring into the tyre surface to true it up. The tyre profile would be OK even though the flange depth might vary a bit. It worked, although on the fourth wheel of four I found I was cutting into to the plastic centre!

I too have some Sharman type B wheels, which are too good to not find a use for. When these were first made, my recollection is that the EM wheels (type B) were intended to be slightly reprofiled to P4, until Mike later on introduced his P4 profile. Mike said that taking a bit off the back off the flange would be enough, and from the wheels I have here, it does seem that his EM wheel is not a lot different to the P4 profile, apart from a fractionally deeper flange.

It does occur to me that although we are helping Tim with possible eccentricities in his wheels, we might be straying into the realms of a more specific thread re wheels problems. I’m not sure how to do this, so Keith and administrators, if you think this a good idea, could you transfer our ramblings please to a new thread?

Philip

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Le Corbusier
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Le Corbusier » Thu Jan 04, 2018 5:53 pm

Philip Hall wrote:John, re Sharman wheels:

Some time time ago, I sorted some old Sharman bogie wheels which were not (unusually) very round. I have an old (very old!) Unimat SL fitted with a Sherline chuck. The SL simply does not have the guts to handle a reprofiling tool, so I made a tool which just related to the tyre surface and flange edge. I reasoned that as long as the the tyre surface was true, a few thou out on the flange wouldn’t matter. The tool was basically a tool with a 20° angle and a rounded point, approximately the root radius for P4, which I could bring into the tyre surface to true it up. The tyre profile would be OK even though the flange depth might vary a bit. It worked, although on the fourth wheel of four I found I was cutting into to the plastic centre!

I too have some Sharman type B wheels, which are too good to not find a use for. When these were first made, my recollection is that the EM wheels (type B) were intended to be slightly reprofiled to P4, until Mike later on introduced his P4 profile. Mike said that taking a bit off the back off the flange would be enough, and from the wheels I have here, it does seem that his EM wheel is not a lot different to the P4 profile, apart from a fractionally deeper flange.

It does occur to me that although we are helping Tim with possible eccentricities in his wheels, we might be straying into the realms of a more specific thread re wheels problems. I’m not sure how to do this, so Keith and administrators, if you think this a good idea, could you transfer our ramblings please to a new thread?

Philip

Don't worry about me Philip ... interested in all of this - still debating the purchase of a lathe, and if so which one ;)
Tim Lee

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Will L
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Will L » Thu Jan 04, 2018 6:13 pm

Re eccentric wheels.

One of the advantages to the use of CSBs, which suit 6 wheel tenders very well, is that they will will much reduce, even eliminate, the visible effects of not entirely round wheels, because the there is no direct rigid connection between the wheel rim and the vehicle body.

Lindsay G
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Lindsay G » Thu Jan 04, 2018 6:17 pm

Post by grovenor-2685 » Wed Jan 03, 2018 4:14 pm

As for how much eccentricity is too much, I am sure someone will be along with a calculator soon to find a number.

Network Rail has a spec for it.


Aha, now we have a reference point from which someone can calculate, to the 1000th of a millimetre, the tolerance of eccentricity that we can work within in P4. 00 and EM modellers must be rather envious that we have the patience and skill to work within such exacting parameters whether for B2B, check gauges, and so on. It must be rather frustrating for them to throw together exquisite models, stick them on the track, turn up the juice and watch them run flawlessly, and then wonder what to do with the rest of the afternoon.

Perhaps all this should be restricted to a Members Only area of the Forum, clearly marked along the lines of Minutiae and Theory. If I had read endless posts on such matters just over a decade ago, I'd have been more inclined to go down the EM road instead.

Here's to some happy modelling, and end results posted on the Forum, in this New Year,

Lindsay

P.S. I presume the Verniers being used for such precision are quality instruments such as Mitutoyo rather than trusting to the accuracy of cheap Chinese items picked up at Aldi or Maplins the last time they had an offer on. Oh dear, I can see a new thread emerging.
Last edited by grovenor-2685 on Thu Jan 04, 2018 7:30 pm, edited 1 time in total.
Reason: Corrected the quote.

Philip Hall
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Re: Making a Start - The Peak District Midland / Monsal Dale pre 1903

Postby Philip Hall » Thu Jan 04, 2018 7:00 pm

Lindsay has a point about minutae. But I don’t often measure such things, preferring to rely on my eyes.

I should say that my penchant for dead true and round wheels also applies to the many EM conversions I have done. Changing gauge from 00 to anything else also demands round wheels. However, as I said earlier, I am quite nuts about such things. I just have this aversion to unpacking a perfectly running RTR model which glides along the track which upon conversion bumps up and down like a duck on speed. That doesn’t give a good impression of either wider gauge. Making as sure as I can that the wheels are on the money, and the engine looks the same, despite the wider gauge, is my aim. I don't always get there... EM, P4, even better wheels in 00, the aim is just the same.

I don’t think I have the patience, much less the skill, to work to exacting limits....

Philip

John Palmer
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Re: Wheels, curing eccentricity and wobble.

Postby John Palmer » Thu Jan 25, 2018 12:36 pm

Philip, apropos turning Sharman wheels, I don't know whether the Unimat SL can be fitted with a top slide for taper turning, but my Unimat 3 does, and I had planned to use this to re-profile a set of such wheels with traversing cuts on a taper rather than plunge cuts such as one would use with a profiling tool.

Those who possess such a top slide for the Unimat will object that the gradations for setting the slide's angle are much too coarse to permit acceptable accuracy for such taper turning. Quite right, but my plan was to align the top slide by employment of a triangular setting gauge having the appropriate 1:20 coning angle and using the near face of the cross slide as the reference relative to which the gauge would be positioned.

Alas, I fear I shall have to abandon this plan because of the considerable eccentricity of at least one of the wheels in this elderly collection, as shown on the attached picture, which may be of interest in showing my set-up for measuring the degree of eccentricity present – in this case .013”!
Wheel Eccentricity.jpg
As can be seen, I am using some decent quality Mitutoyo kit for the exercise, and lest anyone thinks the wheel is sitting on the 6BA thread, there is in fact a short length of journal on which the wheel bore is located.

I had a nasty feeling that an attempt to take .013” off the tread to cure the eccentricity of this wheel would be more than the wheel will bear, so Plan B was to obtain some new wheels. However, submitting these to the same testing also revealed some eccentricity, but of the lesser order of .004” maximum. I'm inclined to go ahead with this, such eccentricity notwithstanding, as I think that on sprung frames it will be barely perceptible (as noted in Will's post). However, the question posed up-thread as to how much eccentricity was too much remained unresolved for a P4 model. If anyone can suggest a threshold value at which eccentricity of wheel rim (as distinct from eccentricity in crank throw) will have unacceptably adverse effects upon performance/appearance I shall be pleased to hear it.

Philip Hall
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Re: Wheels, curing eccentricity and wobble.

Postby Philip Hall » Thu Jan 25, 2018 3:14 pm

Quite right to be cautious, John. When I dealt with an old set of Sharman bogie wheels, I managed three of them, but on the last I found myself looking at black plastic! I had, quite by chance, a loose matching Alan Gibson tyre, so was able to turn down the centre to fit.

My Unimat SL is just fine, but not quite in the same league as a 3. The centre height is not sufficient to fit a top slide, even if one were to be available for such an elderly machine. Taper turning is intended to be done by moving the headstock. My SL is very true along the centre line, so I am sticking to the advice given me which is not to disturb it. This is why I made up a tool with a 20°angle on it to introduce gradually to the wheel, taking tiny shavings off at a time.

I envy you the collet chuck you have, the one I was able to obtain for the SL was not very true, leading to my modifying Brian Harrap’s method of mounting wheel on a rod running in the tailstock end. Generally I don’t measure any eccentricity, I do it by eye and by bringing a tool up to the wheel to judge how the gap between the tool and the tyre increases and decreases. I aim for zero but don’t always achieve it!

Philip
Last edited by Philip Hall on Thu Jan 25, 2018 4:23 pm, edited 1 time in total.

David Knight
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Re: Wheels, curing eccentricity and wobble.

Postby David Knight » Thu Jan 25, 2018 3:35 pm

Is Brian Harrap’s method documented anywhere? I’ve heard about it, seen pictures of his finished work but never seen or read the step by step.

Cheers,

David

Philip Hall
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Re: Wheels, curing eccentricity and wobble.

Postby Philip Hall » Thu Jan 25, 2018 4:22 pm

David,

I don’t think that Brian has ever written it up anywhere, but he has demonstrated it at Scaleforum. I adapted it a few years ago when I first started using my Unimat SL. I don’t think he will mind me describing it again here, although somewhere on the Forum I have written about it before, I think outlined earlier on this thread.

I have an ancient Unimat SL, which has a very accurate Sherline chuck, within about 1.25 thou eccentric, which although very good, is not quite good enough for a wheel. It is also hard to find a collet chuck to fit a SL that is better. Brian’s method mounts a wheel at the end of an axle, running in a bearing mounted in the tailstock chuck. The other end of the axle is secured in the 3 jaw chuck. The reasoning is that any eccentricity in the 3 jaw chuck is almost removed by the other end running in a bearing. I have adapted this by using a longer ‘axle’, about 100mm, rounded and smoothed so the wheel can be introduced onto the axle nicely. The longer axle minimises further any eccentricity.

That’s it really. It only works if the wheel is a decent tight fit on the axle, such as Alan Gibson or Sharman. I have found that it doesn’t work for Sharman really because there is more force required to turn the steel tyre and that might cause slipping. Here John’s turned mandrel with the wheel bolted in place is the best way. For me it’s a useful way to clean up a slightly eccentric centre on a Gibson wheel; they do occur sometimes and I quite like being able to fettle them myself. In this application I take the drive belt off the lathe and turn it by hand, bringing the tool in very gently to skim any high spots off the centre. With such gentle cuts the wheel doesn’t usually slip on the axle.

As mentioned before, the Unimat SL does not have the guts to handle a proper form tool and when reprofiling is required I tend to ask a friend for help. I know Brian uses his method to reprofile wheels to P4 or whatever by eye, so I guess he has wheels that are a good tight fit on their axles.

Hope this helps.

Philip

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Guy Rixon
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Re: Wheels, curing eccentricity and wobble.

Postby Guy Rixon » Thu Jan 25, 2018 5:43 pm

Google found for me a railway group standard concerning wheelsets: https://www.rssb.co.uk/rgs/standards/GMRT2466%20Iss%201.pdf. The relevant bit for eccentricity, which they call "tread run-out" is table G4 where a series of limits are given for run-out in millimetres. The limits differ for different classes of vehicles and the urgency for taking the vehicle out of service.

For locomotives, run-out above 3mm fails the vehicle immediately, 1.3 to 3.0 mm require it to be withdrawn for repairs "at the end of the journey" and <1.3mm requires no urgent action. 1.3 mm scales to 0.0007" in 4mm scale and 3mm to 0.0015".

EDIT: I read more of the document and table G1 gives the limits on run-out and wobble after reprofiling: they are much tighter than the limits for failing a vehicle on inspection. For locomotives, the greatest allowed run-out is 0.25mm (sic!) and the greatest wobble is 0.4mm.

Given that we don't kill anybody when our trains fall off and our plastic passengers don't complain about vibration, I suspect that the on-inspection limits are more relevant to models.

David Knight
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Re: Wheels, curing eccentricity and wobble.

Postby David Knight » Thu Jan 25, 2018 8:02 pm

Thanks Philip. I can visualize what your are talking about and along with a pic that was in the Snooze a while back of Ivan Tan getting instructions from Brian it seems to make sense. IIRC Brian uses a graver rather than a form tool and thus light cuts are the order of the day. He really only seems to be taking small amounts from standard RP25 profile wheels and slimming them down to P87/P4 as needed. I suppose the thing to do is fire up the lathe one of these days and have a go. ;)

Cheers,

David

Philip Hall
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Re: Wheels, curing eccentricity and wobble.

Postby Philip Hall » Thu Jan 25, 2018 8:13 pm

David,

When I visited Brian some years ago I recall him using a normal turning tool with a ever so slightly rounded head (it was one of those tools with a changeable tip and this one was rounded, close to the root radius of a tyre) and this was set up in the compound slide of his Unimat 3 set at 20°. Possibly he uses a graver at times; knowing him it won’t be conventional!

Philip

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Tim V
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Re: Wheels, curing eccentricity and wobble.

Postby Tim V » Thu Jan 25, 2018 9:37 pm

John Palmer wrote:Alas, I fear I shall have to abandon this plan because of the considerable eccentricity of at least one of the wheels in this elderly collection, as shown on the attached picture, which may be of interest in showing my set-up for measuring the degree of eccentricity present – in this case .013”! Wheel Eccentricity.jpg As can be seen, I am using some decent quality Mitutoyo kit for the exercise, and lest anyone thinks the wheel is sitting on the 6BA thread, there is in fact a short length of journal on which the wheel bore is located.

I had a nasty feeling that an attempt to take .013” off the tread to cure the eccentricity of this wheel would be more than the wheel will bear, so Plan B was to obtain some new wheels. However, submitting these to the same testing also revealed some eccentricity, but of the lesser order of .004” maximum. I'm inclined to go ahead with this, such eccentricity notwithstanding, as I think that on sprung frames it will be barely perceptible (as noted in Will's post). However, the question posed up-thread as to how much eccentricity was too much remained unresolved for a P4 model. If anyone can suggest a threshold value at which eccentricity of wheel rim (as distinct from eccentricity in crank throw) will have unacceptably adverse effects upon performance/appearance I shall be pleased to hear it.

I would re-centre those wheels. Mount the wheel by its flange in a mandrel, and using a milling cutter, cut a new hole that can be bushed. I have successfully re-centred drivers and carrying wheels using this method.
Tim V


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