Wheels, curing eccentricity and wobble.

John Palmer
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Re: Wheels, curing eccentricity and wobble.

Postby John Palmer » Fri Jan 26, 2018 1:33 am

Tim, I assume that the wheels you suggest I should re-centre are in the set that includes the one in my picture. That's fine for carrying wheels, and it's a technique I use to facilitate shorting of rims to axles for split axle current collection and have illustrated elsewhere.

However, cutting a new bore concentric with the rim of a coupled wheel seems sure also to require re-positioning of the crankpin. Since the wheel in question is pre-fitted with a screw to carry the crankpin bearing and that screw is embedded in the moulding, its necessary removal and replacement by one one having the correct crank throw substantially increases the work to be done and with it the risk of something going terminally wrong.

I think for mandrel you must have intended to say chuck. I would rather grip the wheel by its tread rather than its flange, as this reduces (but does not necessarily eliminate!) the risk of the wheel being mounted askew. Then you have to decide whether to trust your 3-jaw chuck to hold the wheel on the same axis as your boring tool. On the whole I would prefer to use a 4-jaw chuck, but in order to mount the job accurately I would want the wheel held in a ring chuck so that I have an accurate surface against which my dial indicator can bear – and that's another item to be manufactured.

All of which leads me to think I am going down the right road by purchase of replacement wheels which I can then tweak in the way Philip has suggested to reduce their slight eccentricities.

Philip, thanks for describing again Brian Harrap's method, which I had forgotten. This has some similarities with turning the job between centres, and in principle my mandrel could be used in that way, since it is already centre-bored and has plenty of shaft behind the disc on which a driving dog can be mounted. The disadvantage is that it may be very difficult/impossible for me to taper turn in the way I envisaged in my previous post if the mandrel is mounted between centres, but it's an approach that may repay further investigation.

Terry Bendall
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Re: Wheels, curing eccentricity and wobble.

Postby Terry Bendall » Sat Jan 27, 2018 9:13 am

John Palmer wrote:I had planned to use this to re-profile a set of such wheels with traversing cuts on a taper


This is certainly one way of doing the job but care will be needed to make the depth of cut the same on all the wheels.

John Palmer wrote: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.


This is the appropriate way to do this task. Have you checked that your mandrel is running true? With a collect chuck it should be as long as the collet itself is also running true.

Philip Hall wrote: Taper turning is intended to be done by moving the headstock.


This is quite right but this method is intended for tapering a bar held between centres rather than the tyre of a wheel or things just held in the chuck. In theory it would work for the method devised by Brian and used by Philip but getting the angle correct would not be easy.

David Knight wrote:Brian uses a graver rather than a form tool and thus light cuts are the order of the day.


Using a graver and turning by hand is a perfectly legitimate way of doing the job. I described this in News 161 pages 12 -15 (available in the archive on the Society web site) and it is commonly used in clock making. The trick will be getting the diameter of the wheels the same on all of them which will need careful measuring. Using the compound slide on the lathe means that the tool could either be left at the same setting - if there is not too much to come off, or the cross slide reading noted and the tool fed in to the same setting for the next wheel.

Terry Bendall

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Knuckles
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Re: Wheels, curing eccentricity and wobble.

Postby Knuckles » Sun Mar 11, 2018 7:51 pm

This won't appeal to those of you with high precision and a sophisticated tool set but for bodgers like me I found a way that fits the bill quite nicely.

I've always found Alan Gibson wheels a pain to get on square so this dodge coupled with the MK1 Eyeball and the tweaking hand has worked a treat. No more wheel wobble (unless I bend them later by accident)

Image

Image

Yes that's a naughty background I know.
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https://www.sparkshotcustomcreations.com/
Mostly 3D Printed Loco kits etc.

SCC Price list (7/4/22)
https://www.sparkshotcustomcreations.co ... e77d42.pdf

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Paul Townsend
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Re: Wheels, curing eccentricity and wobble.

Postby Paul Townsend » Mon Mar 12, 2018 6:31 am

So how do you do the second wheel?

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Knuckles
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Re: Wheels, curing eccentricity and wobble.

Postby Knuckles » Mon Mar 12, 2018 8:32 am

GW Models quartering jig.

If it is a bit wobbly after I usually tease it back.

I'm thinking of 3D printing a sort of cup that will go in the chuck bit but the top instead of accepting the axle will accept the wheel instead. Then I can insert a full wheel set into the drill. If I go this route I'll update.

I'm no expert here, just feeling my way around a square wheel.
“He who dares not offend cannot be honest.” Thomas Paine

https://www.sparkshotcustomcreations.com/
Mostly 3D Printed Loco kits etc.

SCC Price list (7/4/22)
https://www.sparkshotcustomcreations.co ... e77d42.pdf


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