New O gauge wheel sets

Discussion in 'Resources' started by Compton castle, 11 December 2016.

  1. Elliot 84A

    Elliot 84A Western Thunderer

    Brian,

    The beauty about my wheels is that as they're all cnc'd milled to the cnc turned spigot. Once you put them in the lathe and use the front dimple for centring they'll be turned true and the crankpin will still be accurate to the axle bore.

    E.
     
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  2. unklian

    unklian Western Thunderer

    Understood, but you do not trust the mill to machine the crank throw accurately enough ? How else do you do it then please ? And as for turning the milled centre concentric would mounting each wheel on a specially turned mandrel not work if you CNC'd the bore in the beginning ? Maybe the CNC would not give an accurate enough bore ? Just thinking it through really, I have had some Gauge 3 centres fully CNC machined and so far they seem to be working out OK .
    Beautiful wheels btw Elliot, I suspect that the cost in G3 1:22 scale would be eye watering !
     
  3. Brian McKenzie

    Brian McKenzie Western Thunderer

    Thanks Elliot,
    I really like what you are producing. The contouring of the spokes and filleting is superb, but I earnestly suggest that you not add crankpin holes prior to completing axle bores. Fellow CNC production engineers might like to comment?
    -Brian
     
  4. Elliot 84A

    Elliot 84A Western Thunderer

    If you want wheels I can do them, until I run the figures I've no idea how much they would cost to be fair.

    E.
     
  5. Elliot 84A

    Elliot 84A Western Thunderer

    Brian,

    Knowing how well these machined then I'd be more than confident that the crankpin centre dimple would be more than accurate. Obviously if they were done using a collet then you'd be more confident but seeing as its only a dimple then people can choose to use it or use a slot drill to set they're own position up.

    E.
     
  6. Steph Dale

    Steph Dale Western Thunderer

    I'm no CNC engineer, but I'm afeared you might be right Brian.

    If the lathe chuck is even a smidge out of whack then the crank throw won't quite be consistent; and that's before considering the alignment accuracy of the mill that's used to produce the original items. But:

    You've both really made me think though and it's worth noting that in a perfect world Elliot is 100% correct and in a reasonably precise world it may well be good enough.

    "The perfect is the enemy of the good enough" - it might be that easing a crankpin hole is enough to overcome any issue, in which case it's good enough and I might not worry about perfection, which generally costs more.

    Which, I think, is roughly where we started. :)

    And I have placed an order, including the crank pin mark...

    Steph
     
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  7. Brian McKenzie

    Brian McKenzie Western Thunderer

    Yes I agree. The crankpin centre dimple will always be accurate relative to the machining of the spoked blank, it being part of that milling process. It was Unklian's suggestion that crankpin holes might be drilled at this initial stage that alarmed me - a cart before the horse situation. :) Crank pin holes should ideally come after turning operations have produced the axle hole. :thumbs:

    While there is every chance that crankpin holes can be drilled satisfactorily, by using the dimple on any wheels "turned with the accuracy of Elliot's supplier equipment", the end result, when turning is done in the home workshop, may lead to variations and any pre-drilled holes would be quite frustrating. Use of a slot drill with wheels locked on an axle spigot is preferable to making use of a dimple in such circumstances.

    An S scale colleague goes so far as to turn crankpins to finished diameter - after they have been secured in the wheel. [With wheels mounted on an offset spigot, it becomes an easy turning operation - rather than a slot-drilling one.]

    Good thoughts, Steph - and I should plead guilty if charged. In my defence, the many exactly scaled wheels delivered to some very discerning EU modellers, but probably few with quite the elegance of Elliot's production. Have a full range of toolroom gear at home which does usurp some model railway space. Such toys 'smoke my tyres' :D though, pun intended. :)

    -Brian McK. (We had a good chat at Guildex some years ago)

    Mitutoyo Optical Comparator_Wheels.jpg
     
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  8. Yorkshire Dave

    Yorkshire Dave Western Thunderer

    That machine looks like it's been designed by John Logie Baird and Wilhelm Röntgen ;).

    Or it it something from Metropolis with an image like that :)?
     
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  9. Brian McKenzie

    Brian McKenzie Western Thunderer

    Giggle, by who ? (I had to look them up). No, designed by Mr Mitutoyo and his honourable chums.

    It's an 'Optical Profile Projector' - using American terminology. In Yorkshire it is probably called a 'Shadowgraph' (as in 'hoover' for a vacuum cleaner). It merely projects an image from a controlled moving stage that offers x - y measurements and angles.

    In the early days, when I handcut wheel patterns, following the lead of my engineering mentor Sid Stubbs, I used an old photographic enlarger to project the embryo pattern on to a wall, to check that spokes were evenly spaced and of even thickness. Machines now take care of that, but the shadowgraph is most useful for checking tyre profiles and the tools that make them and other things (two tyres can be seen at lower right in the photo).

    Surprisingly, there is quite a lot of variation in prototype tyre profiles around the world. North American 'tires' have wider, but slightly shallower flanges than UK. Large South African steam locos imported by enthusiasts to New Zealand are required to have their tyres re-profiled to local standards before they can traverse NZ tracks. An exacting French modeller requests his wheels show the two distinct angles across the tread width, as when new.

    -Brian McK.
     
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  10. JimG

    JimG Western Thunderer

    Brian,

    I've CNC machined my 32nd scale driving wheels and I've spot drilled the crank pin centres using a slotting cutter in the milling machine. In fact the cutter was a 2mm diameter slot mill which profile milled the axle hole to 6mm diameter then spotted the crank pin hole immediately afterwards on the same Gcode run. I realise that I am depending on the accuracy of the CNC mill and that there could be a variation of +/- 0.001" (0.025mm). I haven't got as far as fitting crank pins as yet, but when I do I'll check them out to see what variation there might be. I'm taking a punt that any inaccuracies in the mill will go the same way for each crank pin.

    I opened the milled 6mm axle hole out in the lathe with a 1/4" hand reamer after the spoke centre had been press fitted into the freshly turned inner side of the steel tyre

    1/32 - A Loco for the Garden

    If I do find problems I'll set up a spigot on the mill to hold the wheels through the axle hole and open out the crank pin holes with a larger slot cutter and bush them to the required diameter.

    Jim.
     
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  11. richard carr

    richard carr Western Thunderer

    I have to laugh you are worrying about an error of one thousandth of an inch, it really doesn't matter, 5 thou would fine it would still work.

    Do you realise how inaccurate the real thing was.

    Richard
     
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  12. Brian McKenzie

    Brian McKenzie Western Thunderer

    Thanks Jim,

    Good to hear from you again. I have been admiring your work from afar.
    There are some aspects which I'm not sure are being readily grasped. Your machining process as described is perfectly fine, more so if the OD of the wheel centres was finished as part of the milling process - as I think it was. Even without, I know you would 'clock up' your wheel bores - if any subsequent finish turning of the wheel centres was required.

    What I am suggesting/saying is that any pre-drilling of crankpin holes (as was suggested) is undesirable (unless axle bores were also included) in Elliott's spoked wheel blanks - when such blanks are distributed to modellers for them to finish turn and drill/ream axle holes. Adding a dimple to the crank might be perceived as being helpful, but this is likely to lead to variations in the crankpin throw - if the modeller is reliant on drilling only - i.e. without the benefit of a slot-drill finish to wheels firmly retained on an axle sized peg.

    This is no different to the principle of using siderods on extended axles to locate horn guides in frames.

    The use of plastic centered drivers, such as our local North Yard wheels, gave trouble to some when they were pushed on to sharp-ended axles. The sharp edge would too easily shave a tiny sliver off one side of the bore. While the moulded-in crankpin hole was accurate enough, any shaving of the bore could occur at any place around its circumference, thus creating varying crank throws.

    -Brian McK.
     
  13. Brian McKenzie

    Brian McKenzie Western Thunderer

    Yes, well aware of that Richard. It's the principle I'm expounding. I'm more of a model engineer than a railway modeller, but one working in 1:48 scale.
    If I could make trees for example by using a lathe, I'd have a forest by now. I'd be out of my comfort zone at 5 thou variation though. It would work but its getting a bit sloppy - more so as scales get smaller.

    (It's only the notion of having pre-drilled crankpin holes, without an associated axle hole that I'm bothered about.)

    Brian
     
  14. Brian McKenzie

    Brian McKenzie Western Thunderer

    Thinking more about this, there is a way that turning of spoked wheel blanks can be successful - should the blank be supplied with a pre-drilled crankpin hole, but no axle hole. The sketch shows how consistency can be maintained irrespective of the runout typical of a 3-jaw chuck. Consistency being more important than any particular measurement.
    Chuck+Wheel Blank alignment.jpg

    As it might seem I've been dumping on Unklian's suggestion of pre-drilled crankpin holes, and I didn't reply directly, I'd like to offer to CAD up any axlebox he has an interest in. . . . . or perhaps a wheel.

    -Brian McK.
     
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  15. Hobbyhorse

    Hobbyhorse Western Thunderer

    Having machined a lot wheels from 7mm to 7 1/4" over the years starting with any 3 or 4 jaw chuck is fine for all the basic machining. To keep accuracy when remounting the wheels the best option is a four jaw chuck with soft jaws machined to the wheel diameter. Crank pins hole drilling is always best drilled with a jig as one of the last processes.

    Simon
     
  16. Elliot 84A

    Elliot 84A Western Thunderer

    Andy's been a busy boy knocking these up, he's even going to throw in some crankpins just to keep you guys happy :)

    Elliot


    18817596_10215297834544199_966852581_o.jpg 27707956_10215297829744079_1430395462_o.jpg 27711115_10215297828704053_1775626948_o.jpg 27711579_10215297828344044_420009445_o.jpg 27744787_10215297834384195_1356854992_o.jpg 27746867_10215297834984210_1825241959_o.jpg 27747001_10215297828584050_834236445_o.jpg 27747239_10215297830504098_388013995_o.jpg 27785897_10215297830664102_100747404_o.jpg 27786171_10215297829944084_57659014_o.jpg 27835457_10215297830944109_1288101663_o.jpg
     
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  17. Ian_C

    Ian_C Western Thunderer

    Just come across this thread. Congratulations Elliot 84A. Outstanding stuff. I imagine I'll be throwing money at you for some Stanier wheel sets when/if you get around to it.
     
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  18. Elliot 84A

    Elliot 84A Western Thunderer

    Ian,

    I've done the Duchess wheels but sadly don't have any LMS drawings (plenty of Western ones as you can see) so if you can get the drawings I can do the wheels, simple as that :)

    E.
     
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