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Hattons Dave

Class A3 4-6-2 in O Gauge from Hatton's

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Just for clarification (it's no use to me either because I'm not interested in Heljan offerings):

 

  • nylon gears in some of the locomotives were effectively too tight on their splined axles and they cracked at the root of a tooth - there is nothing inadequate about nylon as a gear material, it was merely the design and/or the manufacture that was inadequate
  • gears did, and do, split whether a locomotive is used or not - the mechanism of the failure is due to the static stresses imposed upon assembly, and not due any subsequent load (so a loco that has been fine for years may still fail at any time)
  • the replacement gears supplied by Howes of Oxford (which you fit yourself) were the same as the originals so they are just as susceptible to failure
  • a sample of the rate of failures by model was collect by Arun Sharma, a trader and a member of the Gauge 0 Guild, and the results were published in a G0G Newsletter earlier this year - May I believe, but I don't keep mine so I cannot look
  • Jim Snowdon took the initiative as a private individual to source brass replacement gears for some classes that have proved most satisfactory by all accounts

David

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8 hours ago, jay*bobble said:

Just of note ill be buying as many broken a3s as i can.the amount ive repaired already. And i dont know if hattons will be doing spares .or howes so makes sence to me .

Out of interest, how many have you repaired. 

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Well to date I have repaired 7 a3s in total .ranging from wheels feeling off to motors not engaging with gears.right down to bits falling off and I don't charge a penny .I do it just to help .and it faster than waiting for a replacement.

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12 hours ago, Isambarduk said:

Just for clarification (it's no use to me either because I'm not interested in Heljan offerings):

 

  • nylon gears in some of the locomotives were effectively too tight on their splined axles and they cracked at the root of a tooth - there is nothing inadequate about nylon as a gear material, it was merely the design and/or the manufacture that was inadequate
  • gears did, and do, split whether a locomotive is used or not - the mechanism of the failure is due to the static stresses imposed upon assembly, and not due any subsequent load (so a loco that has been fine for years may still fail at any time)
  • the replacement gears supplied by Howes of Oxford (which you fit yourself) were the same as the originals so they are just as susceptible to failure
  • a sample of the rate of failures by model was collect by Arun Sharma, a trader and a member of the Gauge 0 Guild, and the results were published in a G0G Newsletter earlier this year - May I believe, but I don't keep mine so I cannot look
  • Jim Snowdon took the initiative as a private individual to source brass replacement gears for some classes that have proved most satisfactory by all accounts

David

Failure of plastic gears is not just confined to Heljan though, quite a few manufacturers models have suffered from similar faults. Is the material Nylon? In other discussions about this I have seen another material was mentioned (Acetyl?). I seem to remember there was something about this material failing because it wasn't being 'conditioned' properly before use.

While poor quality is not acceptable (and Heljan seem to suffer more from this than some other manufacturers) again it needs to be acknowledged that  other manufacturers also have quality control problems. Unfortunately I think such problems will continue while customers continue to regard  low price as a major factor in their purchasing decisions. I would suggest if you want high quality (including metals gears), good customer service etc you need to be prepared to pay for it.

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Jeremy

 

I concur with David that the issue is not the material from which the gears are made - any material has a critical stress beyond which failure will occur, and it is generally possible to design small gears to ensure a suitable safety margin for model train applications, though, I suspect in 2mm it gets a bit tight and in this case a more resistant material may be required to provide adequate strength and stiffness with the very small cross sectional areas available. 

 

I have not owned a Heljan model, but I understand that the failure mode is "almost certainly" a combination of excessive hoop stress caused by excessive interference between shaft and gear, and the notch effect of the edge of a spline on the shaft cutting into the surface of the hole in gear, and producing a significant stress raiser.  Of course, it fails at the root of the tooth, because the cross sectional area is a minimum at that point.  All plastics "creep", that is, deform under stress, over time, to a greater or lesser degree.  If that creep relaxes the stresses (as a well-designed fit of plastic gear on splined shaft would do) then it's a significant benefit, however, if it increases the stress (as appears to be the case here) then failure is inevitable.  Additionally, if the shaft diameter closely approaches the minor diameter of the gear teeth, there will be some additional bending stresses induced by the tooth load from operation - although this is not necessary to cause failure, it may accelerate it.  Later models do not seem to suffer from the issue, which suggests that design modifications were implemented to reduce the stresses - but also these changes mean that "new" gears won't fit "old" models. 

 

The brass gears that have been sourced to fix the failed models are obviously a much higher strength material, which means that they should last indefinitely.

 

My Atlas chassis in Mavis has a failed gear too.  I'd bet at least a pound that it's the same root cause.  The loco is never used nowadays, (the kids for whom she was built are now at university) so I'm not loosing any sleep over it!

 

You are of course right to say that you pretty much have to pay for what you want, but it is perfectly possible to have high quality plastic gears - indeed, they may run quieter than metal ones, and have a similar life expectancy.  They are certainly cheaper to make, if you're making enough of them.

 

atb

Simon

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Simond.

I wasn't suggesting plastic gears were unsuitable in general nor that they were necessarily a cost cutting measure, only that Heljan were not the only manufacturers products to be affected by this problem.

Regarding the material there was a issue a few years ago in the garden railway world to do with Bachmann locos (Google 'Bachmann Connie gears') and that was said to be shrinkage of the plastic. IIRC in that case the material was Acetyl which is why I mentioned it.

Some plastics exhibit considerable shrinkage after moulding https://omnexus.specialchem.com/polymer-properties/properties/shrinkage.

I even understood your explanation of stresses, but then I should having been a marine engineer for 44 years:)

Edited by JeremyC
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1 hour ago, jay*bobble said:

So now it's a debate about Heljan gears no longer the a3s.

... and you have a problem with this?

 

3 hours ago, Simond said:

My Atlas chassis in Mavis has a failed gear too. 

Yes, I have a freelance Steam Turbine Electric Locomotive that uses Atlas F7 bogies; one final drive gear in each has split at the root - but it still seems to run well enough.

 

David

image.png.1d92adb68bef0e93e424e13cab0e4618.png

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Back to A3!!

picture of front steps, made up from brass scrap. 
Interesting that holes exist which look as though they were intended for a step moulding. 
Rgds Brian

3982FBC3-EB1A-4795-9FA2-2EF78E399B99.jpeg.aec5d729898a89eac0e82a3fda05452c.jpegBBCEAB1D-8118-4E1D-BC68-BC6AF987E9D3.jpeg.0db88d634bb3173f49337ef0acca04f8.jpeg

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I see Hornby Magazine front page poses the question "Has Hatton's created the ultimate LNER 'A3'?". 

 

I didn't read to find out their answer though!

 

 

Edited by Hal Nail
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7 hours ago, jay*bobble said:

Well to date I have repaired 7 a3s in total .ranging from wheels feeling off to motors not engaging with gears.right down to bits falling off and I don't charge a penny .I do it just to help .and it faster than waiting for a replacement.

Thanks. So that is at least eight including mine that have failed. :(

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Regarding gears, I'm perhaps more surprised by the choice of nylon rather than delrin, of which small gears are already made. It seems to be one very tough substance.

 

Many years ago I had a rather large off on my racing bike while attempting to ride it down a playground slide, (alcohol not involved, but a rather pretty girl was).

The metal gear hanger deformed badly and almost tore at one point. The delrin Derrailleur was undamaged.  Simplex....those were the days.

 

And no, the girl was not impressed....

 

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20 hours ago, Hal Nail said:

I see Hornby Magazine front page poses the question "Has Hatton's created the ultimate LNER 'A3'?". 

 

I didn't read to find out their answer though!

 

 

Reviews in current BRM and Hornby mag read this morning.

BRM review by Tony Wright, it doesnt say which version he has seen or give a lot of detail, but I believe it was the BR version from comments I have read elsewhere.The article also covers what happened on the release day at Hattons.

Hornby Magazine version, on the BR example reads like the A3  " is the best thing since sliced bread" !!. It does however also cover the solid chimney and the front steps missing in the text. The one they had worked perfectly when run.

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My replacement delayed according to e mail from Hattons as they upgrade packaging to avoid damage to locos that have been reported by people. 
 

No date supplied as to when to expect loco. 

 

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On 05/12/2019 at 18:59, BRIBRI said:

I am really impressed with this addition of the front steps.

 

Incidentally, I am very pleased with my model.  Aside from looking good, it has been on my rolling road and works just  fine.  If I purchased a quality kit and then included the cost of motor, gearbox and wheels I don’t think I would be that far off the £750 I paid for this RTR model and then there is the time/money required to build it.  So, in my opinion, it is a bargain and I applaud Hatton’s for their initiative.  Many people will be satisfied with it just as it is and those of us who want to improve it by adding front steps etc can do their thing with the time saved by not having to build it.

 

Regards

 

Les

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I wonder if anyone has yet tackled the very two-dimensional expansion link?

 

Is anyone aware of a lost wax source? Or a decent etched one?

And then, I suppose, the radius rod would also need work?

 

Maybe Pete Harvey would be interested? Or Michael Edge?

 

Edited to say: Any parts produced would also be needed for the A4's when they arrive.

Wish I knew how to do CAD. I have dimensioned drawings for the radius rod...

Edited by JeffP

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5 hours ago, JeffP said:

I wonder if anyone has yet tackled the very two-dimensional expansion link?

 

Is anyone aware of a lost wax source? Or a decent etched one?

And then, I suppose, the radius rod would also need work?

 

 

Finney7 do a complete valve gear etch for £45 plus P&P. Page W1-26 shows you what you get: http://finney7.co.uk/Downloads/LNER_W1_A3_Pages.pdf

 

Richard

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£45? I was quoted £70 for this a bout a year ago, iirc.

 

Edited to say: does look good though.

Edited by JeffP

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1 hour ago, JeffP said:

£45? I was quoted £70 for this a bout a year ago, iirc.

 

 

Probably so as a one-off. They have since been productionised as part of the W1 kit, so are available as a discrete etch.

 

Richard

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That makes sense Richard, thanks for clarification.

I can highly reccomend the service from Finney 7 to anyone interested.

As a satisfied customer.

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The Finney boys are top notch and nice lads too, the W1 etches are beyond what was available up to their introduction in terms of accuracy and fit, highly recommend them.

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Yep, saving for one as I type....and a V2...and a B1...and another A4, LOL

 

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