Tornado

Thank goodness they don't build aero engines. When I worked at Rolls-Royce we had a part that was rejected by an inspector for being outside of the drawing tolerance. The part was approx 600mm diameter in size but was one micron oversize - that's .001 mm. Bloody computerised measuring machines. Once the data is given and it's in red, the part is rejected. [BJ]

 

I'm glad is wasn';t just me being thick when I pondered why tyre tunring on new already turned tyres was having to take palce. It didn't make sense, but then I'm not an negineetr or project manager. Seems a bit odd to me, and incurring of extra cost with transport etc

 

Without wishing to get all philosophical about it, when it comes down to it the boundary between accept and reject is always infinitesimal. Oh sure, you can concess and accept an out of spec part, but at some point everyone is being asked a question down to the smallest unit of measurement and saying yes or no.

 

So, it seems that all the posts about the boiler not fitting, and the boiler having moved out of true might have been right then, having new corners welded in would go a long way to explaining it, but these were changed before, without issue, so what's the actual problem, wheel size after retyring, or the corners being not the same radios as before.?

 

Probably the same reason that Rolls Royce had to redraw the Merlin before Packard could build it. If every part is made to fit the next, parameters are very different.

If the gap is say 25mm, and you have design of boiler, design of replacement part, thickness of plate used, thickness of tyres, wear/replacement of wheel-bearings, seating of the boiler on the smokebox, and each of those were specified +/- 3mm and they all come up at the wrong thickness, you have a problem. (Clearly these are hand-wavy figures).

I wonder how much of this was sorted out by a discreet wallop or shoogling until it fits (leading to slight variations between every engine)?

 

The firebox corners were renewed part-way through the boiler overhaul cycle so it may have been the case that, even if the replacements were larger than the originals, the tyres had already been turned down, so the gap wasn't an issue at that time.

 

I’m being thick, but I am struggling to see how turning the tyres helps get the boiler to fit. You’d be taking more than a tickle off the treads and having to cut into the flanges a fair bit to have any effect wouldn’t you?

 

The problem clearance appears to be the wheel diameter - if the bottom of the throatplate has moved forwards for some reason, it will start to impinge on the flange, given there isn't much gap there in the first place. Given that the tyres will have been new profile, turning them would mean taking the same amount off diameter all the way across the tread and flange to maintain the profile. If the tyres are say 4" thick at new and 1" thick at scrapping (made up numbers, but probably in the plausible zone), if you turned 1" off them, that wins you an extra 1" clearance, but at the expense of 1/3rd of the tyre life.

 

Would 6 feet 2 wheels fit?

 

Radios.....how do they work into the problem?

 

Thats what auto - correct corrected it to, the correct word would have been radius

 

Vertical movement of the axleboxes, i.e. springing, must also be taken into account. It looks like the owners have entered a minefield.

 

I guess at probably upwards of £50k for a set of driving tyres, taking a third of their life out without turning a mile of revenue earning service (plus the costs of additional transport and turning) is a bit of an “ouch”.

Tom

 

Aye, seems an unnecessary expense to have to low load the engine to Toton and turn brand new tyres down already when surely the aim is to go for maximum tyre life?

 

Surely, all 12 tyres must be turned down to maintain the correct running height of everything.

 

I always wondered if Driving wheel tyres wore more quickly as they, well, drive and are also braked, carrying wheels probably subject to less wear (other than on flanges ) not withstanding they are subject to more rpm

 

Some where I have, although I can't currently find it, the memo from the LMS CME Dept giving the limits in the variation of tyre thickness between coupled and carrying wheels. From memory this was 3/4" one way and 1/4" the other, but I can't remember which way around.

Edit: Found it!

JOB 5207: 2. 4.40:

Alterations to Bogies and Pony Trucks.

To Compensate for the Difference in wear on Tyres.

Limits have been fixed governing the maximum allowable variation between the thickness of the bogie and / or pony truck wheel tyres and coupled wheel tyres, and the methods of adjustment necessary to counteract such variations have been standardised. These limits must be strictly adhered to.

A The tyres of the bogie and / or pony truck must in no case be more than 1/4in thicker or 3/4in thinner than the tyres of the coupled wheels.

B No adjustment is required when the difference between the thickness of the bogie and / or pony truck wheel tyre and the coupled wheel tyres is 0in to 1/4in greater or less.

C Adjustments must be made by fitting suitable bolster pads, etc., in accordance with the attached charts when the thickness of the bogie and / or pony truck tyres is more than a 1/4in less than the thickness of the coupled wheel tyres.

A number of bolster pads should be manufactured as shown on dwg D39 15912 and placed in stock in readiness…..

These adjustments should be carried out as required at General and Service repairs. Charge to maintenance.

 

You have to turn all coupled wheelsets to a very close diameter or bad things will happen with the wheels trying to turn at different RPM due to being different circumferences. From memory, for an 08 shunter it's 0.25mm diameter variation between axles.
Quite large variations can be permitted between uncoupled wheelsets - iirc you are allowed 1" between the two bogies of a mk1 coach!

 

Maybe this is the solution sought … fit small wheels to fit round the firebox, and have those drive rollers on the track to re-instate the lost height …

No?



Tom

 

I pity the poor fireman! Though I suppose he could stand on the tender and try and shot put lumps of coal into the firebox.