5" gauge model of 4472 Flying Scotsman

[nzpaul]

I've always been slightly confused by some commentators labeling it "complicated Gresley valve gear". The math's behind it might be more difficult than average but mechanically it's really quite simple, certainly much less going on than a 3rd set of independent gear. It will be interesting to see if the gear built for the new V4 gets any computer aided analysis to see if any improvements can be made.
Look forward to seeing it in motion, fascinating stuff.

Paul

[Atlantic 3279]

as some of you will know, I have a bad habit of deviating of course...

Pete

I think you've earned the right.

[greenglade]

I would agree Paul....there's nothing complicated about conjugated gear, although I wouldn't want to do the original maths. As you say there's many less parts to make than a 3td set and much easier to maintain in model form. They had issues full size with ash contamination of the fulcrum bearing/pin, the model will have the same but fairly easy to keep an eye on, much easier than full size. Mind you some of the parts pose a challenge for machining, the 2:1 lever being the most challenging IMHO. Still, it's only one part of the puzzle, I just take it one step at a time, hopefully, I finish the model before I fall off my perch...

Pete

[drmditch]

Regarding the 2:1 lever:
i understand it was/is quite a highly stressed component, and was re-engineered at least once.
I think they ended up being a forged item.
(I can't find the reference for that - but will look it up later.)

Is this one of those items where stresses do not necessarily work out to scale? Might you perhaps use something with a higher resistance to bending forces than mild-steel?

[greenglade]

Hi drmditch

There were issues with the conjugated gear but I don't recall reading about the lever itself being weak? There were issues with ash falling from the smokebox into the fulcrum pin bearing which caused excessive wear. This wasn't much of a problem during LNER days when the loco's were serviced properly. It did become an issue during WW2 and later BR days when servicing was much more sparse in it's regularity and thus valve events weren't as good as they should have been.
The middle cylinder from the beginning was found to be overworked at high speed due to the cunjugated gear and thus more wear was sustained. IIRC the later V2 (or waa it V4?) had the conjugated gear set behind the cylinders to avoid the ash, but this made valve setting more difficult to maintain.
As for stresses, although models wear in similar ways to the full size and will need components renewed over time, in general they suffer less wear as long as properly lubricated. As mentioned I'm making all of my motion from gauge plate, this doesn't have the same stresses within the steel as BMS. It's stronger, can be machined without risk of warping/twisting and more resistant to rust. It's only downside is 'cost', it's a lot more expensive than BMS. Once finished the 2:1 lever will be much thinner, most of the material from the 3/4x5/8x7" bar will end up as swarf on the floor...

Pete

[drmditch]

Thank you.
The V2 had and has the 'conjugated gear' in front of the cylinders, as with the Pacifics.
Not sure about the V4s. I think there was a problem with putting the gear behind the cylinders, (which I have read was better for valve examination and avoidance of ash and coping with expansion) and maintaining the concentrated drive onto the centre axle.

It was done with the D49/1s (driving onto the leading axle), and I think the B16/2s (at the cost of lengthening the wheelbase) and the B17s (with divided drive).

It has always struck me how simple in concept the Gresley gear is. On the other hand, a good look at the SR 'Schools' 4-4-0 on the NYMR in the happy pre-Covid days, does illustrate that a neat and apparently accesible job could be done with three sets of Walschearts gear as well.

I can't help thinking that the concentrated drive creates an inherently 'better job', than the later compromises with divided drive.

I'll take great delight in seeing your continuing progress, and thank you for explaining your metallurgy and machining!

[greenglade]

Ah...thanks for correcting me....a friend is building a 5" B17 and another the V2 so seems I got them the wrong wsy around.
IIRC the main issue with using 3 sets of walschearts is maintenance on the middle set.
I thought that I had read that having the 2:1 lever behind the cylinders had an averse affect on timing?... but it was only a passing reference which I think I recall reading.
The early conjugated gear did have issues and required proper servicing which I think may be why other CME's weren't fans. IIRC Gresley borrowed the idea and improved on it a little, Holcroft comes to mind but wouldn't swear on it.

I too am looking forward to seeing it in action, the mill packing up hasn't helped with progress. I have now received a new motor and speed controller which is my first job for today, I've also received the gauge plate required for all of the conjugated gear so as long as the mill works I can make some good progress over the next werk or so.
Fingers crossed...

Pete

[drmditch]

It was indeed H.Holcroft, and his book 'Locomotive Adventure' is a fascinating read, although I think copies now can be quite expensive.

(And I wonder how many electrically powered machine tools there were in Doncaster Works when the first A1s were built. You are probably glad you don't have to have stationary steam engines and line shafting and drive belts all over your workshop!)

[greenglade]

haha.. yes ma'am..

Mind you, I still manage to cut the odd finger, sporting such a cut right now. Having said that, what with the current issue that I'm having with my mill, just fitted new motor and still no joy so next up is the speed controller. Luckily I ordered both as I wasn't convinced that it was the motor despite what Warco and the mill manual troubleshoot stated. So I'm now stripping down the electronics box, steam-operated machinery and lots of straps running above one's head seem very appealing just now...
regards

Pete

[greenglade]

2:1 lever continued






http://4472flyingscotsman.co.uk/gresley ... ated-gear/

Pete

[greenglade]

Well, that's the first part of the 2:1 gear finished, a few more pictures than usual for this one, next will be the 1:1 lever and connecting links.



http://4472flyingscotsman.co.uk/gresley ... machining/

Pete

[silverfox]

Peter

I think i read somewhere that the problem with the 2-1 in front of the cylinders was that it made the middle cylinder valve 'over run' due to the expansion of the two outside valve spindles# Hence tnhat lovely beat, esp the V2 had instead of 1-2-3-1-2-3, nice and even it went 1-2.....3-1-2......3
This didnt happen in the D49/B17 as everything was the 'cool side' of the gear

Went to hobby craft today and got some of those pegs!! and soldered up the smokebox lamp bits today the cloverleaf looks nice and is sitting in the citric acid along with the tender spring shackles, tender hornblocks and fireiron stands
( guess what i have been doing while the lathe motor has gone away for refurb) Now it is back ,i have lost the wiring diagram i drew up. The Myford manual has different colours and motor terminal notations to what i have. Expect wholesale blackouts in the SE while i try and figure it out!!

[greenglade]

Nice one Ron, look forward to seeing your B17 one day...

Pete

[greenglade]

On to the connecting links, after much head-scratching and discussion with fellow modellers of Gresley 2:1 conjugated loco's I have decided to change the fulcrum and 1:1 lever bronze bushes to sealed stainless (shielded) ball bearings, just like the full size. This will be covered in the next entry but I'm out of commission next week so it may be the week after before you see the fruits of my labour. In the meantime, here are the details on the connecting links, or should I say half the details, not finished yet but you can see what I've been up too.



http://4472flyingscotsman.co.uk/gresley ... ks-part-1/

Pete

[greenglade]

Evening all, tonight I have the second instalment for the valve connecting links, I had hoped to conclude these parts in this update but there's still some work left to do. I must say thank you to Doug for his timely tips on the fulcrum pin, you'll see what I mean in the blog entry. Hope you find it of interest.



http://4472flyingscotsman.co.uk/gresley ... ks-part-2/

Pete