London Underground Q38 Surface Stock Trailer

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CornCrake
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London Underground Q38 Surface Stock Trailer

Postby CornCrake » Sun Apr 05, 2020 12:53 pm

A desire triggered by memories of catching District line trains from Wimbledon after finding a sheet of Hamblings litho printed surface stock that I purchased some 50 years ago. I have taken the plunge by purchasing a Radley models Q38 stock trailer kit:-
Q38_trailer_kit.jpg
Q38_trailer_kit.jpg (169.52 KiB) Viewed 1222 times


What you get is a resin body and some flush glaze to suit, plus floor and bogies in white metal, plus a packet of nuts and bolts etc.

Oh and some transfers...

alaninDM
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Joined: Sat Mar 06, 2010 11:09 am

Re: London Underground Q38 Surface Stock Trailer

Postby alaninDM » Sun Apr 05, 2020 4:22 pm

I remember travelling on Q stock to and from school from Sept 65 to July 72 - mainly from. My journey was from Hackney Wick - no 6 bus to Liverpool Street then circle line to St James and then on foot to Palace Street. No Q stock on the circle line of course. But after school - 1600 and a five minute walk to St James - a lot of school friends went to (mainly) Charing X as it then was or beyond Tower Hill on the District Line so I joined them and changed at Tower Hill to wait for the Circle Line - one in four trains: so often 10-15 mins wait and never one at St James to start. I recall that even then the Q stock looked good and ran better than the even earlier clerestory stock still in use until about 1968ish.

Mainly Red livery but not infrequently silver/aluminium which suited Q stock very well I thought. The seating was unusual in the trailers as they seem to have been converted from driving trailers - so a knowledgeable friend told me at the time. So bench seats either side of the communication doors looking in towards the bench seats lining the walls to the doors at one end. I think the other end had a conventional door vestibule and single sliding door. Looks like the left hand end on the shell in the photo would have bee the former driving end. The mochette upholstery could be appalling to comfortable mainly depending on the season. But as young energetic lads we tended to stand despite the cars being not very full.

Now I think about it the Q stock may have gone before 72.... So much did then as it does now. Including travelling unaccompanied across London on a daily basis from age 11. How did we survive...... Happy days.

Alan

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Noel
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Re: London Underground Q38 Surface Stock Trailer

Postby Noel » Sun Apr 05, 2020 5:13 pm

alaninDM wrote:Now I think about it the Q stock may have gone before 72


Yes and no https://en.wikipedia.org/wiki/London_Underground_Q_Stock and https://en.wikipedia.org/wiki/London_Underground_R_Stock. You aren't the only one working on Q stock https://www.ltmuseum.co.uk/support-us/our-projects/q-stock-restoration
Regards
Noel

CornCrake
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Re: London Underground Q38 Surface Stock Trailer

Postby CornCrake » Sun Apr 05, 2020 5:34 pm

Alan,
Ah yes, fond memories of the eclectic mix of stock arriving & departing Earls Court. Then round the Circle line to Baker Street, passing through what appeared to be another world with brooding dirty brown louvre sided beasts. I say beasts, they looked strangely powerful in comparison to the District & Circle line stock!. They even had nameplates!
Still there is nothing like a flared body.

To help with the modelling I am using the following 3 books:-
Steam to Silver by J Graeme Bruce
Underground Train File, Surface stock 1933-1959 by Brian Hardy
The London Underground, Surface Stock Planbook 1863-1959

The last one mentioned has scale drawings.
I am also visiting https://districtdavesforum.co.uk/

From reading the aforementioned books it appears that the trailers were built with the possibility of converting them to motors at a later date.
The kit did not include the seat unit, so I have just purchased that. Here is the Dummy Driving cab end of the seat unit, showing the bench seat you mentioned:-
Seat_Unit_Driving cab_end.jpg
Seat_Unit_Driving cab_end.jpg (185.25 KiB) Viewed 1150 times

And here is the resin body dummy driving cab end:-
Trailer_dummy_driving_cab_end.jpg


Noel,

Thanks for that link, just what I need for colour reference for the interior.
Not sure that I will get down to the detail of the seat construction though!

Steve

CornCrake
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Re: London Underground Q38 Surface Stock Trailer

Postby CornCrake » Wed Apr 15, 2020 8:01 pm

Here is a snap of part of the inspiration that was filed away for over 50 years :-
Hamblings_Merco.jpg
Hamblings_Merco.jpg (170.68 KiB) Viewed 939 times


Review of kit
With only one drawing in my possession, albeit of O/P stock, and looking at photographs, the resin body is good.
I plan to replace the moulded on handrails on the cab ends with wire.

The cast floor is about 3/4 mm too short and as a result the projecting steps are misaligned. If you get one end fitting the other end is out & vice-versa. I could cut the floor in half, and then bot ends & steps would align, but there would be a gap to fill.
The solebars are represented by what appears to be a box girder (ie solid square bar)
I plan to produce a replacement etched floor.

The bogie side castings appear to be a fairly good representation of the 7' 10" wheelbase bogie fitted, but the bogie if constructed as intended is too narrow for P4 wheels. The prototype bogie is also unusual in that it is asymmetrical! the distance from the front axle to the pivot point is 3' 3", and from the pivot point to the real axle is 4' 7". This is to accommodate the single motor between the pivot point and the rear axle.
I do not think that there are any 7' 10" P4 compensated or sprung bogies available, certainly not with the offset pivot.
Now if I took half a 6' 6" bogie and half a 9' bogie and joined them together I could end up with an offset 7' 9" bogie! I must be mad!
I plan to produce an etched bogie frame 7' 10" wheelbase with the offset pivot.

Information Required
If anyone knows what the solebar construction and dimensions are I would be grateful for any information supplied.
Steve

CornCrake
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Re: London Underground Q38 Surface Stock Trailer

Postby CornCrake » Thu Apr 16, 2020 10:02 am

Replacement Floor
As a first step in replacing floor I produced a floor template mock-up. Using Microsoft Word, I inserted a drawing canvas, set grid size to 1mm, and then having measured various resin body dimensions, used insert shapes, rectangles, lines and circles, and then stuck the printed result on 1mm thick card. I also printed directly on to 300gsm card.
This is quite a quick process and revisions can easily be made, so that the floor fits the resin body.

Here is a comparison of a 300gsm cardboard floor with casting that shows the discrepancy in the casting:-
Underframe_Casting.jpg
Underframe_Casting.jpg (153.33 KiB) Viewed 889 times

I have aligned them at the D end.
Apparently axles are labelled A,B,C,D, thus we get a D end and an A end.
I have attached a pdf of my latest floor mock-up.

I now plan to use the Vector Graphics program Inkscape to design the etches, having read the excellent tutorials produce by Mike Trice and others on RMWEB for using Inkscape to produce cutting files for Silhouette Portrait printers.
Attachments
Q38_Trailer_Floor_Template.pdf
(244.51 KiB) Downloaded 19 times

CornCrake
Posts: 111
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Re: London Underground Q38 Surface Stock Trailer

Postby CornCrake » Fri Apr 17, 2020 2:46 pm

As previously mentioned, the bogies are 7' 10" with an asymmetrical bolster pivot at 3' 3" & 4' 7" centres.
Bogie side castings showing the asymmetric bolster spring arrangement:-
Bogie_Castings.jpg


CSB question
I am attempting to design an etched bogie frame with CSB suspension.
Should the middle fulcrum mirror this asymmetry or should it be at equal 3' 11" centres?

Bogie_Fulcrums.jpg

This diagram shows the middle fulcrum aligned with the bolster pivot ie asymmetric fulcrums.

Can any CSB experts offer some advice on this please?

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Will L
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Re: London Underground Q38 Surface Stock Trailer

Postby Will L » Fri Apr 17, 2020 4:59 pm

That's an interesting question. With the bogie pivot off centre the weight distribution will be different on the two axle and so the springing will need to reflect this. If your interested roughly 59% of the wight turns up on the axle close to the pivot point an 41% on the other. The prototype springing must have reflected this or the bogie wouldn't have sat level but I cant say this difference is visible on the castings.

Anyway I wasn't sure what the implications would be for a CSB, so I ran the numbers and I'm pleased to say the it turns out the middle fulcrum should reflect the position of the bogie pivot as on your diagram.

Anybody any ideas why they did this?

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grovenor-2685
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Re: London Underground Q38 Surface Stock Trailer

Postby grovenor-2685 » Fri Apr 17, 2020 5:12 pm

Will L wrote:Anybody any ideas why they did this?

As in Steve's earlier post.
This is to accommodate the single motor between the pivot point and the rear axle.
Regards
Keith
Grovenor Sidings

davebradwell
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Re: London Underground Q38 Surface Stock Trailer

Postby davebradwell » Fri Apr 17, 2020 5:51 pm

On the prototype the motor would be very heavy so the offset is likely an attempt to achieve an equal axle loading. I wonder if you're digging yourself a hole here by trying to get unequal loadings. It wouldn't necessarily be a disaster but the more lightly loaded axles would be more prone to derailment, rather like pony trucks on steam locos. The whole point of a 4 wheel bogie is to achieve equal axle loadings, surely.

DaveB

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Will L
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Re: London Underground Q38 Surface Stock Trailer

Postby Will L » Fri Apr 17, 2020 8:01 pm

davebradwell wrote:On the prototype the motor would be very heavy so the offset is likely an attempt to achieve an equal axle loading.

That sounds reasonable and would explain why the springing on the cast sides for both axles looks very similar. I did wonder why they would chose to drive the lighter axle, but I was only considering the vehicle weight. I hadn't realised that the bogie itself could have a significant off centre load
I wonder if you're digging yourself a hole here by trying to get unequal loadings. It wouldn't necessarily be a disaster but the more lightly loaded axles would be more prone to derailment, rather like pony trucks on steam locos. The whole point of a 4 wheel bogie is to achieve equal axle loadings, surely.

Its true that the nice thing about your normal bogie is that it does ensure the weight is equal distributed across all four wheels which is a good thing and makes springing them a nice simple problem. But if you leave the bogie pivot in the prototype position and the bogie doesn't have a compensating weight of its own, the body weight will be distributed as I suggest and unless you adjust the springing to suit, the bogie wont sit level.

CornCrake
Posts: 111
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Re: London Underground Q38 Surface Stock Trailer

Postby CornCrake » Fri Apr 17, 2020 10:10 pm

Thanks for your replies.
For some reason my intuition leads me to believe that because the spring of the axle with 59% of the load is shorter (22mm) it will be stiffer than the spring of the axle with 41% of the load (27.33mm). If there two separate springs of equal length then I could understand that they would need to be of different gauge, but would that be classed as a CSB?.
I think this will be an interesting experiment. I will add the option of using a centralised fulcrum to further cover my bases. In fact some of the earlier surface stock had 7' 10" wheelbase bogies that were symmetrical. Also it turns out that the trailer cars (for O/P) stock did not have the motors but were asymmetrical. LT museum is currently closed for business so I will have to be patient as far as access to some drawings they hold at Acton depot.
Of course the bogie side castings might not be accurate representations of the real thing.
Steve

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Will L
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Re: London Underground Q38 Surface Stock Trailer

Postby Will L » Fri Apr 17, 2020 10:23 pm

CornCrake wrote:For some reason my intuition leads me to believe that because the spring of the axle with 59% of the load is shorter (22mm) it will be stiffer than the spring of the axle with 41% of the load (27.33mm). If there two separate springs of equal length then I could understand that they would need to be of different gauge, but would that be classed as a CSB?.

No need for different size wires. Calculations done on the basis of a proper CSB. I.e. one wire a side over both axles. All you need to remember is that the centre fulcrum will need to line up with the bogie pivot point. While you can find out the right size wire by trial and error, If you let me know the vehicle weight when your done, I can tell what size wire should be.

CornCrake
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Re: London Underground Q38 Surface Stock Trailer

Postby CornCrake » Sat Apr 18, 2020 7:17 am

Will,
Thank you for your offer.

More questions I am afraid...
I assume that is the weight of everything excluding the un-sprung weight, eg weight excluding wheels & bearings?
So far I have got an approximate minimum weight for the coach of 166gms, but I can easily add more, even if it is in the form of passengers!

Also I have since noticed that where I annotated 9mm for both the outside fulcrum measurement it is actually currently 9.5mm. I can reduce it, but not make it any wider. Are wider springs better than narrower springs?
Steve

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Will L
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Re: London Underground Q38 Surface Stock Trailer

Postby Will L » Sat Apr 18, 2020 1:13 pm

CornCrake wrote:I assume that is the weight of everything excluding the un-sprung weight, eg weight excluding wheels & bearings?
Yes in theory but they don't weigh enough to make a significant difference
So far I have got an approximate minimum weight for the coach of 166gms, but I can easily add more, even if it is in the form of passengers!

Also I have since noticed that where I annotated 9mm for both the outside fulcrum measurement it is actually currently 9.5mm. I can reduce it, but not make it any wider. Are wider springs better than narrower springs?

Based on a 9.5 mm end overhang
If your vehicle ends up weighing 166gm the you want 11 thou wire.
If you weight it weighs above 210 gm you will need 12 thou wire
if you weight it weighs above 290 gm you will need 13 thou wire
If it gets much more than that its probably too heavy!!

Personally I think the 9 mm at the ends would be fine and it's worth leaving yourself a little room.
Based on a 9 end overhang, 11 thou is still right but add 10 grams to the limits above. I.e. it doesn't make a big difference.

Russ Elliot is keen on a longer spring but, while there is nothing wrong with his theoretical argument, I'm not convinced it makes a significant difference within the limits we work to. There's a lot to read on this on the CLAG website.

That said very short end overhangs should be avoided as the calculation becomes less certain as the axle fulcrum moves too close to one end. I would suggest that a good rule of thumb which doesn't require complex calculations would be that we should avoid anything less than
the total wheel base/no of wheels
in your case that would be 8mm so you're OK.

While we are here it is also true that too long an overhang is equally undesirable and leads to unstable solutions which magify the effect of any minor inaccuracies, such as the actual location of fixed fulcrums or the location of the Centre of Gravity. Again a reasonable rule of thumb which should leave us in the methods sweet spot would be nothing greater than half the distance between the adjacent wheel sets.


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