Wheelbase: 44xx versus 45xx

[6892 Oakhill Grange]

Does anyone know why the coupled wheelbase of the 44xx was reversed for the 45xx? I did not believe the drawings in Russell, CJ Freezer etc until I studied the pictures.

[Coombe Barton]

This from the Malcolm Mitchell/Churchward kit instructions

 

45xx 8ft 0in + 5ft 6in + 6ft 0in + 7ft 0in driving wheels 4ft 7 1/2in diameter - 14 spoke

44xx 8ft 0in + 6ft 0in + 5ft 6in + 7ft 0in driving wheels 4ft 1 1/2in diameter - 10 spoke

 

You can use Gibson wheels for the 45, but you have to use Ultrascales for the 44. The 44s also had a reduced axle end. I'm waiting for mine - next month, hopefully, having ordered in December.

 

Why? They had to be different frames to cope with the different when diameter, but as for an engineering reason, don't know.

 

Just read this - the 44xx class originally has 16 1/2in diameter cylinders, but by (I think) 1927 they all had 17in cylinders which increased the tractive effort. The 45s had 17in cylinders from build. The stroke was 24in in both cases.

 

Ref: Stiff, D.R. and Dart, M., (1996). Great Western Small Prairie Tanks. Bodmin: Bodmin and Wenford Railway Preservation Society. ISBN 0 9528828 0 9

Edited April 13, 2014 by Coombe Barton

[asmay2002]

It may have been to move the middle coupled axleboxes further away from the firebox/ashpan possibly to avoid the risk of hot boxes..

[Adrian Wintle]

It is quite possible the weight distribution was different, requiring the centre driving wheel to be further back moved to maintain a balanced axle load.

 

Adrian

Edited April 7, 2014 by Adrian Wintle

[buffalo]

It may have been to move the middle coupled axleboxes further away from the firebox/ashpan possibly to avoid the risk of hot boxes..

 

I doubt it, in neither case is the centre axle close to the firebox and the rear is directly underneath *

 

It is quite possible the weight distribution was different, requiring the centre driving wheel to be further back to maintain a balanced axle load.

 

Adrian

 

The overall weight and the weight distribution were certainly different, but remember the 44XX came first. If anythying can be said to have been moved, it was the centre axle of the 45XX that was moved forwards. The distribution was:

 

44XX: 7T 7c, 13T 0c, 13T 10c, 13T 10c, 8T 8c

45XX: 6T 10c, 14T 10c, 14T 10c, 14T 10c, 7T 0c

 

The trailing wheel weight for the 44XX increased to 9T 16c when the bunkers were enlarged. That for the 45XX was probably a similar increase. Given that the 45XX is much more evenly balanced, it may be that the difference was part of a deliberate attempt to improve on the the distribution of the 44XX.

 

Nick

 

EDIT: ps. I did wonder about clearance for the eccentrics on the centre axle, though. It looks like there's enough but we'll need frame drawings or to send someone underneath a 45XX to be sure...

Edited April 7, 2014 by buffalo

[Castle]

It may have been to move the middle coupled axleboxes further away from the firebox/ashpan possibly to avoid the risk of hot boxes..

Hi All,

 

Another point here is that the GWR 4 cylinder 4-6-0s amongst many other Western designs have rear axles that are in the same area as the ash pan. The ash pan is designed in two parts with dampers fore and aft on both sections and a curved section going up, over and back down to clear the axle so this really wasn't a consideration. It was a very logical seeming answer though Andy - good guess!

 

I hope this helps!

 

All the best,

 

Castle

[steamymel]

Hi everyone,

If you check the drawings of the small prairies, the 45xx and 44xx both have the centre driven axle in the same place - straight under the safety valve. This was so that the same connecting rods and inside motion could be used (so fixed common distance from the cylinders) and then the coupling rods were reversed so that the intermediate small joint in the rods was easily accessible for maintenance and dismantling without having to remove the connecting rod. (Early Castles etc had this problem as well). The leading and trailing wheels were therefore relocated in the new 45xx frames to suit the reversed wheelbase configuration. 

Mel.

[DCB]

Looking at the drawings It seems to me that when they tried to fit 4 '71/2" wheels into a 44XX either in the workshops or more likely on a drawing board the tyres on the leading coupled wheels fouled the motion bracket,  This is the bracket which sweeps down over the driving wheels to support the slide bars at their mid point and is cut away to clear the leading driving wheel.  The easy cure was to move the leading coupled axle back 6" to allow some clearance.  As moving the centre axle would have necessitated new connecting rods the quick and easy answer was to move the rear axle back 6" as well which meant all the motion parts and rods could be the same albeit the coupling rods swapped left to right which moved the pin joint from in front of the big end to behind and only the frames needed to be different in having the cut aways for the horn blocks cut further back.

The only other substantial change was to fit deeper buffer beams so the buffers could be lowered 3" to compensate for the engine sitting higher on the larger wheels.

To be honest I never realised the wheelbase differed between the 44XX and 45XX before reading this.

Edited May 6, 2014 by DavidCBroad

[6892 Oakhill Grange]

Thanks guys, the observation about the coupling rods was an eye opener and I reached for Churchward locomotives to find that indeed the coupling rods knuckle is in front of the crank pin on the 44xx and behind on the 45xx.

 

Oakhill

[Coombe Barton]

Thanks guys, the observation about the coupling rods was an eye opener and I reached for Churchward locomotives to find that indeed the coupling rods knuckle is in front of the crank pin on the 44xx and behind on the 45xx.

Oakhill

Hadn't noticed that - something to look out for on the build

[buffalo]

...If you check the drawings of the small prairies, the 45xx and 44xx both have the centre driven axle in the same place - straight under the safety valve. This was so that the same connecting rods and inside motion could be used (so fixed common distance from the cylinders) and then the coupling rods were reversed so that the intermediate small joint in the rods was easily accessible for maintenance and dismantling without having to remove the connecting rod. (Early Castles etc had this problem as well). The leading and trailing wheels were therefore relocated in the new 45xx frames to suit the reversed wheelbase configuration. 

 

This is GWR standardisation in action. Yes, they share con rods and valve motion but, perhaps more importantly, they also share the same cylinder/valve/saddle castings so the overall dimension from cylinder centre line to driven axle is the same 10'6". The same was true with the longer 30" stroke cylinders of the 3100, 43XX, 2221 and 42XX classes where this dimension was 12'. This gives the fixed points from which the rest of the frame design proceeds. Thereafter, the idea is to place the remaining axles in positions that achieve the best possible weight distribution within constraints imposed by other parts of the design. It didn't have to be a perfect distribution, though, and many weren't. That the simple reversal of the distances between the driving and outer axles led to an equal load on each axle was, perhaps, fortuitous and had the added benefit that the same rods could be used.

 

As to the relative positions of the knuckle joint and big end, clearly it is easier to remove the 6' rod on the 45XX, but I do wonder just how often only that rod needed to be done. In most cases it's far more likely that all rods would have needed to be removed for maintenance. That said, I believe the 44XX is the only one of the standard two-cylinder classes with the knuckle masked by the con rod, although most Saints and Stars were built this way.

 

Looking at the drawings It seems to me that when they tried to fit 4 '71/2" wheels into a 44XX either in the workshops or more likely on a drawing board the tyres on the leading coupled wheels fouled the motion bracket,  This is the bracket which sweeps down over the driving wheels to support the slide bars at their mid point and is cut away to clear the leading driving wheel.  The easy cure was to move the leading coupled axle back 6" to allow some clearance.  As moving the centre axle would have necessitated new connecting rods the quick and easy answer was to move the rear axle back 6" as well which meant all the motion parts and rods could be the same albeit the coupling rods swapped left to right which moved the pin joint from in front of the big end to behind and only the frames needed to be different in having the cut aways for the horn blocks cut further back...

 

You make frame design sound more like blacksmithing than engineering. Yes, the motion bracket may have provided a constraint on the design but, as probably one of the least expensive of the standard components, I would have thought that an alternative design could have been developed if it really was a problem.

 

Nick

[DCB]

Early 20th century frame construction was essentially black smithing with hammer and chisel and ratchet driills and red hot rivets so it made little odds if a slot was cut 6" one way or the other, or if a frame stay was put in a few inches back, but Churchward was very keen on standardisation to the extent of having both left and right hand cylinders cast from the same pattern so as to be interchangeable, which also meant the cylinders had to be horizontal, so moving the wheels back rather than re designing and almost certainly weakening the motion bracket was probably the easy way out.The sectional drawing in the Russel book shows a huge cut away in the 45XX motion bracket so another three inches clearance would would mean a very significant redesign,I am not sure but I always thought the 45XX plate frames ended at the motion bracket and that bar frames continued forward to the cylinders. The fact both leading and trailing coupled axles could be moved so keeping standard rods and a standard motion bracket may have clinched it.  I may be completely wide of the mark but Churchward was well known for visiting the "Shop floor," and talking to the workmen, an essentially practical engineer.

As regards weight distribution the 45XX was a ton heavier on each coupled  axle than the 44XX except the leading which is 10 cwt lighter than the driving and trailing, however the leading pony truck is 9 cwt heavier, with the leading coupled wheel further forward?, logically there should be less weight on the pony truck not more.  

[buffalo]

Early 20th century frame construction was essentially black smithing with hammer and chisel and ratchet driills and red hot rivets...

I think we'll just have to agree to disagree here.

 

...so moving the wheels back rather than re designing and almost certainly weakening the motion bracket was probably the easy way out.The sectional drawing in the Russel book shows a huge cut away in the 45XX motion bracket so another three inches clearance would would mean a very significant redesign...

What you call a "huge cut away", I see as appropriate shaping. Perhaps you should look at the larger standard two-cylinder classes such as the 28XX, 3100, 43XX and 42XX. Yes, they are larger but, in each case, the motion bracket is roughly in line with the centre of the leading driver and is shaped as needed to clear the wheel. I cannot see that this would have been a major problem in designing these smaller classes.

 

...I am not sure but I always thought the 45XX plate frames ended at the motion bracket and that bar frames continued forward to the cylinders...

I'm also not sure, but I thought the main plate frames ended at the rear of the cylinder castings on all of the standard classes. The forward extension was bolted to the main frames in this area and to the back of the cylinders. The potential weakness of this forward extension was recognised at the time and led eventually to the provision of stay bars between smokebox and running plate. In the early types it was also the reason for the large curved plate linking the motion brackets. This was apparently intended to support the boiler in the event of front-end collapse following a collision. This is all covered by Holcroft and it is interesting to note his comment that the 44XX and 45XX had the weakest front ends. Presumably because they were scaled down versions of the larger standard types.

 

...As regards weight distribution the 45XX was a ton heavier on each coupled  axle than the 44XX except the leading which is 10 cwt lighter than the driving and trailing, however the leading pony truck is 9 cwt heavier, with the leading coupled wheel further forward?, logically there should be less weight on the pony truck not more.

Yes, the figures are in my post #5. The proportion of the total weight carried by the front and rear trucks is essentially determined by their springing. Remember also that both trucks are in different positions on the two classes.

 

Nick

[DCB]

I now see that 4410 was Wolverhampton works no 774 /06 and 4500 was 775/06 so it does look more and more as if the change to 4' foot 7 1/2" wheels was a last minute change.

Obviously changing the wheelbase meant cutting the hornblock slots six inches further back on the main frames.  As the mainframes were simply cut from steel plates and bolted together to check alignment before being rivetted together the extra work involved in changing it was a pencil line on a drawing. all the other parts remained the same. No new rods or changes to that big curved plate below the boiler.   Don't forget these were the last engines built at Wolverhampton, this was a 19th century facility unused to building outside cylindered locos but used to 4'1 1/2 " wheeled 0-6-0st  I expect they were drawn at Swindon and I would love to see the original drawing as many books about Swindon 30 and 40 years later talk of design revisions being made and the revision then copied to the drawing, rather than drawn first.

Sadly everyone who built these locos is dead now, and there are no 44XX left to look at

Edited May 8, 2014 by DavidCBroad

[buffalo]

I now see that 4410 was Wolverhampton works no 774 /06 and 4500 was 775/06 so it does look more and more as if the change to 4' foot 7 1/2" wheels was a last minute change...

Pure speculation, and quite contrary to the available evidence. They already had two years experience of the prototype No 115 (later 4400) when 2151 (later 4500) was built, and there was a four month gap between 3110 (4410) and 2161 (4500). Holcroft, who worked in the Wolverhampton drawing office at the time explained the thinking that the larger wheeled version whould be "more generally useful". Subsequent experience showed this to be correct.

 

...Obviously changing the wheelbase meant cutting the hornblock slots six inches further back on the main frames.  As the mainframes were simply cut from steel plates and bolted together to check alignment before being rivetted together the extra work involved in changing it was a pencil line on a drawing. all the other parts remained the same. No new rods or changes to that big curved plate below the boiler...

Interestingly, Holcroft also describes the drawings that were sent from Swindon for these engines. His description suggests that their form was rather different to any in his previous experience. On the cutting out and erection of frames, I'd suggest reading some contemporary sources such as Ahrons or Holcroft to find how it was actually done. There is much precision drilling and machining involved.

 

...Don't forget these were the last engines built at Wolverhampton, this was a 19th century facility unused to building outside cylindered locos...

The Wolverhampton staff were certainly not a bunch of country blacksmiths. Swindon didn't have a great deal of experience with outside cylinders when 115 was built, either. These classes were the last to be built at Wolverhampton because Swindon had plenty of work on its hands and the Wolverhampton works had had no new building work since completing the last of the 2021 class a few months earlier. As the new designs were much smaller than the other standard classes, the job was given to Wolverhampton. Even then, they were rather too large for the Wolverhampton works and Holcroft describes in some detail the contortions needed to get them out of the factory. This experience demonstrated that there was no future in new builds at Wolverhampton without serious re-development that was planned, but never took place.

 

One thing I've not yet been able to find an answer to is whether major components, such as the cylinder castings, were made at Wolverhampton or shipped up from Swindon.

 

Nick

[DCB]

The 45XX  Four foot seven and a half inch leading drivers would have been uncomfortably close to the valve rocker pivot as well as to the motion bracket if the leading coupled axle had remained in the 44XX position.  Did Holcroft say the 45XX drawings were different from any others in his experience or the 44XX.    I am guessing the 44XX were the first taper boiler locos built at Wolverhampton and the first outside cylinder ones as well as being the first pure Churchward design so the drawings would have been very different to the 850 and 2021 class they had been building for years.   

[buffalo]

The 45XX  Four foot seven and a half inch leading drivers would have been uncomfortably close to the valve rocker pivot...

Why? The rocker mechanism takes the drive from the inside motion up over the frame and down outside the wheels. Where would the clearance problem be? See also the larger standard classes where a version of this mechanism with longer levers is used with larger driving wheels.

 

...Did Holcroft say the 45XX drawings were different from any others in his experience or the 44XX...

"When this took place I was in the drawing office, and detail drawings of the new locomotives were sent up from Swindon for issue to the shops." The previous paragraph briefly describes both classes and the orders from Swindon, so I think we can assume that he was referring to the first drawings for the 44XX. There is no reason to suspect that those for the the 45XX were any different.

 

...I am guessing the 44XX were the first taper boiler locos built at Wolverhampton and the first outside cylinder ones as well as being the first pure Churchward design so the drawings would have been very different to the 850 and 2021 class they had been building for years.

 

Yes, they were the first and last Churchward standard designs to be built at Wolverhampton. Even though they were the smallest of the Churchward standard classes, they were more than six feet longer than anything previously built at Wolverhampton. To get them out of the factory, they had to remove buffers and both trucks, and then reassemble them outside in the yard. Little wonder, then, that without redevelopment Wolverhampton was closed down and production from 4520 onwards reverted to Swindon.

 

The difference in the drawings was not solely the different shapes of the parts. Holcroft says "...they were white prints with dark blue lines..." He goes on to describe how they mounted on linen and cloured to identify individual parts. That he remarked on their form suggests to me that they may have been a quite different style of drawing from what had previously been seen in the Wolverhampton drawing office. Whether this was simply a difference between styles that had evolved separately at the two factories or whether this was the result of innovation in the Swindon drawing office under Churchward is not clear, though I suspect the latter.

 

Nick

[gwrrob]

According to RCTS 4407 didn't get outside pipes till 04/45.

[6892 Oakhill Grange]

Has anyone a photo of 4407 circa 1939 I'm checking to see if the engine was sporting outside steam pipes at that time of it's life, many of the photos I have in books show some with and some without but can't fine any reference as to the date when Swindon start to fit them or was it when the boiler was changed with one's from the 45xx/4575 class. 

State of the donor Bachmann locomotive below, I pick it up for a good price at a show the week-end I was lucky as no glue was present and it came apart with a gentle tug.

Hi

 

Please keep us informed about the rebuild. I have thought about this and the query about wheelbase was part of my realisation that it would be quite hard.

 

Cheers

 

Oakhill

[DCB]

The outside steam pipes appeared when new cylinders and curved drop ends were fitted.  

[DCB]

Don't forget the front  buffer beam is noticeably shallower on the 44XX, than the 45XX  The Buffers are central and not offset 3" towards the bottom edge as per the 45XX.  This is because the 44XX sits 3" lower on its 4' 1 1/2 " drivers than the 45XX on 4' 7 1/2 "  This is surprisingly noticeable and is a useful distinguishing point between 44XX and 45XX in photos.  The rear buffer beam is also 3"  shallower and has a spacing block in front of the rear buffer beam showing where the bunker was extended probably in the 1920's   The early 45XX also had this at least up until 4549 though 4555 on did not.

Edited July 7, 2015 by DavidCBroad

[gwrrob]

http://www.ebay.co.uk/itm/Great-Western-GWR-44xx-locomotive-from-the-Ks-kit-OO-finescale-/371343884028?pt=LH_DefaultDomain_3&hash=item5675d1fefc

 

No connection with seller but might be of use to someone on here.

[6892 Oakhill Grange]

RCTS Volume 9:

 

4405 / 08 by 1932

Others by 1937 except 4400/03/09

Suggestion that 4400/03 were never fitted.

No date given for 4409.

 

Russell Vol 2 has photos of 4409 in Great Western green with a fender and no shutters or steam pipes. So pre WW2 seems reasonable for that as well. 4406 in the same source has steam pipes, shutters and a fender. As a further variation 4404 is shown with shutters, no fender and no pipes.

 

I reckon that in the 1930s you could line up all 11 and have no two identical. Then again as I have said elsewhere recently they all look the same to me.

 

Oakhill

[DCB]

A quick inspection of a 55XX at Buckfastleigh yesterday showed a very likely reason for changing the 4ft 7" ebgines wheelbase compared to the 4'1" engines. the leading coupled wheel brake hanger is at the extreme front end of the main frame. If it was 6" further forward as per the 44XX it would need a different brake hanger or different main frames instead of the same main frames slotted differently. Pics to follow