The 200hp Steam Sentinel and a distant cousin.

A little while ago, I bought one of the newish CSP kits for an S&DJR Sentinel. Not, I should add, because I’m a particular fan of the S&D; it was an interesting railway, no doubt, but being bought up in Somerset, I’ve seen plenty of it in model form. That said, the kit does represent a type that Sentinel built for industry in a variety of forms and there is one still - amazingly - working in Brazil. The kit as it comes looks very good; nice etchings and some lovely brass castings and lots of instructions with isometric exploded drawings (in colour) as well as motor, gearbox and a set of spur gears to drive both axles. Here’s even a bit of copper clad and phosphor bronze wire in there. This is the only standard gauge kit I’ve ever built where pickups are designed in. There’s a run down of this and a build as the maker intended by Buffalo over on the blogs and very nice it looks too.

 

Of course, I couldn’t simply build the thing out of the box now could I?

 

What I’m after is something that looks a bit like this:

 

http://www.flickr.com/photos/60790501@N04/5684522437/

 

Sentinel 9569 of 1954 seen here derelict at Cynheidre Colliery in south west Wales in 1969. Not in quite that condition, obviously: I’m leaving the boiler in on mine. The other side looks like this:

 

http://www.flickr.com/photos/60790501@N04/5816445264/in/photostream/lightbox/

 

From the same batch, 9572 of 1954 again derelict, this time at Pontardulais. Anyone know exactly how many of these the NCB bought in south Wales? There were at least two more (9541 and 9542 of 1951 and 1952 respectively) at Garw Colliery near Pontycymer.

 

Of course, what the kit gives you is this:

 

http://www.flickr.com/photos/64215236@N03/6056241423/

 

This is where Sentinel’s tendency to evolve their designs comes in useful. What was basically the same design, mechanically at least, was continued until Sentinel became part of Rolls Royce and went out of steam production and this, the ‘200hp’ version was reasonably popular though only three survive worldwide, at Midsomer Norton, ex-Croydon Gasworks, in Brazil and, the sole post-war representative, at Henllan, Carmarthenshire on the Teifi Vally Railway. Now the tin work is a bit different I grant you, but there are some other things  which I'll come to in due course.

 

The story so far goes like this. There are some errors which have slipped through. I have, for example, replaced both buffer beams because those supplied are too small. I'm not sure why this should be, but the design does build without gaps so it is deliberate! They should be the same width as the footplate and the same depth as the frames but were 1mm shy in both directions though the centrelines on the buffers were correct. The work's drawing in the instructions gives the width as 8’ as does a nice Don Townsley drawing in Model Railways from March 1975.

 

 

 

The cab floor is too short (from front to back) and slightly too narrow. I've left the gap at the front since the boiler will be in the way but had to solder some ‘L’ section to the inside of the outer frames to correct this. If it weren't for the half-etched locations for other components I might simply have started with a fresh bit of metal here though I note that ‘Buffalo’ seems not to have had this issue. Oddly, the hole for the brake standard is on the wrong side of the footplate: it’s right on the isometric drawing! All of this is either easily remedied or doesn't actually show but it is a little puzzling.

 

These things aside, it actually goes together rather well.

Adam

I think Oxfordshire Ironstone had one too "Phyllis" - 9615

 

Is the kit a shrunken Agenoria one, like the rest of the CSP offerings?

 

looking good so far

Paul A.

No, this is a 4mm only kit drawn for the scale with an integral gear train. I don't know if it's been done or is being planned in 7mm as that's not my interest. The Oxfordshire Ironstone company did have one, but that had the later, shorter style of cab (like Swansea Vale no. 1 currently at Henllan). It seems not to have been very successful there, probably because of the gradients on the system, and was scrapped by Cohen's I think. There's certainly a photo of Flickr somewhere on it awaiting the torch.

 

EDIT: OIC Sentinel at Cohen's, Kettering: http://www.flickr.com/photos/the-evanses/8186727718/in/set-72157625005043538/

 

Adam

Adam, nice industrial prototype. Will you have to build the flat panel bonnet from scratch? I presume that the kit doesn't cater for it? I'll follow with interest as I've quite fancied one myself.

Yep, the bonnet will be from scratch, probably in 40 thou' or 60 thou' plastic. Since the bonnet is basically a box with some easily verifiable dimensions this shouldn't be too complicated though doing the doors neatly and with finesse will be a challenge. I can see that I'll have to invest in some Archer's rivets. There's a few other differences too (sandboxes, steps, cab doors[!] and for some reason the drive chains were on the LH rather than the RH side of the S&D pair - I have a list somewhere). The thing I think is to make it 'of a piece'.

 

Something I will be looking out for are handrail knobs which will take 0.3 wire:  those on the prototype are notably smaller in diameter. Perhaps one of the 2mm or 3mm scale specialists?

 

Adam

No, this is a 4mm only kit drawn for the scale with an integral gear train. I don't know if it's been done or is being planned in 7mm as that's not my interest. The Oxfordshire Ironstone company did have one, but that had the later, shorter style of cab (like Swansea Vale no. 1 atHenllan). It seems not to have been very successful there, probably because of the gradients on the system and was scrapped by Cohen's I think. There's certainly a photo on Flickr somewhere on it awaiting the torch.

 

Adam

 

Ah, I thought as much, quite surprising about the incorrect buffer beam widths, as you say..

 

By all accounts it was a complete flop on the OIC - but bought from Sentinel on the cheap, brand new (probably built for another sale which fell through)

 

Paul A.

They seem to have been pretty competent in some applications - the well known examples used by Roads Reconstruction near Frome show that even the 100hp versions could do the job - but where they failed, it usually seems to have been in places where their lack of adhesive weight counted against them. It didn't stop the OIC from buying Sentinel diesels mind. They must have had an excellent sales team.

Adam

They seem to have been pretty competent in some applications - the well known examples used by Roads Reconstruction near Frome show that even the 100hp versions could do the job - but where they failed, it usually seems to have been in places where their lack of adhesive weight counted against them. It didn't stop the OIC from buying Sentinel diesels mind. They must have had an excellent sales team.

 

Adam

The salesman must have gone down the Central Wales on a sales trip, as apart from the Pontardulais and Cynheidre ones, there was at least one example at Llanelly Steel (I can't find the link at present, but it's on Flickr somewhere).

The Cynheidre one might well have been new there (the pit was developed in the '50s wasn't it?), but the Pontardulais one came from somewhere else and seems never to have been used there which isn't terribly surprising. I can't recall where though - it'll be in the relevant IRS handbook I'm sure but I don't have that. I do have the Bylines articles on the Graig Merthyr system somewhere but I can't lay hands on it right now. I suspect their relative cheapness to operate would have been a key factor in the sales patter.

 

Adam

This looks like an interesting conversion, Adam. I'll be following with interest. Thanks for mentioning my 'as intended' build, I really should add another entry to bring things up to date as it is now more or less finished and running. My cab floor was also a bit short though I moved it back only far enough to not leave a gap at the front, so leaving a smaller gap at the rear. The gap is only visible when viewed vertically with the roof off. The hole for the brake standard puzzled me at first, but as you say it was easy enough to fix. The buffer beams were too narrow and probably now look a bit odd if you look closely as the little angle plates between valance and buffer beam stick out slightly. I don't recall having a problem with the height, though perhaps I adjusted the frames to match.

 

Which chassis are you using, or are you making your own? I used the original rigid setup though I understand there is a compensated version now available. This was the bit that caused me the most grief as I found that the body sat too high on the chassis. In the end, I removed the rear part of the chassis with brake cylinder and cross shaft and attached that permanently to the underside of the cab. The rest of the chassis was then fettled to fit at a suitable height. It now runs, albeit a little roughly and I need to get some better wheels (currently its on some Gibson wagon wheels).

 

Nick

 

ps. Here's 7191 as yet without brakes and with a similarly incomplete wagon, though don't ask what it's doing on the GWR

 

Some food for thought there, thanks Nick. My intention is to use the chassis parts supplied which are identical to yours and to work out some form of compensation. Thanks for the tip off about the ride height, I shall have to offer it up to the Townsley drawing when I get to that point. This is the point which helped me spot the bufferbeam height anomaly by the way - the top of the rear beam should be at the same level as the footplate. Obvious on all the drawings and, when you know, on prototype pictures. If you do this then the supplied beams are no longer level with the bottom of the outer frames which the drawings show as being the correct height. This is what sent me to the scrap etch supply.

 

I haven't started the chassis yet - I really need a suitable size taper reamer to open the holes out properly - I don't think this should be too complicated since all is really needed is a bit of transverse movement on the non-driven axle. For about 0.5mm, the mesh should be secure enough. The easy way out would be to only drive the one axle but that isn't the way I want to do things! This is another puzzle which adds to the entertainment so far as I am concerned.

 

Most of the issues mentioned are fathomable. The brake standard thing must come from a small amount of confusion as to which side was 'up' on the artwork. I've spotted a couple of places where a half-etch should go all the way through, the coupling hooks for example. The cab steps are like that as well but since industrial Sentinels had patterned [durbar?] plating on the risers I will be replacing that anyway. Dad has a sheet of this which Intercity Models did (and I think Shawplan do something similar, but with them, you never can tell unless you see them at a show).

 

There are a few things that could have been done differently - I would have preferred the gearbox to have been mounted on the rear axle and for there to have been space for a flywheel for example. A semi-modelled boiler supplied as a whitemetal casting might have been a way around this and have been easier that forming multiple bits of tube but it doesn't matter all that much. In any event, the boiler is a fun thing to do and much more fun if you happen to have a length of tube of the appropriate diameter in stock. That's three loco' boilers from that one length of 17mm tube now so that's excellent value.

 

Adam

I built the chassis rigid really just to see whether it would work adequately like that. I thought about adding a central pivot and allowing some rocking on the front rear axle, but decided I could always go back and do that later if necessary. Maybe I will one day...

 

One thought does occur to me about the fit of the chassis, though I haven't gone back to check against drawings, is to make sure the axle box castings are at the right height. Once it comes to fitting the chassis, the only option is to ensure the wheels line up with the axle boxes. I remember when fitting the castings there were a number of small holes in them and in the frames, presumably intended for alignment, but very few of them lined up with each other. Effectively it was only the dummy axle holes hanging down below the chassis frames that provided a guide to the casting locations.

 

Nick

Here's where I am with the boiler. Note that the gauge glasses are rather larger than the location holes suggest - I should have checked this when using the original wrapper to mark out the tube. Still it'll be filled with Miliput and lead shot when I'm done with the soldering so that will take care of the holes.

 

 

It has also just occurred to me that if the gear train were to move to the centreline of the chassis, the mesh could be undisturbed and compensation added that way. Hmm...

 

I'd spotted the issue with the axlebox castings and done as you say - at least it gives something to aim at. The quality of the castings is very good in my view. I've had some lousy brass castings over the years - the dome on my Gibson O2 was especially horrid and took a lot of filing and filling to make right. These just want a light clean up.

 

Adam

...It has also just occurred to me that if the gear train were to move to the centreline of the chassis, the mesh could be undisturbed and compensation added that way. Hmm...

 

Yes, that was a thought I had but it wouldn't be easy. You can't put an extra idler centrally on the output shaft of the gearbox as that would foul the intermediate reduction gear. It might be possible to do something like this at the rear axle:

 

 

but the gear on the rear idler shaft would foul the frame spacer and require a cutout in the cab floor/front. The one on the axle would foul the ash pan. You'll notice that mine has extra spacing washers on the gear train side and reversed bushes on the other side to give suitable wheel spacing for P4, but otherwise is as intended.

 

I know that Robin (barrowroad) has been building one and he told me about an alternative chassis intended for P4 use that uses a layout similar to one on a Judith Edge Ruston kit (see this page on Paul (halfwit)'s blog). However, I got the impression from Robin that this chassis causes even more problems...

 

Nick

Hmm. Dad has one of those Rustons and that runs pretty well - though being tiny, the wheels get dirty rather fast. I shall have to have a closer look next time I'm there.

 

There's no reason, there being lots of space in the boxy body, that the motor has to be central but the other problems would remain. Watch this space, but don't hold your breath.

Adam

Good point, I was forgetting you had all that extra space under the engine/tank cover. It may well be possible to shift the motor and box over far enough to get the gear on the output shaft in the centre.

 

Nick

The other idle thought was: What's the smallest Delrin chain available?

 

Not as silly as it sounds: Dad has done several bogie diesels in EM with delrin chains just like the 7mm boys do. He's compensated those bogies as well. Besides, for a Sentinel it would be so, so appropriate.

 

Adam

We do seem to have similar thoughts, Adam. I've some Delrin chain sat here on the bench with a view to trying it. The pitch is about 3.1mm and an 8 tooth sprocket with chain warpped around is about 10.1mm max diameter. It might be a bit too visible and would foul the ash pan but, if there's anything smaller available, it might do the trick.

 

Nick

Well, it's an option I guess. The 3.1mm pitch chain is from Branchlines presumably? Some years ago now, dad managed compensated all wheel drive on an Impetus Simplex using, of all things, Mainline Warship gears. I'll have to see how that was done. All these things are related by the way. If you've ever owned one or more Mainline Warships you will eventually have lots of 'spare' gears because one will have split. Hence the chain drive power bogies...

 

The chain drive idea may still be a runner - the inner end of the ashpan is tucked behind the wheels in any event and with the brakegear in the way, how much of the drive chain would be visible? Probably barely as much as the drive gears on the designed in arrangement. A new gearbox with a higher reduction might be necessary of course but with all the rearrangments I might yet get my flywheel.

 

Adam

Mine didn't come from Branchlines, I think it was from a shop that does military vehicles, etc, but I wouldn't be surprised if its the same.

 

Nick

 

EDIT: correction thanks to Paul (halfwit), I saw them in a tank model shop but actually bought them from this seller on ebay.

If you can get hold of it there is an excellent book called 'More of My Life in Steam' by Ken Judkins in which he describes working for Sentinel as a demonstrator of the railway locos including adventures demonstrating a 100hp loco to the coal board in South Wales. He thought they were excellent locos when handled properly.

Thanks, I see that there's a few copies on Amazon, will have to look into that. So far as the model is concerned, the body will probably stay as it is for the moment until I have worked out what I'm going to do with the chassis. My preference, at the moment, is to drive the rear axle (which will mean replacing the gearbox, but I have another project it will suit) allowing three point compensation on the front and, more importantly, a flywheel. The High Level gearbox planner suggests that some small intrusion into the cab might be necessary, but it won't disturb the boiler and will be almost invisible. In the meantime, back to wagons...

 

Adam

Adam,

 

I'm interested to see how you're getting on with the build. A friend of mine is building one and I think he's having the same problems too (currently trying to get the brake gear set up around the wheels.....).

 

Instead of Delrin chain drive, I was wondering if you had considered belt drive using Nigel Lawton's components?

 

Clive.

It's going nowhere in a hurry at the moment, simply because I haven't had the workbench time. The Lawton pulleys are interesting, but I would want to explore their use in a smaller application before I launch into unknown engineering: I'm not an engineer, but I know some of the principles and can copy/apply them! I do have such a project but it isn't a priority.

 

Having had a chat about this with dad, the current thinking is - apart from shifting the drive to the rear axle to allow for a flywheel (taking a small chunk out of the ashpan is a reasonable price to pay I think) - to build the chassis as designed and to see how that goes. There's plenty of space for adhesive weight and I wouldn't normally give a moments consideration to compensating anything else with a sub-6' wheelbase so why should I here? A flywheel - even a very small one should solve any potential pick up issues. The brakegear may be challenging, probably because of the additional width of the wheels relative to the prototype. I shall worry about that when I get to it. 

 

Adam

 

Edited to remove Greengrocer's apostrophe.