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Nick Dunhill's workbench CR 0-4-4T Wrexham Tanks


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The new project is to build a couple of these rare Nasmyth-Wilson 0-4-4T Cambrian Railway locomotives.  I believe they were colloquially known as Wrexham Tanks.  The build is going to utilise a set of Redcraft body etches, that I'm guessing have been blown up from OO gauge and are designed to fit an RTR chassis.  I have commissioned some etches for the chassis though, and the build will feature working motion and all the BAW.  I hope to get around the problem of mounting all the motion and a gearbox on the same axle, which is always an issue on a 0-4-4T.

 

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The frames and stays have been prepared, and I have spent the rest of the afternoon fettling Laurie Griffin's excellent cast Stephenson Link parts.  I am going to scratch a pair of motion brackets and make sure the slidebars fit.

 

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Edited by nickd
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Following with interest...I was half way through designing a 4mm version when I decided to move to 7mm Scale. 

 

Can't say I've ever hear them called Wrexham tanks, though it would make sense having been purchased for use on the Wrexham & Ellesmere Railway.

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  • 2 weeks later...

....so the journey continues with the motion bracket and cylinder block.  I like to do as much as possible before assembling the chassis.  It's easier to open up holes and align them at this stage.

 

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This stage of the build becomes a fettle-fest of valve gear castings.

 

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More fettling tomorrow and hopefilly I assemble the frames......

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.....after a fettle-fest I got to solder the frames up.  The commissioned etches went together very nicely (Cheers to Mickoo) and we have a basic chassis with a cylinder block, a motion bracket and all the other structures in the correct places.  The slide bars will have to come out to be shortened but all well so far.

 

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I think I might build the footplate next.......

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...this will give you an idea of what I am trying to achieve as a drive mechanism.  The gearbox and motor are bog standard Mashima/Ultrascale-type arrangements.  The template for the motor was made assuming the Mashima-type motors would be 1833 or 1826.  In fact they're 1833 or 1524 so a bit more room and flexibility on the smaller motor.  The smaller motor will be fine for a model of this size.

 

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Any thoughts.....?

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....anyway before we get mired in the solution to my power dilema I think I better build a model.  I have the bare bones of a chassis with the stays in the correct places and a cylinder block with slidebars.  I bought some Gresley cast hornguides in the hope that I would be able to modify them, but the amount of modification is a bit too excessive so I'll either find an alternative or scratchbuild some.  In the meantime the sensible thing to do is to build up.  

 

I had my suspicions that the Redcraft etches were a 4mm blow up.  I have had experience of blow-ups (see my NGG16 build) and it's wasn't good.  The Redcraft etches didn't clear the first hurdle.

 

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The inner edges of the footplate etch didn't reach the frames (by a long way.)  The splasher fronts, that fold up, are designed for a 4 mm wheel so are too big in diameter and too close to the edge of the footplate (by a long way.)  Also the centre of the splashers does not match the centre of the front wheel (by a long way.)  I could have modified them but it was easier to make new ones by a long way.  Maybe I'm being a bit unfair and the Redcraft etches are designed for a 4mm RTR chassis.

 

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That's a lot better and I get rivet detail too.

 

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I have checked some other parts on the Redcraft etches.  The body is about 1 mm too wide but I can modify that.  I now live in hope rather than expectation.  (By the way if anyone wants a set of etches for the chassis and bogie for this build PM me, they go together very well.)

 

The buffer beams did at least fit and, although a bit long, the valances (or hanging bars for those with a GWR-19 affliction) do fit.  As you can see I added some footplate brackets and most of the angle iron that  holds everything together.

 

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Next, the postie arrives with more L section and I finish the above......

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...interesting where the journey takes us sometimes.  I had intended this week to build all the brake equipment between the frames (cylinders, plumbing, tanks etc..)  I made a vacuum reservoir tank from telescoping tube as I don't have a lathe (no neeed for comment here Mr DLOS!) and it took a while to cut nice angular cylinders by hand.  So I attached the assemblies to the frames and my immediate thought was that there would be a conflict between the tank and the bogie.  

 

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So I downed tools on the brake system and thought it'd be a better idea to build the bogie first.  I have built a few pre grouping bogies recently and they all seem to be built along the same principals.  I guess this loco had a fixed bogie and was effectively a 0-4-(2+2) arrangement.  The bogie carries roughly half of the loco's weight so doesn't have any vertical springing between the chassis and bogie bolster.  All the springing is in the bogie axleboxes and equalising beams, and there is just rotational and lateral movement at the chassis/bogie pivot.  As I am going to have to make the second driving axle rigid to accommodate the patent Dunhill/Beeson/Smith drive mechanism, so the bogie will have to have some vertical springing or the driving wheels will lift off the rails on undulating track (I'm sure none of you have any of that, but just in case...)

 

So I have learned that buying a cast spring that is similar in size to the original brings inevitable re-designs to the eqalising beams (and almost every component on the bogie.)  I decided to get Mickoo to etch the parts for the spring, together with the other components of the bogie, to test the hypothesis that it would be easier to fabricate individual springs from etched leaves than about making a cast spring fit the rest.  Well possibly maybe is the answer.  I filed etching cusps off dozens of etched leaves, bevelled the edges, filed a taper on the ends and carefully bent them into a gentle curve.

 

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The bogie chassis had phosphour bronze wire side control fitted.

 

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The springs and equalising beams did take a while to make but do look better than a 'nearly' cast spring.

 

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I had to assemble the bogie chassis on parallels blocks as the wheel axles were standard 3/8 tharg and the axles blocks accept 5/32 thargs.  My mistake I forgot to get the axles machined.  I think the finished bogies justify the effort.

 

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Back to the GA and I noticed a plinth between the bottom of the chassis and the bogie bolster.  I decided to make a pair, but a millimetre shorter so I can accommodate some vertical movement.  Some experimentation with my dwindling stock of springs will be necessary!  (Anyone know where to get very small numbers of smallish compression springs?)

 

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Next week I go back to the brake system, via the couplers (if they ever turn up!)......

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Guest Isambarduk
On 02/05/2020 at 12:58, nickd said:

My mistake I forgot to get the axles machined.

Not to worry, Nick ... I think you know a man who can ^_^

 

AxlesTurnedDown.jpg

Standard Slater's 3/16" diameter axles before (left) and after turning down to 5/32" diameter (right)

 

David

 

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Guest Isambarduk
On 02/05/2020 at 14:33, nickd said:

....Oh, and here's the gears I've had made for the drive chain, more of which later.....

This is what happened to two of them:
 

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I have written up 'how I did' it with captioned images in a post in The G0G forum topic In the DLOS Workshop but I shall copy it across to my website in due course.

 

David

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....this week I have added the couplings.  The couplers were kindly supplied by CPL.  They sent enough castings to make the Cambrian style 3 link couplings with the top loop pinned to the hook.  Luckily there were enough parts to make a pair of loose screw link couplings too, as pictures show both locos with loose screw links on the hook.  The first job was to reprofile the cast CPL hooks to look more like the CR ones.

 

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Then the different styles of chain were made.

 

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The drag box for the rear hook is the structure under the cab that supports the frame and bogie, so a long shank was made by splicing the cast CPL coulper to a rod that was threaded on the end.

 

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The front drag box is just the front buffer beam slightly armoured up with angle and gussets.

 

I then moved on to the brake cylinder and plumbing for the train pipe.

 

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I even made a good start on the train vacuum pipe that runs under one side of the footplate until the lure of libations in the bank holiday sunshine got the better of me.

 

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Enjoy the sun............

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.....This week I started by finishing off the vacuum pipe on both models.  It's always complicated by having to keep an eye on how the body and chassis will separate when finished!  (Some modellers are obsessed with taking their models to bits and use thousands of machine screws.)

 

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Next I thought it'd be a good idea to add all the splashers for the bogie.  They took a while to fit, and I also scratchbuilt mounting brackets for them which can bearly be seen.

 

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And after I'd done that it seemed logical to add the water tank balance pipes.

 

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The bogie wheels turned up (they'd gone to visit someone with a lathe who kindly decreased the axle diameter, ta DLOS!) and I duly put them in the bogie.  I had to cut some wheel shims to limit the end float.

 

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So, will the wheels short out on the splashers, and will I have to mount the splashers on the bogie?  The only way to find out will be to test it later.

 

I decided that if I was to fit the driving wheels (to test the above) it would be prudent to make the firebox lower and ashpan first, as the motor and gearing will be contained within......and I like fabrication jobs like this!

 

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This is how I make an accurate box.  Firstly cut the pieces out very accurately, using a square to check all right angles, and then tape the pieces to a machined block.  I tack them first then soldering up off the block.

 

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Then I cut out the pieces for the ashpan.  As more bits are added the fabrication becomes stronger.

 

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This is roughly where the idler gear will sit inside the structure.  I'll cut a slot in the front so it can protrude and engage with the gear that is a crank web.  

 

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More fabricating next week.........

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  • 2 weeks later...

....a big week with the Wrexhams, I've been working on all the mundane bits and pieces that are often overlooked.

 

First I completed a bit more work on the firebox bottom and ashpan.  The damper doors were detailed with straps and hinges.  The rest of the detail will be added when they are installed.

 

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Then I moved on to the hornguides.  I couldn't find any commercially available cast ones.  They're all the wrong pattern or too large to fit between the slidebars and frame, or the crank webs and frame.  I considered scratchbuilding some but in the end opted for some Gresley etchings from the Finney7 Coop.  They have the wedge adjusters so are handed as prototype, and could be modified relatively easily.  The horncheeks are much reduced in height and I added wedges from 1 mm square rod and all the webs.

 

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I added some 14BA screws and nuts as height adjusters.  They're brass items which can be soldered up when all is level.

 

I like self contained buffers as the fixing screws don't interfere with the gusset structures that support the buffer beams from behind.  The semi tapered GWR Dean (?) buffers were an excellent match, and I bought sets of them from Haywood Models.  The GWR version of the buffers have a tread on the stocks which my locos don't, but being white metal they are easy to file off.

 

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The fixing studs and nuts are represented by a cast pip that's just a bit lame!  I filed them off and will add some fake fastners from GHW-Modelbauversand in Germany.  They're cheaper than the ones from Scale Hardware in Florida as we don't have to pay import duty or VAT on them for the time being (thanks Brexiteers!)

 

My plan was to drill out the buffer bodies all the way through and cut off the unnecessary housing on the rear.  The stocks were already partly drilled out to 2 mm, so I just continued on through.  The buffer heads have a shank that is much less than 2 mm at the head.  I decided to sleeve the shanks out to stop the heads rattling about in them.  The sleeve conveniently holds the buffer spring captive inside the stock.  I made some guide/stops for the inside of the stocks, and glued them in place using a drill and tape repurposed as a locating tool.

 

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I went on to make some spring hangers next, 16 of them and handed.  The photo shows how I did it.

 

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They were a lot of effort but will look good on the model.  They are on show through the spokes too.....

 

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Hopefully next week I can finish the springs, build some coupling rods and instal everything else......

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...so after making up bits and bobs last week I could get on and assemble them this week!

 

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First up the spring hangers, quickly followed by the front horn guides.

 

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As you can see I quickly added mounting rods and adjusters.  The springs are mounted on the keeper plates, and will be added once painted.  I used my trusty jury axles and the coupling rods to locate the rear horn guides to ensure a smooth running chassis.

 

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The etchings for the rods turned up this week too, great just-in-time delivery.

 

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After a bit of faffing about I had a nicely running chassis.  The bogie works well and doesn't short out on the mud guards.  As a belt and braces measure I lined the inside of the mudguards with insulation tape and turned 0.5 mm off the diameter of the bogie wheel flanges.  The side to side motion of the bogie was restricted to a minimum and the side control turned out to be more than adequate.

 

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So there we have a couple of running chassis with footplates and buffers (the fake nuts and bolts turned up from Germany.)  Next I'll either build the rest of the brake system or the inside motion, depends how I feel on monday morning.  Enjoy the weekend........

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...so inside motion it was.  I've built a few LGM sets of inside motion and they're pretty comprehensive.  Laurie mixes and matches castings fffrom his rage for you to get the most appropriate stuff.   Because of their universal nature they do need a fair bit of fiddling and fettling to get them to fit.  The eccentric straps are now cast in two halves, but they still have an ID when assembled that's less than the OD of the eccentric sheaves.  When the straps are assembled mine had some distortion from the casting process, so weren't round either.  It took a lot of grinding and filing to make the eccentrics fit the straps, but I got there in the end.

 

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Similarly the big end eyes of the connecting rods are a much smaller diameter than the cast crankpins on the cranks, file, file, file etc.  And just as my patience and finger ends are getting a but frayed I found the crank webs aren't parallel, or anything like square.  A cup of tea and sit down later and I tried tweaking a crank casting before packing them up and sending them off for replacement.  They aligned pretty well after some prying in a vise, success.

 

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I made a jig for attaching the eccentric rods to the straps (measurements taken from GA.)

 

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The eccentric rods have to be cut to length and scarfed to the strap casting.  The rod castings are pretty badly cast too.  They're wobbly and not of constant thickness, but never the less with a bit of care I got a decent set of rods.

 

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So on to assembly, first I pinned the valve rods to the expansion links and then the eccentric rods.

 

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Next the weighshaft and lifting links.

 

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And finally I assembled the crank axle and cut the axle from between the webs.

 

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I just solder them.  I did get a very nice running chassis though, although no video until I rig up the layshaft and motor.

 

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Brakes next week........

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....I have attached the ashpans between the frames.  The photos give an idea of how the final drive will be arranged.  I'm sure there's enough space to accomodate a sub frame to support the layshaft and gearbox.

 

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Next last of ashpan detail and then the brakes......

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.....I have moved on to the brake rigging.  The shoes and hangers were an amalgam of some etched hangers on the original Mick Davies derived fret and the shoes from the Redcraft etch.  The pull rods and spreaders were also in the MD panel but were modified a lot.  Anyway I ended up with lots of small parts.

 

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They assembled up into the brake arrangement shown here.  The rigging is detachable so the crank axle can be removed for painting.

 

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Next I made the sand hoppers from the Redcraft etches.  They had sloping filler covers which had to be scratchbuilt.

 

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The hoppers were attached to the chassis and augmented with some cast pipes and fittings from Laurie Griffin.

 

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I need to attach the steam pipes to the sanders and also attach cylinder drain cocks.  I'm not sure whether the drain cocks are steam or mechanically operated, anyone know?.......

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