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Construction of 5" Merchant Navy, Part 3 – when there are no proper drawings!

Part 3 of an Article by Kevin Neate 

Smokebox, brakes and platforms

A friend made a video of the chassis running on compressed air, which I have put it on You Tube - click here to view – or look for 5" MN chassis on air test.  There is plenty of detail that I hope will be useful for other builders doing the valve gear etc.  I then made a few of the odd bits.

The outside to inside cylinder exhausts were made from 15 and 22 mm copper pipe fittings.  A commercial 22 mm end feed copper pipe bend squashes down perfectly over a piece of 6mm steel to fit the slot on the inside cylinder.  The 5 hole blast nozzle was next, and I made it with a separate blower ring to be fitted over the nozzle later.  The nozzle has 3/16" holes - will this give the right amount of draught ?  It can easily be replaced with alternative nozzles.  It seems the 5 hole nozzle was used in full size as the inner cylinder protrudes into the smokebox, making a single nozzle impractical due to reduced height. 

I had forgotten to make the sandboxes and pipes that fit in the chassis and protrude under the boiler.  I silver soldered 10mm brass tubes at a 45 degree angle into 1" thin gauge steel box section, and then fitted the assemblies to the relevant stretchers.

The saddle is there from before and of course did not fit now that the frames and cylinders are all bolted up, so I had to skim a bit off each side.  The KW saddle drawing doesn't show an overhang at the front so I added on a piece 7/16" wide to compensate and put in a lot of dummy screws and nuts, and also the small gusset at the front.  It also needs a front cylinder access cover with screws and the hole on the KW drawing is not the right shape, but this doesn't matter as the battery box hides it.

The smokebox was rolled from 1/8" steel as part of the original work, and I had cut some of the bottom away to clear the inside cylinder and allow it to sit on the saddle.  In full size the smokebox is riveted to the boiler and there is a ring fitted behind the rear of the smokebox that supports the boiler cleading.

With the smokebox still split after rolling, I pushed the boiler into it, clamped the smokebox shell using a big jubilee clip to close the gap, then welded a temporary brace to hold the size before silver soldering the smokebox joint.  If you haven't built the boiler yet and wish to do it to the KW plan, I would suggest adding another 3/8" length to the front end of the boiler barrel.  I found when fitting the smokebox there is not a lot of overlap to the barrel and the holding fasteners.  It is easier to cut off than add on, and gives a bit more to adjust at the back end!

In full size the bottom of the smokebox needs an inner platform and just the same in 5" gauge.  My solution was to fit a sheet steel liner tapered to match the slope of the inside cylinder and having 2 end pieces.  The liner is tack welded to the smokebox barrel but not fully welded to avoid distorting things.  This leaves a cavity underneath sealed with Gun Gum.  I fitted an M6 screw welded to the saddle that clamps the smokebox tightly to it, and the blast nozzle screws through the plate as well.

My outside cylinder modification left two upstanding 10 mm steam inlet pipes and the inner cylinder pipe.  Whichever way you go there is a need to connect the cylinder steam pipes to those inside the smokebox.  In full size, complex cast iron stuffing boxes are used that will be difficult to make in our gauge.

I cut the three steam pipe holes through the smokebox with a 5/8" slot drill, and then made adapters from 5/8" steel bar.  These are threaded 9/16" x 26 each end, drilled 10.2 mm to clear the 10 mm pipes, and have matching nuts from 11/16" AF brass hex to grip 10mm pipe olives.  The lower end connects to the cylinders, and the upper end will eventually connect to the superheater.  After setting up I tack welded the adapters to the inside of the smokebox and then silver brazed all round to seal.  Now it is quick and easy to take the smokebox off (along with the boiler).

The next bit is to silver solder the front plate casting to the smokebox barrel and skim flat.  Then there are lots of holes to be marked out.  The KW drawing shows some, and the rest I have taken off the full size drawing that I have, but it is missing the number.

The tricky bit is the smokebox door, and getting the hinges aligned to fit the hinge brackets to the smokebox.  In full size the door is a pressing made from 5/16" steel, and the rim of the pressing fits into a grooved section welded to the front of the smokebox front plate.  I cheated and made a dummy ring using sheet steel flanged around the casting, fitted to the rear of the door.  When the door is closed it looks correct.  The MJ door casting is an oval but needs a bit of fettling to form semi flats top and bottom.  My smokebox door is cast iron.

There is a boss on the full size door for the dart, and this can be formed on the casting.  I clamped the part machined door on the miller, and using the centre hole scribed x and y lines to line up with x and y lines on the smokebox front, and then made the dart and crossbar and clamped the door in place to make and align the hinges.  There are angle brackets on the smokebox not shown by KW that support the outer part of the hinge brackets, and these need to be silver soldered in place.  The lamp brackets were another nasty, I milled 1/16" slots in the casting to locate, and silver soldered them in place - yes cast iron will take silver solder with amalgum flux.

The rest of the smokebox and chimney is reasonably straightforward – except! - I used the MJ Eng chimney casting (a cast iron version), and after minimal fettling it fitted the smokebox perfectly.  However I was caught out when the flange that bolts to the barrel proved to be so unbelievably hard that it was impossible to drill the holes, even with carbide drills – this part of the casting had obviously chilled severely.  The rest of the casting was quite easy to machine.  I spoke to MJ and they had not encountered this problem before.  I heated the casting to a bright red heat to try to soften it, not even then would a diamond dentist's burr cut into the flange.  So I put it in my wood burner stove and really brewed the stove up for the casting to spend a long time at a very red heat and cool very slowly.  That did the trick!!!

There are also 2 sandboxes attached to the smokebox not shown by KW, and I took dimensions from the full size drawing and milled them from 1 ½" square bar.  Four small tabs need to be soldered on, to attach to the smokebox, and I Loctited the filler pipe caps and the outlet pipes.  The last bits on the outside of the smokebox are the angled pipe connections on the LH side for the blower and brake ejector - another fiddly job made from odd bits of brass - althought these are available as lost wax castings.

There are other holes to be drilled in the smokebox for the smoke deflectors later.  I drilled a ring of 60 holes in the rear of the smokebox as I had an easy way of indexing and it looks right, then fitted 1/16" dummy rivets countersunk inside; leaving out 6 to hold the boiler once aligned.  These are 8BA with heads made to look like rivets as suggested by KW, and long 8BA nuts that are easy to get at inside the smokebox.  How many rivets in full size ? – I have no idea.  There are a few other odd rivets as well, looking at full size photos.

Next I pushed the front end of the boiler into the back of the smokebox and put it on the chassis.  It all aligned up incredibly well with no alterations needed!!!!

I put a ¼" spacer under the boiler to hold vertical alignment, and made two support brackets to sit on the rear brake hangers and these give vertical and sideways alignment.  I cut slots in the top of the brackets to take a 1/8" cross bar to support the centre ashpan.

You may see in the photo that the rear part of the frames taper inwards.  I discovered that in full size the frames are like this, and after the chassis derailed on the club track I altered the drag box to 3 1/2" at the front tapering to 2 15/16" at the rear.  This gives the bissel truck greater side movement, the wheels just miss the frames at full swing, and the loco no longer derails.

After that I made the two brackets that sit on the inside motion stretcher wings, that in full size fix the boiler at the front.  These are dummies that don't connect to the boiler and were milled out of odd bits of cast iron.  So now the boiler/smokebox assembly is done for now.

The brakes are next and I started by making the brake blocks – I had a scrap cast iron (car) brake disc and set it on a rotary table to flycut 12 radii matching the driving wheel diameter.  I then drilled the 3/16" locating holes at 11/16" from the shoe as per drawing, before them cutting apart with a slitting saw, and then cut the slots and tenons.

As for the rest of the brake gear, the KW drawings appear to be far from correct and a lot of detail is missing.  Other builders seem to have had all the parts laser cut, but I have no information about how successful this has been.

It took a while to work out what is what, and I looked at a lot of full size photos before cutting anything.  The hanger brackets are already on the chassis and I hoped they would be OK.  If built to the KW plan, the one on the reverser bracket is off centre and totally wrong, and the rear boiler support hangers needed a bit cut out as well.  The rest seem OK.

I ended up cutting and gouging out the hanger bits inside the reverser bracket, and made a sub bracket from cast iron to support the LH middle upper hanger, and this resembles full size and matches the one on the other side. 

The compensation brackets appeared fine as drawn, but didn't work and the centre and rears had to be extended.  The front upper hangers and rears didn't need too much alteration to get right, but those between the driving wheels were a real pain to get them to work as they are such odd shapes!

I cut out the shape for the centre hanger from thin sheet steel with the positions of the holes scaled from full size photos.  Even then it took a couple of attempts to get it right.  The upper hangers are all the same but the lower centre hangers seem to differ slightly between the front, middle and rear wheels.  I used the templates with the brake blocks attached to prove all is good, and then marked the shapes and holes on 3/32" steel plate to make one of each hanger.

I drilled the holes on blanks of the steel, and then hacked the shapes with an angle grinder and finished to size on a linisher – much quicker than machining.  The next step is to set up the hangers with the brake blocks on each bracket to test fit and all is good.  To make multiples I clamped the originals to the 3/32" plate, drilled the holes and fitted 2BA screws to hold in place and chain drilled, hacksawed and milled as best around the outlines before grinding to size on the bench grinder; of course the 8 off upper hangers are a real odd shape and were a pig to do.  Then a lot of clevis pins need to be made in varying lengths.

Next I set up all the hangers and brake blocks on the LH side with the compensator brackets and put wires between to represent the pull rods and the whole assembly works fine.

Spacers are needed to align everything in plan, and I used the sizes obtained from packs of washers to make a lot of spacers to braze onto the hangers and then ream through.  The driving wheels are 9/16" thick so I have worked to a width of 11/16" to give clearance either side so the connecting links don't rub the paint off the wheels.  The front compensation bracket needs to be made as a brazed assembly as per the full size welded one.  I tack welded spacers to the other hangers and brackets to make them easier to fit.

The connecting links between the hangers cut from 16G steel – these are relatively straightforward but very time consuming to cut out and make to shape, and it took me a while to sort out the adjusters between the centre and rear drivers.  The real nasty here is the small tee shaped piece that braces the adjuster and has to be attached to the centre link – I used a 1/16" rivet through to hold the bits in place before silver soldering and it was a real pain to do !!!

The flat front cross bar braces the compensation levers, the next one is 5/32" dia with spacers and the rear 3/16"; one goes between the upper holes in the rear bracket.  To hold the brakes together lots of pins, spacers and clevis pins are needed.  All in all lots and lots of fiddly bits plus washers and split pins.

The very last stage is to make the brake operating levers, no real problems here and I made these to my own design fitted to the existing holes in the frame brackets.  I can't yet decide whether to use steam or lever operated brakes – neither of which are much use in stopping 3 cars of passengers as the loco will slip with the brakes locked up – so I have left two unfinished levers sticking up in the air until later.

Making the brakes has been as much of a pain and eater of time as the valve gear, but what I have made seems not too far off the real thing and works really well.  In full size the brake gear is quite close to the track.  I have deliberately made mine slightly higher as it is so easy to damage the brake gear when moving the loco.

I have left all the brake parts unfinished for now as I hope to get them chemically blackened instead of painting, also I have not taken photos of the individual brake parts but will add these when the loco is stripped down for painting.

Although the boiler has been temporarily fitted I want the chassis finished as far as possible so what is next – the cylinder relief valves, drain cocks and sander pipes and also the lubrication system can be left for now.

I have a 24" Warco sheet metal multiworker, and it is a great machine for this sort of work, and there is a serious amount of sheet metal work to do on the MN.  In full size, much of it is welded, making it quite tricky in 5" where we can only soft and silver solder, and can't use rivets unless made flush.


The KW drawings are rather vague for the platforms but do give the basic shapes.  In full size the side platforms are in sections made from sheet steel and lots of angle, and there is a rear upstand that will be added later.  After looking at lots of full size photos I made the platforms in 4 sections, each side with 1/8" brass connector plates soft soldered on.  The rear ones need to follow the outline of the firebox cladding so were cut oversize to be matched later.  There are cut outs under the lubricators and suspension link.  My previous use of the 17/64" height gauge made sure the whole assembly aligns flat on the various support brackets.  For once this was all quite quick and easy except for the cutback on the front platform that connects to the sloping front plates – a bit of cutting out, welding and grinding flush.  There are a host of connecting screws and other screws for I don't know what! – I have put them in where appropriate using 10BA small head for connectors and riveted behind for dummies.

Next are the three front sections between the platforms and buffer beam.  In full size these are made up of steel plates as a welded assembly, and are not so easy to replicate in 5".  Again the KW drawing is not much use and I scaled from photos.  For the LH and RH I bent up two zig zag back plates and tack welded the side pieces before silver soldering.  The odd shaped 'box' in full size allows clearance for the outside valve spindle.  I made dummies from a brass offcut to resemble the box and with a groove to hold the deflector plate before silver soldering.  This was screwed to the backplate before silver soldering the deflector, and then soft soldering the footsteps.

For the centre section I put in a lower flat plate and a vertical front plate with a horizontal top plate all attached with screws and angle.  To this fits the battery box casing and a front flange with radiused corners welded and soldered.  Then the battery box front lid – I bought a photo etched brass plate with hinges at a show long ago.  The last items are the lamp brackets.  The front end platework now looks about right.

The rear part of the platforms cannot be completely finished until the boiler casing is done, and before this the cab floor and its support brackets and side plates under the cab should be made, and by doing this will allow all the platework to be correctly aligned.  Look at a full size loco and the cab floor is lower than the bottom line of the platforms by about 1/3 of the platform depth with a compensating curved piece.

Get this bit wrong and the whole loco will not look right and I spent a lot of time measuring and checking before starting this bit of the build.  Fortunately I have a full size cab arrangement drawing, but nothing for the bits underneath and the KW drawings are not much use.  Full size photos show a mass of copper pipes and brass fittings under the cab.

I made the vertical cab support plates, and then a top rectangular frame from 3/8" brass angle silver soldered together, flush riveted on to hold the side plates and extension pieces of brass angle around.  The forward cab support plate has been left about ¾" back from the boiler, to clear the bottom feed clacks, and I have bracketed it to the frame with adjusting screws to level and align with the platforms.   At last the little curved piece can be silver soldered to the rear platform and a connector plate joins the platforms to the cab base, giving a solid assembly for the cab to sit on.  The lower cab side plates are an odd shape - the LH has a cut out for the generator fuse box, and the RH for the injectors and a host of pipes.  Both have cut outs for access to boiler washouts so have to be cut to suit.  I scaled all these from photos.

The loco is now beginning to look something like a rebuilt Merchant Navy.  Three big stages remain before the pipework and boiler fittings etc - boiler casing, cab and ashpan. I have already made all of these but have found many alterations are needed.

I did a lot of work on the boiler casing only to find that the first ten full size boilers have a tapered front barrel, and a parallel rear barrel; and the later twenty the reverse!  The KW boiler drawing is correct for the second two batches of 10 full size locos, and the boiler casing must therefore match the type of boiler for the particular loco.  There are significant differences as was pointed out to me by someone who had been involved with the restoration of 35006.

Hence what I made for the boiler casing was correct for Nos. 35021 – 30, but not for 35006, and quite a bit of alteration was needed.

I will end this article here, and the next article will cover the ashpan, boiler casing and cab; and my mistakes along the way.