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GNRi Class V Merlin Gauge OO Build

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This is the build of a Studio Scale Models Kit of Merlin, building it to Gauge OO and not decided on suspension type yet!!

Main chassis components & coupling rods removed from the fret, edge cusp removed and ready all for soldering.


Soldering the frame spacers to alternate frames, the ash pan sides and the coupling rods.


The frames are then bolted together with screws supplied in the kit and then all soldered.


Note;- **** The Motion Plate frame spacer, Part No. 108 - is in upside down in this sequence of photos. I will show it in the correct orientation in later photos when the error is fixed*****

Captive screws and nuts are also fixed into the frame spaces to hold the front bogie and body onto the chassis.


Crosshead parts ready for soldering, the long bits are a jig when soldering the parts together with a bit leftover as the sliders! see below.


Jigged up and parts being soldered in.


Soldering complete.


Then the jig ends are cut off to complete the crossheads, a pit of filing and clean up is required.


Motion brackets, cylinder wrappers and ends removed from the fret, cusps removed and ready for soldering.


Motion brackets jigged up on a piece of MDF for soldering.


Bracket folded n soldered.



Preparing the relief valves for the cylinder front covers- these small bit of wire have a tendency to float out while soldering the covers on so I put a burr on one end with a hammer, thread the wire through the hole from the inside and solder on the inside, this stops the wire popping out later.


Embossing the bolts on the covers.


Inner cylinder wrapper bent to shape around a 6mm brass bar and ready to be soldered.


Solder applied to inside of the wrapper, then the top is soldered onto the bracket first, then the wrapper is forced around the bracket, held with a strip of wood to save the fingers and the bottom soldered.




Front cylinder ends soldered on.


Bogie front splashers were bent up and soldered to the chassis, gusset plates also done at front and at the firebox.


Crosshead slide bars being folded up and soldered.


Installing the slide bars into the back of cylinders and the motion bracket. A bit of fettling was required to the crossheads to ensure they could move freely in the slide bars, this was done before soldering the bars in!


Outer cylinder wrappers bent up and ready to be soldered as per the inner wrapper method.


Wrappers on and whole assembly cleaned up.










Edited by murrayec
Part 108 in wrong orintation
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I Fixed up that frame spacer and did a bit more of the build.

De-soldered the frame spacer, also the bogie mounting plate to facilitate bending the frames to sneak the spacer out of it's half etched tabs!


Now its soldered back in the right way up.


Bogie parts prepared for soldering up.


Main parts folded and front axle hornblocks prepared with a bit of solder to sweat them onto the frames.


Frame soldered and stretcher parts ready to be soldered in- oops! upsidedown parts again- that main stretcher is in the wrong way up and I did not notice until the bogie was complete but it was easy to rectify.


Stretchers in and now the outside frame laminates are prepared to sweat solder them on.


Soldered on and the iron is run around the edges to fill any gaps.


Bogie cleaned up and holes being sized for rear axle bearings to be soldered in.


This is the bogie end plate for the compensation beam a 10BA screw is the rubbing pin which is bolted through the plate, this allows adjustment of the beam.


After soldering the nut onto the plate a 10BA tap is run through to clean the threads.


The bogie pivots on a 3mm long 3/32'' tube fixed with a 10BA bolt to the bogie fixing plate on the chassis, the tube is not supplied in the kit. Thin tube is easy to cut with a craft knife by rolling the tube with the knife blade, after a few goes the tube eventually cuts- light pressure should be used otherwise the tube will deform at the cut.


All the bits to fit the bogie to the chassis. Note the bogie main stretcher is now in the right way up!


Test fitted.


After a good rummage through the spares box I found a 'Puffers' Flexichas Hornblocks and bits, this will do the front driver axle bearings and compensation beam.


Chassis holes cut out and hornblocks made up.


Coupling rod holes are sized to fit the Alignment Jigs.


The rear axle bearings are soldered in and all is jigged in the chassis.


The hornblock frames are set at the top of the chassis opening and then soldered in on the inside.







M-34 20210501_123143.jpg

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@Galteemore That first photo is pretty handy after a bit of contrast adjustment a lot of cab detail can be seen.

Getting ready to do the compensation beam so we need wheels n axles. Alan Gibson wheel sets came with the kit- not my favourite type, with their push on axles. I prefer squared end axles and screw on wheels, easy to put on & off as the build requires, where if one pushes the Gibson wheels all the way on their a devil to get off! But I do have a trick for working with these.....


.....the trick is to make up 1/8'' dia brass axles with the ends filed down slightly in the lathe so that the wheels are a slight push fit and then easy to get off again, I estimated the length required- 24mm and made them to this length which can be used to size the final steel axles.


As you see in the photos the drivers come with separate crankpin wheel boss! This adds 2.14mm to the axles which will push out the rods by the same- Not sure about this and have an enquiry out to SSM.


.45mm NS wire keepers soldered onto the bottom of the hornblocks of the bogie front axle.


Axle'd up.



Front axle compensation test, the axle pivots on the central bearing downstand from the stretcher.


All wheels on.


In this photo one can see the 3mm long tube above the rear bogie wheels that the bogie pivots on.


Parts for the comp beam- 1.6mm brass wire beam, front screw plate from the kit, 1.6mm brass cross pin, 1.6mm internal dia brass pivot tube, and little bits of tracing paper with holes in, which will be used while soldering in the cross pin to stop solder wicking through into the tube- we want that to pivot!


This is a handy tool for punching holes in things, I got it in the Art & Hobby shop- in the paper card section, with heads of 3 hole sizes and 3 dome sizes.


Screw plate soldered onto the front of the beam first.


Then it has it's 10BA screw fitted and threaded into the chassis, which will only work with the front driver axle removed. The bogie mounting screw also has to be filed down flush with it's corresponding nut, otherwise the end of the screw fowls the beam! The cross pin is soldered on the outside of the frames with the tube threaded on and the paper washers on each end of the tube against the frame.


Then the front axle is fitted and the beam soldered under and to the pivot tube, soldering at the top is easiest. One can now see the screw at the beam front protruding through the fame stretcher which will act on the bogie creating a 3 point compensation suspension system with the front drive axle.


Wheels back on.


The beam front screw is now adjusted to level up the wheels, the front driver axle ends up in mid position on the hornblocks. After running and weight tests a splash of Loctite will go on the screw.


Next will be the gear box and motor......


.........in a while! other projects to be getting on with!




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It looks like the loco may have been supplied with a set of plain driving wheels and outside cranks intended for a GWR outside frame 4-4-0.

There is a 4880G 6'8" spoke outside crank driving wheel listed in the Alan Gibson catalog with are used with the 5000 outside cranks and extended axle.

The driving wheels listed OC are for outside framed locos, the outside cranks and extended axles are supplied as a separate part


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53 minutes ago, Mayner said:

It looks like the loco may have been supplied with a set of plain driving wheels and outside cranks intended for a GWR outside frame 4-4-0.

There is a 4880G 6'8" spoke outside crank driving wheel listed in the Alan Gibson catalog with are used with the 5000 outside cranks and extended axle.

The driving wheels listed OC are for outside framed locos, the outside cranks and extended axles are supplied as a separate part


@Mayner I reckon you right there, I'll wait for SSM to come back on my query and see if they have replacements drivers.


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  • 2 months later...

After getting the replacement wheels I decided to finish off the chassis bits before doing the gearbox & motor!

The right wheels this time, I got them from Alan Gibson in the end- after weeks of telephoning and just getting the answering machine.....


The crankpin BA screws were installed, all was assembled and wheels quartered to broach the coupling rods for free running. In the foreground is the brake parts, connecting rods & wheel weights all cleaned up, holes sized and ready for folding/soldering.


Connecting rods and brake shoes folded/soldered, yet to be cleaned up.


These are the break hanger brackets being folded up. Their threaded onto the .5mm wire pins through the chassis for hanging the brakes off.


Now to solder them on to the chassis.


The rear brake frame bracket are fitted onto a .9mm brass wire through the chassis brackets, I left the brackets free on the rod to be soldered when the brake pull rods are on for positioning.


.5mm wire pins soldered through the chassis frames with the little spacer brackets threaded on and soldered.


Next the shoes, pull rods and beams were joy rigged in place and soldered up- very fiddly as one wants no contact between the shoes n wheels which will cause a electrical short. Those rear brackets are now soldered to the .9mm brass pin. The back end of the pull rods and the top of the shoe hangers are not soldered so that the assembly can be removed.



And removed.


Wheel weights being epoxied on.


The connecting rods were cleaned up and the crankpin end generously broached as these will be at quite an angle out to the crosshead. Wheels back on and time to assemble the gear.





The connecting rods are at a crazy angle, causing binding on the crankpin bearing and the coupling rod, the bearing is not long enough, which also needs a washer and a bit of free space for this angle. I'll make up a bearing to suit.




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On 16/7/2021 at 8:50 AM, murrayec said:




The connecting rods are at a crazy angle, causing binding on the crankpin bearing and the coupling rod, the bearing is not long enough, which also needs a washer and a bit of free space for this angle. I'll make up a bearing to suit.




One of the challenges of building an Irish Broad Gauge steam locomotive in OO gauge!

On the majority of outside cylinder steam locos the conrods are on the outside of the coupling rods but not on some outside cylinder 4-4-0 classes including the GNR Compounds and Metropolitan 4-4-0T.

It basically leaves the builder with the choice of cranking the coupling rods to avoid running problems or fitting the conrods on the outside of the connecting rods and using a longer crank pin bush.


Edited by Mayner
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  • 3 weeks later...
Posted (edited)

The gearbox & Motor is next, so that I can work out the space I have for the electrical pickup system under the ashpan!

The gearbox bearing holes are sized while the parts are held in the fret.


The drive axle bearings are filed down so that they only protrude .5mm outside of the gearbox.


All folded, 2mm lay shafts cut ready to solder into the bearings. I soldered the bearings into the gearbox frame first (the folded bit), dry fitted the shafts and gears in that side, then checked the fit of the gearbox cover with loose bearings to see if all works OK. It goes together fine but the gear under the worm has to much side play so washers will be fitted on final assembly.


Then the cover bearings and the gear shafts are soldered in- the shafts are soldered into the gearbox frame bearings only.



3 no. 10BA bolts n nuts are used to assemble the gearbox and then the drive axle bearings were soldered in using a 1/8'' aluminium dummy axle to check alignment and solder wont stick to aluminium, the drive axle gear also requires a washer to be installed to take up side play.


When fitting the unit to the chassis the lower gear shaft, bearing and BA bolt end had to be filed back to stop it fouling the ashpan inside the frame.




Now I can see what I have to play with for the pickups......


Next up is starting on the loco body, but first the etches, which were heavily tarnished were cleaned up with W5.


Footplate parts cut out and yet to be de-cusped, folded and soldered.


Thats for next time.......




Edited by murrayec
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  • 2 weeks later...

Footplate, buffer beam and steps being folded up and getting ready to solder.


The footplate cab end drag beam is folded down, then the curve is folded over a 3.15mm dia brass rod.


Then the 90 deg bend is folded down.


Checking the folds with the cab side and making adjustments.


The folded up steps are sweat soldered onto the valances, the front buffer beam structure is also soldered and all is ready to tack solder together! But the jig part 38 (top far left in the photo), is supplied in the kit to hold the valances at the front while soldering them to the underside of the footplate, doesn't fit! So have to do it by eye.


All tacked in place with some minor adjustments at the drag beam end.



Next is the detail etch cover to the buffer beam, but before soldering it on I decided to look at the buffers to see if any adjustments are needed. The fact that the buffer beam structure is a box type affair the buffer bushes at the back are not long enough to support the spring and keep the buffers out where they should be! Easily remedied with a brass tube spacer behind the spring on final assembly.


The buffer shanks have a rib on the end which needs to be filed down, one is done in the photo.


So after checking the buffer fit and making adjustments the whole footplate was soldered up.


Then the buffer detail was sweat soldered on.



The buffer bushes soldered into the rear of the beam structure.


The rear chassis fixing captive nut was soldered on.


And the front steps grab handles soldered in.


Now a bit of turning- a 16mm dia brass flywheel for the motor, flywheels like all their weight on the outside of rotation for maximum torque, so a grove needs to be cut in the front face. This is done on the lathe which is called 'trapanning' - cutting a recess in the end of a bar. A tool 3mm wide was ground to shape for doing this which is on the right of the bar stock.


Stock cleaned up in the lathe, drilled 1.9mm for the 2mm motor shaft which will be reamed 2mm after the part is parted off as this is not a through hole and cant be reamed here. The trapanning was done leaving a 1mm collar at the motor shaft, very slow speed, loads of lube, and slow feed into the work does the job.


Parted off at a depth of 6mm, cleaned up and reamed 2mm......


and test fitted, which will be Locktited on final assembly.


Next up are some cab parts, cut from the fret, de-cusped and ready.........


........that will be later.





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  • 2 weeks later...

Continuing on with the cab;-

The holes for the cab side wind deflectors are drilled 3.5mm and broached to take 3.7mm pins to imitate bolt heads, all other holes in the cab parts are also broached to this size. The deflectors will be soldered on at a later stage as they will be in the way while clamping and soldering the cab structure.


The inner cab part is folded up to form the splasher tops and backs.


The cab sides are jigged up for folding the roof curve.


Once in the correct position the top portion is folded with a flat piece of metal up to about 45 Deg.


Checking for fit on the cab front, the tape is there to hold the part in position just in case it needs to be re-jigged and folded a bit more. This is fine, a bit of pressure on the roof portion will push it home when soldering.


Both sides done.


The front cab overlay forms the front of the wheel splashers so I decided to get rough folds in it to make the soldering job a bit easier.


After setting the correct location the part was clamped, a 2mm bar to create the turn out was held on top, then a 12mm bar was slid in under,  and the part was folded over to give the rough shape.



The inner cab and overlay parts are prepared to sweat solder them together. A light coat of solder was applied as these parts form a rebate on the edges for the cab sides and roof to sit into- to much solder would fill the rebate!


This was the clamping arrangement after lining up the parts through some of the 3.7mm holes with pins, as the soldering progresses the clamps are removed while applying pressure with a stick to ensure the parts fit snug together.


Sides tack soldered on and all is checked with a square.


Then the roof rib is soldered in and the whole assembly is soldered up.



The wheel splasher fronts are adjusted slightly and held down with a stick while soldering to the cab side that forms the splasher sides. The pre-folding was pretty close but a lot of pressure was needed to get a good fit.


Testing on the footplate..... it fits!




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Boiler & Belpaire Firebox;-

Clean up of the parts, drilling holes for ejector piping in boiler and to mark the location of the firebox stay covers- Merlin has 3 on both sides.


After measuring up the firebox plate I found the half etch relieving lines for the folds were bang on! So I set about folding the lower curves first using 4mm and 6mm here.



Top curves were done with the 6mm bar.





Checking the fit on the front plate and the back template- the template is only for construction.



I started the rolling of the boiler on a 16mm bar in the bench vice, taping the sheet down square on the bar first.


Both ends done.


Then rolled the sheet to size.


This was far enough.


Binding with rusty binding wire- solder wont take to rust, so I keep roll of rusty wire for this! The clamps held the join in position while tightening the wire. The soldering is done on the inside of the join with the part held in the fingers to put pressure on the tube to ensure a good join- using wood between the part and the fingers.


Soldered up on the inside.



A bit of fettling is required to fit the firebox square to the cab.



Next will be the stay covers onto the firebox and I will assemble the smokebox parts before soldering all up- just in case some adjustments are required.


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All the parts removed from fret and cleaned up.


Main structure folded and ready to solder the captive nut on- this is the body to chassis mounting nut. The structure is partly folded as a stretcher part slots in after the nut is soldered, the stretcher has tabs front n back hence 'partly folded'.


Nut soldered and stretcher in I soldered the sides first, if one was to force the front & back closed to solder first the base bows and the smokebox will not sit level on the footplate- so sides first.


Then front and back, ensuring they are perpendicular to the base.



The reverse curves on the wrapper are bent over a 6mm rod to the rough shape.


The wrapper was then curved over a 16mm rod and then bolted to the main structure with 10BA bolts- the bolts pull the wrapper in at the bottom, the shape can be assessed while doing this and adjustments can be made by removing the bolts- I like this idea.


The base of the smokebox front needs a 2mm dia curve outwards which slots into a half etched recess in the running plate, this was a bit tricky getting things to line up- the curve starts just under the holes for the front grab rail.


Just a test fit before I start soldering.


The unit will be soldered on the inside through the holes front and back, the front cover will go on at the same time while soldering on the inside so the front has solder applied to the back face in readiness.


Some pushing and clamping was required to get the return curves up tight to the structure, working on short sections at a time, moving to the other end alternately until the unit was soldered up- reward! = burnt fingers!



Needs a bit of a cleanup and maybe a few soldering touch ups at front bottom sides!


Joy rigged on the running plate to assess fit.



A bit of fettling to the firebox junction with the cab is required and then I reckon the smokebox, boiler and firebox can be soldered into one unit!!





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  • 2 weeks later...

After a lot of fettling and trial fitting on the firebox cab end, then the boiler, smokebox and firebox were ready to be soldered together;-

First soldered in was the front plate to the fire box, soldered on the inside and then the construction piece at the base was removed.



The smokebox was fitted to the running plate with a 10ba screw then the boiler fitted by tabs into the back of the firebox, and then the firebox & cab. The whole assembly was then clamped from back to front and adjusted to get it all to line up square- some paper shims were used between the firebox and cab join on the right side to aid alignment.



The join at boiler and firebox has to be soldered on the outside, tack soldered first and then soldered throughout. The other end is soldered through the smokebox- soldering the tabs on the inside.


After the soldering was complete its now time to check fit the parts to the chassis and over the motor!! - after removing the fret in the middle of the running plate.


The running plate rear nut fixing is a good 1.5mm out of line with the captive screw in the chassis! So the plate does not sit down properly at the rear- this will need a bit of attention!!


The firebox slides over the motor OK but a bit of jiggery-poke is required to thread it over the flywheel as the firebox front plate is a tight squeeze on the weight- though it fits.




The boiler assembly needs a bit of a clean up and then the body detailing bits start.

Very satisfying to see it at this stage.......


Edited by murrayec
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1 minute ago, Galteemore said:

Brilliant Eoin. Reminds me of when 85 was being rebuilt at Harland and Wolff 40 years ago.,..

Yes, I have that kind of feeling to.

When looking for photos on line of 85 I found a lot of H&W restoration photos to.....


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