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A SR Z Class loco - Nick Dunhill's Workbench

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The brief is to build a SR Z Class from a DMR Kit with the inside cylinder and some sensible upgrades.  I have heard good things about the kit so I am going to enjoy the build.



The box had a set of Laurie Griffin cast coupling and connecting rods within.  I'm not a fan, normally, of pre-made rods (Premier, LGM etc.,) preferring to laminate etches, they just need some patient filing and polishing.  Also I like to be in control of the rod and axle centres.  I looked at the etchings for the coupling rods and thought that they were a bit two-dimensional, so I decided in retrospect to use the cast ones.  They needed a bit of fettling but came up nicely.






The frames are a pretty good representation of the real loco, well below the chassis at least.  The bits of the chassis on view above the footplate are designed to be planted on the footplate, I'll deal with those bits later.  The frame stays provided are very functional, but if you're building the inside motion and cylinder they're all in the wrong place except the rearmost.  Luckily I have a GA so I just made what was on the real thing.















Anthony Garton of Poppy's Woodtech fame sent me one of his Loco Builder's Boxes to try out as a chassis building jig.  Below is a short video of how I put the axle boxes in the chassis using the box.  I suppose I should note this in the Register of Member's Interests (unlike Hancock and the rest,) although I only got a free box for making the video, no royalties.  The box does make the process much easier though.



Thanks to Tito Puente





One thing that won't make the job easier was the ridiculous way the boiler etch had been pre-rolled.  It would have certainly been better left flat.






I'll have to scratchbuild a boiler now.  Thankfully the etch for the smokebox was salvegable.



I also made a start scratchbuilding the outside cylinders.  As I'd already gone a bit far off the script the etches provided for the cylinders didn't fit.  They weren't quite right anyway.





More pics here:  https://www.flickr.com/photos/[email protected]/with/51257753329/

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So this week I was mainly finishing my BG Armstrong Convertibles, but did get something done on the Zs.  I didn't like the look of the kit etches for the cylinders, and also they weren't going to fit as I'd made an inside cylinder.  As you can see above I cut out parts for new cylinders.  I made a test cylinder rear, using the GA as a guide and the cast DMR cylinder covers didn't fit.  I assumed I'd cocked up some measurements so made another with the same result.  I measured the diameter of the cylinder head covers on the GA and they came out at 12.5 mm diam or thereabouts, the cast kit items were 14 mm diam.  So I reduced them in diameter and all was well.






These were soldered to the chassis and a motion bracket/stay for the inside cylinder fabricated.






So I have asked Mr. Griffin if he'll sell me some eccentric rods and a big end crank and were good to make the inside and outside motion.

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Posted (edited)

I have moved so far off piste with this build that I realised I would have to fabricate much of it myself.  With this in mind I started to compare the drawings I have with the motion parts supplied by DMR.  The main motion and valve rod brackets supplied are a very simplified version of the real thing.  The expansion link is after the style of Gresley, a 3 bar arrangement with a bifurcated radius rod gripping the centre section.  The kit isnt like this, and also the parts for the valve rod swing link don't really fulfil the correct movement.  So it was out with the piercing saw!  I made all 4 brackets and began laminating the etches supplied, modifying them as I went along.




I began to get a bit exasperated at this point as the two halves of many of the rods did not match, and the hole centres didn't coincide.  I had to solder them together and make good as best I could.  The etches that fold up into the expansion link were particularly bad.  They weren't the same length, the lightening holes were all over the place, the mounting holes weren't in the same plane and they were not symmetrical.  I modified them, but in retrospect it would have been quicker to make new ones.








The kit seems to have all the hallmarks of a 4 mm blow up.  The simplified valve gear and brackets are  probably ok in OO gauge but doesn't really cut it in 7 mm scale.  Also all the errors will be exaggerated when enlarged.  Anyway I managed to produce something that looks and functions as real loco.








To fit up the motion I needed to fit up the slide bars and crossheads.  I had seen on another thread how the etched slide bars provided don't fit the crossheads without a big reduction in size.  I reached for some 1.6 mm square bar and gently eased the insides of the slidebar to accept it without loads of slop.  I then checked some measurements on the GA and saw that the real slide bars are rectangular and not square.  The crosshead also would put the slidebar far too high in the cylinder, ie it's far too tall.  More parts to weigh in!  I saw that Laurie Griffin has some alternatives in his range that look correct so I placed an order and moved on to the footplate while they turned up.


The footplate etch is a one piece affair with relief strips for forming the folds and curves.  I began forming it and offering it up to the etched valance.  I wasn't surprised to find that they didn't match!  I fractured the footplate etch into 3 sections so I could tackle them separately.  Also at this stage I offered the valance etch up to the chassis.  If the completed footplate was going to land on top of the chassis at the rear and front, and hopefully in the middle, then the valance should be the same shape as the top of the chassis.  It wasn't, by a mile!  And the completed footplate would end up being too long by about 5 mm.  This would also mean that the buffer beams would overhang the ends of the chassis by about 2.5 mm at each end.  Also the completed footplate would need to sit on a beer mat placed above the cylinders to make it level.




It took a day and a half to make a new footplate but it does now fit the chassis perfectly, and now meets the top of the chassis frames without the usual unsightly gap.  I also made the bits of the chassis that stick up above the footplate.  The valence is the original etch cut twice to fit.  The lower platform, under the bunker, is as supplied as well.




This pic shows all the cut out and formed parts taped to the chassis prior to tacking together.








I'm glad all kits aren't as ill fitting as this, but I have to say that I have enjoyed all the fabrication.

Edited by nickd
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Posted (edited)

First job of last week was to modify the buffers so they became self contained.  This would allow me to fit the gusset plates between the buffer beams and frames, the rear ones are quite visible.  The buffers were easy to modify.  I threaded the stem on the heads all the way along and cut them shorter.  The boss on the rear of the stocks was cut back to match the thickness of the buffer beams and the hole in the rear of the stocks were partially drilled to allow a 12 BA nut to pass within.




The corners of the stocks were drilled and fake fastners added.






You can see that I fitted the destinctive SR 3 link screw couplers, and in actual fact the loco I am modelling has normal 3 link ones!




I ditched the cast crossheads and etched slide bars supplied in the kit as they were just wrong in every way possible (slide bars square and not rectangular, centres wrong, etc etc) but luckily Laurie Griffin sell some which are much better and fit nicely.  I married them to the cylinder rear covers I had previously modified.  The motion was then quite easy to fit up.  A fair bit of bushing and shimming was needed to make it all work smoothly.  I also had to recess the crankpin nut of the front wheel into the coupling rod boss.  I thinned the boss to the necessary thickness and drilled part way into the journal to allow it to contain the nut.






The eccentric rods supplied in the kit are too long (or more to the point are too long if you've built prototypically and not as designed) so I shortened them as required.



So here we are at the close of play on friday.  Most of what you see has been scratchbuilt or heavily modified. 









Inside motion next, but first a short break on the N Yorks coast!  Happy days.

Edited by nickd
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  • 2 weeks later...
Posted (edited)

After a lovely few days in the sunshine at Robin Hood's Bay it's back to the bench.  First up was the connecting rod for the middle cylinder.  I had an old con rod casting from LGM with a marine style big end.  I modified that and mated it up with a rod made from the etches for the outside cylinder connecting rod, suitably shortened.  Laurie Griffin sent me a crank casting that was pretty much identical to the one in the drawing.




All the rest of the rods are scratchbuilt from scrap nickel siver strip.  The expansion link parts were made alongside the ones for the outside motion and I scarfed some Laurie Griffin eccentric straps onto the eccentric rods.  I used my own eccentric sheaves.






Next I had to make the 2 motion brackets, the drop links and a valve chest cover.  Again all are made from scrap etch.




The whole lot was assembled into the chassis and the crank and sheaves soldered to the axle.




The cylinder head, slide bar and crosshead are modified Laurie Griffin castings.  Here it is running;



I then added the remaining frame stay, cut from scrap brass.






At close of play yesterday afternoon I had nearly installed the weigh shaft and lifting links, but not quite.  You can see that I made the steam reversing cylinders too.




You can see that I broke one of the lifting arms late on in the afternoon and called it a wrap at that point!  


There are more pictures here; https://www.flickr.com/photos/[email protected]/  and if anyone knows what the mechanical lubricators provide a feed for on a Z I'd be grateful to know.

Edited by nickd
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Looking at photos of the class you can see the lubrication pipes for the cylinders coming from the cab, suggesting hydrostatic lubricator (s) there . On that basis the mechanical would be for the axleboxes. 

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That's what I thought.  The pipe and rod (drawn before mech lube fitted) shows drip feed pots supplying the horn cheeks and axleboxes but I'd bet the axleboxes became pressure feed.

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17 hours ago, nickd said:

That's what I thought.  The pipe and rod (drawn before mech lube fitted) shows drip feed pots supplying the horn cheeks and axleboxes but I'd bet the axleboxes became pressure feed.

There could still have been some drip feed, look at Stanier locos which have both as an example,

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A bit more progress this week, I finished off the lifting links for the motion.  I also fettled the LGM Silvertown mechanical lubricator and added some feed pipes.  I extended the drive lever so it would reach the outer eccentric rod (union link?) and obtain it's movement.








Not surprisingly the guard iron etches were waaay too short, so I made more.




I also made the brake hanger/brackets/shoes and modified the spreader tie rods. and a few other parts.  Because of the 4 mm origins of this kit the brake parts are very basic or non existant, so an upgrade is needed.




I'll fit up the brake system next but after my holiday!



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  • 3 weeks later...

I have now built up the brake system from a few of the kit brake hanger and block etches (as before the brake hangers are hand drawn and are all different sizes!) and a lot of scratchbuilding and repurposing of castings left over from other projects.




There's a Heath-Robinson style handbrake operating arrangement on the brake shaft, and all of the rigging is detachable for ease of assembly and painting etc.






Mick Davies printed me some axlebox/horn plates/keeper plates/springs and hangers.  They're just cosmetic and designed to be glued around the brass horn cheeks after painting.  The dummy axleboxes are just glued onto the brass structural bearings.  They just add a nice touch of realism.  I made a start fitting them up.




More next week.

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Posted (edited)

The fun continues.  I added the rest of the printed horn guides etc last week.  They are cosmetic items but really give the model a lift, thanks to Mick Davies.






Next up was the cylinder drain cocks.  They're steam controlled, and once I had seen the pipe-and-rod view of all the pipework I decided to make it all, I just couldn't resist!






Next I aimed my ERSA at the front buffer beam.  I had to laugh at the etches for the lamp irons.  Remember they're hand drawn, all different widths and sizes!




I also made the sand pipes and pick ups.  More of those later.....


More pics here https://www.flickr.com/photos/[email protected]/with/51407429142/

Edited by nickd
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This week I have completed the build from (and including) the footplate down.  I added all the pipework for the vacuum and steam heat buffer connections.




I'll have to revisit the vacuum brake upstand later when the bunker is installed and make it fit.  I added all the angle that is unsually on a loco between the tops of the frames and the underside of the footplate.


Attention then moved to the upperworks.  The etch for the cab/tank/bunker side actually fits.  According to the drawing I have the bunker tapers in from about half way along.  The kit is designed such that the bunker sides taper in fron the cab rear, but this isn't the case.  I scored the back of the etch in the appropriate place to form a subtle bend in the bunker part way along.  This was achieved by soldering a thick strip of waste etch to the bunker and running my slitting disc along it.


You can see the fold lines I produced here.




A closer look at the drawing revealed that the footplate tapers in towards the rear from a point in front of the cab opening.  The kit is designed (and I built it so) to taper in from the rear step in the footplate.  This will have to be altered but I decided to do it when the cab, tanks and bunker are installed to support the footplate when I remove the valence.


I spent the rest of the week detailing the cab sides and front and rear.  I got very lucky and found some spectacle beading from a previous job that was exactly the same as the etched ones supplied.  I wasn't so lucky with the rectangular side windows so made some beading using the etched ones supplied.








Now I have brass window frames for the inside as well as the outside of the cab.


The rear window frames had very crude protection bars etched in them.  I didn't like that so cut them out and drilled the cab rear for the 12 vertical bars over each rear window.  It took a while to fashon them from 0.5 mm rod!


The curve in the sides of the cab (that becomes the lower roof) was formed to match the front and rear.  This was a tricky job, and to prevent the rest of the etch becoming distorted I soldered a wide strip of waste etch across the cab opening.  The etch has some fold lines to help you along, but in reality you end up with a threepenny-bit shaped curve.  I formed the curve, smoothed it to remove the folds and then formed the rivets.  The plate join for the roof panel was also scored.


I added the 'reveals' for the cab doors, and the doors themselves (including hinges and latches,) and the upstands for the cab floor.  The upstands also serve to hold the side etches straight while attaching them to the footplate.  The beading round the cab openings were added.  This was a tricky job as the bead has to match the curve of the roof.




Here are all the sections test fitted.  I will cut out a new bunker rear on monday and solder it all up.  Hopefully I can finish all of this structure by the end of next week.



Edited by nickd
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More battles with the Z.  As I said in my above post, as designed the footplate shape at the rear of the model is just wrong.  The taper of the footplate starts in front of the cab opening, straightens along the cab opening then tapers again to the rear.  Also the bunker side is straight to a point about half way along it's length and then tapers to run parallel with the footplate edge. 


It took a few attempts to tack one tank/cab/bunker side in position.  I added the cab fronts and rear and the other side.  Please note if you're following this as an aid to build the kit, that the sides are hand drawn and so aren't exactly the same (ffs) so you'll need to make sure the LHS one is moved back a bit so that the cab rear is perpendicular to the sides, and the bunker sides end at an equal spacing to the rear of the footplate. This creates a gap where the footplate drops down inside the cab.  (Please learn how to use CAD if you're a kit designer.)




The footplate valence was cut off where the tapering begins, the footplate reshaped and the valence matched and soldered back in place.




To my complete shock the cab roof etch looks like it might fit.  It did however require a lot of reshaping and some creases dressing out.  (If manufacturers aren't capable of forming curves in etches correctly then please leave them flat, otherwise they become scrap, see boiler etch earlier in the thread.)


Next my attention turned to the cab interior.  There's nothing in the kit for all the structures in the cab (pile o'sh**e,) so all the internal 'boxes', handles and levers in the next two pics are scratchbuilt.






More hair pulling and profanities next week.

Edited by nickd
poor use of english
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  • 2 weeks later...

This week I finished the cab interior.  Planking went down and I was able to fit the 3D printed sand boxes and locker.  Thanks to Mick Davies for the prints, they saved my customer lots of money, it would have easily taken me a day to make those complex shapes in brass.




I then detailed the cab roof.  The roof etch in the kit did fit and I added the 2 roof vents and some handles and straps.




The rain strips are conveniently located and hide the join.


The next job I tackled was the bunker rear.  The etch in the kit is too narrow so I cut a new one and formed it to shape.  I realised at this point that the step-outs in the bunker sides don't match, one is higher than the other, also the top portion of one bunker end sticks out further than the other and isn't perpendicular to the footplate.  If you're building one of these I'd solder both cab/water tank/bunker etches together and make them match before soldering to the footplate.  I have quite a nice picture of a bunker rear and used it as a reference for the handrails, steps and lamp irons.




The etched beading for the bunker top did actually just fit!


The final job this week was building a backhead.  The cast whitemetal back plate was usable and the fittings were supplied by Laurie Griffin and my bit box.






I just need to make the reversing handle and the cab will be done, well nearly, as there are some protrusions into the cab from bits of the steam fountain on the rear of the firebox, but I'll need to build the boiler first......which is where we will go next week.

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