MOK Standard 4 2-6-0 in S7

[SteveB]

I’m sorry to have confused everyone. That was not my intention. I’m just comparing the distance between the outside of the frames and the inside of the wheel. Where Ian put his fingers when he was 13 years old. I’m comparing my S7 version with what it would have been if I built it straight out of the box as FS O gauge.

The reason why I’ve been quoting the 28mm ‘between frame dimension’, is because that’s the thing I’ve altered. The frame thickness is as supplied in the kit and has not changed. They’re actually very close to being exact to scale.

To reiterate, it’s no one’s fault other than my own. I just wish I had increased the distance between the frames more than I did. Just another lesson learnt the hard way.

Regards

Steve

 

[SteveB]

Moving on..... The cab is an absolute masterpiece of design. Its gone together quite well and I’m generally pleased with it but there are a couple of areas that I could have done better. The bit I found the hardest was the ‘overlay’. This consists of a half etched item covering the roof and both sides. It took be ages to get the various curves and folds reasonably close. The kit provides two overlays. One is exact to size and one is slightly bigger to allow for any small errors in the frames construction.

I chose the larger one but I should have used the other one. I spent so much time on it though; I couldn’t face doing it again. The problem is the amount the overlay overlaps the front. Its so difficult to file it down without damaging the rivet detail. It’ll do though.


I need a bit of help please. The tender is a type BR2 and I know the loco I’m building had the canvas screen fitted. I’ve found a useful picture of the side but I have no idea how the upper frame attached to the roof, or indeed what it looked like from the tender. From the vertical line of rivets, it had a profile at 90 deg to the outside, but was this just an angle piece or something more? Any help would be greatly appreciated. I’ve indicated on the picture below the area of interest.


I’ve had an initial attempt at assembling it all to the frames, so far so good. There's a bit of work to do, but it’s not far off. I’m fast approaching the bit I’ve been dreading which is altering the whitemetal firebox.



Regards

Steve

 

[Scale7JB]

I built an L1 a while back in S7, and if I'm honest I built the frames far too wide, but didn't really realise until it was too late to strip it down again. I don't have a test track at home.

I got lucky though, even though the wheels scrape the frames, it doesn't seem to short. I got lucky.

My point is that, I'd rather have frames that are that little bit too narrow now rather than too wide.

JB.

 

[SteveB]

My point is that, I'd rather have frames that are that little bit too narrow now rather than too wide.

Hi JB

That's a very valid point. I would hate any model I built to be confined to the display shelf because it won't go round curves. Thanks for your comment.

Regards

Steve

 

[Scale7JB]

Luckily I got away with it, and it will happily go round an 8ft curve which im more than happy with, but yes, every cloud..

JB.

 

[SteveB]

What was I worrying about? Altering the firebox was much, much easier than I was expecting. The whitemetal casting itself was quite clean and the detail quite sharp but it was somewhat distorted. I tried, as best I could, to sort out the distortion before starting the alterations. I had previously trialled the firebox assembly on the chassis along with the cab, boiler, smokebox and running boards to make sure there weren’t any nasty surprises waiting for me.

I cut a slit either side of the throatplate.


Then I temporarily fitted the boiler to add a bit of strength to the ring, and then gently prized out either until there was about a 1.5mm gap.


Next job was to solder on the two etched extensions.


The extensions were clamped to the chassis and the firebox was held in place with a high tech elastic band.


I filled the gap with 145 deg solder with the iron set to around 350 deg. Plenty of solder on the iron, and then just dab it on. Keep repeating it until you’ve built up sufficient material. It looked a mess to start with but then I used the iron (still at 350) like a hot trowel to spread and smooth it out. Then, I just filed it down to blend in with the rest of the box.

Incidentally, a good tip to stop files becoming clogged with soft metals, is to rub some chalk into the teeth. I didn’t have any available so I used talc. It seemed to work better than chalk. It doesn’t solve the problem totally but it does make a significant difference.


There’s a small gap between the cab and the firebox, so I intend to do a half etched overlay to go between the two and then add a thin nickel silver strip so it looks like a retaining angle. The kit includes replacement etches for firebox bands and safety valve base, so that saves me having those to do. I’ve got an etch to redo for my 8F tender, so I’ll just include the new overlay with that.

Regards

Steve

 

[john lewsey]

Very nice

 

[Eastsidepilot]

I've standardised on a 30 mm o/a frame dimension assuming 0.6 mm frame dim. giving a frame stretcher dim. of 28.8 mm when scratch building S7 loco frames, but this can vary as the sheet metal, although listed as 0.6 mm can come in at 0.56 mm.

Col.

 

[SteveB]

I've standardised on a 30 mm o/a frame dimension

Hi Col

That's exactly what I'm going to do next time. Its a steep learning curve for me. I shouldn't be too down heartened though. My 8F did manage to go round the inside track of the S7 test track at Bristol and I think that's a 7' radius.

Regards

Steve

 

[farnetti]

Hi Steve, afraid I can't help with canvas screen frame but another member of our S7 group has the same sort of issue with a Britannia. What material were you thinking of using for the canvas?

My MMP BG is supplied with a model aeroplane covering which is trapped between etches for the corridor connections which works beautifully. This material would not work for canvas at this scale but perhaps worth looking at other thinner coverings from other modelling areas.

Was most impressed with your 8F at Bristol in January.

Ken

 

[SteveB]

What material were you thinking of using for the canvas?

Hi Ken

I haven't even thought about the canvas yet. How about thin nitrile sheet? You can get as thin as 0.010" perhaps thinner, or maybe material from a balloon or even some knicker elastic (non frilly type preferably). No idea really.

Thanks for you compliment about the 8F. I must get around to getting it finished.

Regards

Steve

 

[SteveB]

Thanks for posting - always interested to see developments like this. I've always considered bronze was harder and more brittle than brass, so I'd be interested to see how you get on with tapping the various attachment points. Personally I'd have chosen brass for being easier to tap and solder.

I’ve made a small amount of progress with the replacement castings. The bronze solders perfectly, but it is a bit ‘sticky’ when threading compared to brass. I managed to thread the Brake Brackets 14BA without breaking a tap though. I think Adrian was right, next time I’ll be specifying brass.

So, Adrian, if you ever get around to finishing your MOK Std 4 tank, if you’re interested, I can let you have the 3D files for the replacement Brake Brackets.

Steve,

I'm wondering if your castings may have been buffed before rumbling? The coarse finish inside the cylinders (not that it matters) is a puzzle. One imagines that the manufacturing process involved would provide the same finish inside as out.

My experience with 'shrinkage' at Shapeways is as they advise - no allowance is necessary. At first I added 3% - and received oversized castings. I continued cautiously, gradually reducing the percentage added for subsequent items. Most purchases are spoked wheel centres and now with no allowance added they arrive within a thou or three of file size (in the size region of 1 inch dia). Two batches were one thou over and all are remarkably concentric - which I wasn't getting with waxes popped out of vulcanised moulds by workers on piece rates.

(An allowance for shrinkage is necessary when the Shapeways item is to be used as a pattern for 'silicon tooling'. I don't take this route as shrinkage can be as high as 8% or more, and variable when casting businesses chop and change between brands of RTV without informing the customer.)

-Brian

Closer inspection of the castings has shown that Shapeways have done a bit of mechanical cleaning of the castings before the rumbling process. I can’t tell if this was done on the wax or the actual casting, I suspect the former, but this may help to explain why some dimensions of the castings are slightly undersize compared to Brian’s experiences.

After successfully fitting the Injector and Brake Brackets I trialled the Cylinders, mainly to make sure that the ‘overlays’ of the front section were free to be removed with the Cylinders in place.





There’s quite a bit of detail still to add to the Cylinders, but before I get too carried away, I wanted to make sure that the Motion & Slidebar Brackets were okay.





I had made a mistake with the positioning of the pilot hole indents in the rear casting but other than that, it all seems to have gone together as it should. My conclusion, so far, is that its not worth substituting replacement castings for the Cylinders themselves. Modifying the originals would have been perfectly okay.

Regards

Steve

 

[SteveB]

Progress is a bit slow at the moment, but I am getting there. I’ve come across a couple of problems with the new castings. The centreline of the left hand weighshaft bracket is about 0.5mm too far forward, easily sorted by just slotting the fixing holes in the chassis and moving the whole assembly back by 0.5mm. The right hand side was fine, but that’s a much simpler casting.

The second issue is that the centreline of the cylinders is about 0.2mm too close to the chassis frames. Again easily sorted with some packing shims. It took me a while to work out why I was struggling to get the valve gear to align.

I think both issues have been caused (or at least made worse) by taking measurements off existing castings rather than referring to original drawings. I should be able to alter the 3D files so anyone else using them should be okay.

The kit provides all the items for the lubricator drive to work from the expansion link. You can just about make some of it out in the photos. The various bits are really small and unfortunately one of the smallest items decided to ‘ping’ out of my tweezers. I searched for a while, but I don’t think I stand much chance of finding it. Hopefully Dave Sharp can sell me another one.





Regards

Steve

 

[SteveB]

I’ve finished the Lubricator Drive last night. If you saw my earlier post then you’ll remember that one of the little connecting rods had been lost. I didn’t manage to get hold of Dave at MOK yesterday, but I did find a similar connecting rod, albeit twice as long as needed. I just cut a piece out the middle and silver soldered it up. It’s the horizontal connecting rod, linked to the ratchet arm of the lubricator in the assembly on the left in the photo.

The mechanism does work, but the amount of movement in the Lubricator Ratchet Drive is only just about noticeable. No one will ever notice it when the loco’s moving, but I know it’s there! It has been quite a satisfying exercise and it would be a shame not to incorporate it after MOK have gone to all the trouble of providing it.

It’s given me a bit of insight into what 4mm loco building must be like as the components are, I guess, roughly similar to 4mm sized valve gear. I think I’ll stick to 7mm!


Regards

Steve

 

[Len Cattley]

Believe me Steve it's nothing like 4mm valve gear

Len

 

[SteveB]

The sub-assemblies for the valve gear and cylinders are done. The cylinders have an awful lot of parts on them and it wasn’t easy soldering very thin small overlays on big thick heat sinks of the cylinders. I almost reverted to gluing them on!

If you look closely at one of the snifting valves, then you’ll see its somewhat distorted. I forgot to change the setting on my resistance soldering unit, so I almost melted it! Dave Sharp is thankfully sending me a replacement.

Much of the valve gear is attached using 14BA steel screws. I’m not sure if this is a good idea or not. The loco is unlikely to get a huge amount of use but I wonder what the wear characteristics will be like? It’ll hopefully outlast me.


Next job will be to do the brake gear. This’ll need some modification to fit on the S7 chassis but it should be pretty straight forward.

Regards

Steve

 

[daifly]

That really looks like it could DO something! Like what it was designed for? Super work.
Dave

 

[SteveB]

Where does time go? It’s been a month since my last post. I haven’t done any posts recently primarily because most of the build is fairly standard and not related to the S7 conversion. The only alteration, not supplied with the MOK kit, has been a special etch to go between the firebox and the front of the cab. I’m not sure it was worth it as you can hardly see it with all the pipes in the way.

The smokebox, boiler barrel, firebox and cab assembly all went together really well. I had a small amount of filing to do on the firebox, but it really only took a few minutes. Testimony to the kit design more than anything else.

The holes for the safety valves will be so I can fit one of my steam units. I’m working on the backhead details at the moment and then it’ll be back on to the chassis. I hope to fit a servo for the forward/reverse movement. I’ll make sure I provide some photos of that because its relatively straight forward to do. I’m surprised that more DCC controlled locos don’t feature it. It doesn’t cost a lot and only adds a small amount to the kit construction time.

I’ve been watching Mickoos and Dikitrikis construction posts. I wish I could keep mine as clean. I’ve just bought a cheap soda blasting gun. Has anyone ever tried this for cleaning kits?

Regards

Steve

 

[Yorkshire Dave]

Nice pipework around the turret and injectors.

 

[Scale7JB]

Very nice!

JB.