Nick Dunhill's Workbench - Pair of EM2s

Nick Dunhill

Western Thunderer
Not a lot to report this week. I built some mounting structures for the bogies and tested one of the locos on DCC. It ran well. The job was held up slightly as printy parts from Mick Davies were held up in the postal worker's strike (which I support and so I seem to have become part of an Anti-Growth Coalition :)))

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richard carr

Western Thunderer
Hi Nick

The E2 is looking good, but I did notice that the delrin chain is very visible at the bottom of the bogie.
The joking aside earlier in the thread, you really do need a chain tensioner, I use a piece of brass 3mm in diameter, with a 6mm diameter base.
It gets superglued to the side of the chassis after the chain has been fitted, in a position to take up the slack, you don't want the chain super tight,, just tight enough so it doesn't sag into view. I would add a picture of one of mine but I'm away on a business trip at the moment.

Richard
 

Nick Dunhill

Western Thunderer
Thanks Richard. I had noticed the sagging chain and wondered how to disguise it, but a lot of the problem is due to the thin open nature of the side frames. There's a massive inner chassis there too that's not on the real thing either!

As an aside the chains are marginally different overall lengths. Some of the 4 chains sag more than others. Depending on which way the loco is running the top or bottom run is under tension. If slack at the top the chain rubs on the centre axle. The system works well but is a bit unsatisfactory in appearance. I'm not going to do anything until all the brake rigging is installed, that may hide the chain a bit more. I have always thought there was a need for a tensioner, but see above. The tensioner in other applications is always on the slack run of the chain, and these chains run in both directions. Can't help thinking a tensioner might inhibit the operation when on the tight run of chain? I would appreciate your thoughts.
 

Paul Tomlinson

Western Thunderer
If there's room, you could introduce a reamed-out 8T sprocket as a jockey wheel.
Each link adds about 1.5mm to the wheelbase. I've decided to stretch the wheelbase on mine by 0.5mm to remove the slack.

A jig from Poppy's helped with the measuring.

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simond

Western Thunderer
forgive me if I missed it but I think only outer axles are driven, so the chain loops around but does not engage the centre axle.

Why not put two sprockets on the middle axle and drive that too? The loops of chain would be much shorter and therefore sag far less. And arguably you get more traction.

though I don’t think an idler wheel would cause any issues, it would be more complicated to install.
 

Renovater

Western Thunderer
I use roller bearings to lift the chain up, the diameter of the bearing depends on how much i want to lift it up by. You need the space though or a place to hide it.
 

richard carr

Western Thunderer
Nick

My experience has been that the chain system works fine even if there is considerable slack. It will not work if you get it too tight, I have been there and got the T shirt. Yours runs fine it is just that the chain is visible.
The delrin plastic is designed to be very low friction so it should be fine running over a steel axle, or a brass tensioner, I haven't had any problems with wear and some of my locos have done a fair amount of running now. The main reason I use the chain "tensioner" is that you can make the chain a link longer than it needs to be which means it is easy to join when you are building and testing the loco then you can position the tensioner to stop the chain drooping into view when it is finished. I just super glue mine in place, it is then very easy to remove it if you need to at some point in the future.

Richard
 

Nick Dunhill

Western Thunderer
Final furlong this week. All my 3D printed parts turned up, well almost, and it was on with the bogie mods and details

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Mick printed some end beams that fitted perfectly over my modified side frames. I added the brake cylinders and some air pipes.

The next bit of the job was to fit up all the brake shoes and rigging. Mick made some amazing prints for the shoes and hangers. I scratchbuilt some spring planks with their supports for the rigging. I decided that all the brake system should be soldered/glued to these supports. I scratched my head for a while and made a simple jig to support all the cross beams and allow the brass pull rods to be fitted up.

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I think that the brake rigging solves the dangly Delrin chain issue....luckily!

So here it is, almost finished. I need some air tanks which hang on the inner ends of the bogies and a large auxilliary air tank (or maybe it's a water tank) between the battery boxes. They've been printed and are in the post as I type. it'll be finished by monday lunch.

The total time to build both locos was around 450 hours. This was quite a lot longer than I had imagined, it takes me about the same time to build (say) an F7 large tender loco. The pantographs took 3 weeks to make (I work 40 hr weeks) as did the bogies.

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I took quite a lot of pictures of one of the spare EM2 bogies here; EM2 bogie
and more pics of the model here; nick dunhill
 

Nick Dunhill

Western Thunderer
Hello Mr Star. Of course I've been staring at my photos of EM2s for a while now and I think added later in NSR ownership, but pics inconclusive!

Nick
 
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