Stour Valley Dream - Evolution of a cassette design
Entry posted by Fen End Pit
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So, this one is a bit detailed and has a few ramblings.... Sorry
Some modellers are very clever, they come out with perfectly formed designs, work tirelessly to bring them to fruition and produce superb pieces of work first time. Some practice 'slow modelling', being superbly organized, only getting out the tools and materials needed to for the job in hand and breathing deeply while wielding their scalpels. Much respect it due to these folks, if you feel you fit into these categories then good for you. I'm afraid that I have neither the skill nor the patience.
I tend to build things the best I can at the time and have no qualms about 'going back and having another go'. One of the great benefit of the automated tools I have at my disposal is that a lot of the grunt work of redoing something can be done in CAD and on the lasercutter/3D printer. Sometimes I waste a bit of raw material but if can make something better in increments then I'm happy. Perhaps I should coin this 'Agile' modelling after the current trend in software development. I guess I work on the principle that sometimes it is better to build something, even if it turns out to be wrong or could be made better, than not to make anything - 'slow modelling' can risk becoming 'no modelling' if all you ever do is sit in your armchair. Even if all I do is learn how to make a better one then I feel that is a gain.
Anyway to the case in hand.
I've had a few iterations now of cassette design for my fiddleyard which I thought I'd share.
The original design had two low ply sides and a curved handle. The end has a tongue and a slot which aligns the cassette.
I realized that these would fit nicely in the 3 larger drawers of my Ikea drawer unit but not the 3 slightly shorter drawers, the handle over the top of the cassette was unnecessarily high and could be cut down a lot without impacting the strength of the unit. I also found that if I flatten out the top of the handle it would be possible to stack one cassette on top of another and they wouldn't slip off which could aid handling and storage.
Both these designs though had a common flaw, the sides of the cassette, even though they were only 25mm high, made getting stock onto the rails very difficult if not impossible. As you can see there is no way to get your fingers into the align wheels with the rail particularly with bogie stock.
So we come to the third iteration. By extending the sides up to the top of the handle and cutting large holes in the side the unit keeps its strength, still stacks, if anything better than before and you can get the sides of bogies.
A pile of cassettes can be made without the risk of them slipping off each other.
The other change I made was on the arrangement for current collection on each cassette. On the original version I had made a sort of 'side scraper' design with a phosphor-bronze wiper mounted to engage with the side of the adjacent cassette, this worked from an electrical point of few but I found it could introduce a slight sideways force on the cassette. The original arrangement looked like this.
As the cassettes are held in compression by the sliding end clamps I realized that this was unnecessarily complicated and that just a sprung upstand on end of the cassette would press against an identical upstand on the next cassette. These are very much simpler to make and easy to clean and tweak to give a good connection.
So in the end I got the cassettes converted to this new arrangement and built another four long and two short cassettes. All this cassette work obviously lead to running a few trains around and it was very satisfying get some stock out of the drawers again. The Class 15 made an appearance with a very mixed bag on a parcels train.
There is a Mk1 full brake, a ex-LMS full brake, a GUV, a Gresley full brake and a couple of CCTs on the rear.
The station building now has the roof on, I was pleased with the way the various pieces went together, trying to draw up the hipped sections strained the brain a little! I've also had a first short at the toilet block.
So I hope you liked this longer than usual entry and please enjoy you modelling, at whatever speed or style works for you.
David
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15
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