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Of garden sheds and statistics

Of garden sheds and statistics

27th October 2013

Right then, I've battened the hatches over the windows, guy-roped the tv aerial and covered the cars in bubble-wrap secured with 15 metres of gaffer tape. Do you think I'm ready for this hurricane?

At the beginning of the week I had one of those run-rounds that I delight in, seeing how many suppliers I can get to in one day. Amongst them were Mattersons to collect the first brake unit and drop off the other three, and another supplier to collect a set of valves and joints for Cheedale's second compressor. The weather was pretty rubbish both Monday and Tuesday, but a spot of sun on Wednesday tempted me out, and donning my best hivi jacket I walked the track from Bridge 35 at Matlock for about a mile north in search of my lost watch. And I have been forced to the conclusion that either it came to rest somewhere totally hidden, or, more likely, it landed up in plain sight and some passing walker has given it a new home. I wish them luck though – resetting both the analogue and digital timers as I would otherwise have been doing last night to put it back an hour is such a complex procedure that I could never achieve it without following, step-by-step, the written instructions. And I still have them to remember it by...

I've also ordered up a new set of windows for Pluto and a fan for Libby. Andrew popped in to Rowsley and to his consternation found that the first part of the exhaust he had fitted to Libby last weekend was now adrift. The turbo clamp bolt had snapped while his back was turned so I've ordered up a couple of those as well.

The end of ownership of Briddon Towers approaches (not soon enough as far as I am concerned) and one thing I had in mind was to drop the garden shed. When we first moved in there, in my youthful exuberance (I was youthful once, but after so many years I just can't remember what it was like) I created a large concrete base, 6” or so thick, and bought a 12 x 8ft garden shed to stand on it, bolted down with Rawlbolts. Of course this was not to keep the odd spade nor even the lawnmower. Much of the space was envisaged to store parts from the various narrow gauge diesel locos I owned. (Yes, didn't you realise it runs in the family? Andrew never fails to remind me that the lightest of his locos – Pluto or the Drewry – at 22tons weighs more than the 6 locos altogether that I once owned.) Anyway, I added a work bench and more especially shelving in one corner using Dexion bolted to the roof beams and another Rawlbolt at the bottom. Over the last few years the shed has shown increasing signs of decrepitude. The frame members that bolted through the Rawlbolts have largely rotted away. The walls at each end developed a peculiar lean, and the door – which I rebuilt about ten years ago and was thus probably the strongest bit of the structure – no longer fitted the doorway, which was now trapezoidal. When it came to listing the fixtures and fittings of house and grounds, I declared the Garden shed to be N/A.

So Andrew had a day off (he had escorted the 458 which was being taken from Wabtec to SWT at Wimbledon in the early hours of Tuesday morning and the translator carriages are part of “his” fleet) and I had a 6 cu yard skip booked. Between us we pulled out the front of the shed and the attached workbench but despite that, it remained standing. As I feared, the Dexion upright was all that had been stopping it collapsing, so we chiselled through the Rawlbolt, put a long rope around it and pulled it down (and away from next door's fence!). We'd filled the skip by noon so had them bring another 4 yarder and filled that too by 3pm. Andrew then set off to collect his partner and children and so I had Saturday free to get some paperwork and other things sorted.

Today though I popped down for the afternoon to Rowsley.

Over the last few weeks we have amassed some interesting readings about 14 901. With a line that is 3.75 miles in length, 5 round trips plus a bit of incidental mileage to and from shed should amass around 37-38 miles per day. But '901 has consistently been recording about 27-28. This was not entirely a shock – I had had my suspicions when we had run up and down the line at Gwili and again on test runs at Peak Rail. '901 works this out by means of special pcb in the cabinet which contains a “PIC” – a Programmable Interface Controller – which is a microprocessor device but on a reduced command set, and even then, probably packing more processing power than the Apollo lunar lander. But it can only count the pulses it sees from the unit we fitted on the side of the gearbox (where the old speedo drive was located) and that our calculations of how many pulses it would see per mile were made by counting the teeth in photographs of an open gearbox that Don Townsley had sent us years ago. The trouble is of course, that such photographs only show a section of the gears, and counting so many and guestimating just how many teeth there were on the entire gearwheel is bad enough, but even a tooth or two, multiplied up through the geartrain, could so easily make a substantial difference. And so it seems that our error was around 33%.

Changing the values in the PIC is straightforward if a little “old tech”. A special interface cable plugs on to the PCB and connects into the serial port of my old laptop. Trouble is, the software only runs on MS-DOS (yeah it's that old) and it took me a while to remember how to get through to the Setup and then into the specific menu of values. That done, I reduced the number of pulses per mile from around 25000 to 18000 and the number of pulses per second per mph from 7 down to 5. For although '901 does yet have working speedos, the electronics for them are there – it's just that Andrew didn't want my usual 90 deg movement/square cased speedo and demands a traditional round bezelled 240degree one. I have a movement – but a suitable case or two are still on a wants list.

Having packed away the laptop I was overcome with curiosity as to how much fuel 901 has used. I have been dipping the tank, using a stick marked off in inches and the loco parked at the same place, and the level has reduced progressively by about 3/4” per working day. So I did a quick measure of the tanks, checked the calculation twice to make sure my keying was OK, and the answer comes back at around 14 gallons, but as some of the measurements are a little rough I'll give myself a further margin and suggest 20. Which then provides the answer for a question I often get – how many miles does it do to the gallon? As a question it is of course flawed, as it treats the loco as if it were a car. Now if you take your car and hook it up to caravans about 6 times its own weight you too would not quite achieve the 'urban cycle' efficiency claimed by the manufacturers, but in round figures 20 gallons for 38 miles would lead me to an answer of 2mpg. But then half the trip it is being towed, idling, so I suppose if it were a longer journey and sole loco, the answer would be nearer 1, or maybe there'd be downhills and it would come back towards 2. And it was a silly question in the first place.

Back in the shed I cleaned off the old gasket and assembled the new valve block and cylinder head to Cheedale's compressor – that may well be on the loco in a week or so. And finally I moved over to Ashdown and measured up the compressor pulley, engine pulley and the gap between to determine what belts are required to separate that weird belt drive.

Tomorrow at 07.30, hurricanes permitting I am to open up for the contractors as they start breaking out the concrete and digging out the second siding at Darley. It may be later than planned, but at last we might be getting somewhere.

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