Stour Valley in P4, Double slip laid
Entry posted by Fen End Pit
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I was really not looking forward to building the double slip. Two crossing Vs, eight switch blades and the horrible obtuse crossings. Building this lot off the baseboard is the best idea and I tend to build the crossings and solder them up individually on nickel-silver scrap etch. These sub-assemblies then get stuck to the sleepers with epoxy carefully jigging them to gauge.
The obtuse crossings are the hardest to make and get aligned but they are the most critical bit. I'm prepared to sacrifice a little detail to get them solidly made and once the half chairs are stuck on it doesn't look too bad.
I was able to make such rapid progress on this because I could reuse some of the components from my previous layout. My previous attempt at a double slip was slightly longer which was handy as I could refinish the switch blades and shorten them to fit. This is one place where the lost-wax brass casting C&L fish-plates are worth their cost because it makes fastening the switch blades to the obtuse crossing so much firmer. With the length of the switch rail there are only 2 or 3 chairs to hold the switch rail otherwise.
With the assembly completed, just waiting for the tie-bars, holding the blades open with a bit of scrap ply allowed for the 'WEEEEEEEE' test. (you put a wagon on, push it along and hopefully it go 'WEEEEEE' not 'WEEEE-crunch')
I removed the double-slip from the temporary base and fitted the tie-bars. Again I was able to reuse ones I'd made before using brass scrap etch and some very thin double-sided paxolin. These are a pig to solder on, particularly to the two 'inside' blades where there is very little room. One of the potential problems is a tie-bar rubbing on the rail of the opposite polarity so I was careful to check for short circuits with a meter. I've stuck a little bit of insulation tape under the rails where the tie-bar might touch just to make sure.
Once again the marking of the cork sheet with the track alignment came into its own when sticking the pointwork down. Just knowing that the alignment is right is so helpful. I had to make the holes I'd cut in the baseboard for the operating mechanism a bit bigger than I'd cut them on the laser cutter. I was able to use the two 'double-slip turnout operating units' from the previous layout to move the blades and get a couple of servos connected up. Wiring is straight-forward with the relay which switches the servo at one end also switching the polarity of the crossing V at the other.
In the background you can see the test train. The rewheeled and unsprung Hornby class 31 is the most fussy locomotive I have, the 6-wheel bogies have a tendency to pivot on the centre axles and derail unless the track is level. The nice thing is it doesn't fall off! I had to do bit of minor tweaking to get some of the longer wheelbase steam locos to go around one of the slips, there is a tendency for these to get tight on gauge and I had to ease the rails a little bit. I've also found a couple of wagons which didn't like it but then found they had a slightly wide back-to-back on their wheels.
The alignment doesn't look too bad. First view is from the cattle-dock towards the goods-yard and then from the yard-entry.
I'm really looking forward to being able to reverse a long pickup goods train back into the yard siding and then shunt wagons in and out of the shed. Now I've got the double slip built I think I'm one step nearer.
David
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8
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