Martin Wynne wrote: JFS wrote:
davebradwell wrote:Can I point out that your blades are still not opening far enough - only about 1mm. The prototype opening was 4 1/4" or thereabouts so you need almost half as much again for safety.DaveB
... but any more Dave, and he will have a short on the opposing slide chairs. Anyone who says double slips are easy is being economical with the truth!
Edit:- just to mention that Tony is S4 not P4 so he has that on his side
The prototype allows 3" (1mm) minimum opening where conditions make it necessary (in level crossings, for example).
Thanks for the comments.
I agree that the lower blade in the middle picture is not open enough even for my liking and I will take another look at it. Funny how things show up in photos so much more clearly.
I have also spotted some excess solder that may need to be dealt with.
The biggest problem is getting both pairs of blades to close concurrently and adjusting one side throws the other out. I quite deliberately began fitting this design to these double slips because I knew they would be the greatest challenge. If I could get these to work consistently then standard turnouts would be relatively easy. I was always aware that I was unlikely to be able to get the full standard width opening with the center blades, but reckoned that anything plus 1mm would be sufficient. This in turn limits the opening throw of its partner the other way. As it is I have tapered the very end of rail foot of the center blades to reduce as much as possible the chances of touching the opposite slide chair. The gap between the first two slide chair halves is a fag paper job as it is. The real thing was one continuous casting of course. A non-conducting slide area may be a better option if you don't want to live dangerously or alternatively, make the isolating breaks next to the obtuse crossing units.
The standard opening of 4 1/4" is particularly important on the prototype with sprung switch blades in order to maintain sufficient clearance at the narrowest point between the stock rail and the back of the switch blade. If the back of the flange contacts the switch blade, this will produce wear and can damage the switch blade. In model terms, this is not really a factor, but one still needs at least the minimum flangeway spacing.
I was aware that a reduced opening width was permissible with turnouts in check or guard railed track, but these generally employ loose heeled switches.
It is a case of hopefully knowing how much one can bend the rules without incurring problems.