Hi all,
Coming off the mixed gauge crossing on my diorama is a left-hand point leading, with one road to an engine shed and, on the other road, to a siding.
I'd like to try a single blade point (hand-made) with the 'toe end' of the point connected to a shared rail in the shed (for space reasons).
I can't really see any electrical (DC) problems with this, but, I thought I'd run it past the experts first ! I'm planning to use the pivoting single blade to switch the current unless there is a good reason to do otherwise....
Cheers for any assistance,
Dave
Do you mean one like this?
(https://www.rideonrailways.co.uk/paul/page108a.jpg)
Live frog or dead frog? Are you adding switching to point blade-cum-closure rail or letting the contact with the running rail do the electrical switching?
Functionally I see no reason why it should be any different to a normal set of points and could be wired in a similar fashion to any of the above variations.
Sounds like an interesting project!
I would be tempted to back up the point blade electrically with a switch of some sort...
Quote from: Graeme Dunbar on December 15, 2024, 15:37Do you mean one like this?
(https://www.rideonrailways.co.uk/paul/page108a.jpg)
Live frog or dead frog? Are you adding switching to point blade-cum-closure rail or letting the contact with the running rail do the electrical switching?
Functionally I see no reason why it should be any different to a normal set of points and could be wired in a similar fashion to any of the above variations.
Sounds like an interesting project!
Yes, as per your image Graeme. Probably, live frog, which brings in Hugh's point about a separate switch. The shared rail in the shed will be 'live' from time-to-time as it's on the standard gauge line. (One loco at a time)...I'll have to watch polarity here ! A possible solution may be to combine a mechanical 'throw' of the blade with an electrical switching at the same time (Omega loop style).
That's the summit station at Snae Fell, I think..? (as an aside)
If it's the summit shouldn't that be an atop rather than an aside?
(Sorry, I can hear the groans from here but couldn't resist it!)
Back on topic (ahem)...
With good contact the single blade should be energized to the correct polarity from contact with the stock rail, but as we all know from using normal 2 bladed points relying on contact between the stock rail and point blade is not sufficient.
On that basis I would wire feeds to the frog and the point blade and switch the polarity of the feeds together.
That's the simple bit, but I'm not sure about the mechanics as I can't think of a switch that has a large enough throw (9mm) to match the movement of the single blade between the stock rails, but by moving the pivot of the operating link closer to the frog the distance moved is decreased.
Whatever linkage is used I suspect the blade will need to pivot on it as if relying on a 'fixed' (soldered, glued, etc.) I would imagine that the amount of twist needed would lead to a rapid failure.
Making pivots for point blades is not impossible as I've done this on my hand built 'normal' points. I got some tiny brass tacks (brads?) from the "Hobby's" catalogue, drilled a hole through the foot of the (flat bottom) rail and copperclad sleeper, then inserted a brad from beneath the sleeper and soldered it to the rail. Each blade has 2 of these pivots, one near the frog (common crossing) and the other at the tie bar.
For a single blade point I'd use the same set up, but the dificulty might be that with the pivots not quite on the centerline of the rail alignment at the frog end may not be so easy, but one could solder the head of the brad to the underside of the rail and use a retaining washer on the underside.
I hope those thoughts help...
For the polarity switching the solution may be linked to the means of actuation. If it is manual then as mentioned some means of setting the mechanical advantage so the throw of the point blade and electrical switch are matched. This could be done via the linkage or if there is a push rod then some sort of sliding cam that engages with the lever of a microswitch as it passes rather than when it reaches its extremes.
Just use a frog polarity switch, just as I do with any electrofrog point.
As mentioned, again as with the electrofrog points, this switch will need to be set to change mid-way through the blade movement to avoid a short.
I should add that I doubt that a point like this can be used to save space as to keep the inevitable kink in the rail to a minimum the moving blade will have to be quite long, probably longer than a normal point. For example, the blade on the point in the photo at Snaefell works out at about 10cm long on 00 scale, and that may not be enough for some 009 locos with six or more driving wheels.
I think the complication is that the blade has to move close on 9 mm and not the 1.5 mm - 2 mm of normal point blades. It may be possible to arrange the actuator position as a third order lever (near the pivot rather than near the tip of the blade). That might be the way to do it if moving the blade manually using an attachment the switch dolly (or use a long throw switch).
I guess the downside is that the movement at the tip may be fairly uncontrollable due the the amplification in the throw. It might be better to apply the actuation nearer the tip, needing greater travel, particularly if slow motion operation is wanted. The extra distance travelled might make the movement a lot more obvious.
Thanks for the replies all,
Just to clarify a little : the main space saving needed is actually in the shed (hence the 'shared rail' bit). I think I will have room for a conventional, small radius, 009 point to feed it. Like the hand-made mixed gauge crossing, I just fancied the novelty of trying to make a 'single blade' work. For the extra throw /electrical contacts, I was planning to use bell-crank actuation (more novelty !). Of course, the whole thing may just be impractical but as the "Inveterate Tinkerer", I have a reputation to think of...