Yet another question about electrofrog points!

Justin Phillips · May 12, 2023, 09:36

I know that this has been done to death in other threads but I have a specific question I have not been able to find the answer for.

I am embarking on adding frog polarity switches (activated by microswitch via rod and tube). I have seen this video that (for me at least) explains things very clearly: https://www.youtube.com/watch?v=HIlTTigMhXY

In this video he talks about electrically isolating the frog using insulating rail joiners but also by, in his case, removing the bonding between the point blades and the frog (see here: https://youtu.be/HIlTTigMhXY?t=262). Now that fine for those points he is using, but for 009 points you would need to cut the rail.

So this leads to two questions. First, is it necessary to fully isolate the frog, and if so, how do you go about cutting the rails between the point blades and the frog, given how tight space is. I don't feel that confident getting a Dremel in there!

B.Meldon · May 12, 2023, 10:17

No it is not necessary to isolate the frog from the blades.

If you are using DCC and intend for all rails to be live at all times for sound and lights etc. Then both rails from the frog will need isolating fishplates.

If you are using analogue DC then only rails from the frog that are conected to another frog, or to a power feed have to be isolated.
In dead end sidings for example the rail from the frog does not have to be isolated and the point will switch the power on and off to the siding as it switches.
(In fact both rails in the siding become the same polarity when the point is switched against the siding.)

Graeme Dunbar · May 12, 2023, 10:24

If you want to attempt it a piercing saw is possibly the best tool. You can thread the blade through the gaps between sleepers and attach and tension the blade in situ. It doesn't seem to matter if you cut through the plastic webbing immediately under the rail too. It is a bit difficult otherwise.

They are possibly dreadful quality compared to what jewellers use but I got a pack of various grade blades

https://www.amazon.co.uk/dp/B015ALFYOK?psc=1&ref=ppx_yo2ov_dt_b_product_details

The tricky part is the web of the rail as it is so thin and a coarse saw blade will catch. Another advantage of cutting from the side, between the sleepers is that the rail web can be cut on the slant rather than straight down from the rail head.

Alec Hudson · May 12, 2023, 12:30

I use a Dremel with a smaller worn down cutting disc. Then I put some glue in the gap to make sure they don't touch. If you don't want to rely on blade contact you need to put in some jumpers between the blades and stock rail.
Take your time and a steady hand.

JulienW · May 12, 2023, 14:34

Not quite sure what the video is suggesting - I gave up trying to watch them due to the plethora of adverts! But here are some of my thoughts...

Adding frog polarity switching is a good idea as it removes the reliance of the point blade pressing on the side of the stock rail to get current to the frog.

As a general rule we use insulating rail joiners on both rails coming out of the frog to avoid shorting out power feeds to the siding(s) beyond the point. But as B.Meldon suggests you may not need these for a dead end siding on an analogue system (where the point effectively isolates the loco in the siding the point is set against as both rails will have the same polartiy).

It is not necessary to isolate the frog from the point blades. The reason that this is suggested for DCC use is that on the 'open' side of the point the stock rail and point blade are at opposite polarities and with a metal wheel there is a chance that it can short across and shut the system down. But if your wheel sets are to the correct gauge (and back to back) this should not happen.

If you do decide to cut the rails between the 'blunt' end of the point blades and the frog (as shown in the video - though this looks to be using 16.5mm gauge track) I would use a jewellers piercing saw and the finest blades you can get (6/0 or 8/0), as by threading the blade in this will allow you to gap the rails without loosing any of the structural strength of the point. Also, don't forget to add electrical links between the point blades and stock rails, but in my experience its probably not worth the hassle.

Justin Phillips · May 12, 2023, 16:46

Thanks all for the responses. I should have said I am using old skool DC. Also I would rather not be altering points any more than I need to, so I wont then be cutting gaps in the rails!

Justin Phillips · May 12, 2023, 21:29

So, I have wired in and tested my first point with no need to cut any rails 8)

JulienW · May 13, 2023, 20:44

Quote from: Justin Phillips on May 12, 2023, 21:29
So, I have wired in a tested my first point with no need to cut any rails 8)

Well done Justin! The next one will be easier, and the one after that easier again...

B.Meldon · May 15, 2023, 08:17

If your layout is a complete circuit then you will need one isolating fishplate on the rail from the frog that forms the circuit.
If your layout is end to end and does not form a full circuit then you will not need one.

Justin Phillips · May 15, 2023, 16:54

Quote from: B.Meldon on May 15, 2023, 08:17
If your layout is a complete circuit then you will need one isolating fishplate on the rail from the frog that forms the circuit.
If your layout is end to end and does not form a full circuit then you will not need one.

That is already marked on the base board so I don't forget!