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The three Ts. Lift the lid on the secrets of how you do things so others can have a go.....

Points - the achilles heel

Postby dkightley » Tue Jul 01, 2014 8:40 am

I've been intending to try and get some technical biased threads on the board to stimulate the practically minded members into developing things for the gauge. Having seen Ivan Furnace's superb thread on custom points, I thought I'd provide some background information.

Points...or switches..are the one weakness in T gauge, and there have been attempts to create custom versions as an alternative to the Eishindo standard versions. For those not familiar with the points, here's one point in Robins Run.
Points01.jpg
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For information, the manual switching bar has been replaced with one that is operated from underneath by a cable....which is why there's no sign of anything to change it!

So...whats the problem with the point?

Mechanically its not that bad. Everything seems to run through the points fairly reliably without derailing. My own experience is that there needs to be a straight leading into the point to reduce the likelyhood of carriages derailing.

The big issue is the electrical properties of the point. A power unit picks up power from both axles in both bogies. Referring to the following photo, a loco entering the points in the direction of the blue arrow will be picking up power from all 4 axles. As the front bogie passes from A to B, it can't pick up power....and the same thing happens for the rear bogie.
Points02.jpg
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Theoretically, at least two axles can pick up power at all times....but in the (dirty) real world, the chance of the loco stopping or stuttering is very high. And as 4-wheel power cars are getting nearer, the distance from A to B is likely to be greater than the wheelbase....resulting in power loss!

Now how do we solve the problem? The problem being the excessively long "dead spot" in the metal rails. With a bit of magic with Paint Shop Pro, lets replace the two little brass strips with bigger moving blades made out of rail profile steel:
Points03.jpg
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The point looks better...and it looks as if wagons, etc should run more reliably through the point. And the "dead spot" has been reduced down......but I'm not sure if the stopping/stuttering issue has been addressed. The "dead spot" is still greater than the wheelbase of a bogie...so there will still be a point where the power pick-up capability drops from 4 to 2 axles.

Okay...continuing the design change in Paint Shop Pro, lets get rid of that triangle of plastic and replace it with metal:
Points04.jpg
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Thats got the "dead spot" down to a couple of millimetres, which is less than wheelbase of a bogie...which is about as far as we can go. Problem solved? Not really! Put power onto the track, +ve to the upper rail and -ve to the lower rail...and BANG! You're PWM controller is shorted out and blown! The metal insert has shorted the rail!

We now need to consider how the point needs to work electrically. Here's my suggested solution:
Points05.jpg
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Put an isolation break at the two points indicated by the orange arrows. (I've put these far enough away from the points to make modification to the existing point feasible. There shouldn't be any issue with them being closer to the triangle.) The three sections of rail, the "vee" where the rails converge A, and the two blades B & C need to be powered via a switch operated by the blade movement so that they're the same polarity as the rail the blade is moved to.

So there's the design challenge. Ivan has made a start on his version. I'd love to know if there are any others out there.....
Doug Kightley
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Re: Points - the achilles heel

Postby mattd10 » Tue Jul 01, 2014 3:20 pm

Ive been thinking an awful lot about scratch building points but have never scratch built any track at all.....ever!
I'm looking into making my own oo9 track (I wont go off topic here...) and hopefully learning the techniques to transfer down to the smaller gauges.
For me the skill will lie in accurate soldering and precision which I don't think I could manage right now!
However I will be following this with interest.
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Re: Points - the achilles heel

Postby hhearle » Tue Jul 01, 2014 10:54 pm

I think it's a great idea to include topics such as these to encourage the development of the more technical aspects of the scale...

Here is a standard "0" point and its "00" equivalent.

9cf2copy.jpg
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From what I can see there is little if any difference except for the fact that it does away with the moulded part altogether. Instead it has the metal running all the way through the point, if you get what I mean. In actual fact, there's very little plastic at all, although the triangle bit still has to be plastic to prevent shorting. Looking at it the point blades are a lot longer, so wouldn't that cure the problem?

I suppose another thing you could do would be to insulate the sides of the point blades, but I'm still not sure if that would prevent electrical arcing... :ugeek:
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Re: Points - the achilles heel

Postby ivanf » Wed Jul 02, 2014 7:20 pm

I think Doug has covered the issue nicely. I'm going for option 3 and plan on wiring the frog and the 2 blades together somehow through a switch. Although the 2 blades do seem to pickup enough power by being in contact with the powered rails...

I was a bit worried about accuracy but the point was quite easy to put together... I've got a very shallow groove in the sleepers which is enough to locate the track accurately while glueing it down. Much easier than traditional track building methods that seem to require expensive templates and quite a bit of skill.
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Re: Points - the achilles heel

Postby hhearle » Thu Jul 03, 2014 12:45 pm

It's definitely got me considering having a go at making some of my own trackwork (when I get the time!). There have been so many occasions when I've wished for a wider selection of track pieces! Thanks Doug :D
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Re: Points - the achilles heel

Postby hugwa » Wed Oct 15, 2014 9:29 pm

Hi everyone.
This is my pre-prototype of #6 switch, milled in modelling wax to verify dimensions.
Designed to be joined with flex using FlexiTrack joiners, with tie spacing and dimensions similar to Eishindo's flex.
Maybe it will work out...

T_No6_01s.jpg
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Re: Points - the achilles heel

Postby ConnorL » Thu Oct 16, 2014 2:33 pm

Whoa! That's a pretty switch! What kind of 3D printer did you use?
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Re: Points - the achilles heel

Postby hugwa » Thu Oct 16, 2014 2:58 pm

It's milled, not printed.
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Re: Points - the achilles heel

Postby hugwa » Tue Mar 17, 2015 10:36 am

Small step forward - milled PCB ties for the switch :)

T_No6_02.jpg
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Re: Points - the achilles heel

Postby NeilM » Tue Mar 17, 2015 2:21 pm

Very impressive. Can not wait to see how this one turns out (is there an unintentional pun in there?). For my first layout - alas very much still under construction - I have elected to not use any points at all so as to optimise the chances of good running, but if somebody can develop pointwork that looks good and runs well then then opens up a whole number of possibilites.
Neil

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