Points - the achilles heel

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

Post by dkightley »

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
Webmaster here and volunteer at the National Tramway Museum http://www.tramway.co.uk

mattd10
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Re: Points - the achilles heel

Post by mattd10 »

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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hhearle
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Re: Points - the achilles heel

Post by hhearle »

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

Post by ivanf »

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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hhearle
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Re: Points - the achilles heel

Post by hhearle »

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
Wolfie
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hugwa
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Re: Points - the achilles heel

Post by hugwa »

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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Hubert

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Re: Points - the achilles heel

Post by ConnorL »

Whoa! That's a pretty switch! What kind of 3D printer did you use?

hugwa
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Re: Points - the achilles heel

Post by hugwa »

It's milled, not printed.
Hubert

hugwa
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Re: Points - the achilles heel

Post by hugwa »

Small step forward - milled PCB ties for the switch :)
T_No6_02.jpg
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Hubert

NeilM
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Re: Points - the achilles heel

Post by NeilM »

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

T gauge items in my Shapeways shop http://www.shapeways.com/shops/t450

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Nutter
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Re: Points - the achilles heel

Post by Nutter »

hugwa wrote: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
Looks interesting. Still getting to grips trying to build Zm points at 4.5mm gauge using a Fast Tracks Jig.
Don't see why it shouldn't work providing there are gaps so you don't get shorts.
Have seen the milled base as well.

Have looked at Ivan's 3D printed base as well and will get more involved in this when I have a fully functional Zm point using code 40 rail.
Mike
DON'T knock it at least I am trying to do something, with only one good hand.

hugwa
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Re: Points - the achilles heel

Post by hugwa »

Friday report :)
After four frustrating attempts mounting tool is finally milled and it seems to work.
T_No6_03.jpg
T_No6_03.jpg (252.4 KiB) Viewed 11852 times
Picture shows my idea of making frog, points and guard rails - they are etched from nickel silver plate.
Hubert

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dkightley
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Re: Points - the achilles heel

Post by dkightley »

Now that is looking really nice...

No. Not nice.....Brilliant! :lol: :lol:
Doug Kightley
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hugwa
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Re: Points - the achilles heel

Post by hugwa »

Little progress. Some work left to do - a throw bar under switch points, wires, isolation gaps... Not much, but not easy.
T_No6_04.jpg
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T_No6_05.jpg
T_No6_05.jpg (66.69 KiB) Viewed 14938 times
Hubert

henningz
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Re: Points - the achilles heel

Post by henningz »

Excellent work, I hope it will work as fantastic as it looks like. Would be a great achievement in combination with flexi track :)
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mattinair
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Re: Points - the achilles heel

Post by mattinair »

How totally neat! .......

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Re: Points - the achilles heel

Post by ivanf »

looks very good. :)

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Nutter
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Re: Points - the achilles heel

Post by Nutter »

Drifting slightly on the topic of points, I am going to need to build a passing loop and wondered if I will be wasting my money buying the one way units or should I go to the proper ones. Stock powered by 19M chassis - only 2 autorails per train.
Need to be able to have trains pass each other on what would otherwise be a single track line. Wiring and isolating sections not a problem.
Mike
DON'T knock it at least I am trying to do something, with only one good hand.

henningz
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Re: Points - the achilles heel

Post by henningz »

Nutter wrote:[...] and wondered if I will be wasting my money buying the one way units or should I go to the proper ones. Stock powered by 19M chassis [...]
One-way-turnouts have a space of about 33 or 34 mm without power supply (as measured by photo here, turnout length = 90 mm). The 19M chassis has a bogey spacing of 28 mm and an axle spacing of 4.5 mm, that's 32.5 mm from first to last wheelset. I guess it will stop or stagger at slow speed.
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barneyadi
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Re: Points - the achilles heel

Post by barneyadi »

Has there been anymore progress with points? What hugwa was doing looked brilliant, did he get any further?

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