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topic: 3306Catch points and how to make them.
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posted: 15 Jul 2018 21:30

from:

ScottW
 
Perth - United Kingdom

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I am finally getting round to finishing off a track plan that I started a number of years ago. It is based on the NBR and is of a fictitious branch line set in East Lothian c1912. Unfortunately, being away from Templot for so long I feel I have forgotten much of what I knew.

My intention is to install a catch point in the run round loop prior to it joining back onto the main line (right hand end of the plan), one with two blades rather than the one. Catch points have been covered several times on this Forum but having conducted a search I find that some of the results have bad links, so I was hoping for some advice. What I would like to ask is what is the best way to construct a catch point, how long should it be and what would be the best angle?

I have attached a copy of the plan for reference.

Thank you,

Scott
Attachment: attach_2699_3306_S_Scale_Borders_Branch_Line.box     187

posted: 15 Jul 2018 22:17

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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ScottW wrote:
My intention is to install a catch point in the run round loop prior to it joining back onto the main line (right hand end of the plan), one with two blades rather than the one. Catch points have been covered several times on this Forum but having conducted a search I find that some of the results have bad links, so I was hoping for some advice. What I would like to ask is what is the best way to construct a catch point, how long should it be and what would be the best angle?
Hi Scott,

Sorry about the bad links. There is an old video showing how to insert a set of catch points here:

 http://templot.com/old_videos/catch_points.exe

As in the video a short loose-heel switch is the most likely size, but they can vary a lot on the prototype. Normally the crossing angle isn't relevant because a set of catch points is only a switch, although a full turnout trap leading to a buffer stop or sand drag is possible. In which case it would likely be a short 1:5 or 1:6 turnout or similar.

p.s. no doubt it is a work in progress, but you may not have noticed that there are a couple of check rails missing in your tandem: :)

2_151712_420000000.png2_151712_420000000.png

cheers,

Martin.

posted: 15 Jul 2018 23:13

from:

ScottW
 
Perth - United Kingdom

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Thanks, Martin the video is a great help.

Yes, I need to get round to finishing off the tandem. As well as altering the check rails on the tandem I need to adjust the timbers on the facing turnout leading into the loop.

Another question has just come into my head, would there have been any requirement for another catch point at the station end of the run round loop (left hand end of the plan)?

Thanks,

Scott

posted: 16 Jul 2018 18:51

from:

Phil O
 
Plymouth - United Kingdom

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There was a thread on RMWeb about that and the conclusion is there seems to be no hard and fast rules on the subject. Some places had fpl's and some didn't. There would be no need for detection, either bars or track circuits.

Phil.

posted: 17 Jul 2018 11:16

from:

Judi R
 
Sutton-on-Sea - United Kingdom

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Some trap points did have detection in the form of a cast iron break-away block. A passing wheel flange would permanently break the track circuit even if the whole vehicle had left the track.

Judi R

posted: 20 Jul 2018 21:35

from:

ScottW
 
Perth - United Kingdom

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Thanks for all the reply's.

Being North British and a backwater branchline I think it best to keep things simple.

Having thought further about the inclusion of a second catch point, if there was a catch point situated at the station end then the runaway rolling stock would have been sent hurtling towards the end of the platform. For this reason I think it is most probable that there never was one.

Scott

posted: 23 Jul 2018 22:30

from:

Richard_Jones
 
Heswall - United Kingdom

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I think I did my catchpoints by just taking the "switch bit" from a turnout and blanking the rest out - here's a picture of the finished product.....

I trimmed them back looking at photos of the prototype - one of them was a weighted points to protect against wrong line run away on a falling gradient - I presume the lever would have "bounced" every time an axle went through it in the normal direction?

cheers

Richard

1763_231727_350000000.jpg1763_231727_350000000.jpg

posted: 25 Jul 2018 21:41

from:

ScottW
 
Perth - United Kingdom

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Thanks, Richard for sharing your photograph.
Lovely work.

posted: 26 Jul 2018 06:59

from:

rodney_hills
 
United Kingdom

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Richard,,
Your immediately preceeding post mention catch poInts on gradients.

Actually what your  original thread is about TRAP points, difference explained eg here
http://en.m.wikipedia.org/wiki/Catch_points

This suggest springing catch is usual...

Construction  of CPs and TrapPs is very similar, it’s the location and application that distinguishes them.

I recollect a discussion on this matter in this forum a while back...

Regards,
Rodney Hills

posted: 26 Jul 2018 09:11

from:

Martin Wynne
 
West Of The Severn - United Kingdom

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rodney_hills wrote:
Your immediately preceeding post mention catch poInts on gradients.

Actually what your original thread is about TRAP points
Hi Rodney,

We have been here many times before. :)

The term "trap" refers to the function of a set of points, a term used by the signalling and operating departments.

In bullhead days the physical object was generally known in the Permanent Way departments as "catch points" and is shown as such on the manufacturing drawings.

See for example the whole chapter on "catch points" in David Smith's GWR book:

cvr_track_200px.jpgcvr_track_200px.jpg

   http://gwsg.org.uk/GWSG_Publications.html

Templot is about track, and defaults to bullhead, so that is the term we use:

2_260347_230000000.png2_260347_230000000.png

which shortens a turnout template to contain only the switch.

The "trap points" function may be implemented as a set of catch points, or may be a full turnout or slip leading to a spur or sand drag.

It's interesting to refer to the PWI handbooks "British Railway Track":

BRT3 (1964 edition) refers to the physical object as "catch points" and "catch roads" throughout. See p.154, and the same wording in earlier editions.

So clearly it was not only GWR practice at that date.

But in BRT4 (1971 edition) all such references have been changed to "trap points" and "trap roads". See p.150. The sprung trailing catch points installed on gradients are now called "runaway catch points".

So both are right. But for most of the bullhead era popular with modellers they seem to have been called catch points by p.w. staff. Referring to the physical object as "trap points" seems to be a modern flat-bottom usage.  

regards,

Martin.

posted: 26 Jul 2018 10:03

from:

rodney_hills
 
United Kingdom

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Hello Martin,
Yes, that’s exactly what my last two sentences in my post alluded to.

Now, about Scott’s WEIGHTED catch..

Your refs also indicate springing was usual practice....

I am reminded of a visit that I made to London Transport’s White City training centre many years ago. The guide demonstrated the operation of a rather large wall mounted circuit breaker. Another visitor then asked the guide why the breaker did not use springs to operate rather than use gravity, to which came the answer that springs can break but that you can absolutely rely on gravity.


Regards,
Rodney





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