Choosing which switch and crossing to use.

[whart57]

I have been involved in a lengthy discussion about point kit specification which eventually came down to asking whether a B6 configuration was best for finescale use or whether an A6 or a finer crossing such as an #8 would be a better choice. I'm posting here because I am not fully convinced there is a simple answer and because I can't find a place where this discussion has been held before.

 

There is a page on the Templot website which examines whether A or B switches should be used and the writer comes down firmly for B switches on the grounds that they have a 1:32 deflection rather than 1:24 and thus the effective radius of the point is greater.

 

The counter argument is that an A switch allows for a wider radius curve between switch and crossing. The argument there is that the wider radius means that the leading wheelset of a rigid chassis reaches the crossing better aligned to the path it has to take

 

My personal take is that as the prototype only uses A switches in tight locations then so should we. Against that of course is that nearly every model railway ever built is a tight location in the eyes of the prototype.

 

As I said, I see no simple answer.

[martin_wynne]

11 hours ago, whart57 said:

which eventually came down to asking whether a B6 configuration was best for finescale use

 

That's a strange way of putting it. What is "finescale use"? The choice of switch and crossing size depends on the site and the traffic. A turnout in a fast running line is not the same size as one in a goods yard. There is also the question of curving -- if laying a turnout of similar flexure into a curved running line, it needs to be longer than in straight track. Usually for any significant curving of similar flexure you need a C switch, not an A or a B. Whereas for contraflexure you can often consider a shorter switch to save space. So for example a 1:10 crossover in curved track might have a C-10 turnout on the outer road, and a B-10 turnout on the inner road.  

 

There is a page on the Templot website which examines whether A or B switches should be used and the writer comes down firmly for B switches on the grounds that they have a 1:32 deflection rather than 1:24 and thus the effective radius of the point is greater.

 

I very much doubt that "the writer" comes down very firmly for anything in trackwork. I shall have to have a word with him.

 

That page discusses A and B switches with reference to minimum radius in P4, and the tendency of many modellers to use A switches where a B switch would be better.

 

More discussion recently here:

 

 https://www.rmweb.co.uk/community/index.php?/topic/160234-new-range-of-simple-to-assemble-00em-gauge-pointwork-kits/&do=findComment&comment=4578129

 

cheers,

 

Martin.

[whart57]

1 hour ago, martin_wynne said:

 

That's a strange way of putting it. What is "finescale use"?

 

 

Perhaps I should phrase it as, if you are commissioning a point kit is B6 the best one to start with?

[martin_wynne]

31 minutes ago, whart57 said:

Perhaps I should phrase it as, if you are commissioning a point kit is B6 the best one to start with?

 

If "start with" means a full range of sizes will follow, possibly yes. If it's a kit you will be able to use the B-switch components in a wider range of other sizes than an A switch.

 

But a lot depends on the gauge and scale, and flat-bottom or bullhead? For 00 a lot of modellers expect to fit pointwork into a smaller space. For that I would go for shorter straight switch rather than an A. The A switch is such an unhelpful size that the GWR didn't have one, preferring to retain their older short switch designs. I think there would be a good argument for doing the same in a 00 model. But for EM you might feel that since the EMGS has now done a B-6 bullhead, and Wayne Kinney has done a B-7 bullhead, you would do better to do something different, a B-7.5 or B-8 perhaps. In P4 the Exactoscale kits seem to have dried up again, so maybe a B-7 bullhead would be a good choice for P4. For flat-bottom there is very little available, so maybe the B-6 would be a good start for any gauge if you can only do one size. In 7mm scale you would be competing with the Peco bullhead, so you might want to do something in 0-MF? 7mm modellers are as pushed for space as 00, so again a short straight switch with maybe 1:5.5 might do well.

 

Ideally any new range of pointwork would start with at least two sizes. Maybe an A-5.5 and a B-8? With both of those available you could create a good range of track plans, but with only one of them you would be very  stuck and need something in-between.

 

cheers,

 

Martin.

[NCB]

3 hours ago, whart57 said:

 

Perhaps I should phrase it as, if you are commissioning a point kit is B6 the best one to start with?

For general use an A switch is plain wrong and looks wrong. On my 3mm/ft 14.2mm gauge layout I used B7 for crossovers on the grounds that it gave a gentler reverse curve than using B6; however I wouldn't go as far as to say that B6 would be wrong. I think there's about an inch difference in length between B6 and B7.

 

In the later stages of my layout I started using GWR loose heel turnouts, and if building from scratch would stick to those. But for point kits I've no preference over those and REA B switches.

 

If you've found there are problems with B6 I think you should try B7, rather than mess with A switches.

 

You  might want to think in terms of providing a B6 or B7 point kit, but also commissioning whoever is doing it (I'm assuming it's British Finescale) to produce the crossing in that and one or two other sizes, plus the switch blades, for those who want other turnouts and are prepared to build their own.

 

Nigel

[whart57]

10 hours ago, martin_wynne said:

 

But a lot depends on the gauge and scale, and flat-bottom or bullhead?

 

 

For the record this is for 3mm scale 14.2mm gauge, using code 60 BH rail and following 3mm Society finescale wheel and track standards.

 

As this is for a minority scale choosing where to start is a decision that needs to be carefully considered.

Edited September 25, 2021 by whart57

[ikcdab]

When I designed my layout on templot (see my thread) I determined b8 as the minimum I would use. This is based on the fact that B8 just look so much"right" to me.

When I then planned the mainline junctions, I made these c10 and I felt very adventurous doing so. And the mainline junctions do look really good.

Then when I did the main  crossovers in the main station, I went further and made these D12. And they look even better again.

Go for the longest and shallowest angles you can. They just look so much better and the running is hugely improved.

Ian C

[dhjgreen]

35 minutes ago, whart57 said:

 

For the record this is for 3mm scale 14.2mm gauge, using code 60 BH rail and following 3mm Society finescale wheel and track standards.

 

As this is for a minority scale choosing where to start is a decision that needs to be carefully considered.

Wayne Kinney is already working with the 3mm Society.

[martin_wynne]

59 minutes ago, whart57 said:

 

For the record this is for 3mm scale 14.2mm gauge, using code 60 BH rail and following 3mm Society finescale wheel and track standards.

 

As this is for a minority scale choosing where to start is a decision that needs to be carefully considered.

 

It would have been helpful to have mentioned that from the start.

 

For the smaller scales you have more room to follow the prototype, so a B-8 would be a nice size to start, if you have to pick just one size.

 

Wayne Kinney is already working on turnout kits in 3mm scale, so you may need to bear that in mind.

 

Martin.

[Izzy]

I would hazard a guess that the OP was to garner a range of opinions regarding what might be the preferable/best choice to go with. Not an easy task.

 

Personally I probably think that choosing a base crossing angle that could be used with turnouts and diamonds/slips might be the way forward. Anything that reduced the number of dies/castings would I presume be welcome, so either 6 or 7 I guess. In a sense the blades are secondary being more easily altered/changed to suit.

 

Your never going to satisfy all, so always a compromise whatever and why a B6 is seen as the default option.

[whart57]

2 hours ago, dhjgreen said:

Wayne Kinney is already working with the 3mm Society.

 

Correct, it's me he is working with

[whart57]

I should perhaps add that we in 3mm are committed to a B6 now. However that did trigger an inordinate amount of internal debate, particularly on the relative merits of A and B switches. Debate which I do not see reflected elsewhere. I note too that the EMGS also went to PECO for a B6 point.

 

So I am interested in experiences in the scales either side of us, especially among the more exacting varieties such as 2mm FS and P4.

 

I should add that my take is that while I can build points, I'd rather not.

[martin_wynne]

1 hour ago, whart57 said:

particularly on the relative merits of A and B switches. Debate which I do not see reflected elsewhere.

 

That's because there is nothing to debate. Most modellers choose a switch size based on the prototype location they are modelling. For a goods yard you choose mostly A. For loops and branch lines you choose B or C. For fast main lines you choose D or larger. There are no relative merits, you build whatever is required for the location. No modeller restricts themself to only one size -- even Peco users have a choice of 3 turnout sizes.

 

Martin.

[NCB]

2 hours ago, whart57 said:

I should perhaps add that we in 3mm are committed to a B6 now. However that did trigger an inordinate amount of internal debate, particularly on the relative merits of A and B switches. Debate which I do not see reflected elsewhere. I note too that the EMGS also went to PECO for a B6 point.

 

So I am interested in experiences in the scales either side of us, especially among the more exacting varieties such as 2mm FS and P4.

 

I should add that my take is that while I can build points, I'd rather not.

 

Think that's a reasonable decision. Reasonably compact layouts are popular in 3mm/ft which would make something like a B8 less attractive as a single option.

 

Nigel

[Dungrange]

5 hours ago, whart57 said:

However that did trigger an inordinate amount of internal debate, particularly on the relative merits of A and B switches. Debate which I do not see reflected elsewhere.

 

I think that's because as @martin_wynne has indicated, there is no technical debate to be had.  You would use the most appropriate switch for the location that you are modelling.  However, there is a commercial debate about which combination of switch and crossing angle is likely to sell best and therefore give the greatest return on investment.  That therefore means asking who the customers are.  Who models in 3 mm scale?  What types of layout do they build?  If most 3 mm modellers build cramped dock layouts, then an A6 may be desirable.  If they build compact branch line termini, then a B6 or B7 is likely to be more appealing.  If they use the smaller scale to produce closer to scale mainline track work than is possible in the larger scales, then a C10 may be more desirable.

 

I'd suggest that the commercial reasons for choosing a B6 or B7 over any other combination is that you could use it in place of either an A6 or C10.  That is, it could look 'okay' in both a yard and on a mainline, whereas a C10 would look ridiculous in a cramped goods yard and an A6 would look wrong on a mainline.  Therefore, if constrained to only producing one, produce something in the middle of the range.

 

Peco would have asked themselves the same question when they produced their 00 Bullhead point work.  Should we start with the small, medium or large radius point?  They went with the one they thought would sell best.

 

I model in 00 where a B7 will be my minimum.  If I were modelling in N gauge, then I'd be very tempted by British Finescale's EV15, but if they were to upscale their concrete flat bottom range to 00, then I suspect I'd have to 'make do' with a CV10. 

[whart57]

You'd be amazed how much technical debate there was.

 

The thing is that in 3mm scale at least most have to build their own chassis. If they do so in finescale then they use the Society's driving and carrying wheels which have a flange depth of just over 0.5mm (approx twice as much as the real thing scaled down) and a flange width of around a third of a millimetre (just over the strict scale dimension). It has been suggested that the Society wheels are suited for curves of radius of six foot or more. Of course no-one has curves that generous but there is a rule of thumb that a six wheel chassis with flanges on all wheels is likely to need a curve of at least 30" radius, preferably three foot or more. Sideplay can of course be provided but too much sideplay and the driving wheels start fouling splashers or there is no clearance for fitting outside valve gear.

 

So if we aim for a radius of 36" as that being necessary for the larger six-coupled locos (let's not even think of a 9F or eight-coupled locos) then a B6 gives us a problem. It's effective radius over the curved part of the point is 32" in 3mm scale. Now that can be overcome with gauge widening.

 

The deflection at the switch itself also has an effective radius and a B switch there is comfortable over the 36" radius we aim at.

 

An A6 on the other hand has a wider radius on the curved part of the point but against that the effective radius caused by deflection at the switch is over our target.

 

However it has also been pointed out that when a rigid chassis loco approaches the crossing (aka frog) on the curved path the leading wheels enter the crossing "gate" at an angle. If that angle is too great then the effective flange width will exceed the check rail gap and foul the crossing

 

It could be argued that the answer is to use #8 or greater crossings to overcome this. Unfortunately a B8 is a longer point than a B6 and most users don't have room for B8s all round.

 

So we have competing compromises, and I was wondering if we are alone in that or not.

 

[NCB]

In my 3mm/ft layout I deliberately put in a 32" radius curve in one siding as a means of testing stock; 32" was the minimum I was aiming for. All my locos managed it, including a GWR 42XX 2-8-0T. Templot gives 32.3" as the minimum internal radius of a B6, so I'd be reasonably comfortable with using a B6. A main consideration to me in using a B7 is not so much the question of individual turnouts but to obtain a shallower reverse curve in crossovers; I used body-mounted couplings (B&B) on coaches and this mattered. As regards steam locomotives I'm confident B6 would be OK.

 

One consideration with the BF point kit is that it should be possible to assemble them to consistent standards, which should aid good running. Scratch-built turnouts (like mine!) are more prone to minor variations; I'm sometimes puzzled as to why mine work as well as they do

 

Nigel

 

 

[martin_wynne]

1 hour ago, whart57 said:

So if we aim for a radius of 36" as that being necessary for the larger six-coupled locos (let's not even think of a 9F or eight-coupled locos) then a B6 gives us a problem.

 

If radius is a concern, forget the non-natural REA turnout sizes, and go for the older straight switches. They are listed in Templot ready to use. Also use a generic-type V-crossing instead of the default regular type. I've posted this stuff on RMweb many times over the years, but here you go again:

 

 

By changing to a 12ft switch and generic crossing, you can get the radius up from 32.3" to 39" in almost the same turnout length. The 12ft switch has the same 1:32 deflection as the B switch, so the switch blade planing is identical and you can use the same blades in B switches on longer turnouts.

 

For more info, ask on the Templot Club forum -- which it would have been a good idea to do in the first place.

 

cheers,

 

Martin.

[NCB]

Wonder if using a generic crossing would affect the shallowness of the reverse curve in a crossover.

 

Nigel

[martin_wynne]

43 minutes ago, NCB said:

Wonder if using a generic crossing would affect the shallowness of the reverse curve in a crossover.

 

Hi Nigel,

 

Not significantly:

 

 

Yellow lines = generic crossover

Blue lines = regular crossover

 

The middle straight portion between the crossings is the same for either. The overall straight portion is longer for the regular crossover, but against that vehicles are on sharper curves with more end throw.

 

cheers,

 

Martin.

[martin_wynne]

On 25/09/2021 at 09:07, whart57 said:

For the record this is for 3mm scale 14.2mm gauge, using code 60 BH rail and following 3mm Society finescale wheel and track standards.

 

Hi,

 

For 3mm scale, describing pointwork as "14.2mm gauge" is confusing. That is just the name of the gauge. The actual track gauge for pointwork is 14.125mm (specifying the dimension to a 1000th of a mm is extremely daft).

 

The 3mm Society's published standards are something of a mess, having been unchanged since 1995 -- all this, and not including the ScaleThree (S3) standard:

 

In Templot I gave it the name FM because it was too illogical to call it 14.2mm:

 

 

cheers,

 

Martin.

[bradfordbuffer]

13 minutes ago, martin_wynne said:

 

Hi,

 

For 3mm scale, describing pointwork as "14.2mm gauge" is confusing. That is just the name of the gauge. The actual track gauge for pointwork is 14.125mm (specifying the dimension to a 1000th of a mm is extremely daft).

 

The 3mm Society's published standards are something of a mess, having been unchanged since 1995 -- all this, and not including the ScaleThree (S3) standard:

 

In Templot I gave it the name FM because it was too illogical to call it 14.2mm:

 

 

cheers,

 

Martin.

9 different gauges it gets worse....but thanks for info just need a snazzy name!

It could of been called S3 or P3 as its as close as possible to scale does not matter to end user if gauges are used and are constant....but uk has a particular habit of putting scale and gauge in a blender and blitzing...

Some one should bring out a book ....scale and gauge screew ups of the 20th century...best seller...

Never heard it called FM...what does it stand for?

Regards 

G

[martin_wynne]

6 minutes ago, bradfordbuffer said:

Never heard it called FM...what does it stand for?

 

Hi G,

 

In the absence of any other logical name from the Society, I changed TM to FM, F for "Fine". That was over 20 years ago, I might find a better name if starting now.

 

Note that S3 is separate standard with 0.5mm flangeways (ScaleThree). I have a recollection that there is/was a separate ScaleThree Society, but Google doesn't come up with anything. I shall have a rummage through my old papers.

 

cheers,

 

Martin.

[bradfordbuffer]

1 hour ago, martin_wynne said:

 

Hi G,

 

In the absence of any other logical name from the Society, I changed TM to FM, F for "Fine". That was over 20 years ago, I might find a better name if starting now.

 

Note that S3 is separate standard with 0.5mm flangeways (ScaleThree). I have a recollection that there is/was a separate ScaleThree Society, but Google doesn't come up with anything. I shall have a rummage through my old papers.

 

cheers,

 

Martin.

with developments in 3mm  that are happening may be a good time for society to have rebrand of gauge combos and get it in to mainstream to attract members from other scales that dont want to run on 4ft gauge track...nothing wrong with 4ft gauge track or 63ft coaches that don't look 63 ft, just coz it doesn't mirror p4 s4 tolerances doesn't mean it cant be called s3 or p3....gust a name to a set of standards.

G

[whart57]

3 hours ago, martin_wynne said:

 

Hi,

 

For 3mm scale, describing pointwork as "14.2mm gauge" is confusing. That is just the name of the gauge. The actual track gauge for pointwork is 14.125mm (specifying the dimension to a 1000th of a mm is extremely daft).

 

The 3mm Society's published standards are something of a mess, having been unchanged since 1995 -- all this, and not including the ScaleThree (S3) standard:

 

In Templot I gave it the name FM because it was too illogical to call it 14.2mm:

 

cheers,

 

Martin.

 

The lesson here is don't form a scale society, form a gauge society. If you are a gauge society you can have and promote a single set of standards.

 

The problems the 3mm Society have in maintaining common standards is in the history of the Society. It was initially formed to keep the scale going when Triang ceased production of TT gauge. Most of the original members ran Triang kit so that was the standard. Even 50 years ago however there were proposals for a more accurate scale/gauge ratio. 13.5mm was proposed (three quarters of 18mm so an EM equivalent) and I believe an article had appeared in the model press extolling "TM gauge". 14.2mm gauge was also proposed and worked with very early on.

 

Track standards are only half the story though, wheel standards have to match. Apart from Triang the only early source of wheels were from Romford. The early Romfords - as with OO scale - were a finer profile than the commercial equivalents. That was fine, but then Romford stopped producing wheels for TT and just re-badged the smaller OO wheels as suitable for TT if a TT gauge axle was used. Profile and spoke numbers were way off.

 

For a while Chris Hardy produced wheels for the 3mm Society using techniques which can best be described as "hair raising". When Chris stopped production the Society prevailed upon Kean-Maygib to produce some wheels - and very nice ones too - and Mike Sharman produced his "millimetre" range which were also nice.

 

Add in the arrival of East European TT during the 1980s and things were a real mess.

 

The standards you see on the web site are the result of a lot of work by people who had both a lot of practice in building model railways in 3mm scale and a good theoretical understanding of how wheel and rail interacted. If you think it looks a mess just imagine what putting all the 4mm standards together on a single page would look like. Much the same I think.

 

Consider the equivalents:

• "Triang" is the equivalent of the old 1960s coarse standard of Triang "Super4" and Hornby Dublo
• "Intermediate" is the later finer scale now used by commercial ready to run
• "Finescale" on 12mm track is the equivalent of OO finescale
• TM standard is the equivalent of those who attempt EM merely by pushing commercial wheels further out
• "Finescale" on 13.5mm track is sort of EM equivalent, but so is:
• "Finescale" on 14.2mm track (I'll cover the 14.125 bit in a moment)

One or two people have proposed an S3 standard, an exact scale version of standards equivalent to S4/P4 but there is zero demand for that within the Society.

 

The discrepancy between 14.125mm and 14.2mm has two sources. One is that a significant number of people were already using 14.2mm gauge when the Standards Sub-Committee decided on 14.125 as it was the exact scale equivalent of 4' 8½". And secondly some people don't read all the standards, including those who set the requirements for the Society's flexible trackbase. This was set as 14.2mm gauge and not 14.125mm. For compatibility purposes the point bases Wayne Kinney is producing for 3mm will also be 14.2mm with other dimensions receiving appropriate adjustment.

 

We are talking gnat's (insert organ of choice) differences here, in most cases all that is happening is that the tolerances are pushed to the max. The first points produced have thrown up no issues and everything tried on them has trundled through brilliantly. We recognise the standards require revision, but no-one has the courage to do that right now.