What back to back setting do you use?

Model and prototype rolling stock, locos, multiple units etc.
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James Moorhouse
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What back to back setting do you use?

Postby James Moorhouse » Tue Jan 03, 2012 1:53 pm

In the Alan Gibson brass centred wheels thread mention has been made of the George Watts adjustable back to back gauge:

Philip Hall wrote:
James Moorhouse wrote:You mention the George Watts back to back gauge is fully adjustable, but how useful is this feature really?

This gauge was produced to suit all 4mm gauges, but I use it to fix my chosen back to back setting (within the tolerances of the P4 standard, of course). I use 17.7mm, which seems to work very well, allowing a degree of play between the railheads. This also means that an ever so slightly wobbly wheel has less effect on the running than it would if the wheels were a tighter fit between the rails.


So, what's your chosen back to back setting and why?

As I see it 18.83 gauge modellers are using back to back settings within the 17.67 to 17.87mm range. 17.67mm being the original P4 BB recommendation and 17.87mm representing the 4mm equivalent of the minimum back to back dimension on the prototype. As well as there being a fully adjustable back to back gauge on the market, other 'fixed' gauges are available which fall within the above range, there is also the Tony Sissons gravity gauge, which I have always treated as a checking as opposed to setting gauge, and of course there are home-made gauges (I have a few brass roller gauges which I produced on a watchmaker's lathe, again primarily used for checking). So presumably with all these gauges about there is some awareness concerning which back to back setting a modeller uses.

My chosen back to back setting is 17.82mm, which I call the CLAG setting. I use this because I believe the increased width gives better performance, for example reducing side play between wheels and track. My compromise choice is because of the actual tolerances used in the manufacture of 4mm components and reflects my own ability with regard to assembly and maintenance of models. The back to back gauge I use is by Exactoscale and is made to a very high standard.

Exactoscale currently list two back to back gauges on their website: 4CW 801A, P4 Back to Back gauge 17.75mm and 4CW 802A, S4 Back to Back gauge 17.87mm.
The gauge I have is labelled "4CW 803A, Intermediate Back to Back gauge 17.82mm" and, I believe, was produced as a special batch. The choice of 17.75mm (the current P4 recommendation) for the P4 setting was summed up by Andrew Jukes in the EM wheels on P4 track thread:
On The P4Track Co. turnouts, we have aimed to set our crossing flangeways at 0.65mm (the P4 minimum). This was done as part of the process we have seen since the early days of P4 of trying to reduce unnecessary ‘slop’ in the original MRSG P4 standards - a process which we have supported by providing our standard Back-to-Back gauge at the Society recommended dimension of 17.75mm (compared with the original P4 setting of 17.67mm). Our scale width wheels can also be regarded as part of this trend.

A few years ago when Exactoscale released their back to back gauges, Andrew said that a number of the S4 (17.87mm) gauges had been sold, which suggests to me that there are a few modellers out there who really are in control of standards. I heard somewhere that Ray Hammond no longer uses the S4 back to back setting and has adopted a compromise setting.

I know there was quite a bit of discussion about back to back settings in the EM wheels on P4 track thread, but it would be interesting to get picture of what settings are being used across the membership and also ensure that modellers are aware when it comes to making the decision as to which BB setting to adopt.

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Tim V
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Re: What back to back setting do you use?

Postby Tim V » Tue Jan 03, 2012 4:53 pm

I use my original Studiolith back to back, and I've just measured it (at 19°C) at 17.69mm. I've chosen the lower end of the range as the curves are minimum 3' radius.

My Tony Sissons gauge is set to the same figure.
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craig_whilding
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Re: What back to back setting do you use?

Postby craig_whilding » Tue Jan 03, 2012 6:22 pm

Finding someone using 17.87mm is a great way of discovering if your C+L track has gauge narrowed at all...

I use the Exactoscale 17.75mm gauge, I would have used a 17.82mm one if i'd known about that special batch when I first started. I believe the slight extra width is an improvement and recommend the Exactoscale gauge to anyone asking me about P4. That particular gauge also offers better support when dealing with wheels with a gear on them though it is more expensive than the alternatives.

martin goodall
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Re: What back to back setting do you use?

Postby martin goodall » Tue Jan 03, 2012 10:51 pm

Like Tim, I use the old Studiolith B-B gauge. (I seem to have two or three of them, although I only remember
having bought one of these myself). I usually reckon that this gives a B-B setting of 17.7mm, but I only have an old fashioned steam powered vernier gauge, and if Tim is using a modern electronic version, then 17.69mm is probably a more exact dimension, although I have never really been bothered with hundredths of a millimetre myself.

This BB setting is what I use for re-gauging EM wheels to P4, but the use of these wheels does require the track gauge to be not less than18.83mm, so the old Ratio P4 EMtrack (which was only about 18.75mm) is definitely not going to accept EM wheels re-set to the P4 B-B gauge, whereas re-gauged EM wheels run perfectly happily on my riveted and soldered (Brook Smith) track, which has its track gauge and its crossing flangeways and check rail gauge all set to the standard P4 dimensions without any easing or adjustment.

If using orthodox P4 wheels, you can set the B-B even wider, which is what Ray Hammond's "Scale Four" standards do. I cannot recall the precise "Scale Four" B-B setting, but it is a shade under 17.9mm, which gives a running clearance (i.e. between the outside of the wheel flange and the inside of the head of the running rail) almost exactly the same as you get if setting EM wheels to the 'standard' P4 B-B gauge. I do have one of Ray's "Scale Four" B-B gauges, and did at one time set my P4 wheels to this wider B-B gauge. I found that they ran perfectly happily on P4 track at this wider setting, but in the end my preference for a deeper wheel flange led me to adopt the EM wheel profile set to the normal P4 B-B gauge (which, in my case, as mentioned above, is 17.7mm, give or take a gnat's whisker).

"You pays yer money and you takes yer choice."

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Flymo748
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Re: What back to back setting do you use?

Postby Flymo748 » Sun Jan 08, 2012 10:38 am

James Moorhouse wrote:So, what's your chosen back to back setting and why?

As I see it 18.83 gauge modellers are using back to back settings within the 17.67 to 17.87mm range. 17.67mm being the original P4 BB recommendation and 17.87mm representing the 4mm equivalent of the minimum back to back dimension on the prototype.

I know there was quite a bit of discussion about back to back settings in the EM wheels on P4 track thread, but it would be interesting to get picture of what settings are being used across the membership and also ensure that modellers are aware when it comes to making the decision as to which BB setting to adopt.

Hi James,

For no other reason than to give you another data point, I've measured my BTB gauge. It is, to the best of my accuracy and consistency with a digital micrometer, 17.70 mm.

This one of the Brook Smith gauges:

BTB Gauge.jpg


So the setting that I use is only "chosen" by me in the sense that it turned up "out of the box". However I never make any claims of being an engineer ;-)

HTH
Flymo
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Paul Townsend
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Re: What back to back setting do you use?

Postby Paul Townsend » Sun Jan 08, 2012 4:07 pm

martin goodall wrote:I seem to have two or three of them, although I only remember
having bought one of these myself
"


Now I know where mine went!

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Re: What back to back setting do you use?

Postby martin goodall » Mon Jan 09, 2012 8:24 pm

paultownsend wrote:
martin goodall wrote:I seem to have two or three of them, although I only remember
having bought one of these myself
"


Now I know where mine went!


Actually, I do know where my other two came from. They were thrown in when I bought some surplus P4 items as a job lot quite a few years ago now.

It's useful having two or three of them, as I nwever have to go hunting around for the B-B gauge, there always seems to be one handy when needed.

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Tim V
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Re: What back to back setting do you use?

Postby Tim V » Mon Jan 09, 2012 9:50 pm

Ah, but are they all the same? Have you measured them? Perhaps this is where the EM wheels comes in, by using ad hoc BB gauges, how can you be sure all your settings are the same.....

Could explain those "random" derailments.....
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Horsetan
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Re: What back to back setting do you use?

Postby Horsetan » Wed Mar 07, 2012 12:20 pm

I use 17.87 back-to-back. Gauges used are a Ray Hammond, and an Exactoscale.
Last edited by Horsetan on Fri Mar 09, 2012 12:50 pm, edited 1 time in total.
That would be an ecumenical matter.

martin goodall
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Re: What back to back setting do you use?

Postby martin goodall » Thu Mar 08, 2012 4:21 pm

Horsetan wrote:I use 17.87 back-to-back. Gauges used are a Ray Hammond, and an Eactoscale.



The 17.87 BB gauge from Ray Hammond is a 'Scale Four' gauge, designed for use in combination with reduced clearances through the check rails and flangeways. The whole idea of 'Scale Four' is to tighten up on the over-generous clearances in the orthodox P4 standards.

Yes, (shock! horror!) this is yet another deviation from the true faith of Protofour! :o But it goes back for more than 35 years, and I know that Ray has used these standards with great success throughout this period, as have a number of other people.

One intriguing point is that if you set your P4 wheels to the 'Scale Four' back-to-back, the running clearance (i.e. the space left between the outside of the wheel flange and the inside of the rail head is more or less the same (within a gnat's whisker) as it is if you re-gauge EM wheels to the P4 back-to-back gauge. :twisted:

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Horsetan
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Re: What back to back setting do you use?

Postby Horsetan » Fri Mar 09, 2012 12:51 pm

martin goodall wrote:
Horsetan wrote:I use 17.87 back-to-back. Gauges used are a Ray Hammond, and an Exactoscale.



.....Yes, (shock! horror!) this is yet another deviation from the true faith of Protofour! :o But it goes back for more than 35 years, and I know that Ray has used these standards with great success throughout this period, as have a number of other people....


...which is precisely why I chose to use them.
That would be an ecumenical matter.

Trevor Grout
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Re: What back to back setting do you use?

Postby Trevor Grout » Fri Mar 09, 2012 3:31 pm

Thought I would take a couple of pics of the back to backs that I have

This one is an Exactoscale Gauge. I have applied the calipers to it and read 17.67mm
Original Exactoscale P4 B2B - 17.67mm.jpg
Original Exactoscale P4 Back to Back - 17.67mm


Now If memory serves me correctly, the intermediate gauge were specially made to the settings that were suggested by CLAG, hence I think all the claggies have at least one, including the one that James has.
the calipers applied to this reads 17.82mm.
Intermediate Exactoscale P4 B2B - 17.82mm.jpg
Intermediate Back to Back - 17.82mm


Both sitting together, you will see that the intermediate on the right has to holes through it, these were suggested to allow the setting of the back to back with a exactoscale gearbox mounted on the axle.
Two types of exactoscale B2B Gauges.JPG
Two types of Exactoscale back to back gauge


Thought I would share.

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Horsetan
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Re: What back to back setting do you use?

Postby Horsetan » Fri May 25, 2012 11:47 am

Trevor Grout wrote:.....the intermediate on the right has to holes through it, these were suggested to allow the setting of the back to back with a exactoscale gearbox mounted on the axle.
.....


Exactoscale's 17.87 BTB gauge (4CW 802) also has the same facility. Having the holes /gaps for gears, etc. there is very useful.
That would be an ecumenical matter.

DaveHarris
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Re: What back to back setting do you use?

Postby DaveHarris » Mon Mar 18, 2013 9:33 pm

Being a 'new boy' to the society, i have just read this thread and have to say that i am totally confused! Surely there is only one back to back measurement that all should be working with? I would like to obtain a gauge as illustrated with the 'drop in' facility as shown by the exactoscale gauges(s) but my question has to be which one should i use; the P4 or the S4 gauge, particularly if i use the ready made 18.83 straight track offered by the society and other retailers and also points kits offered by a number of manufacturers?

Philip Hall
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Re: What back to back setting do you use?

Postby Philip Hall » Mon Mar 18, 2013 10:17 pm

Dave

I think as a new member to the Forum you are entitled to be confused. Put simply, there are maximum (17.75mm) and minimum (17.67mm) values for the B-B gauge, just as there are in the prototype, and so long as your stock falls between those two dimensions running will be fine. Some of our number prefer, with the benefit of experience, the higher setting, to give less 'slop' between the railheads, and some of us prefer the lower setting, which gives a little more 'slop' and consequently can ease stock around tighter curves. The gauges you can buy will all fall within this tolerance, and any of them will enable you to produce locomotives and stock that will work on any track built to P4 standards. Gauge widening of curved track (as per the prototype) is another thing that is already built into most of the standard P4 gauges you can buy, or you can buy gauge widened track bases from C&L/Exactoscale.

The P4 standards to which most of us work are the ones recommended by the Society in normal usage. However, those standards have a degree of manufacturing tolerance built in, and consequently there are still some variations from exact scale. Now, there are some of our members who prefer to work to exact scale standards and it is these which are known as S4. These feature an exact scale flangeway gap and an increased B-B dimension (17.87mm). These S4 standards are really for experienced practitioners who, to coin a phrase, want to go the extra mile.

So if you stick to the P4 gauges you can buy from the Stores and elsewhere, you will be fine. I hope this has lessened the confusion for you, and be assured there is a huge amount of knowledge and experience on here which we will be only to happy to share with you.

Philip
Last edited by Philip Hall on Mon Mar 18, 2013 11:59 pm, edited 1 time in total.

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grovenor-2685
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Re: What back to back setting do you use?

Postby grovenor-2685 » Mon Mar 18, 2013 11:28 pm

The P4 standards are defined in the Digest sheet here, http://www.scalefour.org/forum/digests_download.php?f=1-2v2-4.pdf and this does explain the use of exact scale and the implications.
You can also check the original version here, http://www.scalefour.org/history/p4manual.html
Keith

Chris Mitton
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Re: What back to back setting do you use?

Postby Chris Mitton » Mon Mar 18, 2013 11:30 pm

Philip Hall wrote:Dave
These feature an exact scale flangeway gap and an increased B-B dimension (18.87mm). These S4 standards are really for experienced practitioners who, to coin a phrase, want to go the extra mile.
Philip

A back-to-back greater than the track gauge - that really would give rough riding! :twisted: That's really "going the extra mill" - I assume you meant 17.87 .....otherwise thanks for the very helpful info.
Regards
Chris

Philip Hall
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Re: What back to back setting do you use?

Postby Philip Hall » Tue Mar 19, 2013 12:00 am

Chris

I checked this so carefully...! Now edited, and thanks for spotting the typo.

I should also have pointed out that it is virtually impossible to guarantee the perfectly true running of a wheelset; there may be a tiny amount of wobble, virtually invisible, but none the less there, and therefore with these tolerances of maximum and minimum B-B figures a very slight wobble can be tolerated.

Philip

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Rod Cameron
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Re: What back to back setting do you use?

Postby Rod Cameron » Tue Mar 19, 2013 2:31 pm

Philip Hall wrote:Chris
I should also have pointed out that it is virtually impossible to guarantee the perfectly true running of a wheelset; there may be a tiny amount of wobble, virtually invisible, but none the less there, and therefore with these tolerances of maximum and minimum B-B figures a very slight wobble can be tolerated.


A bit OT but I was just reading about a (real) Black 5 in February's BRILL which was described as an extremely rough rider (or similar). After much head-scratching they discovered that one of the drivers was a full half inch different in diameter from its pair due to a 'gross machining error'.
Rod

DaveHarris
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Re: What back to back setting do you use?

Postby DaveHarris » Tue Mar 19, 2013 3:21 pm

Philip and grovenor,

Many thanks for your replies. I have read the links as well now, the 'fog' is clearing, thanks very much for your responses

Regards
Dave

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Tim V
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Re: What back to back setting do you use?

Postby Tim V » Tue Mar 19, 2013 4:49 pm

At least a tolerance is specified in the standards. OO does not have a tolerance on its standards.

The prototype used to have a tolerance of 1/32" on the back to back.
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Andy W
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Re: What back to back setting do you use?

Postby Andy W » Tue Mar 19, 2013 6:40 pm

"The prototype used to have a tolerance of 1/32" on the back to back."

That's incredible, the workshop men really knew their stuff.
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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Thu Dec 07, 2017 4:59 pm

Reviving this thread ... I wondered if anyone had any further thoughts following Roger Sander's article in the Snooze and the recommendation of 17.75 min B to B to ensure good running? I was interested in the suggested improvement of running on Sidmouth as a result and particularly with reference to my own experience on my test track for Monsaldale.
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grovenor-2685
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Re: What back to back setting do you use?

Postby grovenor-2685 » Thu Dec 07, 2017 8:37 pm

and the recommendation of 17.75 min B to B to ensure good running?

Nothing new there, the same recommendation is in the Standard and is explained by Philip just a couple of posts back.
Regards

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Thu Dec 07, 2017 9:32 pm

grovenor-2685 wrote:
and the recommendation of 17.75 min B to B to ensure good running?

Nothing new there, the same recommendation is in the Standard and is explained by Philip just a couple of posts back.
Regards

Maybe I misunderstood .. I thought that the articles contention was that the digest range was too wide and that 17.67min was too close ... an rather than being the maximum within the P4 range 17.75 should rather be the minimum?
Tim Lee


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