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.