009, 00n3, 3mm etc

[Guest]

Could anyone please advise me what the back to back and pinpoint to pinpoint dimensions are for  009,  00n3,  3mm,  and TT. I have tried the Internet, but have been unable to get very much information.

Edited April 16, 2021 by Guest

[Dungrange]

The critical dimension is the back to front dimension, so that when the running edge or front of the flange on one wheelset is against the running edge of the rail, the rear of the flange on the opposite side just clears the check rail.  Therefore, there would be two pieces of information that you would need to know in addition to the track gauge to determine the optimum back to back dimension for any gauge.  What is the effective thickness of the flanges on the wheels that you intend to use and what checkrail gap do you intend on using?  The difference between the track gauge and the flangeway gap through point-work would give you the check gauge and the back to front dimension minus the effective flange thickness of the wheel would give you the back to back dimension.

 

To give you an example, in 00 the optimum back to back with commercial track and modern wheels varies between 14.4 mm and 14.6 mm depending on the wheelset of the rolling stock (assuming RP25/110 wheels or finer) and if moving to 00 'finescale' standards, which involve using 1mm flangeway gaps (as per EM gauge), then the optimum back to back (with EM profile wheels) becomes 14.8 mm.  Older 00 stock, with thicker flanges, will have a smaller back to back (sometimes just 14 mm).  Therefore, to answer the question for 00, I could say somewhere between 14 and 14.8 mm depending on your wheel and track standards.

 

The back to back is therefore a function of both the track standards and the rolling stock wheel standards.  Knowing the scale / gauge alone isn't enough.

 

The NMRA give back to back data for a range of scales at https://www.nmra.org/sites/default/files/standards/sandrp/pdf/s-4.2_2019.01.04.pdf.  For example, TT (1:120) is given as 10.54 mm + 0.05 mm - 0.20 mm, which means a back to back in the range 10.34 mm to 10.59 mm.  These of course assume that the wheel profile is in line with NMRA standards and similarly the track.

 

There is a lot of information about 3mm scale on the 3mm society website - wheel and track standards are here - https://drive.google.com/file/d/0B0KD5_ptqrd7bFJVeUNXeXJQd2s/view.  There is a range of back to back dimensions quoted depending on which of the 3mm scale standards you are interested in.

 

With regards the pinpoint to pinpoint dimension, I'd say it's pretty much whatever the manufacturer uses.  In 4mm scale, it should be 26 mm, but that's not to say that there aren't 00 models with a pinpoint to pinpoint dimension of as little as 24.5 mm.  In practise it doesn't matter if running on 00 track, but if there is a desire to convert to P4, then it should be easier to convert if the model has a pinpoint to pinpoint dimension of 26 mm, as no-one produces P4 wheels with any other pinpoint to pinpoint dimension.  It's really only critical to know that if you intend replacing the wheels on a model, in which case either measure the existing axle length and buy a replacement with the same pinpoint to pinpoint dimension, or use a reamer to remove material to make the model match the new axles (assuming they are longer).

[Guest]

Thanks for that, I managed to unpick some of the info from your post and the links, and think I can work out roughly the information I needed.