Sorry for the delay in blog updates recently but I have been busy both on the layout and around the house. There will be a few updates in quick succession.
After much thought and discussion with Andrew over the last nine months or so, we have decided to abandon Proto-87 wheel and track standards and to adopt the NMRA Fine:HO track and wheel standards.
Ever since we built Bowen Creek, we thought that diesel locomotive conversion was going to be straightforward – just a matter of swapping out the wheelsets. However, during the few outings of the layout, we soon realised that some form of suspension was required to keep the wheels on the rails. Since the P87 flange depth is only around 0.3mm, the slightest bump in the track or lack of lateral movement in the axles would cause the wheels to ride up over the railhead, most frequently on curves. These issues, we found, relate mainly to three axle (Co-Co) bogies, and the centre axle in particular.
So, most of you may not be aware, but over the last three years or so, we had been developing a suspension system for retrofitting to RTR locomotives to enable the use of P87 wheelsets.
With greatly appreciated assistance from Andrew Lee of AndIan Models, we had designed an etched suspension ‘kit’ that would have replaced the pickup plates on the locos and incorporated sprung axle boxes.
Our initial testing, on the Trainorama 47 class bogies, proved the concept worked, but over time we realised that there were major reliability issues. On the test track, the loco would run OK in one direction, but not the other, and derailing on curves was still an issue.
We both realised that whilst Proto-87 certainly looked nice, to get the suspension to work reliably on the locomotives was going to mean far too much work, and neither of us were prepared to further invest that amount of time and finances. We both have layouts to build and quite substantial locomotive fleets to convert!!
Also, with the release of the new Auscision 45 class, it was noticed when I pulled a bogie apart, that the design of the pickup system is totally different to that of a Trainorama locomotive, which made the conversion to P87 almost impossible in my opinion.
So with heavy hearts, we are heading down the RP25/88 wheel route. These wheelsets comply with the NMRA Fine:HO standards, and by keeping a track gauge of 16.5mm, we can achieve a flangeway of 1mm. There is a requirement to open out the back-to-back of existing wheelsets to a minimum of 14.8mm. Generally this is only about an increase of 0.2 to 0.3mm from factory wheelsets. RP25/110 wheels will also still run through these frogs with a back-to-back adjustment.
Using the information in the NMRA standards S-3.1 and S-4.1, I have come up with a single page datasheet with all the relevant measurements shown. Click on the image to open a larger PDF.
I have commissioned Keiran Ryan to design and manufacture some new etched vee crossings to suit code 70 rail with a 1mm flangeway in both 1:6 and 1:8 sizes.
I have recently received the first test etches of these and they are very nice.
With some minor corrections to be done, it is hoped I will have the production versions in a month or so which will allow me to continue on with the much delayed task of turnout building, along with changing out the thirty two vee crossings in the staging yards.
The images below show the two test etches for 1:6 and 1:8 vee crossings, the 1:8 crossing assembled and removed from its fret, and the 1:6 crossing installed in a section of track to test wheel operation.