B2B and frame width advice please

Members Forum RTR Conversions Locos B2B and frame width advice please

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    • #240738
      Richard Spratt

        I’ve just decided to move over to EM and joined EMGS earlier this month. I’ve given up with P4 even though I’ve built a couple of locos and a lot of stock as I struggled to succeed with track. My locos etc have generally run well on others track. The RTL points was the decider.

        I’ve already got very confused as to what B2B I should be using and I’ve trawled the EMGS forum and handbook with no success.  I’ve also bought a couple of B2B gauges but they’re not the same width!! On rmweb there has been a lot of discussion about the topic and Chuffer Davis has even said that there is no EM forum on rmweb because all the information is here! At the moment I so confused and full of despair that I’ve stopped my conversion of my Hornby Peckett and I’m reconsidering my decision.

        Whilst I’m asking questions, what is the recommended width for inside frame loco frames?

      • #241098
        Trade Officer

          Hi Richard
          The BtoB is 16.5 mm. Below is a link to the track standards that give you back to back plus tyre width as well as track standards

          Are the 2 BtoB gauges you refer to the ones you recently purchased from the stores? If so, can you let me know the widths as they should be the same. If there is a problem I will replace them.

          Frame widths are generally 13.5mm between the insides. That is the width of the EM spacers. That has probably been based on 15thou frames. Thicker frames may require narrow frame spacers


        • #241102
          John Cutler

            As stated above, the EMGS Back-to-Back is 16.5mm.
            I have read somewhere that you might need to reduce that to 16.4mm if you use RTR wheels which tend to be to the RP25 standard, but I have very little experience of that.
            Some people use a BB of 16.7mm but I would not recommend that if you are not going to build your own track.
            I confess to using 16.5mm as a minimum so my BB often wanders towards 16.6 or even 16.7mm.
            I do not think it gives me any issues that I am aware of.
            No doubt that will horrify some people but hey, this is not P4!

            As to frame width, there is no standard.
            I find the 13.5mm width often supplied in kits a waste of space resource.
            All too often one ends up using spacing washers to reduce sideplay on drivers; why not just make the frames wider?
            If you build (or in my case, try to build) split frame chassis, you need all the frame width you can get so as to fit a gearbox and a split on the driven axle.
            Likewise if you want to build working inside valve gear (I have no experience of that; you must be joking!).
            The sensible approach is to work out how much sideplay you need on the driven axles.
            That will be determined by the minimum curves you hope to traverse and the loco wheelbase.
            I have built a Connoisseur LSWR G6 0-6-0T with 15.3mm wide frames (i.e. the kit default P4 frames) that traverses 30″ radius curves in EM with no problems (much to my surprise I admit!).

            Good Luck!

          • #241103
            Paul Willis

              @John Cutler said:

              If you build (or in my case, try to build) split frame chassis, you need all the frame width you can get so as to fit a gearbox and a split on the driven axle.

              Hi John,

              It doesn’t have to so difficult to get a gearbox to fit into a split chassis. Do a cut-and-shut on an appropriate High Level gearbox like I did in the attached pictures.

              Okay, the actual locomotive is in P4, but as you will see, there’s yards of space between the gaps in the axle and the bearings themselves.

              Have fun!

            • #241104
              Paul Willis


                Hmmm… Gearbox-4.JPG

                Hmmm… These didn’t attach to the original post!

              • #241107
                John Cutler

                  Thanks for this, Paul.
                  I have lots of questions, but I do not want to hijack this thread so will start a new topic and try to copy your pictures.

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