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From FLM Br 50.849 to NMBS 25.001

Additional tools allow a different approach for conversion of RTR models, demonstrated with a NMBS/SNCB class 25 loco.
See also part 1 with introduction on these loco's here


The NMBS had 2 machines of the Br 50 ÜK series with the old form of Wagner deflectors numbered 25.001 and 25.013. The latter was always coupled to a 32 m³ 'Wannentender', where 25.001 can be coupled with the 26 m³ 'Kastentender' after 1955. The 32 m³ tender requires far more work for conversion thus the easy approach is for 25.001 after 1955. An excellent photograph and published in a host of literature was taken by J.H. Renaud in 1956 showing it with a 26 m³ tender.

Photo of SNCB 25.001 by J.H. Renaud.

A model of this loco can be build using the older FLM Br 50.849 model with Wagner deflectors, but it needs a boiler with the frostprotection, 1 dome and 2 sandboxes and removal of the preheater and numerous tubes and handrails and a cab with single window and ÜK type of roofvent. Of course it is possible to scrape the existing boiler bare of all superfluous detail and fill up the holes again but this means a lot of careful work with a high risk that something goes wrong and leads to havoc. You also have to convert the cab by replacing the vents and close front window or use Br 52 cab with 'only' a window change , but this won't fit on your Br 50 boiler because of different arrangements in the r-t-r models. Building an entire new boiler from metal is feasible, such as shown in part 1 on the type 25/26 elsewhere, but adding all the fittings from scratch to a bare boiler is also lot of work. An intermediate way looks to be using a 3D printer as this allows the major parts to be directly printed only needing the thin free standing parts, such as the hand rails and sanding tubes, to be added by hand. There is no longer any need for castings or additional models as supplier of parts. Another advantage is of course that with a good base drawing other variants with slightly different appendages and even different boilers can be easily developed by changing those specific parts in the drawing and put the printer at work again. To produce additionial drawings access to sufficiently detailed information of the original is of course necessary, as well as some experience in 3D drafting and knowledge of what your 3D printer is capable to print. The latter here is still a learning process as the printer seems capable of finer detail than thought. For instance if the resin would be more rigid than even free standing handrails and tubes would be feasible too. I decided to make these of metal wire, because I expect that these will not survive the handling of the model in practise. Thus this still leaves some craft work in order to finish this loco.

Drawing and design

All dimensions for the drawing were already available because of the earlier exercise of making a new boiler in brass. This allowed a quick approach in 3D of a first sketch of the boiler. The cab however had to be drawn up from zero. The drawings were made in Cinema 4D (C4D-R21) a professional package for visualisations.
In order to make it a replacement job all holes and screw fixings for fitting it to the frame were measured and copied from the original FLM Br 50 boiler. Of course this involved a test run with a redo for further adaptions but actually the first print was pretty much spot on and useable as oneoff. Of course some things come to light such as the differences between the FLM Br 50 and Br 52 frame, the earlier made metal example was finally combined with a FLM Br 52 frame.

new boilernew boiler drawn in C4D.

The new boiler as seen on screen, below chimney adapted with a large opening for the Br 50 frame and one of those horrible tubes for fixing it.

ÜK Cab with the 'old' rounded front windows but with a 'new' roofvent. Through the ring for fitting it to the boiler you can see a 'click' space for fixing it to the existing FLM frame.

The new cab to go with this loco complete with lifting hooks on the roof and wind deflectors at its window and a set of 'click' spacings on the inside of the cab. The rivets are left off on purpose as this allows refining the cab sides with wet and dry for a smooth surface.

printed results
class 25 boiler with frost protection, 2 cast sandboxes and 1 dome and various tubes and appendages.

This is what the printer delivers, a new boiler and cab still on their printed ladder network. Several amendments (some adding, but mostly deleting) in the posts of this ladder network were done for later prints.

The new class 25 boiler showing its belly, these ladder remains can be quite quickly smoothed

There is some cleaning up to do after cutting off of the ladder network. The ladder remains can be easily removed and the remaining tips first flattened with a stick with #180 coarse sanding paper and then polished smooth with #600 wet and dry. The big rectangular hole still shows a small piece of the ladder network going through, this can be pulled out from the front with tweezers. I found it necessary to include a structural reinforcement in the boiler to keep it circular during the printing and hardening. The original lead weighting piece fits between this reinforcement and the front of the cab, but, when necessary, this part can be cut out with a jewellers saw, for instance when you want to fit a loudspeaker below the chimney.

Test fit on the loco of the first design
first impression

The printed boiler and cab fitted to the loco, the white stuff collected in corners is dust from sanding that still has to be washed off with a soft brush under running tapwater.

To be followed up with further updates, but having already too many projects to finish on the desk this will be a low profile project as older items will get preference. Particularly this outcome leads to a review for the class 64 (P8) and trials to finish this model with a 3D printed boiler complete with ACFI and all of its tubing.
Click here to visit that page.

copyright: Henk Oversloot
date: 27 May 2020