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K3s Progress 2013 to 2014

The outside cylinders

After the 2013 Harrogate Exhibition, I made a start on the outside cylinders.

I had eventually come to the conclusion that the cylinders would need to be fabricated because there were no suitable castings available. I had looked at the Enterprise and V2 castings for the Martin Evans designs and those for the V2 from Michael Breeze, but whilst these were well enough designed none had the ability to properly represent the prototype design used for the LNER pony truck locomotives. In the early designs like the K3s and O2s the three cylinders were separate, the outside bolted to the frames, which had a large cut out each side into which the inside cylinder was located. This was bolted to the outside cylinders. This created a massive and very stiff assembly that I wanted to replicate on the models.  Later engines were fitted with a single casting (the monoblock) for the three cylinders.  I spent a lot of time deciding on the materials and looked at cast iron, steel and bronze. I ultimately discarded cast iron due to the difficulties associated with joining it. I have silver soldered and brazed cast iron, but it is a process that can be unreliable and I considered it would be liable to serious problems on such complex fabrications. Steel was a much more attractive prospect but having discussed it with a number of experienced model engineers who were concerned about the cylinder friction and corrosion issues and who suggested cast iron liners in the cylinders which would have created issues with cylinder wall thickness or maintenance of scale bore dimensions, I concluded that bronze cylinders with brass supporting sections would be the way to go.

  I'd actually drawn the cylinders about 15 years before, mostly during lunch breaks at work, until the use of non-company software on our computers was banned. The details were put together from the H4 and K3 GAs, photographs of them under construction and a certain amount of knowledge I had from working on the full sized A4 and some drawings where a lot of the details were LNER standards. I didn't actually get a drawing of the K3 cylinders until after I had started construction and I was surprised to discover I hadn't done too badly and decided not to change what I had done and accept the minor deviations from prototype.

I have shown the outside cylinder GA and drawings of the individual components to give some idea of what you are seeing in the following photographs. These are the original drawings and some changes have been made to simplify the assemblies as the work progressed.

Figure 1 Outside cylinder GA

Figure 2 Cylinder Parts 1

Figure 2A Cylinder Parts 2

The 1/8 inch thick cylinder end plates were the starting point, these being cut from the sheet and machined to accurate rectangles prior to marking out.

Figure 3 -The marked out cylinder end plates are set up for drilling

Figure 4 - Drilling the reference holesthrough four 1/8" thick plates

The block of four plates was pinned and screwed together and then mounted in the four jaw of the lathe for boring the cylinder and valve chest holes.


Figure 5 - Setting up the end plates for boring the cylinder opening using the wobbler

Figure 6 - Drilling the end plates for the cylinder

Figure 7 - Boring the cylinder opening in progress

Figure 8- Boring the end plates for the valve chest

A second set of four plates then followed for the other engine.

The next operation was to make the cylinder backplates. These were made from 1/4" thick brass plate to give plenty of machining allowance as I wasn't sure how much distortion I might get during the silver soldering process.

Four plates were cut and mounted in the milling vice for machining the edges to form accurate rectangles.


Figure 9 - Preparing brass plate for cylinder backplates

After squaring, the plates were mounted in the milling machine for drilling and profiling and are seen in Figure 4 being spotted using a centre drill, positions determined from the co-ordinates drawn in CAD


Figure 10 Drilling the backplates

Multiple clamps were needed to allow for moving them as the drilling progressed. After spotting the four plates were through drilled undersized for 7BA.

Next the large rectangular hole was milled out

Figure 11 Milling the large opening in the backplates

Then the profiling of the outer edges of the plates again using co-ordinate location of the milling cutter

Figure 12 Profiling the backplates 1

Figure 13 Profiling the backplates 2

 Figure 14 Profiling the backplates 3

Figure 15 Profiling the backplates 4

Figure 16 Drawing showing the path of the milling cutter dimensioned in 10 thou intervals for profiling the backplates

Figure 17 Cutting the exhaust passages through the backplates

Figure 18 squaring the corners of the holes

Figure 19 close up of a profiled corner

Even with a resolution of 10 thou the finished profile is a little rough, but a drum sander on the Dremel soon improves the finish

Small diameter holes were drilled in the corners and finally finished square by hand.


Figure 20 close up of a profiled corner after finishing with the Dremel

Figure 21 - Set up for making the locating slots for the front back and internal plates

Figure 22 Locating slots completed

Figure 23 - The end plates were returned to the mill to form the projections that locate them in the backplate

Figure 24 - First trial assembly of the back and end plates

The next operation was to make the cylinder barrels. I had checked the LG2 material chosen could be silver soldered and I was fairly sure that provided the material was unstressed during heating that there would be little distortion, so I was confident proceeding with this material. I bought continuously cast thick walled tube and cut it into suitable lengths for machining

Figure 25 - Bronze tube marked for cutting

Figure 26 - Cylinder barrel external machining

Figure 27 - Internal boring

 Figure 28 - A Cylinder barrel ready for final machining

At this stage the barrels (six of them) were machined close to finished size. The ends of the bores were opened up and a tapered transition to the bore size made to facilitate easy entry of the ringed pistons. I failed to photograph this work. Following this the cylinders were then set up again for the rebate to be machined on the ends of the outside of the barrels so they would fit into the end plates

Figure 29 - Setting up the barrel in the four jaw for rebating the outside ends. Note the internal ends had already been opened up and chamfered



Figure 30 - Machining the rebate

A similar machining process was done for the valve chests and once these were machined all over to the near finished dimensions, final machining of the external surfaces could proceed. To achieve this a mandrel was made so the valve chest could be mounted between centres

Figure 31 - Valve chest mounted between centres

Figure 32 - profiling the exterior of the valve chest

Figure 33 - Profiling almost complete

Figure 34 - Valve chest in cylinder frame

Likewise the cylinder barrel was mounted on a mandrel between centres for external profiling

Figure 35 - Finish profiling of the cylinder barrel

Figure 36 - Cutting the ports in the barrel

Figure 37 - View of ports and location flat

Figure 38 - Cutting the ports in the valve chest

As the cylinders and valve chest ODs intersect it was necessary to machine a flats on the cylinder at each end, on the internal ribs and along the length of the valve chest. These also located the components so they have the correct angular relationship to orientate the ports correctly.

Figure 39 - Machining the location flats

At this point I thought it would be useful to drill all the cylinder bolt holes in the frames. Two holes had been drilled at frame drilling stage which fairly accurately located the cylinders so the backplates could be attached and drilled through.


Figure 40 - drilling the frames from the cylinder backplates

Figure 41 - Not the most elegant set up for the drilling machine but it sufficed

Once done, the embryo cylinders could be temporarily bolted to the frames, one of those moments in the construction that gives a much needed morale boost.

Figure 42 - Cylinder fitted to the H4 at last

Figure 43 - The H4 at the 2014 Harrogate Exhibition between Jim Scott's magnificent Terrier and Ian Spencer's B1

The next page in this diary will cover the assembly and silver soldering of the outside cylinders and exhaust passages and the subsequent machining operations, along with the machining of the smokebox and the start of the inside cylinder fabrication.



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