Meny Stäng

A Swedish 2-6-2 in 16 mm – 2

Part 2 – Pre-conditions

My main objectives for the build are:

– Capture the ”look and feel” of the prototype
– A working, steam driven locomotive
– Use pre-machined parts (e.g. steam engine parts) as far as possible

The obvious start would be to start out with the last bullet, getting some parts to start with. As a way to invest my dedication in the project, I decided to go on and buy the parts required. Spending money on something does really put some worth into the project and gives you a desire to finish as opposed to if you just ”plan to do” something.

A few E-mails with the staff at Roundhouse both saved me some money and had the parts I needed on my workbench within a week or so. What I needed were the ”Lady Anne” Chassis and boiler kits. I want to send my appreciation to the RH staff, good help and quick response, really nice people to deal with.

With parts in hand I started out to draw up the locomotive to be in Fusion360. I’ll likely not be drawing the complete loco in Fusion, only the parts I need to be assured that it will go together and fit within the prototypes outline.

First finding was that if I kept the location of the driving wheels and cylinder per the prototype, the connecting rods would foul the cylinder. So I pushed the cylinder forward and the wheels backward. I think I ended up with a total deviation of ca 15 mm. This made the locomotive look a bit chubby, I’ll keep it that way for now, only way to solve is to move the rear bufferbeam backwards a bit. I will think about this for a while, likely I need to add the cab, boiler and side tanks before I can decide.,

Reality vs model, as seen the driving wheels are a bit further back on the model.

I think the look is there, I could stretch the rear cut-away of the frames a bit forward to improve visually. In reality, I think it will not be noticeable that the wheels are a bit back, I’ll leave it as is.
On the other hand, it is noticeable that the model has Walschaerts valve gear but the prototype has Allan. The superheated prototype had Walschaerts but again, I like the look of the loco with Allan more and I decided to live with that.

After asking on the 16 mm loco builders E-mail list, I was told that as long as I don’t manipulate the strokes of the motion, I can adjust the length of the rods quite freely.
I decided to try two things, one was to tilt the cylinders to point the cylinder rod centre line straight at the driving wheel centre (that is standard practice I think) and also move the expansion link forward about 10 mm.
Right now the bushing for the expansion link will just touch the centre (flange-less) wheel, I can remove about 1 mm of the thread and all will be OK, but moving the bushing forward will place it at a more prototypical location and also give more clearance. The radius rod looks to be very short but I hope it will work…

Back at the drawing board I drew up a new set of frames and had to go through the somewhat tiresome task to re-attach and re-align all parts in the cad to the new frames. However, doing it all over again, I had the opportunity to correct some mistakes and update all pieces to get the 3D model more accurate, time well spent! I thought…

After assembling it all once over, with several adjusted parts, I found that going to far towards a more scale appearance would result in 3-4 tight spots that were not that bad in the first attempt. The hours spent with Fusion had paid off! If I had found this out after cutting the frames and assembling the parts, the project would likely have been put on a shelf and forgotten, investment or not…

Turning back to the old design and tidying up some parts resulted in the video of the motion below. I tried to move the expansion link a bit forward to avoid the turning down of the threads, but… No, I think I’ll rather turn the threads down, the margins are very small and I saw no need to push my luck.

Video of the completed design assessment in Fusion360.

With the movie above I think I have made sure all will fit, there will be a very close fit at some locations but there are margins for adjustment.

All pre-conditions are there, the steam engines built with standard Roundhouse parts will fit, the look and feel of the prototype is still there I think (as far as the motion goes). We have a project!

Learning that the CAD will assist in finding out how things likely will come together has resulted in another decision. I will also draw and fit parts such as the boiler, gas tank, lubricator and other necessary parts in Fusion too. Furthermore I will sketch the body and get the outline for the etch frets to be produced, no rivet detail or tabs, that will be done in another tool, but the outlines would be helpful. It may also be a training session in Fusion sheet metal mode…

Goto to Part 3 – CAD completion (not yet available…)