Evening all.. I've decided that my next task is to set the chassis up as well as I can at this stage in the build, there will be a fair bit more weight added but it shouldn't involve too much work in adjusting the springs to suit. Going by the current weighbridge results I have a fair amount of playing around to get the chassis balanced.
Why do this now I hear? simple, during transit on Saturday I broke a top leaf spring on the left-hand side trailing axle. All my own fault, I had tightened the spring hangers to the max to bring the weight down at the rear for when fitting the pistons/rods so that I could roll the chassis without needing to push down hard on the rear to get the chassis level, what I forgot to do was loosen the springs when the boiler was fitted and thus putting them under a lot of stress, with zero movement left in the spring during transit it was inevitable that hitting the first pothole would not end well. Some may recall that I have slowly been replacing steel for Tufnol on the rear Cartazzi springs as the weight increased and I had a better idea of how much springing I need. Going back even further into the build when the springs were first made, it took over 100lb to get the springs to sit at their ride height, clearly, the springs were far too strong but I left for the reason above.
So with all the weight greatly increased and suffering a broken spring ( only took an hour to make a new one and it could be fitted without removing anything else) it is time to get the chassis close to balanced and going by the results today, it has a long way to go.
This picture is weighbridge MK2, nothing wrong with the first except for me leaving it outside in the rain resulting in the screen no longer working, I could still see the weight via Bluetooth but wanted the screen to be working too. I have made better use of the original casing this time around but the basic design is the same as before.
I have made better rising plates which now have a machined recess so that they locate better on the weighing plate, as with before, with two plates fitted this weighs the axle, remove one plate to weigh the opposite wheel to it alone.
I have the prototype's axle weights from one of my reference books which I then scaled against the model's total weight against the known axle % rates
Prototype weights are engine 92 tons
Front bogie 17 ton
Leading driver 20 tons
main driver 20 tons
rear driver 20 tons
trailing axle 15 tons
percentage split, 18.5%, 21.7%, 21.7%, 21.7% and 16.3% respectively
using the above percentage splits and a little maths I can get a ballpark figure for the model
model weight (currently) is total of 231.4 lbs (more than I had thought, this makes the boiler alone over 90lbs empty, IIRC the volume is 9 Ltrs full, so nearly 20 lbs with perhaps 15-16 lbs running weight)
Front bogie leading-axle 33.8 lbs
Front bogie trailing axle 35.8 lbs
leading driver 20.8 lbs
main driver 27.8 lbs
rear driver 69.4 lbs
trailing axle 43.8 lbs
What I need to find with the current total weight approx is
front bogie (total weight) 42.8 lbs
leading driver 46.28 lbs
main driver 46.28 lbs
rear driver 46.28 lbs
Trailing axle 37.71 lbs
So I have a bit of work ahead of me in adjusting the spring rates to get them closer to those above.
At least when looking at the current axle weights and noting how tail heavy the loco currently is I can understand why the trailing axle spring failed when it had been left badly adjusted at full deflection, it's not surprising that the top leaf snapped on one side. I should also add that my son's van is lowered with large alloy wheels and the side nearest the loco's broken spring has its own suspension issues with a damaged spring resulting in it sitting lower that side. Something that I wasn't aware of at the time of loading and had secured the loco down on that side as it was the opposite side to the driver and thus trying to equal the weight and also following good practice and not sit with a heavy weight behind me.
This info isn't on the blog, two reasons, one where the server is located is having some maintenance by Virgin and thus it's down and two I have been asked to do an article covering the weighbridge for the mag which will be in much more detail and will hopefully include the final measurements and pictures of the weighbridge construction.
Hope this is of interest, it's very much early days and the final figures will change. The current weight shows that the model is certainly going to weigh a fair bit more than Don's design, at 231 lb now ( design weight with tender is listed at 230lb), and with still a lot more parts to be added she's not going to be light. All those extra details and the modified boiler will see to this for sure..
Pete