Main drivers.
The main drivers are obviously a large part of what the locomotive looks like, and I was keen to do a good job on replicating them. This was the second pattern I had made, the first being the front truck. By now I had decided I was on a one way trip and it was too late to jump so I had better forge ahead.
There were a number of decisions to made in creating the patterns for the drivers. Mostly this came down to how much money you wanted to spend and how much detail you got for your £. You also needed to decide how much detail you could sacrifice to get the cost to a reasonable number.
Just a few word for the uninitiated and those not that familiar with steam locomotives that may light upon this page. Steam locomotives work basically by converting the energy contained in the steam via reciprocating pistons in the steam cylinders into a rotary motion. To do this the wheels are connected by rods that transfer the reciprocating action of the pistons into the rotary motion of the wheels All this linkage is heavy and where it connects to the wheels on the crank pins it creates widely out of balance forces. To combat this each wheel has a balance weight opposite the crank pin. So much for theory then, what's so complicated about that ? All you need are eight wheels with some weights on them. Well yes and no, because dependant on where the wheel is means that there may be more or less force acting on it due to the reciprocating mass attached to it.
With it so far? Well there is one final double six to add to the mix. The wheels are handed as one side leads and one side trails. What do I mean by that well it means that the balance weights on the wheels are in different positions for one thing. Basically on one side of the locomotive all the crank pins will be 90deg ahead of the opposite side and that's as far as I am going on theory as my head is hurting. If you need more explanation do a search on how a steam locomotive works and see what you get.
So lets get back to the patterns as I said a number of decisions had to be made prior to making the patterns. This boiled down to a few key points. Did I want the wheels to have flat backs with only detail on the front. Did I want to add the balance weights on after casting as this would cut down on the number of patterns but be less realistic, and how much money did I want to spend ?
Well I wanted full detail on the wheels,I did not want to add the weights on after casting and I wanted to spend as little as possible, so over to you Terry.
Well after some deep breaths Terry came up with the following solution that seemed to tick all my unreasonable boxes. The locomotive although it has eight wheels only has three different wheel types. They are the main, leading and trailing and intermediate. So first off was a master pattern from this 6 castings in aluminum would be cast to produce the base form for the three different wheels and left and right hand versions.
Master pattern ready to pour in aluminum
The best pattern to see the differences from our staring point is the main driver. The next two shots show the patterns for the left and right hand version
And by way of comparison the three patterns shown together
So we now had all the patterns and it was off to the foundry to get the first pour done
First pour of 32 wheels and front truck components.
.jpg)
Second pour, main's bottom right, intermediate; center upper, and the rest are leading and trailing
So that's the pattern making and casting dealt with next up we will look at the machining.