While the turntable hasn't been a secret, those of us involved have kept it largely under the radar, not wanting to distract from more current projects. Now that the turntable is at the forefront of activities for the coming year, I suppose it's time to shed some light on the project, it's design, and what's been done so far.
Two years ago Jason and Dave Crow were discussing ways of forming the ring rail, and spider rails. Dave got in touch with me to see if I would be interested in getting started on the patterns so that we'd be in a better position to get going on the turntable when the time was right. So he sent me a scan of the Portland Co. drawing, and I started to scale it to design the patterns. It just so happened that my dad was visiting me at school that weekend, and we broke out my copies of NGSV just to scope out the design. It wasn't more than an hour or two later that he was drawing things up in Autocad, trying to reconcile the pictures and the plans. Dave and Jason indicated that nobody had yet set upon designing it, so I talked my dad into taking it on.
During the winter and spring of 2014, I made the patterns for the center pivot, and the wheel which would be used for the spider bearing, and outer supports, and Harold worked through the design and the stress analysis. As he said previously, the whole thing will be and look very much like the original. For the structure of the turntable itself, there were very few compromises made, in order to maintain the integrity of such a recognizable feature of the original railway. However, there was at least one design flaw with the original Portland design which needed to be addressed. If you look at any pictures of the Wiscasset or Albion tables, you can see substantial blocking placed inboard of the cross beam which the inner truss rod is mounted to. The truss rod is trying to tilt that beam inwards, and the only thing holding it in place is the tension of the bolts holding it to the main beams. The blocking which the railway added was a divergence from the Portland Co. Plans, and was their effort to keep the cross beam from folding inwards, and you can see that it was only marginally successful. The mounting configuration of the outer truss rod is much more appropriate, in the way that it's load is directed through the main beams. In order to achieve a similar loading configuration for the inner truss rod, we designed a large bracket for the truss rod to pass through, and be tightened against. The bracket will be set into and bolted to the main beam, and butted against the offending crossbeam. This should shift the majority of the load onto the main beam, and prevent the cross beam from being rolled over. We designed the bracket to be a casting to be within the same spirit as the original designers might have done. My dad made the pattern for this bracket, and it was visible in the Facebook post from earlier this week, that sharp eyed viewers may have noticed was not in the original plans. All of these patterns were delivered to the museum in the summer of 2014, with a mess of #11 patterns as well.
My role with the turntable largely ended with the patterns. Since then Harold has been refining the design to suit, and creating part and assembly drawings. However we did spend a day last summer gathering up and counting all of the bridge washers on the campus. There were hundreds of them, and we have enough on hand to cover the ~500 which are needed for the turntable.
Now, we're both really looking forwards to the real work getting started. The project is now in the hands of the talented and dedicated on site crew.
