September 28, 2010

Turntable - Part Deux

I was not happy with the look of the first turntable. The actual Manassas turntable was quite rough in construction. Mine was looking too "square and regular."
Excerpt from Railroad and Engineering Journal, Vol LXIII, No 10. 

Further research into early turntable designs revealed that gallows style turntables did not have rail stringers. In looking at the Manassas turntable, I concluded that it was very similar to a gallows style where the ties form a suspended deck. However, the Manassas turntable uses a wrought iron rod tension truss instead of a gallows.  I was concerned about racking and twisting  forces on such a design without a rail stringer, but a passage from an engineering book on early turntables explained that due to the low speed involved, those forces are minimal.



So I am rebuilding the Falmouth turntable be be a closer match to the Manassas prototype.   I did not use the laser to cut these parts as I intentionally wanted some subtle variation in dimensions that comes with hand cut parts.   I sanded the sharp corners and distrressed the wood slightly to make the parts look more "homemade." These parts form the main chords. I find it hard to believe that they mortised the main chords to accept the vertical truss supports, but the photographic evidence clearly shows this.



I am going easier on the black stain this time around as the wood should not be overly weathered. I'll have to make a new shaft and pedestal to make sure the height is correct.


Each tie has 4 visible bolts that hold it against the main chord. The bolts are in a distinctive pattern (see the prototype photo on the previous post). Adding these will be tomorrow's project. You really have to like adding NBWs to be an O Scale modeler in this period.


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