RodTT wrote:As to tie spacing - figures seem to vary. According to the Railway Tie Association (they had to exist, didn't they?), http://www.rta.org/faqs, the spacing is 19.5in. According to Wikipedia it's 18. So for TT something like 0.15 to 0.175 inches should look about right. But I suppose you have to take into account the tie thickness too, a thicker tie would presumably look better with a bigger gap.
The tie spacing depends on the type of the track, railroad, and era.
Here is Pennsy's track spacing as an example:
http://prr.railfan.net/standards/standards.cgi?plan=61030-B