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Foam vs plywood
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[quote]QUOTE: <i>Originally posted by fwright</i> <br /><br />Some cautions and experiences I haven't seen mentioned in this particular discussion: <br /> <br />The jigsaw method for plywood sub-roadbed DOES NOT work for grades on curves (unless you have very large curves and very modest grades). If you use reasoanble thickness plywood - I used 1/2 inch - you cannot bend/twist it in 2 dimensions simultaneously to follow the grade and keep the track level (or constant superelevation) across the rails. Prove it to yourself by raising one side of an oval higher than the other (use corrugated cardboard for the experiment). The only place the track will be level crossways will be at the 90 degrees of curvature point. The upper half of the curve/grade will have the outer rail raised, while the lower half will have the inner rail raised. The steeper the grade and/or the sharper the curve, the more pronounced the effect is. If the plywood is flexible enough to make the twist to keep the track level crossways all the way around the curving grade, then it is not rigid enough to be stable in flat areas. The best solution I have heard of - but quit that layout before I tried it - is some form of spline roadbed. You can still use plywood sub-roadbed on straight grades and flat areas - just not on curving grades. <br /> <br />Foam does not suffer this problem because you carve the grade into the foam, and can make the adjustments during the carving. <br /> <br />Fred Wright <br />jack of all trades.... you know the rest <br />Picture Gorge and Western Railway - none more picturesque <br />Tillamook Head and Bethel Railway - to Heaven and back <br />[/quote] <br /> <br />Fred, <br /> <br />I haven't experienced that probblem with my layout. I've got approximately 50' of elevated track on my around the room layout currently under constructions. I used 3/4" plywood throughout. All of my curves are flat and smooth. I DID make the horizontal to grade changes slow, making the first 18" at half grade before diving into the full grade. I intentionally used 3/4" as it would better foce the gentle vertical transitions that I wanted. <br /> <br />I've overlaid the 3/4" ply with 1" foam and so far so good. Put cork on top before laying the track. Have another 15' of track to lay before I'll have a continuous loop and will start running trains on the main line. I'll still have +50' to run for the local track, plus the yard and engine maintenance area. <br /> <br />Some people must see the problem you've described, and some don't. <br /> <br />Mark in Utah
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