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Good points. I think it depends mostly on wall thickness. The PVC used for furniture, medical carts and other structural uses is thick-walled and very strong, same as the stuff I make critter cages out of. The stuff used for fluids in generally thin-walled. Brittleness resulting from weather changes would be more of a factor in my part of the country, and from a lot of UV exposure, possibly.
If a PVC lawn chair can handle a 300 pond load, and a PVC patio table can handle a huge dinner spread, I think PVC will hold a model railway, at least in N or HO scale! I'm still deciding whether or not to try it. It's very tempting.
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I'm sure it could be done. Something else that just jumped to mind though is that careful planning will be needed well in advance. Especially when knowing where to locate structure under the layout, as in the case of support pipes running the width of the bench work. You could place a length of pipe in the wrong spot and then find out that it's where you need to install a Tort for example thus interfering with your design goals and if you cut it to make room for the Tort, you've just compromised the bench work structure.
I'd like to see someone try it and be successful. I don't mind being proven wrong, its one of the many ways I learn.  
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MasonJar Wrote:Re: Splitting plywood.
1) Corner blocks as suggested, so no screws have to go ing the "end grain" of the ply.
2) Predrill and countersink for proper wood screws, not drywall screws. Drywall screws have a different profile under the head to pull the paper covering of drywall down without tearing. However, this creates a wedge action that can split wood, as most countersink bits have a different profile.
3) Use minimal screws, but lots of good carpernters/yellow glue. And clamps!
Andrew
Another couple of problems with dry wall screws is that they are brittle, and rust like crazy if they get wet. I think an alternative to wood screws would be deck screws designed for construction of wooden and composite decks.
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Posts: 2,269
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Russ Bellinis Wrote:MasonJar Wrote:Re: Splitting plywood.
1) Corner blocks as suggested, so no screws have to go ing the "end grain" of the ply.
2) Predrill and countersink for proper wood screws, not drywall screws. Drywall screws have a different profile under the head to pull the paper covering of drywall down without tearing. However, this creates a wedge action that can split wood, as most countersink bits have a different profile.
3) Use minimal screws, but lots of good carpernters/yellow glue. And clamps!
Andrew
Another couple of problems with dry wall screws is that they are brittle, and rust like crazy if they get wet. I think an alternative to wood screws would be deck screws designed for construction of wooden and composite decks.
You are correct - deck screws are brass, making them rust-resistant. The key to avoiding splitting, however, is drilling pilot holes and counter-sinking. The usual practice of just power-driving screws doesn't work on the edges of plywood. For a permanent layout, I would even consider placing threaded sleeves into the plywood edge, and then suing the appropriate fastener, especially if any dis-assembly for maintenance or repair was likely. Otherwise, dowel pins or biscuits would work as well or better and fasten permanently using only glue.
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If you may have relocation problems, then L girder is the answer. With it you can undo and relocate struts and support (remember to screw from the bottom up!)
OK, I've said that: let's see someone develop a relocation method in some other medium
David
Moderato ma non troppo
Perth & Exeter Railway Company
Esquesing & Chinguacousy Radial Railway
In model railroading, there are between six and two hundred ways of performing a given task.
Most modellers can get two of them to work.
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You can pretty much relocate cross members easily if you screw from the bottom up in most types of wood frame work. We do it all the time when changing the track work on a module and we really can't use "L" girder in modular construction.
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So far everything is working alright I have a few sections built and standing on their own. Too lazy after work to do much on it usually, but hopefully after the weekend Ill have a plywood top on most/all of it.
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Got even more done tonight, and so far the benchwork is much better than the last layouts. Cant wait to start laying track!.
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MountainMan Wrote:You are correct - deck screws are brass, making them rust-resistant. The key to avoiding splitting, however, is drilling pilot holes and counter-sinking. The usual practice of just power-driving screws doesn't work on the edges of plywood. For a permanent layout, I would even consider placing threaded sleeves into the plywood edge, and then suing the appropriate fastener, especially if any dis-assembly for maintenance or repair was likely. Otherwise, dowel pins or biscuits would work as well or better and fasten permanently using only glue.
Some deck screws appear to be brass, but most are either steel or stainless steel. The brass-coloured ones are usually steel, plated with yellow zinc, and many others are available galvanised or in various colours. You're right about pre-drilling to avoid splitting, though, whether into the edge of plywood or the ends of dimensional boards.
Wayne
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