Significant L girder benchwork design question...

Model Railroader Layouts and layout building
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On the layout that’s impending in my newly refurbished basement, I’m planning to do the L girder design. In the past I had done open grid, because that’s what I always had done, and those layouts were smaller, more rectangular with a right angle or so. I now want to have the extra flexibility and easier curvatures that L girder provides.

But a question for benchwork mavens in the know~!!!

I have a lot of wood left over from my basement remodel. I’ve been looking at the book on L Girder, and the "L’, they say a 1x2 flat on top of a 1x3 long. My distance is about 12’ at the longest spot for a girder, which will require one splice. But I have a lot of 2x2s sitting around in nice lengths, so do I really need to have an “L”, or can i just glue/screw the 2x2 into the legs as the girder without an “L” support…is there a real compromise in terms of stability and strength? Will the 1x4 joists sit fine and be strong enough on that kind of sole 2x2 girder? Is it ok for an L girder not to be, um, an “L”?

I plan to use 1/2" plywood as a base on that for track, some cookie-cutting for the track, but a lot of open plywood though, for the towns, yards and industries and stuff. So it has to support some extensive 1/2" plywood weight, plus foam, scultamold and gypsolite mountains and stuff.

So, i’m no engineer, and any thoughts on strength and durability are much appreciated. On the face of it, I think it would be all right. Seems a shame not to use this leftover lumber, so i thought why buy more if it might not be necessary…

I’ll also be using some 4x4s and 2x4s for legs…super sturdy with the 4x4s, I assume…because I also have several lengths of that lying around after a different project. Don’t know whether that might affect the girder question.

Hey, thanks so much for helping me sort out my thoughts!

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L-girder is a style of construction that increases the strength of a structure while decreasing the amount of materials required.

Think of it this way: take an 8 foot long 2x4. Set it flat on two supports 6 feet apart. Push down on the center of the 2x4. It will bend with the pressure. Now, turn the 2x4 on edge and apply pressure in the center. Much less deflection! Imagine doing the same test with a 1x4. Even MORE deflection when laying flat! Now imagine either board secured and standing on edge. Push the center of the board and you get side-to-side deflection.

What L-girder does is provide that on-edge strength for support with side-to-side stability. A 1x2 capping a 1x3 uses LESS wood than a single 2x4, yet provides MUCH more strength to the structure. An important point: supporting strength is created by the widest board set to stand on edge. That’s where the real load is supported. A narrower board is used as a cap to provide resistence to side-to-side movement where the forces applied from the side are much less than the downward force of the supported load. In L-girder construction, the top cap also provides a convenient ledge for securing plywood from the bottom.

New home construction takes advantage of this principle with engineered floor joists. These joists are made with 2x4 (or smaller) top and bottom pieces laying flat and connected with an 8" or 10"vertical plywood or pressboard spine. These things are so strong that they can span over 24 feet with NO center supports! To get the same thing in a single piece of wood would require a timber about 8" wide and nearly 20" deep! And there would STILL be deflection in the middle! Engineered floor joists are made with less expensive woods yet provide superior strength. It’s L-girder construction in the real world!

The best use of your 2x2’s is for legs. If you w

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I have to agree with Darrell not to use the 2x2’s for the girder.

They may work if the legs were spaced every 2’-3’ apart. Also they would be fairly thick requiring a 2/12" to 3" screw to attach the joists.

I would use the 2x2’s for legs and the cross supports for the legs and use 1x4’s with 1x2’s glued and screwed for the “L” girder.

I have a 12’ span that I used 1x4’s with 1x2’s glued and screwed as the “L” girder and 2x2’s as legs for the ends with 1x4’s for legs in the middle (at the 6’ mark). So it is supported by 6 legs 6’ apart. It is strong enough to support me at 250 lbs. It doesn’t flex at all.

Here are a few pictures:

Bill

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The other advantage of true L-girders that was sort of hinted at in the other replies is being able to use ordinary 1-1/4" (or smaller) screws to fasten risers, joists, or plywood from underneath. Using 2" square girders negates this advantage. And as others have pointed out, with only 2" nominal in the vertical dimension, IIRC you will need legs at about 3ft intervals to control girder sag. Westcott’s book on benchwork construction has a table showing maximum span for various girder configurations.

yours in training

Fred W

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Guys, all this makes sense. Thank you. I’ll save that leftover lumber and find a use for it, I’m sure. Bill…thanks for the pics, it’s always good to see it.

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I agree. It is a bother to have all this nice lumber and no real use for it. That’s just it, though, in you layout there is no real use for it…not a defensible one. Okay, except for the legs.

The idea of the L-girder is to rigidify the beam in two dimensions to the extent permitted by load and the wood, itself. The vertical member that I used was 1X4, and the cross piece, or cap if you will, was simply half of another 1X4 ripped down its length. I then glued and screwed the caps along the edge of the 1X4. Very strong.

I would listen to Darrell, too, about using one span where you can. That means a purchase of the appropriate lumber no matter what.

Gosh, think about the fantastic yard you could have on something that long!

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Yes, I know…the day is coming fast when I’ll be putting my plan into action. [:-,]

Thanks, all…it’s off to Home Depot I go!

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Only additional suggestion I’d add here–try a lumbar yard instead. Might be a touch pricier, but in viewing multiple threads on this forum, most feel better quality cuts (i.e. less irregularity, warping, etc.) may be found at local lumbar yards vs. HD or Lowes, etc.

Jim

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Believe me, I’ll second the trip to a quality lumber yard. I’ve been working with wood for over 30 years. You can actually select your pine from the racks of #2 pine and find far superior pieces than you would ever find from the so called “Premium” pine at HD or Lowes. There’s no such grade as premium, their #2 is such crap it forces one to buy the so called better grade.

Many have mentioned that there’s no lumber yards near them, ask a carpenter where they buy their stock. They surely don’t use the home center for supplies.

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I’ll take a wander by the local lumber yard to check it out. Drove down the street this morning, and serendipity struck…someone was throwing out perfectly good 1x4s and 1x3s…no warping to see, had some screw hole marks but no screws sticking out! Got about 10 pieces…that’s ok by me. The stuff will be hidden, anyway. I can use some of them for scenery risers.