L-Girder Benchwork

[mrazz]

Hi,
I am making my first attempt at designing and building two 8'x2' L-girder style sections. I recently purchased both Westcott's and Wilson's Kalmbach books on benchwork. These books are extremely helpful. I have a couple of questions:

Everything I've read calls for a 1 x 4 capped with a 1 x 2 to construct the flange on the L-girder. Is there a definite advantage to using these dimensions? I was going to use a 1 x 3 capped with another 1 x 3 to give the underside of the flange a little extra room.

Is it necessary to use 1 x 4's for the joists? Again I was going to use all 1 x 3's for my joists. The only advantage I could think of for using 1 x 4's is that it would give a little more room between the L-girder and the plywood base. Which leads me to my next question:

Does anyone use 1/4" plywood? Everything I've read calls for 1/2" plywood. Does it really make that much of a difference?

Is there anyone out there that has ever used exactly what the books suggest? I would like to hear your thoughts on my minor adjustments in regards to wood dimensions. Any info will help.
Thanks, Mark

 

[CNJ999]

Mark - Westcott chose 1x4's for his L-girders mainly because that was/is a common dimension lumber comes in and by simply cutting the 1x4 in half lengthwise, it gave you the 1x2 (more or less) top-plate for the L-girder. Now a 1x4 L-girder will indeed be more structurally solid than one built using 1x3's. Thus, if you are planning to put some sort of heavy scenery on top of it, then it would be better to go with 1x4's. With just a thin-shell type of scenery the 1x3's would probably work out just fine as long as everything above it is really light. If in doubt, go up in size. Likewise, don't skimp based on pricing alone - if it's only a matter of a few bucks difference, go with the larger dimension.

Re the second question about using 1/4" plywood...that's a no-no. Such thin plywood is not stabile/solid enough to serve as the deck of a layout, unless the support joist are placed very close together. Using Westcott's design, stick with full 1/2" plywood. The last thing you want to see is a sag, or undulation, in your layout deck after putting down the track!

CNJ999

 

[pgandw]

Mark

In Westcott's book there is a chart for allowable spans for various girder types and lumber sizes. IIRC, the chart states 1x4 with 1x2 flange is needed for spans greater than 7ft. Flange lumber size has little impact on the stiffness of the girder, but vertical size has a great impact.

The span chart is based on a maximum deflection of 1/500" with a 250lb point load. Can you get by with less? Yes, the chances of that load aren't that great unless you climb on your layout. OTOH, an accidental fall or lurch that results in a plant of a hand or elbow to stabilize yourself can create some significant 100lb+ point loads. Also realize that vertical deflections in the track work as small as 1/100" are enough to derail trains - especially in N scale. The bigger the scale, the greater the tolerable vertical mismatches.

Finally, consideration should be given to long term sag if a layout is to be used for decades. This is not easily quantifiable, and is a function of the materials and construction methods as well as lumber sizes. Lumber supported closer than just the ends has less tendency towards sag, in my experience. Bookcases and shelves that sag under loads are examples to me of how not to build my layout.

1/4" plywood definitely sags unless reinforced in some way. Perhaps the best reinforcement for 1/4" ply is 1" or thicker extruded foam laminated together - makes an excellent, lightweight subroadbed. 1/2" plywood is been good for me in the past, but I'm not so sure anymore with the deteriorating quality of available plywood. If using 1/2", I would insist on good quality supported no more than every 18". Many modelers have switched to 3/4" ply due to issues with 1/2" ply quality.

The Westcott book really opened eyes to reasonable lumber sizes for layouts when it first came out. The 2x4s and 2x6s were overkill, and the 1x2 frames eventually sagged or bowed.

my thoughts, your choices

 

[seanm]

I am building a large garage layout in n-scale and am using 1x4 capped with 1x3 L's and 2x2 legs and 1x2 joists. Joists span less then 2 feet and the L's sometimes span 6-8 feet. I am also using 1/2 birch ply for the sub roadbed. Works well for me.

 

[60103]

I used 1x3+1x3 Ls. I have a lot more support under the girders than most because it's on a set of shelves. I use the 1x3 flange because I can't drill holes any closer. I have a lot of different lumber for the joists -- much of it 3/4"x1/2" or so, but all sorts of other things as it rises.
I'm a heretic -- I don't use plywood at all, just Homasote.
I have a 6' unsupported span using the 1x3. I haven't noticed any sagging, but I don't have plaster scenery.
Follow the directions and remove the screws from the girders after the glue sets. I left them in and ruined an exensive drill bit. wall1

 

[seanm]

David,

I never pull out my screws out of my Ls... never had a problem with it.

 

[VunderBob]

I have 2 sheets of 3/4" plywood waiting to be ripped into (nominal) 1X3s and 1X4s for my layout. Two reasons: 1) plywood, by virtue of the glue and the respective layer grains being perpendicular, is more resistant to moisture related swelling and shrinkage; and 2) is cheaper than buying the same amount of dimensional lumber by the stick. You may want to consider this.

A 1X3 capped by a 1X2 is more than sufficient to support a foam base over an 8 ' span without sagging, for what it's worth.

 

[doctorwayne]

I must be missing something here: There's not much reason to use L-girder construction to support a plywood tabletop-style layout. Open grid uses less lumber and is probably stronger, too. I was going to use L-girder for my layout, which has a lot of grades and multi-level topography, but I found open grid to work just as well, and I suspect that, should I ever need to move the layout, the individual sections will have more torsional rigidity than would L-girder. I used 3/4" and 5/8" plywood for the roadbed, along with 1" dimensional lumber in some places, mostly because that's what I had on hand. Risers for roadbed, scenery, and facia support are also from whatever was on hand. Support is mostly 2"x4" (left-over, sorta :-D) from building my house, but also includes 2"x6" and 2"x8". All crossmembers on the layout are 16"o/c, and the same under the 3/8" plywood shelving that I installed under much of the layout.
One of the advantages of L-girder is the ability to create flowing curves on the layout facia, but I found that the same can be had with a modified open grid, too.
Here's a LINK that shows, if not benchwork construction details, at least what can be accomplished with open-grid construction. I think that a couple of the photos even show the under-layout shelving for storing non-train related junk.

Wayne

 

[60103]

L-girder is much more forgiving of bad carpentry and easier to modify when your switch machine comes out over a joist.