Plywood Benchwork question

[Big_Boy_4005]

Wood is a very forgiving material?[swg] On the other hand, a wooden space craft would have some serious problems.

[Buckeye Riveter]

Ron, it doesn't get hard until you start working with a variable moment of interia beams with prestressing tendons. Of course my favorite is radial and tangential moments in circular plates, but then again; what are computer for anyway? And I used to do this stuff with a slide rule....................thank you HP.

But then again, we sent a man to the moon using slide rules.

[Brutus]

[bow]

[Anonymous]

QUOTE: From Buckeye Riveter:

That is if the material is homogeneous. A non-homogeneous material, i.e. reinforced concrete or composite laminates do not follow those simple rules. It was this same lack of understanding of reinforced concrete design that led to the collapse of a parking garage in Florida many years ago. The engineers mistakenly thought concrete sections acted the same way as homogeneous materials. In other words, they were practicing outside their field of expertise.

Analysis of load distribution, bending moments, shear, etc. of reinforced concrete is very technical to say the least because cross sectional load analysis along the structure's length is a must to understand the behavior of concrete beams. Add the forces for pre-stressed reinforced lightweight concrete and it complicates the analysis quite a bit more.

How do you figure so many engineers and architects missed that on the parking deck?

Must have all received their degrees from the same party university (Florida University)?[:O]

I would think anyone handling the design / construction would have to have a PE in that state as a minimum.

Truely scarey thought. Thought most heavy structures were designed for 2X expected maximum load anyway? At least it was in the '70's.

Because of such poor performance of concrete (even reinforced) many new bridges in NC now are almost 100% steel main beams and major cross members. They have to be maintained by an occasional coat of paint over their lifetime, but, the steel is 'already cured'. [:)]

Ya, think they'd have figure that out in CA by now with the earthquakes.[:)]

[Big_Boy_4005]

QUOTE: Originally posted by Houdy

Maybe check with FEMA on the benchwork codes [:D]

They just say higher than the expected storm surge, no wind loading info provided.[swg]

[Anonymous]

Maybe check with FEMA on the benchwork codes [:D]

[Buckeye Riveter]

QUOTE: Originally posted by lionelsoni

Some thoughts:

The strength of a rectangular beam is proportional to its width and to the square of its depth. The stiffness is proportional to the width and to the cube of the depth.

The strength of a rectangular beam under a point load (you standing on the layout) is inversely proportional to the length of the beam; the deflection is proportional to the cube of the length. The strength of a rectangular beam under a distributed load (the trains) is inversely proportional to the square of the length of the beam; the deflection is proportional to the fourth power of the length. Locating the legs back somewhat from the edge greatly increases the strength and stiffness for the same size beams.

That is if the material is homogeneous. A non-homogeneous material, i.e. reinforced concrete or composite laminates do not follow those simple rules. It was this same lack of understanding of reinforced concrete design that led to the collapse of a parking garage in Florida many years ago. The engineers mistakenly thought concrete sections acted the same way as homogeneous materials. In other words, they were practicing outside their field of expertise.

[lionelsoni]

Some thoughts:

The building codes consider that fasteners into end grain offer no resistance to withdrawal at all.

When plywood is used as a beam, only the plies whose grain runs lengthwise to the beam are contributing much strength.

The strength of a rectangular beam is proportional to its width and to the square of its depth. The stiffness is proportional to the width and to the cube of the depth.

The strength of a rectangular beam under a point load (you standing on the layout) is inversely proportional to the length of the beam; the deflection is proportional to the cube of the length. The strength of a rectangular beam under a distributed load (the trains) is inversely proportional to the square of the length of the beam; the deflection is proportional to the fourth power of the length. Locating the legs back somewhat from the edge greatly increases the strength and stiffness for the same size beams.

[3railguy]

Spankybird, things go much faster when using 2x stock because it's easier to nail too and you don't need to strike off nail lines or spend a lot of time ripping and squaring things up. The concern was wieght and portability. BTW, did you test your basement floor PSI rating, rebar spacing, and dia before putting all that weight on it so it doesn't fracture?

[spankybird]

Hey Buckeye, you have seen my layout and yes I overbuilt it with 2 x 4 frame in a 4 ft by 8 ft frame with one cross member and 2 x 4 legs. It was the fact that I could by 2 x 4 cheaper than 1 x 4 and they were straighter.

I do know that if Ohio would ever have a large earthquake (we do have them, but not much more than 4) or if a twister were to hit my house, you would find me under my table. I believe it is stronger than most of my house. It must be the engineer in me that made me over design it. [^]

[Buckeye Riveter]

QUOTE: Originally posted by pigseyes

QUOTE: Originally posted by Buckeye Riveter

From what I have read in this post, I figure my layout should be hitting the floor due to the collapse of the bench work any day now.

Hey Buck, not to worry, my under supports are very similar to yours ( layout that is ) so we should collapse at the same time. Did we go to the same engineering school?????
Tim

But, Tim these Toy Train Layouts weigh so much. [:0] Do you think the floors of our homes will handle all this load? [:D]

[Anonymous]

QUOTE: Originally posted by Buckeye Riveter

From what I have read in this post, I figure my layout should be hitting the floor due to the collapse of the bench work any day now.

Hey Buck, not to worry, my under supports are very similar to yours ( layout that is ) so we should collapse at the same time. Did we go to the same engineering school?????

Tim

[3railguy]

Big Boy is right about ripped plywood. It is perfectly straight and structurally strong. Much like LVL beams, It is stronger than dimensional lumber of the same thickness because it is laminated veneers.

1/2" CDX plywood ripped 3" wide is fine for girders and plenty strong. 1/2" CDX is a structural plywood used for exterior sheathing and fairly inexpensive. There is no reason for the better cosmetic grades because the work will be hidden and no one will see it. You are not building furniture. Personally, I would prefer 3/4" subfloor grade for more nailing meat. It's likely you'll run in to knots and the ripped pieces will collapse. That is OK. Just use them as shorties or toss them as waste. I would go no less than 3" wide. This is so you can drill holes on the centerlines and not hit the nalis that hold the top. That is if you use 1 1/4" or 1 1/2" nails and a 1/2" or 3/8" drill bit.. You can offset the drill line a little to miss 1 1/2" nails but It is not good to stray too far from the centerline of the girders because you weaken them otherwise.

1/2" girders will easily bow before you nail them and you will miss them when nailing down the top. The trick is to screw a 1x2 firring strip or left over ripped piece to the underside of the girder work to line up the girders with a tape so they are very close to perfectly straight. Then you can strike off nail lines on the table surface with a cheap 4 foot straight edge. You only have about 1/16" in either direction for tolerance when using 1/2" thick girders. Once you are finished nailing the top, you can remove the firring strip. That is why I suggest screws. Or you can use 8D scaffold nails with two heads too.

3/4" for the top is way overkill. 1/2" is plenty to crawl on even with your girders spaced at 24" OC. You are not building a house. 3/4" subfloors are not only designed for supporting people walking, they are designed to support heavy appliances, furniture, and non load bearing walls which support ceiling rafters. Roofs on homes are typically 5/8" on rafters 24" OC. These are designed to support two layers of asphalt shingles, snow, and people walking on them. So a 5/8" or 3/4" table top is really a waste of money.

Like others say, Use lots of glue along with light gauge ring shank nails because plywood does not hold nails very well in parallel to the laminations. it has a tendancy to spread. Structural adhesive that comes in tubes and applied by a caulk gun is best. There are adhesives designed for decking subfloors over joists. This is what you want to use. It not only holds everything together well, it helps deaden sound.

[Buckeye Riveter]

From what I have read in this post, I figure my layout should be hitting the floor due to the collapse of the bench work any day now.










I don’t walk on it and there are castors on the legs so the layout can be moved. The new section will have an hidden hatch in the widest part to gain access. The table is 16 feet long with only four 2x2 legs.

[Anonymous]

Just had to jump in here and tell you all that I built my entire layout with 3/8" plywood. True enough I cant stand on it ,but lets face it, when the layout is finished there probably wont be room to place my foot.
The plywood is braced underneath with 3/4" plywood strips ripped into 2" strips and placed @ 12" on center. The plywood is stapled with a air stapler with 3/4" narrow crown staples.The layout is 2 levels with the first level at 28" off the floor and the 2nd level at 40".
Now let me explain my reasoning. The train room is above the garage, a room with a sloped ceiling. We have some nice furniture in the other end of the room, and my wifes sewing room. The last thing I wanted to do was use a saw or any other messy power tool inside my house. I pre fabed all the modules in my cabinet shop and brought them through the house and up the stairs all by myself (very light weight) I then assembled them with a cordless drill and drywall screws, no muss no fuss.
In retrospect I think I could have used 1/4" plywood, and just put the supports a little closer. And just in case any of you are wondering, I am a building contractor, and have been in business for 25 years building homes and commercial buildings, so I am no stranger to construction.
This method worked for me , but probably not for everyone. As Big Boy stated, there are a thousand ways to build benchwork. A friend of mine has a small layout built from solid oak with walnut inlays, with about a hundred coats of Polyurethane on it. Whatever you use , just have fun , and keep us posted......Tim

I have added some pics for your enjoyment.... STILL UNDER CONSTRUCTION

[Big_Boy_4005]

Jim, I think it's cool that you build furniture, and for that type of project lumber quality makes a big difference.

Personally, I use a construction method for benchwork that doesn't rely on perfect lumber for good results. All I do is create a framework that is reasonably even. In most places the actual roadbed is raised off the framework with risers made from scraps of 2x4. This way any irregularities in the frame are compensated for. Using 3/4" plywood as a base also helps smooth over things in areas where a large flat top is needed.

Here are a few of photos to illustrate my methods.

The first one shows the track raised off the frame.



This is a little before and after of a town on my layout where the plywood is resting on the 1x4 frame. Once the fascia is attached all evidence of the benchwork is covered. Eventually skirting will cover the legs. This is strong enough for me to walk on, and I weigh 325 pounds.





There is no right or wrong way to do things. Everyone needs to find a method that works well for them. I just find this method to be quick, strong, fairly inexpensive, and above all effective.

One final comment regarding the World's Greatest Hobby program, It is clearly geared to the HO and N scale potential markets. Because of their smaller size, those scales require closer tolerances for smooth operation. 3 rail O is very forgiving by comparison.

[Brutus]

I usually buy red oak, poplar, or dimensional 2 by materials at HD or Ls, so I believe you - I was guessing. So, $30 (which I think is a little high, but probably coming due to hurricanes) for a sheet of BC pine versus 32.50 for dimensional 1 by lumber. I last bought a sheet for $22.50, but I think that was a good while ago.

Even though the framing won't show, I would still joint it at least. Here is why - if you take the time to do it right now, you won't have any weird high and low spots in your benchwork. I'm not saying I would get it down to 0.01 necessarily, but I wouldn't trust any 1 by material to be straight and not twisted, especially after it dries.

About 8 years ago I bought about 200 board feet of 1 by pine to build a dresser and every single board of it was bent, twisted or otherwise uneven when I started. Like I said, just take the board and put one corner down on the floor at the store, then sight down the top edge of it toward the floor and see how straight it is.

Plus, with plywood, you don't have to worry very much about it warping once you put it together, whereas with dimensional lumber, you must let it acclimate to your house first or it will rack/warp on you. Then straighten it out.

[Big_Boy_4005]

Jim, I think you are a little off on your 1x4 prices. At least around here, they are about $2.49 for an 8 foot standard grade.

Benchwork does not need to be pretty, it needs to be functional. Beside, it all gets covered anyway.

[Brutus]

I'm sorry - I misspoke. 5/8 plywood is usually 45/64. 3/4 plywood is also often 23/32. Sometimes they have 3/4 and sometimes 5/8, depending on grades and types of plywood.

[Brutus]

Cool! At my Lowes and Home Depot, you only get so many cuts for free. Plus, they use a crappy blade, so the cuts are pretty jagged. I guess yours is better than mine!

Birch plywood would be great to use, because it will generally (count them) have more plys of wood. Plywood is a sandwich of thin wood veneers, sometimes other materials, and glue. That's why nailing or screwing into the edge (between the plys) isn't a good joint method for your purposes - even though it is what they did in that video. I bought and watched it last Spring or early Summer.

3/4 inch thick plywood isn't really 3/4 thick. It is 45/64 inch thick usually.

1/2 inch thick plywood is usually 31/64 inch thick.

I'm not exactly sure on this, but I seriously doubt you will find plywood that is actually 1 inch thick.

A board that is 1 inch by 4 inch by 8 foot (dimensional lumber) will actually measure 3/4 inch by 3 1/2 inch by 8 foot.

This is because they take a 1 x 4 board and surface it at the mill, before Home Depot gets it - they joint it and plane it on 4 sides to make it nice and clean and square for you, and when you get it at the store this is that is left. It is "nominally" 1 x 4, but actually .75 x 3.5. But, for woodworking purposes, you still call it a 1 by 4.

If you go to the store and buy 1/2 plywood, which is what they used in the video, it won't really be 1/2 inch thick, but so what? The only thing you have to wory about is widths and lengths of the plywood strips to follow their directions.

Also, before you decide where the legs will go, you need to think about how long the stretchers can be. They can only be 8 feet long in our example. So if they angle down to the legs from the opposite side, like they did in the video, then the long side of the triangle can only be 8 feet long. (A*A) + (B*B) = (8*8=64) etc. That's probably why they put the legs in a bit - to conserve resources.

Just go up to HD or L and have them cut down a sheet for you, make a 4 x 4 table, and see how it works. You can always incorporate that into your layout even if you end up doing 1x4 dimensional lumbar or 2x4 or whatever.

[pmilazzo]

Okay, Let me clear a few things up. I would have Home Depot or Lowes rip the 3" planks for free. If fact they will precut all your lumber for you if you ask them. My wife has done this before on other projects so by the time I came home from work, all I had to do was attach everything for her. The planks would not be 1"X3", but 1/2"X3" birch and there lays the question. I was going to go with 1X4's until I saw the video. The producers chose 1/2" birch plywood to keep the weight / cost down and to make the calculations easy versus 3/4" plywood. One could easily using 3/4" if desired.
If I do go this way, I'm going to move my legs to the four corners rather than 16" inside the table. I'm also going to build my benchwork sections smaller like 4X4 and 4X5 to make them "managible" and reconfigurable.
The big question remains, would 1/2" plywood struts 3 inches thick every 16" with 1/2" plywood decking be strong enough for O gauge and possibly supporting human weight if necessary?
Do they even make 1" plywood in birch? That would give you 1"x3" dimensions that people seem to like. It would also make all the calculations extremely easy like 1/2" not that that's a big deal either.

Again, my goal is to make benchwork strong, low cost, light and easily to move if necessary. Believe me it would be extremely easy to over engineer the benchwork for strengh, but the other variables get compromised.

[Brutus]

Okay, this is theoretical for me, in that I haven't built this table, but I have made some furniture. Here are some thoughts.

1. Plywood moves less with humidity changes than dimensional lumber. MUCH less.

2. It's cheaper than dimensional lumber. Let's say a sheet of 48 x 96 = $30 for Pine BC 3/4 plywood. 48 x 96 = about 13 1 x 4's (which are really about 3/4 by 3 1/2) x 96 - even if they are only $5 each, you're at $65. So, if you use one sheet of plywood to replace the 1 x 4's used for the framing, and one sheet for the top, you are at say $60 for a 4 x 8 layout versus about $95.

3. If you have a tablesaw and some outfeed rollers, you can rip down a sheet of plywood in about 15 to 30 minutes into identical 3 inch pieces. If you use a guide and a circular saw and buy a sheet of foam to put on the floor so you can lay it all down on the floor and cut on your knees, this would take about 1 to 1 and 1/2 hours, depending on how practiced you are at it and whether you have someone to help set up the guide.

NOTE: You can reuse the sheet of foam on the layout. Also, If you are using a circular saw, you can make a jig for cutting the plywood out of plywood. Measure the bottom of your circ saw from the inside edge of the blade to the edge of the base that is under the handle (usually from the blade to the left side looking down at the circ saw). Let's say that is about 7 inches. Now, you can use one sheet of plywood as a guide for cutting a 2 inch wide strip (8 ft long) from the other sheet. Lay one sheet on the foam on the floor. Lay the other sheet so it covers 2 inches of that sheet - prop it up with something so it's nice and level with the bottom sheet and have someone sit on it or something so it doesnt move. Then, use that cut piece as a guide to cut a 8 inch wide ( 7 inches for the saw and 1 inch for scrap) strip (8 ft long). Then attach the 2 inch wide piece on top of the 8 inch wide piece along one long edge, placing the factory edge (the original outside edge of the plywood) on the inside. Glue it and screw it. Now, place this on your foam and carefully run your circular saw down the length, up against the 2 inch fence you made, so that you cut through the bottom piece and cut off the extra. Now, you can mark your plywood at 3 inch intervals at the top and bottom, place the bottom guide even on the marks, and rip away pretty quickly.

4. If you have a mitersaw (or access to one) you can size your plywod strips in about 10 minutes or so. This is a wash, because you would have to do this on either plywood or dimensional lumbar.

5. If you use dimensional lumbar, you should buy it about a month or so before you plan to build your table. Place it in the room where you will build and keep it off the floor and separate the layers with some sticks, so it will equalize moisture content with the room/house.

6. No matter how hard you search, you will be hard pressed to find perfectly square, flat and even boards, and even if they start out good, after they have adjusted to your house for a while, it will change. If you want everything to be nice and square and furniture grade, buy them bigger than your final design calls for and then joint and plane them square etc. If you don't care how even your tables turn out, then you can skip some of this, but not for leg pieces etc. Don't believe me? Go to the local Home Depot or Lowes (etc) and sight down some boards. Believe me, you will not find very many that start off good and fewer will stay that way once the moisture comes out in your house! Using dimensional lumber, if you take the time to straighten it out so your table won't rack etc, will take as long or longer than working with plywood.

If you use $40 worth of steel angle brackets to tie your plywood together, you will still be ahead on the time it would take using dimensional lumber, if you take the time to straighten out your dimensional stock, and you can do it the same weekend you bought it and not worry about your table twisting in a few months as dimensional lumber shrinks.

Just some thoughts. I've made some furniture and there is a reason most furniture you buy is made with plywood - it's cheaper and easier/faster to work, once you get set up for it.

I do have a planer, a jointer, a cabinetsaw, and a mitersaw, but I would still do plywood with a circular saw over dimensional lumber, just because of the time difference. Personally, I would get the steel angles. I would place my cross pieces at 16 inches on center, attaching them at either side with angles. Then I would attach the table top with glue and brads and let it set for a few hours. Then I'd put it up on some sawhorses and climb on top. If it didn't move, I'd forget about the torsion box stuff. If it moved a little, I'd add some brace pieces between the cross pieces, using steel angles, from end to end.

For the legs, I would personally use 2 x 8's after they had dried in the basement for a while, straigtened out into eight 1.25 by 3 inch boards, laminated into four 2.5 by 3 inch legs, etc. But, plywood "L"s with some bracing would do well and you wouldn't have to buy any materials earlier.

Let us know what you end up doing - and how well it works out for you! I really agree that you shouldn't scrimp on this part of the layout, whatever you decide.

[Dr. John]

For a small layout, say a 4x8, plywood can work and make a very nice, stable layout. It is more labor intensive and, as has already been stated, will probably cost more than the required amount of dimensional lumber.

I am an advocate of the L-girder method of layout construction (the late Linn Wescott, former editor of Model Railroader, coined the term back in the 50s) as it is easy to build, strong and flexible as to fitting available space.

[Big_Boy_4005]

Don't be so quick to think that there will be a big cost advantage using plywood instead of dimensional lumber. That point is very close to even, and with the potential cost increase in plywood due to higher demand post hurricaine, dimensional may be cheaper, though those prices may rise proportionally.

The big advantage to plywood construction, as I see it is, uniformity and straightness of the pieces. No warping or knots to contend with.

Structurally, plywood is as strong or stronger than a similarly sized piece of dimensional lumber.

The disadvantage is fastening, you get no strength going into the edge of the plys. A corner block is the simple solution to that problem.

This method is not for the faint of heart. You really need to own a table saw to make it work. Then you have a LOT of cutting to do.

Personally, I use all 1x4's for my benchwork, except the legs which are 2x4's. Plenty of strength, no problems. 3/4" plywood on top works great.

[Anonymous]

I am going to offer an alternative point of view on this subject:

You are building an O gauge layout. Use 2x4 for the supports and thick plywood (3/4 inch) for the top. You want this to be strong, and you WILL be climbing up on it at times. You definitely will be happier with yourself down the road if you build it strong to begin with and do not skimp on what is perhaps the most important element of the layout building process -- the benchwork. Don't take the cheap way out when you can do it right the first time. No one who has good solid benchwork looks at it and says, "I should have built this in a more flimsy way". But plenty of people look at their benchwork after the layout is done and say, "I wish I had built this better and stronger."

[Brutus]

Plywood - at last something I can talk about!

If you are thinking of climbing on top of your table, then I would further strengthen it by adding cross supports - this is called a torsion box.

What you do is build a frame of cross pieces that go from side to side and also lengthwise. Where they intersect, you cut out a notch that is the width of the plywood and 1/2 the depth (eg: 45/64 by 3 inch supports would each have a 45/64 by 1.5 inch notch. Be sure to actually measure the thickness of your plywood. It says 1/2 inch, but it's not 1/2 inch - that is nominal thickness. It will be narrower. 3/4 inch stamped plywood is usually about 45/64 thick. When assembling, the side to side pieces should have their notches facing up and the lengthwise pieces should have their notches facing down, so they interconnect, with the notches mating, and you end up with a solid framework. You want the notches to be as snug as possible, so that the plywood transfers weight along the full edges of the notches.

If you have a tablesaw, or access to one, you can do this with a dado blade. You could also do it very carefully by hand with a jigsaw or make a jig, some connected guideblocks, to make it more uniform. Once you get all those pieces cut, assemble them and glue like crazy. Then, before the glue sets (read the bottle), use a square to make sure you have it all arranged correctly and attach them to the inside of a standard frame like they did in the dvd, using nails or pre-drill and use screws and glue if you like.

If you have a few extra $$$, then I would use steel angles (find them in the decking supply area at a Big Box store like Home Depot or Lowes etc) to connect the torsion frame to the skirt frame. Nailing or drilling into the edge of plywood can be a problem and it's very easy to split it. This is where your table will most likely fail under heavy weight or over time due to humidity etc. Nailing or screwing into the face of plywood is a very stable join and easy and the angle makes it possible to screw into the faces of perpendicular pieces.

In fact, if you don't want to cut all the notches, you can just cut shorter pieces and use angle brackets to attach them all throughout.

For the legs, I would certainly glue along the edges and make them in an "L" configuration. I would put some blocks in at the top and bottom to make them more stable, or use more angle brackets (or both).

For the framing, I would buy the more expensive plywood, even though it won't show, because it has more plys and less voids, making it more stable.

Plywood joists or supports, taking the weight of a table on edge, are very strong and will not deflect very much under a great deal of weight. Making a torsion box will add stability and also decrease deflection. It is only a few more strips of plywood and well worth the effort.

Remember, use lots of glue. But, glue doesn't fill voids. If your notches are just a little too big, fill the void with paper or something, until they dry fit pretty tightly, then do a final assembly using lots of glue.

[Anonymous]

If you use strictly plywood you should screw AND glue all joints. When using screws out near the edges of plywood you should pre-drill pilot holes so you don't split/shatter the wood. Another good idea would be when putting in the screws, add some glue into the pilot holes just as you screw in the screws. This will give strength and make sure that the screws don't work out or loose over time as the wood will expand and shrink with humidity. I believe that the legs are set in some to avoid being damaged by bumping and kicking as well as to spread the table load a little better.

Hope this is helpful.

[jxtrrx]

I'm no expert, but it seems to me that the ripped plywood would provide as much strength as 1X3s. I am interested in your post, because I am getting ready to add some new benchwork and am considering this method also (after seeing the video). I have also wondered why they located the legs as they did (inset from the ends). May I add another question: I wonder if you could use screws into the edges of the plywood supports if you pre-drilled? Will be interested in comments from the experts! Thanks.

[pmilazzo]

I like the idea of using only plywood to create the complete benchwork as demonstrated on the World's Greatest Hobby DVD. It would be much lighter and cheaper to construct than using 2X4s, 1X4s, and plywood.

My question is since they are using 1/2" thick 4X8 sheets ripped to 3 inch boards , would this be strong enough for O-gauge trains which are much heavier than HO. Also, could support any "real" weight incase one does have to crawl around on it?

The idea is not to over build it and keep things light enough to be easily changed moved, or reconfigured in the future.

Another design improvement for stability is to move the legs to the four corners.

Any opinions?