Plywood vs 2x4

[treesprite]

I have only built stands with 2x4 frames, not the kind where the primary support is the plywood without extra 2x4 support. I see people mention DIY plywood stands, and see pictures of finished projects, but can't find many suitable detailed enough plans for actually building one (plans that are not from first-time builders, are not actually just plywood shells on 2x4 supports, do not have extra fancy joints and such that require more than just standard power tools, or are only intended for small tanks when mine is a 120).

 

Can anyone share information about building plywood stands versus stands with 2x4 supports?  "Pros and Cons"? Crucial points/info which applies specifically to plywood stand building and which may or may not be the deal breaker in deciding which type of stand to build?

 

Is it particularly any harder to build an even stand with plywood than a 2x4 stand? I'm always worried about 2x4s being a hair off size from each other, or being warped or whatever. I am wondering if using plywood could alleviate this concern, as long as the edges of the plywood are clean straight cut.

 

I have to finish dealing with the tank itself before I build the stand, so I have some time to settle something, but I have been trying to figure this out for like a year already.

 

Thanks.

Edited April 22, 2017 by treesprite

[Origami]

Forrest, simplifying stuff and putting it in a nutshell: A conventional 2x4 is really 1.5x3.5 inches. Let's say that you build a stand with four legs with two 2x4's at each corner. In really simple terms, you're transferring the load through eight members, each having a cross section of 5.25 square inches, or 42 square inches total. So, all the load is being transferred to the ground through 48 square inches. So, for a 1500 pound tank, you're talking about 30 psi. Now, let's assume that we have a 3/4" plywood stand beneath a 48" x 24" tank (e.g. a 120). Furthermore, let's say that the wall on the back is, for the most part, continuous, and that the sides are the same. Let's say that the front side has six inch sides (or a 36" opening). Again, I'm really simplifying stuff here to promote a basic understanding. Anyways, in this example, the load of your tank would be spread across 48" + 24" + 24" + 6" + 6" = 108 linear inches of 3/4" plywood. That's 81 square inches of cross section. You can see where this is going, right? 1500 pounds across 81 square inches, that's 18.5 psi. Now, plywood is actually more stable (less prone to warping) than most conventional 2x4 softwoods. That's a bonus.

 

That said, both materials are very effective when making strong stands. The so called "rocket engineer" template that so many 2x4 stands are modeled on is really over-engineered and will support loads well in excess of what we typically put on them. That particular design overcomes the warping issues by doubling up the corners using two members nailed together at right angles to enhance stability. 

 

Joining plywood corners can, if prepared reasonably well, be done with a wood screws (pre-drill your holes) and a good waterproof glue (like urethane). Personally, I use wood biscuits for that sort of joinery. I also "hide" the exposed end of the plywood edge using a veneer tape (iron on) when I'm putting something together quickly. It's a reasonable alternative to running a mitre joint along the whole corner (in my opinion) for somebody like me (who's definitely not a cabinetmaker). 

 

Tool-wise, using 2x4's requires fewer tools. A decent circular saw is probably the minimum that I'd want to have on hand when building a plywood stand. Maybe a power drill and a framing square, too.

[treesprite]

Thank you, Tom.

 

I love that iron-on veneer tape! I used it on the edges of the plywood top of my 75's stand, and on a computer table I made for my son.

 

I am kind of thinking to use a sort of either country-looking paneling to dress the stand, or go rustic with old wood planks, both of which would require plywood under them. It just seems in my head to make more sense to have a plywood base to begin with, than to use all the 2x4s then a layer of plywood, then a layer of the other stuff.

Edited April 22, 2017 by treesprite

[treesprite]

I don't want to get too far ahead of myself planning dressing before the structure, but I can't help myself.... If I go with planks and attack them to thin rails with something like industrial Velcro, I could get really creative and change them up so easily any time I want something different. They can be painted, stained, covered in fabric, or just about anything. It would also make the task of doors very easy.

 

The thought of the doors leads my thoughts back into the building of the structure, because if I use plywood, I will have to cut in openings for doors and will need to know how to do that without compromising the supportiveness of the plywood.

Edited April 22, 2017 by treesprite

[AlanM]

Do you have a way to move, store, mark, and make very accurate cuts on 4x8 sheets of plywood, and do you own a set of good clamps to hold it all together while glue dries?  

 

If so, building a 3/4" plywood stand is very simple.  If not, it's impossible.

[treesprite]

That's something I'm trying to figure out.

[Jon Lazar]

AlanM and Origami are both right.  The RocketEngineer stand is a proven design that's easy to build.

 

I'm sure it's possible to build a sturdy frame out of plywood if you have woodworking experience and the right tools.

 

Go with the RocketEngineer design.  There's a reason there are so many of the RE stands.  You'll have a better stand and cut six months off your build time because you won't have to figure out how to build a plywood stand, source the tools, and redo things as you gain experience.  

 

You can check your 2x lumber at the store and only select the straighter pieces.  Sight down the board and look for warping (left/right and up/down), as well as twist.  It doesn't have to be perfect.

[treesprite]

That guy did not invent that standard design, he just posted it in a simplified way.... so I don't credit him with no it. But I am not looking for 2x4 plans, I am looking for more info on plywood stands and designs.

 

Regarding the plywood, I think the issue would be with the accuracy of the wood cutting. Wouldn't that vertical cutter in the store be more accurate than a circular saw?

[AlanM]

Regarding the plywood, I think the issue would be with the accuracy of the wood cutting. Wouldn't that vertical cutter in the store be more accurate than a circular saw?

 

In theory it could be more accurate.  In practice good luck getting the tolerances you need from the dude working that saw.  Also, the blade on those saws has been cutting god-knows-what for god-knows-how-long and is a pretty coarse blade for doing the finish cut work you will want if you're trying to make a nice looking stand with Home Depot or Lowes quality hardwood plywood.  Their plywood has a very thin veneer of finish-grade material on it which is super-duper chippy.  The good plywood has a thicker finish layer but costs $100 per 4x8 sheet instead of $42.  It can also only be bought at a good wood store like the Woodcraft shop in Rockville.

 

I have made two plywood stands now.  I used the cheap plywood from Lowes.  One for a 75g and one for a 180g.  Both turned out great.  I don't have a good table saw.  I've got a super crappy one, in fact.  I had good results with a circular saw by being very careful and making very good measurements on flat sheets, then marking up the wood and measuring again, then doing a test cut to verify the kerf width, then finally cutting the wood, then measuring again to make sure I did it all correctly.  I also bought a new blade for each one.

 

I also used a biscuit cutter and additional careful measurements to cut the biscuit slots and assemble it with glue and clamps.

 

Here was my stand design for the 75g one I built:  http://wamas.org/forums/topic/54660-alans-rimless-75-build/?p=482911

 

I don't think I did a post on the 180g anywhere, but it's basically the same design, just different dimensions.

[Origami]

+1 ^^^

 

What you're referring to, Forrest, is called a panel saw. The blade on most panel saws may give you more tear out. Not horrible, but may give you edges that don't finish as nicely. Also, the operator may not be as concerned with precision as you might be. It's may also be limited to a 4' cut. 

 

At home, I'm able to limit tear out by using a high quality blade and setting my finish side so the teeth bite "down" into it rather than tearing up and out. For a circular saw, this means finish side down. For a table saw, it's finish side up. One can also apply masking tape on top of a cut line to help limit tear out.

 

Getting a straight cut needn't be difficult. There are saw guides (clamp on straight edges) that are made for this purpose. However, when I was a kid and money was more limited at home, Dad could always make do with a "factory edge" from another sheet of plywood. One tip is to remember that your saw blade has a width and leaves behind a cut, or kerf, slightly larger than the teeth. So, when you're making a cut where accurate dimensions are important, you have to be mindful of what side of the line you're cutting on. 

[Jon Lazar]

Regarding the plywood, I think the issue would be with the accuracy of the wood cutting. Wouldn't that vertical cutter in the store be more accurate than a circular saw?

 

You'd think so, but no.  

 

The panel saw at Home Depot or Lowes is not intended to make accurate cuts.  It's designed to cut very large sheets into smaller pieces to make them easier to handle and transport.  It will certainly not make accurate cuts when operated by a harried HD employee when you roll up with your big ol' cut list.  The saw is likely to have an inexpensive blade that cuts quickly but has lots of ugly tear out.  It will probably burn the edges of your wood.  The saw's travel may not be exactly square to the roller track, making your cut slightly off angle.  The cut will not be at exactly the correct length.  There's often a sign by the panel saw that says the store can't guarantee accurate cuts to within more than something like 1/8".

 

A free-hand circular saw will probably be even worse for you unless you practice or have a fair bit of experience.  Trying to follow a pencil line across a long board is a lot trickier than it looks.  It can be done, but I don't recommend it.

 

A decent table saw with an outfeed table would also work, especially if you cut the pieces down to a manageable size (with, say, a panel saw) that's a little bit bigger than your final dimensions.  Then you make your final cuts with the table saw.  Plan your cuts so you make all the height cuts consecutively without disturbing the rip fence's position.  

 

The best way to go for most people who don't have a table saw but want good cuts is a circular saw with a many-toothed carbide blade and a DIY ripping jig that's as big as your longest piece of stock.  The jig guarantees a straight cut and eliminates tear out.  You just have to make sure the straight line is where you want it.

[AlanM]

Yep.  Jon is right.  

 

This is what I use as a fence to run my circular saw along.  I am hopeless cutting along a line freehand.

 

https://www.lowes.com/pd/Johnson-Level-Cutting-Guide-Metal-Ruler/1000085725

[Jon Lazar]

This is what I use as a fence to run my circular saw along.  I am hopeless cutting along a line freehand.

 

https://www.lowes.com/pd/Johnson-Level-Cutting-Guide-Metal-Ruler/1000085725

 

This is what my jig looks like.  I made one that's 8' long, and another that's 4' long.  The drawback is that they take up a lot more storage space than the aluminum cutting guide.  They're also matched to an individual saw.  The advantage is that they completely eliminate tearout with even a mid-range saw blade...cuts look like they were made with a razor blade.  

 

Also, the cut will be _exactly_ where you put the edge of the jig.  Because when you assemble the jig, you make the base piece slightly oversize.  Then you run the saw along it to trim off the extra, making it an exact fit.  That's the most important step.

 

[AlanM]

That's great Jon!  I fart around with that metal one a lot, but this looks really great.  Looks like you could cut either side of it too depending on which side the saw is on.

[malacoda]

Getting a straight cut needn't be difficult. There are saw guides (clamp on straight edges) that are made for this purpose. However, when I was a kid and money was more limited at home, Dad could always make do with a "factory edge" from another sheet of plywood. One tip is to remember that your saw blade has a width and leaves behind a cut, or kerf, slightly larger than the teeth. So, when you're making a cut where accurate dimensions are important, you have to be mindful of what side of the line you're cutting on. 

 

^^^+1

 

This is what I did as well when making an all plywood stand for my 24g (24"x16.5"x16.5").  I CLEARLY MARKED the 4' factory-cut edge on a piece of plywood and trimmed off a 4" wide strip of it to use as a saw guide. (If you don't mark it before you cut it, when you set it down to do something else you can easily loose track of which edge is the factory-cut edge.)

 

Then to cut my actual stand panels:

- I laid 3 scrap pieces of 2x4 (each ~3 to 4' long) down on my garage floor.

- Laid the working piece of plywood (e.g. piece I would be cutting panels from) nice-side down on top of the 2x4s. 

- Measured and marked the panel width on the working-piece of plywood

- From the 'panel edge' mark that was just made, I measured and made a second mark to account for both the 1/8" blade width and the width of the saw base plate to the outer edge of the saw blade.

- Set my 'poor man's' saw guide on to the working piece at this 'second mark' so that the factory-cut edge was facing the cut I was about to make.

- Used two c-clamps to clamp it in place.

- Then grabbed the circular saw and made my cuts.

 

You can get good old, straight, clean square cuts for nice, flush finishes where two piece join together. (Don't waste any time trying to make miter cuts with a circular saw this way though.  They'll never be straight and true enough to make a nice, flush seam when joined together...)

 

And making a guide like Jon's will save you a lot of time and potential trouble measuring.  I would've made one myself ... but I would've had to would've had to pick up another large piece of plywood to make it, and I wouldn't have really had any use for it once my stand project was finished.

Edited April 25, 2017 by malacoda