# Platforms: weight vs strength, 2x6 vs 2x4 best practices



## Uncle Dirtnap (Oct 8, 2018)

I've found scatter parts of answers through searching, but most of those were almost 10 years ago so I'll go ahead and get a fresh perspective.

I'm working with a high school theatre, and helping them build their set for the upcoming play. It's a fairly simple design- 2 8x16 areas at low heights (1-2 feet) and a 8x20 area thats 8 feet high. It seems that we can make everything out of platforms, and leave them with a decent stock of new, solid pieces to work with going forward. Going through their platform inventory, it seems that they have 3 decent, solid platforms, leaving us to build 12 or so

I've seen and made a variety of platforms depending on who I was working under - 2x6, 2x4, 2 toggles, 3 toggles, osb, ply - and with done it with nails, screws, staples (yikes). What is the current 'right' way to do it? I'm hesitant to put something like these ancient battleship platforms they have (2x6, inch thick ply) up in the air, but 1x6 seem so light. I know it's all legging, but still....

I'm looked for local source of 5/4 lumber, but no luck - no yale triscuits for me.

-rj


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## RonHebbard (Oct 8, 2018)

Uncle Dirtnap said:


> I've found scatter parts of answers through searching, but most of those were almost 10 years ago so I'll go ahead and get a fresh perspective.
> 
> I'm working with a high school theatre, and helping them build their set for the upcoming play. It's a fairly simple design- 2 8x16 areas at low heights (1-2 feet) and a 8x20 area thats 8 feet high. It seems that we can make everything out of platforms, and leave them with a decent stock of new, solid pieces to work with going forward. Going through their platform inventory, it seems that they have 3 decent, solid platforms, leaving us to build 12 or so
> 
> ...


 *@Uncle Dirtnap* _ *GLUE!*_ Don't omit glue. Even an inexpensive glue designed for wood is better than zero glue. Don't worry about glue's complications with future salvage. If you're planning on constructing platforms to amortize over five to ten years, they're going to take a beating no matter what materials you utilize thus you may as well use glue and gain its many structural advantages. (Correctly sized pilot holes with correctly sized clearance holes and #8 or #10 self-countersinking wood screws get my vote along with the liberal application of *GLUE*.) 
Toodleoo! 
Ron Hebbard


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## BillConnerFASTC (Oct 8, 2018)

I'm not endorsing it but when I was in college all or our platforms were built with 1x6 framing with 3 toggles (24" OC) and 3/4" ply, usually glued and screwed. (This was before drywall screws were much used in theatre, and air nailers not heard of.) Worked fine, not too heavy, and the 6 1/4" height worked nice for a step without legs. Legs were 2 x 4 with 2 or 3 - 5/16" carriage bolts in the corners.

I'm sure lots of people use 2x4 to span the long side of a 4x8 but I don't think that engineers out to 50 psf with just legs at the corners. Dept to strength is an inverse square relationship. Twice as deep (for same width and material) is 4 times as strong for bending - the usual limitation.

And I'm with Nancy Reagan sentiment on OSB - just say no. A few years ago when there was a rash (3?) of homemade high school pit filler failures, the photos looked like all were OSB. Not saying that was the problem - seemed to be more the connections like nailing into the trim on stage edge - but just don't like OSB.


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## Uncle Dirtnap (Oct 8, 2018)

Glue! Yes, always glue! I forgot that part.

is 3/4 ply overkill? 

After cruising some threads, I now have a healthy fear of using drywall screws, especially for anything in the air. 

I am going to have to meditate on the twice as deep inverse square depth strength equation - for some reason my brain is refusing to make sense of it. I suppose because it's monday....

Thank you all for your responses!

-rj


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## kicknargel (Oct 8, 2018)

For me, 2x4 framing is standard, toggles 24" OC, with legs every 4' (and certainly at every seam). I like to screw together with wood screws (stronger than drywall screws, although many people use these). I use McFeeley's promaster sawtooth. Expensive but awesome, and reusable. Ring shank nails from a framing nailer also work. I don't use glue; I don't believe it does anything on end grain, but we could debate that.

OSB for one-offs, 3/4" CDX ply otherwise (if you've covering with a masonite skin). Don't be tempted by the fancy birch/maple ply that's sometimes a good price; it's not rated for use as subfloor. Maybe it's just as good, but not tested for it. I bet we could debate that, too.


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## BillConnerFASTC (Oct 8, 2018)

Huh - no insert quote prompt.....the old fashioned way then......"2x4 framing is standard, toggles 24" OC, with legs every 4'" is fine. But not 8' please.


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## derekleffew (Oct 8, 2018)

BillConnerFASTC said:


> Huh - no insert quote prompt.....the old fashioned way then......"2x4 framing is standard, toggles 24" OC, with legs every 4'" is fine. But not 8' please.


It's still there, just hard to find. Click on the toolbar icon that looks like a newspaper.


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## BillConnerFASTC (Oct 8, 2018)

Uncle Dirtnap said:


> Glue! Yes, always glue! I forgot that part.
> 
> is 3/4 ply overkill?
> 
> ...




Glue for ply to frame - and then the screws don't matter as all they do is serve as a clamp to the glue cures.

As for the inverse square rule, I forget its derivation I learned in grad school but look at it this way. Set up a simple span to walk on - like a 2x4 or any plank or board between two supports and stand in the center and see how much it bends. Rearrange things so it bends several inches but comes back to straight when you get off. now double it - but no fastening. Lay one plank on the other. It should bend about half as much. They could be side by side and do the same thing - half the load on each. Now get a plank twice as thick (like a 4x4 with 1/2" planed off so ist same cross section as 2 - 2x4s) and stand on it. Half again or 1/4 the original is going to be pretty close.

I specify 1 1/8" plywood for subfloors for stage flooring that's on sleepers 2' on center. In some areas the contractor doesn't order this in time - not always a stock item - so inevitably they want to substitute - maybe 1/2 and 5/8 or 3/4 and 3/8 or even 3/4 and 1/2 - but its can be shown time and time again that this is but half as strong as a single layer of 1 1/8", and the concentrated load of your fork truck, scissors lift, seating wagon, super duty shell tower, or whatever may break the ply between sleepers. At the very least, it will sound so bad you back off rather than proceed across the stage.


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## Uncle Dirtnap (Oct 9, 2018)

1 1/8 for platforms?! I've either been underbuilding or I've described something badly. I'm talking the 4x8 platform units - nothing a fork truck or seating would ever go on. I'm mostly wondering about the platforms I'm sticking 8-10' up for an 'attic' scene with 6 people (Anne Frank). Do they all need to be built that beefy?

In essence, that's where I get confused between the 1x6s and luan constructions vs the 2x6's and 1 1/8' ply construction. They seem diametrically opposed, but similar. I'm torn - part of me wants to build lighter the higher I go (potential kinetic energy! Yikes!) and the other part wants to build it more like a tank the higher I go. (6x6 legs!)

Thank you for the inverse square refresher! It all comes makes sense now. I think one of the words went in my ear sideways and got stuck the first time.

-rj


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## kicknargel (Oct 9, 2018)

BillConnerFASTC said:


> Glue for ply to frame - and then the screws don't matter as all they do is serve as a clamp to the glue cures


I think the glue is helping here, but I wouldn't trust it without screws unless you're jointing and planing the frame dead flat. Wood glue doesn't fill gaps, and we don't build with the kind of precision that creates great glue joints. IMO the glue and fasteners reinforce each other. 

OP, the 1 1/8" Bill is talking about is for permanent stages (and to illustrate the point about inverse square), not scenic platforms. 3/4" ply is standard on 24" OC framing for platforms.

Oh, and Bill, another new easy way to quote is to select the text in the post; it pops up a reply option that will quote the selected text.


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## Colin (Oct 9, 2018)

My stock is 3/4 CDX on 2x4 frames built 24" OC. Frames are glued and nailed, or sometimes screwed with GRK R4 screws which have shear test data. Covers are glued and screwed with R4s. But I also have some old stock still with drywall screws and that doesn't bother me under many circumstances - how you support the platform makes a big difference. I rarely do anything other than studwall support - quick to build and very quick to install, and keeps all joints in compression so not much chance of snapping drywall screws. Each platform joint and seam centers on a studwall's top plate with a stud directly below to catch the load. Screws through the top plate from below into the platform frame, screws through the bottom plate into the floor, add plywood facing or diagonals (sometimes done in advance to individual studwalls).

As far as glue or no glue, sure we're not jointing boards and doing perfect glue-up but whenever I take apart a platform that has been glued I still break the wood before I break the glue, especially between cover and frame. I still don't trust a properly glued joint alone without fasteners when someone's walking or jumping on it though. The glue to me is largely about reducing squeaks.

Here's an article that might be useful: Are You Playing With A Full Deck.pdf


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## BillConnerFASTC (Oct 9, 2018)

Colin said:


> so not much chance of snapping drywall screws



Amen to NOT attaching legs to frames with drywall screws! I prefer 5/16 carriage bolts - at least two per 2x4 leg.

I never heard of the stud wall approach to supporting decks when I was active in production, but did just that when I was designer/td at Bates College in early 1980s. Very efficient and worked especially well for large raked decks.

Nice article!


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## gafftapegreenia (Oct 9, 2018)

I’m a big fan of compression legs for small groupings and truss/knee walls for larger decks. Either way tho I’ve been in steel frame land for the last 4 years so my opinions on all wood construction and dusty.


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## BillConnerFASTC (Oct 9, 2018)

gafftapegreenia said:


> I’m a big fan of compression legs.


Put that in the wiki please, so I know what you mean.


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## TimFrancis (Oct 9, 2018)

Some files that may prove helpful-

Platforms Revisited- a presentation at USITT 6-10 years ago. I do not recall the presenters.

A January 2011 Tech Briefs article looking at 4 types of platforms.

I have used 2x4 framed, 1x6 framed and Texas Triscuits over the years. 

Regards,

Tim


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## gafftapegreenia (Oct 9, 2018)

A handy image i stole from here http://www.ia470.com/primer/platform.htm


If you can afford them, I also like the Leg-a-Matic, as they both strengthen the corner joint (the weakest part of a standard 2x4 platform) and eliminate the need for carriage bolts, whose holes inevitably round out after a few uses.



http://www.theatricalhardware.com/Leg-a-Matic.html


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## BillConnerFASTC (Oct 9, 2018)

Makes sense I guess. I think by definition a leg is in compression. Never saw it used that way. But then again they call it a trestle and seems more often referred to as a stud wall.

Tormentor, cyc, ......


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## jcslighting (Oct 9, 2018)

For all of the high schools I build in I have been using 3/4" CDX or Sheathing grade - not AC for decking and 2x6 outer frames and 2x4 toggles at 24"o.c. Everything is glued including the frames and I use 1/4" x3" lag screws and washers in the corners - 2 per corner and use a paddle bit so the heads recess flush with the surface of the 2x6 then putty or spackle the hole flush - just use standard 'construction screws' for the toggles and decking. These are heavier but I can feel safe using just 4 legs if needs be unless there is a large load expected. I also use them for stage extension platforms with stud walls under them spaced at 24" o.c.

I used to do the 2x4 thing that I learned in college but the need to only use 4 legs from time to time plus the additional safety was worth the weight added. One summer theatre I used to work for had some old 1x6 stock with 5/8" tops - lots of those frames were actually cracked. Oddly they even had carpet padding between the tops and frames - I guess for noise but I'm not sure how that would help honestly I just thought it weakened the whole structure. 

Finally I agree 100% about using a decent wood glue vs just mechanical fasteners - you get a much more solid one piece unit with glue vs only mechanical fasteners and I've never had a top come loose in 20 years of building them.


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## JonCarter (Oct 9, 2018)

Where on earth do you guys store all these monsters? Doesn't anyone build parallels any more?


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## BillConnerFASTC (Oct 10, 2018)

JonCarter said:


> Where on earth do you guys store all these monsters? Doesn't anyone build parallels any more?


I dont think too many here have ever seen a parallel, let alone build one.


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## gafftapegreenia (Oct 10, 2018)

JonCarter said:


> Where on earth do you guys store all these monsters? Doesn't anyone build parallels any more?



I’ve seen one but it had been permanently set open. I’ve never built one.


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## sk8rsdad (Oct 10, 2018)

BillConnerFASTC said:


> I dont think too many here have ever seen a parallel, let alone build one.


Me! Me! Me! That was the old system back in the day.

Our current stock risers use triscuits on a knockdown 1x pine frame assembled with 1/4-20 bolts and T-nuts;. The frames bang together pretty quickly but the decks are a bit finicky to align. Coffin locks would be a better option for holding those down. Storage space is at a premium in the venue.


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## RonHebbard (Oct 10, 2018)

sk8rsdad said:


> *Me! Me! Me!* That was the old system back in the day.
> 
> Our current stock risers use triscuits on a knockdown 1x pine frame assembled with 1/4-20 bolts and T-nuts;. The frames bang together pretty quickly but the decks are a bit finicky to align. Coffin locks would be a better option for holding those down. Storage space is at a premium in the venue.


Me! *Me!! *_*Me*_*!!! *_Too! _* Too!!  Too!!!*
Toodleoo!
Ron Hebbard


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## gafftapegreenia (Oct 10, 2018)

Here’s how we do our show decks. Steel framed decks, lip & ledge connections. The corners share a 3/4” plywood block.


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## derekleffew (Oct 10, 2018)

JonCarter said:


> Doesn't anyone build parallel s any more?


No. We're all out of clinch nail s, animal glue, and dry pigment. Sorry.

This would be the current-day equivalent:

https://www.camelbackdisplays.com/stages-stage-skirting/duro-deck-collapsible-stages/


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## JohnD (Oct 10, 2018)

derekleffew said:


> No. We're all out of clinch nail s, animal glue, and dry pigment. Sorry.


Oh wow, how about bronze powder?


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## gafftapegreenia (Oct 10, 2018)

derekleffew said:


> No. We're all out of clinch nail s, animal glue, and dry pigment. Sorry.


A friend of mine uses hide glue when she builds chairs, but she’s a props carp, and they’re weird. ;-)


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## RickR (Oct 10, 2018)

You guys are killing me with all these 2x4s. Hem/fir is way too heavy for scenery.

In my carpentry days I built #3 pine 1x6 (5 1/2") frames, 3 (or 5 stiles for dance) w 1/2" CDX. And wood glue - stronger than screws! Compression legs bolted on of course. Easy to carry, stacks for simple steps (6" tall), stores well and not so expensive we couldn't beat them up and build new.


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## kicknargel (Oct 11, 2018)

BillConnerFASTC said:


> I think by definition a leg is in compression.



True. I think "compression" here is referring to the joint between the leg and the platform. With a bolted leg, the weight transfers through the bolts and friction between the surfaces; with a compression leg (or studwall / trestle) the weight transfers straight down through compression. Both are acceptable in some circumstances; compression is better. Not acceptable (and seen all the time) is a non-compression leg joint held on by screws.


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## kicknargel (Oct 11, 2018)

JonCarter said:


> Doesn't anyone build parallels any more?



I have for certain circumstances (a touring / repping show) but not often. Today's design environment does not lend itself to stock scenery. Designers don't want to be constrained to the sizes and heights of platforms you have in stock. 2x4 platforms are quick to build and easy to customize.


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## microstar (Oct 11, 2018)

RickR said:


> You guys are killing me with all these 2x4s. Hem/fir is way too heavy for scenery.
> 
> In my carpentry days I built #3 pine 1x6 (5 1/2") frames, 3 (or 5 stiles for dance) w 1/2" CDX. And wood glue - stronger than screws! Compression legs bolted on of course. Easy to carry, stacks for simple steps (6" tall), stores well and not so expensive we couldn't beat them up and build new.



Same here. In my scenery-building days I was a firm disciple of Bill Raoul's "Stock Scenery Construction" handbook where everything was made of 1x. Platforms were 1x5 1/4" framing on 2' centers with 3/4ply lids, also giving the built-in 6" step. Screwed and glued. They lasted well over 20 years of 4 shows per year.
Legs were 1x3 "step legs" extensively X-braced if over 18" or so tall. The "step" directly supported the platform framing as below.


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## StradivariusBone (Oct 12, 2018)

RickR said:


> You guys are killing me with all these 2x4s. Hem/fir is way too heavy for scenery.
> 
> In my carpentry days I built #3 pine 1x6 (5 1/2") frames



I inherited a space with a ton of stock 4x8's built with 2x4 framing and 3/4 ply tops. I've built a few more over the years, but I have done several with 1x6 if we need a one-off. Soooo much easier to move around. However, HS kids have more trouble with the 1x vs. the 2x in terms of aligning fasteners. One day I'll bite the bullet and start replacing the "concrete forms", but it is very cost-prohibitive in the south. Don't know if 1x is cheaper elsewhere, but 1x6 that's not treated is hard to come by in Florida.


microstar said:


> In my scenery-building days I was a firm disciple of Bill Raoul's "Stock Scenery Construction" handbook where everything was made of 1x.



As a TD that took a very roundabout way to being a TD that book is a Godsend. 1x for days.


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## Ted jones (Oct 17, 2018)

We used to build them when I worked in a scene shop in Baltimore. The parallels were easy to store and so were the tops being plywood with no framing. And easy to build.


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## Richard Young (Oct 23, 2018)

BillConnerFASTC said:


> I dont think too many here have ever seen a parallel, let alone build one.


I don’t think the kids could build one if their life depended on it, let alone afford the clear 5/4 stock. 
Knee walls ( standard in film construction ) are the next best thing. 2x4 legs and bolts are just stupid amateur night. You can’t level that in anything that could remotely be called a short period of time. And try to do that on an outdoor gig.


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## RonHebbard (Oct 23, 2018)

Richard Young said:


> I don’t think the kids could build one if their life depended on it, let alone afford the clear 5/4 stock.
> Knee walls ( standard in film construction ) are the next best thing. 2x4 legs and bolts are just stupid amateur night. You can’t level that in anything that could remotely be called a short period of time. And try to do that on an outdoor gig.


*@Richard Young @BillConnerFASTC* In 1973 we built parallels of 1 foot and less (8") using 3/4" ply and windowing it to reduce weight, create hand-holds and feet. Standard 5/4 stock with glue, clinched nails and corner blocks et al were more economical both material and labor-wise for our 2', 3', 4' and 5' parallels. All tops were 3/4" 4' x 8' ply with corner blocks and were identical. We built at least 8 of each height plus a couple of 4' x 4' and a couple of specially angled units for choral riser set-ups. Fortunately we had a large trap room for convenient storage and soon added dedicated storage / transit dollies. 
Toodleoo! 
Ron Hebbard


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## RickR (Oct 23, 2018)

I once saw someone rip 3/4 ply into 5 1/4 strips for deck framing, claiming it was far cheaper than #2 pine.


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## gafftapegreenia (Oct 23, 2018)

RickR said:


> I once saw someone rip 3/4 ply into 5 1/4 strips for deck framing, claiming it was far cheaper than #2 pine.



I’d have to compare prices, but it IS straighter and more consistent.


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## sk8rsdad (Oct 23, 2018)

We do this from time to time, not for any cost saving but for dimensional stability.


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## RonHebbard (Oct 23, 2018)

RickR said:


> I once saw someone rip 3/4 ply into 5 1/4 strips for deck framing, claiming it was far cheaper than #2 pine.


 *@RickR EXACTLY!* Plus you save on IA labor to cut, assemble, glue, nail and clinch so many, many, joints. Use at least one bolt on each half of every hinge and rock on.
Toodleoo! 
Ron Hebbard


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## kicknargel (Oct 23, 2018)

We frame flats out of ply for dimensional stability, and I would do platforms that were sitting on the ground. I would not use ply for platforms legged up in any manner, because I don't trust fasteners into end grain of plywood for structural uses.


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## bobgaggle (Oct 23, 2018)

RickR said:


> I once saw someone rip 3/4 ply into 5 1/4 strips for deck framing, claiming it was far cheaper than #2 pine.



I've built many many many platforms that way. Depending on the plywood you buy, it may be cheaper, straighter, easier to work with. Lots of pros and not many cons for the plywood framing method. As long as you understand the expected loads and leg appropriately, I don't see a downside to it...


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## RonHebbard (Oct 23, 2018)

kicknargel said:


> We frame flats out of ply for dimensional stability, and I would do platforms that were sitting on the ground. I would not use ply for platforms legged up in any manner, because *I don't trust fasteners into end grain of plywood for structural uses*.


*@kicknargel* Surely if you're assembling parallels you're using at least 8 or 12 2" back-flap hinges, mostly secured with 2 flat head wood screws plus one flat head machine screw and nut or T-nut per hinge half with zero fasteners into any end grains. 
Toodleoo! 
Ron Hebbard


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## Chase P. (Oct 26, 2018)

JonCarter said:


> Where on earth do you guys store all these monsters? Doesn't anyone build parallels any more?



Parallels for the win! We used these in college, but I haven't seen a single one since. We also had stock knee walls, both for flat platforms and rakes. It was opera. So many rakes.

Does anyone have an opinion on using 5 1/4" wide 3/4" ply as the box/framing of a platform? I've seen it done, but have never gotten an accurate weight comparison, or a solid opinion on the strength.

Edit: Just saw and read the additional pages of responses on ply as framing. I got distracted and excited by parallels. I'd still love more input on the ply as framing concept.


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## RonHebbard (Oct 26, 2018)

Chase P. said:


> Parallels for the win! We used these in college, but I haven't seen a single one since. We also had stock knee walls, both for flat platforms and rakes. It was opera. So many rakes.
> 
> Does anyone have an opinion on using 5 1/4" wide 3/4" ply as the box/framing of a platform? I've seen it done, but have never gotten an accurate weight comparison, or a solid opinion on the strength.
> 
> Edit: Just saw and read the additional pages of responses on ply as framing. I got distracted and excited by parallels. I'd still love more input on the ply as framing concept.


 @Chase P. When we built our 8" and 1' parallels as 4 foot x 8 foots with 3/4" ply for framing, we windowed the sides and ends with a sabre saw to reduce weight, create hand-holds and make feet. After roughing out the openings with a course sabre saw blade we finished all of the cuts with a 3/8" ball-bearing piloted, round over bit to make quick work of finishing all of the edges that would be subject to handling. This worked well for us in 1973 and, with the addition of many, many coats of flat black paint, all of the parallels were still in service the last time I saw and touched them somewhere around 2010. They definitely had a few miles on them but were all still in serviceable condition. (Yay IA 129 with much help from Jimmy Burns and IA 58's opera shop arpenters.
Toodleoo! 
Ron Hebbard.


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## Chase P. (Oct 26, 2018)

RonHebbard said:


> @Chase P. When we built our 8" and 1' parallels as 4 foot x 8 foots with 3/4" ply for framing, we windowed the sides and ends with a sabre saw to reduce weight, create hand-holds and make feet. After roughing out the openings with a course sabre saw blade we finished all of the cuts with a 3/8" ball-bearing piloted, round over bit to make quick work of finishing all of the edges that would be subject to handling. This worked well for us in 1973 and, with the addition of many, many coats of flat black paint, all of the parallels were still in service the last time I saw and touched them somewhere around 2010. They definitely had a few miles on them but were all still in serviceable condition. (Yay IA 129 with much help from Jimmy Burns and IA 58's opera shop arpenters.
> Toodleoo!
> Ron Hebbard.



That's a significant run for any piece of scenery! I'm curious how a platform would hold up over a parallel. Platforms are basically glued butt joints with a few fasteners, while parallels use hardware to make those corners. I know ours in college were all stove bolted through the hinges into t-nuts on the back. It seems like that would offer a lot of additional corner strength.

These days, I guess it'd be pretty simple to have the shorter parallels zipped out on a CNC router, bolt holes and all. They'd basically be IKEA scenery, only less MDF and longer lasting.


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