Large Cabinet Build

[Bryan Cramer]

I am commissioned to build 4 library bookshelves for my local school's library. Each cabinet is 54" high by 84" long and 13" deep. Are there any suggestions on building a temporary assembly table to assemble the cabinet? I have a traditional style work bench that is 30" by 60"; way too small for this project. Can you help?

Also do you have any pointers when working with a large scale project like this. I will break the sheet goods down with a track saw. The joints are but joints with biscuit renforcement. I will use screws and pocket screws to hold it together while the glue dries. I only have so many long clamps.
Tonight I will post a sketchup drawing of the cabinet.

Thanks

[Prashun Patel]

You can get a 24" or 30" x 84" luan hollow core door from HD for cheap. That on a pair of saw horses makes a wonderful assembly table.

[Richard Coers]

I just curious, and more than a little apprehensive. You have a commision to design and build bookcases, and you need help with a design for an assembly bench? I just hope you do your homework on shelf strength and sag under the huge loads that books can put on a shelf. Under designing a piece that goes into a public place could end up with you testing your liability insurance.

[Michael Dunn]

84" WIDE?!? Geeze... My brain first told me you said 84" tall. I know that's what you were told to build, however, I would try to convince them to change the design. Sure, you could reinforce the shelves, but a complete design hangs would be best IMHO.

[scott vroom]

What is the longest shelf span in your design?

You'll find this helpful: http://www.woodbin.com/calcs/sagulator.htm

[Bryan Cramer]

You'll see in the sketchup drawing I have a divider in the middle so the shelf span is about 42" instead of the 84". That is the shortest shelf span they want. It will be built with 3/4" maple hardwood and plywood. I will edge the shelves with 1 1/4" front and rear edging. I did use the sagulator; what a great tool it is! I wanted extra renforcement so I added a rear edging as well as the front. The sagulator doesn't have that as an option so adding the extra edging should give it the extra reinforcement needed.
A door was my first thought for an assembly table. I suppose I will end up doing something like that.

[scott vroom]

12" of books from my shelf weighs 34 lbs. Using this figure, and your supplied data, I get .02 in/ft sag using Sagulator. Adding the rear edging will only inprove that number....you should be fine.

[Bryan Cramer]

That is what I got too. The ends aren't fixed (per thier discresion) so I will use strip (pillister) metal shelf supports dadoed into the case sides.

[Mark Bolton]

Pretty substantial span for a school. I dont mean to sound like chicken little, the liability factor is one thing, and the "ladder effect" of some kid(s) sitting/climbing, laying, and so on would be something I would be thinking hard about in my design as well. It gets you nowhere to say "well its what they wanted". Its your responsibility to inform them of any concerns with regards to the end product.

Unfortunately in the public arena unless your covered by a pretty solid indemnification agreement you had just better make sure your covered. If something happens a parent, insurance company, or both, will try to get a piece of everyone they can and being the maker, you'll likely bear the brunt.

[Dave Zellers]

I don't care what the sagulator says, a 42" long 3/4" plywood shelf is going to sag significantly if it is loaded up with books. I would probably glue a 1/2" and 3/4" ply together and if they had a slight crown, I would align them, not oppose them to start out with that in my favor. In a situation like this, I like to make the shelf solid and symetrical e.g., 1 1/4" thick with a nosing applied and trimmed flush so even if THAT sags, it can be flipped over down the road.

Also, I don't think you will be happy with a luan door for this project. These will be fairly heavy and I would want a more substantial assembly table. Mine is a 4x8 sheet of 3/4 UL plywood screwed to 2x4's on edge that were carefully hand picked for quality, left to acclimate in the shop for a week or so then jointed straight and ripped parallel. All around the permitter and 2 down the middle lengthwise with 2" coarse thread screws about 8" apart. Having that available has made me much more productive. I actually built it as the table to build an assembly torsion box on but pushed that to the back burner since this is already so flat. I rolled on 3 really heavy coats of urethane and couldn't be happier. If you don't have room for a 4x8 table I would say the length is more valuable than the width. Or maybe something hinged that could be dropped down when not needed.

[David Weaver]

Sag. I'd split those in half and put dividers in, even though it makes for ugly shelves.

I'd use hollow doors, too, they were the gold standard for us when I was building model airplanes as a kid - cheap and flat.

[Mark Bolton]

I would probably glue a 1/2" and 3/4" ply together and if they had a slight crown, I would align them, not oppose them to start out with that in my favor

I would agree completely that a 42" shelf span using 3/4", regardless of the solid wood edging, is a guaranteed sag. A bookcase I built 20 years ago has 3/4"BB shelves, rabbeted solid wood edging both sides, less than 36"OAL, and they sag.

That said, I think you'd be guaranteed a crown with an unbalanced glue up (1/2&3/4) even though its ply. Would seem two 5/8" or bump to 1" with two 1/2" or 1 1/2 using 3/4" would be safer.

Though the sag will definitely be an issue my concern would less be the sag and more to make the shelf flush on both faces for two reasons. One, as you say its flip-able when it does sag, and two it eliminates the "hand hold" that will be built into the shelf edge with an 1 1/4" solid wood edge on a 3/4" ply shelf. You can walk into any municipal library and see signs telling children not to climb for a book but rather to ask. I would imagine those signs are effective about 6% of the time.

If I wanted 42" clear span in this application I'd be looking at a lot more than 3/4" ply, sagulator or not.

[Bryan Cramer]

I am glad I posted this thread. I thought I coved all the issues with in the design process, but you guys raise new questions I have never thought of before. Let me add more info: The library currently has 48" bookshelves with a full shelf span. They said they have had no trouble with kids climbing the shelves because they were filled with books which also helped weight it down to the floor. The original shelves were just 3/4" particle board wich sagged quite a bit. I expressed my concern with the shelf length but they still insisted on long shelf spans. The idea was to have a long unit divided out to match their existing shelf span. The longest I agreed to go was 42". All four units would be placed together along a wall. I plan to bolt the four sections together, but not to attach them to the wall. This would add to the stability of the whole unit. The school wanted the long units because there was less wasted space from multiple sides. A single unit with a divider gave the most shelf length in the smallest foot print.
In short, I had to design a multiple unit book shelf that could come apart, had shelves as long as possible, and had to fill up 28' of wall space. I should ask how would you have design it? Would it be better to build the shelves in 8 42" sections or 4 84" sections with a divider?

They agreed that I was to be liable for the construction of the units, not the misuse, but I will still restate our agreement upon completion (and put in writing). I do know about liabilities but I have had little experience with liability issues. I am also not a professional woodworker.

Thanks for all your help!

[Mark Bolton]

Are you planning on getting insurance for this project? Again, not trying to be a chicken little but just defending yourself against some outlandish allegation could bankrupt you. Its sad that in this day and age you cant get to do a little something you like (woodworking), help the school (very rewarding), and make a couple bucks while your at it (assuming you will have some profit). But unfortunately its the truth, liability is a major major issue. Absolutely anything could happen with these cabinets and even if its eventually deemed misuse or lack of supervision you will still have to defend yourself through the process. Its a very serious concern.

Im sure I, and others, could be overstating the sag issue however I know in my experience, with a shelf that long, I'm not. How I would design the shelves would depend on several things the main one being budget.

[Bryan Cramer]

I strongly encourage them to choose the option of strengthening the plywood for the shelves, but they insisted on a single layer with front and rear edging because of budget. Anything will be better than the existing particle board! I do understand the l liability concerns. I have made it clear to the school I am not liable for misuse. Maybe I should write up a sort of warranty stating what and what not I am liable for, but I have no legal experience so any lawyer could punch holes in it. At least the superintendent understands woodworking (he does some himself) and agreed to my proposal about my liability.