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what is stronger - biscuits, dowels or pocket screws?

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Forum topic by fiddlebanshee posted 07-12-2010 02:04 PM 19854 views 0 times favorited 14 replies Add to Favorites Watch
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fiddlebanshee

195 posts in 2411 days


07-12-2010 02:04 PM

We are moving to a new house and in the new living room we want to make an 18 foot wall of bookshelves (18’ long, 8’ high, and 9” deep – this will house about one third to half of our book collection). The idea is to make one strong permanent center case of 8’x26”x9” to give the assembly stability onto which we would then make a detachable system of supports and 26” shelves so that it can be taken out of the house at a later date should we ever move again.

We are only beginning woodworkers so things like dovetails and m&t is out of the question at this stage. So I was thinking about a butt joint that would be strong, and wouldn’t rack. The three types of joints that I can handle with the equipment I have are biscuits, dowels or kreg pocket screws. Which is superior for strength? To give it stability there will also be a 1/8” plywood back to this case, and to all the add-on shelf units.

Secondly, if I may tag on a second question, we were thinking of a way to attach the detachable shelves so that they would be strong, and I came up with a cleat system, whereby the shelf would have a metal strip sticking down about 1/8” from the edge, that would be seated in a groove in a cleat attached with glue and screws to the support. Is this a valid way of engineering this? I am working on a sketchup file, and can post pictures later.

For materials we are thinking cabinet grade plywood or a not very expensive light colored solid wood. I’m a little unsure what to do about the plywood edges if we go that route. I’m not confident that I can veneer them in a pleasing manner, having never done it I don’t know how difficult that would be. The side supports will probably be 9” boards (the full depth of the bookcase).

Thanks in advance for your suggestions and ideas.

-- As if I needed another hobby!


14 replies so far

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richgreer

4541 posts in 2540 days


#1 posted 07-12-2010 02:44 PM

You didn’t say it, but I assume you are using 3/4” thick boards. Books are heavy. I don’t think plywood or a softwood (pine) would be sufficiently strong to support a 26” span. I recommend a strong hardwood such as oak, hard maple, ash etc..

Biscuits are definitely out. They are not met for a job like this.

Dowels would work but they will be hard to work with.

IMO – Your best option is pocket holes and, for added strength, I would probably put 4 pocket screws at the end of each board. Pocket holes, especially with the Kreg system, are very easy to work with.

If you use a common wood (oak, maple. . . ) you can buy wood plugs that do a pretty good job of hiding the holes.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View fiddlebanshee's profile

fiddlebanshee

195 posts in 2411 days


#2 posted 07-12-2010 02:52 PM

Yes, the assumption was standard 3/4” stock. How about poplar? We can paint it, it doesn’t have to be a wood that would be stained or oiled.

-- As if I needed another hobby!

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Stosh

65 posts in 2387 days


#3 posted 07-12-2010 03:11 PM

wood band for the edge of the plywood, just cut the shelf 8 1/4 ” and use 3/4” stock to make a front edge peice. if the peice is 3/4×1 1/2” it will keep the shelves from sagging under the weight of books. I usually use this as my standard plywood edge treatment on everything that doesnt get painted. Its fast, easy and strong. route the edge and it gives a nice finished edge treatment. Glue the entire length of the plywood/wood joint of course. for 4 and a half foot shelves as i am suggesting u would make a 3/4×2 1/2” edge treatment with one running on the back of the ajustable shleves and then the wouldnt sag unless you stacked bags of concrete on them.

As for how to secure the shelves and make the unit. I could not get a mental picture of what you were trying to do. There are one million ways you could make this and probably more. Im not sure what you meant by a “permanent center section” as nothing installed in a house that i have ever seen is truely permanent. I would make four seperate identical Shelf units to cover the 18 feet, so that they are more mobile if you think you might want to take them elsewere and make it easier. thats 4 1/2’ wide 8’ tall and 9” deep. Make “nailers” 3/4 X 5” pywood strips that run across the back of the cabinet to secure it to the studs with two lag bolts at the top of each cabinet to secure it to the wall. When you want to move again, remove 8 lag bolts and you will have 4 shelving units that could be easily used elsewhere and this is how i would build them regardless of if you ever planned to move again …. Make the nailer at the top of the cabinet but the “top” under it with a peice of crown molding on the front and only people taller than 8 feet will ever see the lag bolts. hope this helps, good luck

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fiddlebanshee

195 posts in 2411 days


#4 posted 07-12-2010 03:26 PM

Stosh,

The word permanent was confusing. What I meant was that one section would have the bottom, top and sides all glued and permanently attached to each other. The shelves in that unit would be resting on cleats and across the back would be either a sheet of plywood or strips of wood across about 2” above each shelf to avoid shear. We do not want to attach anything to the studs – my DH has absolutely vetoed making holes in the wall, so I would probably make sure it tips to the wall slightly by putting small pieces of shim under the front of the frame. We also always slide our books all the way to the back of the shelf.

Then to expand this I would have removable sections that attach to the side of the fixed unit with a cleat system. The way I see this is that I have a strip of 3/4”x1” glued with the 1” side to the side of the vertical support. I would rout a grove in the 3/4” side of the cleat about 1/8” wide facing upwards. Then at the bottom of the shelf I would attach a metal 90 degree strip that slides in the groove and the weight of the books would press that down and make sure it wouldn’t be able to move. So when we want to detach this, we simply first remove all the shelves and then lift the top and the bottom piece out of the groove. The next unit would be attached to the previous one in the same manner.

I hope this explains better what I had in mind.

-- As if I needed another hobby!

View ND2ELK's profile

ND2ELK

13495 posts in 3239 days


#5 posted 07-12-2010 03:27 PM

I would think pocket hole screws would be the strongest but I still glue the joint when I use them.

God Bless
tom

-- Mc Bridge Cabinets, Iowa

View richgreer's profile

richgreer

4541 posts in 2540 days


#6 posted 07-12-2010 04:15 PM

Poplar is not a very hard wood. There are really 2 strength issues. One is the ability to support the weight of the books without sagging. The second is to have a wood that the pocket screws can get a firm grip in to. With poplar I would worry more about this second strength element. Your pocket screws are only going to go into the vertical board about 5/8th of an inch. I would have no concerns about those screws holding with oak or hard maple. Option – use poplar for the horizontal boards and something stronger for the vertical boards.

Before using poplar, I would recommend setting up a test to see how well poplar can support the books.

Someone else mentioned glue. It’s messy to deal with in a project like this and if you have squeeze out (likely) it can affect how the wood accepts a finish. However, it will definitely add strength

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View childress's profile

childress

841 posts in 3007 days


#7 posted 07-12-2010 05:17 PM

Using plywood with 3/4” stock as a face to the shelf like Stosh said should be fine fiddle. trying to build this thing out of solid wood will be expensive and, in my belief, is not needed. Your not building fine furniture, just bookshelves that are 9” deep. I would follow stosh’s advice and use pocket screws and glue for everything. You’ll be amazed at how strong it will be

-- Childress Woodworks

View Michael Murphy's profile

Michael Murphy

452 posts in 2471 days


#8 posted 07-12-2010 06:15 PM

Plywood would work just fine, even just using Edge Tape on plywood works well. If you are using Fixed Shelves then in my opinion you wouldnt need much more lengthwise support than securing the back to each shelf with screws or even nails or pneumatic staples. Pocket screws would help with the ends attatching to the shelves but so would screws through the sides, countersunk and plugged, which would be easier.

I have built a couple of Bookstore’s worth of shelves in my career. Here is one in projects. It is all edgebanded plywood, deeper than 9”, and built in sections, then stood up on a platform to hold them at about a 5 degree angle off the vertical. I try to keep the shelf span below 32”. After years of the shelves being full of books, they are still there and still straight.
Each shelf is attached through the back along it’s length.

-- Michael Murphy, Woodland, CA.

View fiddlebanshee's profile

fiddlebanshee

195 posts in 2411 days


#9 posted 07-12-2010 06:19 PM

Ok, I’ve given it some more thought. I think the issue with the shelves is not going to be a big one as the shelves will only be either 26” or 24” long, we have to decide how many columns we want to divide the space into. The shelves will rest on cleats that are screwed and glued to the side support boards. That’s plenty of support I think. Then the top and bottom that need to provide the strength to keep everything plum and level, but will not have much vertical weight on the joints. So I think pocketscrews there in plywood side supports should be fine. I’m still on the fence about a face frame and front edge for the shelves, as it’s a lot of extra work that we wouldn’t have if we went with all wood.

-- As if I needed another hobby!

View Moron's profile

Moron

5032 posts in 3359 days


#10 posted 07-12-2010 06:51 PM

try to break a biscuit with a downward force…............incredibly strong, combined with a pocket screw…..good enough. If you drill a dowel 5/16th into 3/4 board your only left with 9/32 above and below….....very weak.

26” span you could easily use 2/4”particle board core with no worries

-- "Good artists borrow, great artists steal”…..Picasso

View GregD's profile

GregD

783 posts in 2602 days


#11 posted 07-12-2010 07:17 PM

This link might be helpful – it calculates shelf sag:

http://www.woodbin.com/calcs/sagulator.htm

-- Greg D.

View Vicki's profile

Vicki

1043 posts in 2810 days


#12 posted 07-13-2010 07:08 AM

Here’s my 2 cents from another female on a tight budget. My first set of bookshelves were with cleats for the shelves to rest on and made from pine. I used 2X10X8 for the uprights. Here’s pics of those early shelves and much better ones after my skills improved. “http://mysite.verizon.net/v.hayden/index.htm”

You can also see the bookshleves with luan on the back for a more finished look. I just routed a dado the depth of the luan and attached it with brads. I used pocket hole screws to attach the top (top of the case that nothing sits on) and the bottom shelf. Also, for the piece that goes accross the bottom in front and in back. On one case i put a 2” board accross the top, front and back. I would really suggest shelf pins instead of cleats. I found a bag of nice gold pins on eBay for a song and it makes the case look nicer, IMHO. Oh, all my case are from pine and some were 35 yrs old. They held tons of books and never sagged, even though some were 3 ft wide and some even 4ft. I’m not recomending you disregaurd the sagulator advice, just trying to point out that pine can be plenty strong and durable.

-- Vicki on the Eastern Shore of MD

View fiddlebanshee's profile

fiddlebanshee

195 posts in 2411 days


#13 posted 07-13-2010 12:47 PM

Thanks to all for replies.

@blondewood: The reason for the cleats is not that we don’t want to use pins, we think it is much stronger and will add to the stability. The shelves are not just lying on the cleats, but are fastened. Newest thinking on that part is metal pins that stick up from the cleats and are received with blind drilled holes in the bottom of the shelf. That way the shelves help pull the sides together. I have no problem with the looks of the cleats, although I know that it is not a very traditional look, but I think it’ll work for us. Thanks for the sharing your experience with how pine holds up over time.

-- As if I needed another hobby!

View jlsmith5963's profile

jlsmith5963

297 posts in 2814 days


#14 posted 07-18-2010 07:30 PM

I didn’t read the entire thread but I caught the discussion regarding spans capabilities. Here is some info from Highland woodworking

MAXIMUM SPAN FOR SHELVING
3/4” MDF – 28”
3/4” Plywood – 32”
3/4” Softwood – 34”
3/4” Hardwood – 40”
1” Softwood – 34”
1” Hardwood – 46”

The information can be found here

Also FWW did a joint strength test back in 2009 you can take a look at the results here

-- criticism: the art of analyzing and evaluating the quality of an artistic work...

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