fasteners

[mnero01]

Good Afternoon,
I just joined, Im looking for a recommendation (or two) about which size screws I should use to attach book shelf side cleats (3/4" x 3/4") to the 3/4" thick plywood side panels. Im installing bookshelves into the space vacated by the removal of a murphy bed. I have cleats for each shelves sides as well as the shelf back (to be attached to the wall). I will have to drill the cleats and predrill the plywood sides. Although I dont plan on moving the shelves I dont want to glue the cleats in place at this time. The 3/4" x 17-1/2" x 56-3/8" shelves have a 1-1/2" x 3/4" support attached to the front. Thanks in advance for your help and recommendations.
Mike

[AHill]

If the combined thickness of the cleat and bookshelf side are 3/4 + 3/4, then total thickness is 1.5". I'd use 1-1/4" screws. Don't countersink the screw too much. Just get it flush or just under flush to the surface. I think a No. 8 screw is the size that would work.

In general, the screw needs to penetrate into the bottom piece of wood at least half the thickness of the bottom piece of wood. The No. 8 size is recommended for 3/4" plywood. So, in other words, a 1-1/4" long No. 8 screw. Make sure it's a woodworking screw and not a drywall screw. Drywall screws can be brittle and break. Drill a pilot hold for the screw to mitigate the chance of wood splitting.

[KyleD]

Another vote for 1 1/4" screws. These are my go to for 3//4 to 3/4 construction. I am partial to the square drive #8 screws. I probably go through as many of these as the rest of the screw sizes combined.

[mnero01]

If the combined thickness of the cleat and bookshelf side are 3/4 + 3/4, then total thickness is 1.5".  I'd use 1-1/4" screws.  Don't countersink the screw too much.  Just get it flush or just under flush to the surface.  I think a No. 8 screw is the size that would work.

In general, the screw needs to penetrate into the bottom piece of wood at least half the thickness of the bottom piece of wood.  The No. 8 size is recommended for 3/4" plywood.  So, in other words, a 1-1/4" long No. 8 screw.  Make sure it's a woodworking screw and not a drywall screw.  Drywall screws can be brittle and break.  Drill a pilot hold for the screw to mitigate the chance of wood splitting.

Thank you for your reply. I was browsing yesterday and started to wonder if a threaded insert would be better. I appreciate the woodscrew specification. Thanks again.

[mnero01]

Another vote for 1 1/4" screws. These are my go to for 3//4 to 3/4 construction. I am partial to the square drive #8 screws. I probably go through as many of these as the rest of the screw sizes combined.

Thanks for your reply, yea Im a pretty good sawdut maker, not really qualified as a woodworker. Thanks.

[Hank Knight]

If your shelves are plywood or a single board of any kind and will span the entire width of the murphy bed enclosure, they will almost certainly sag if they have no other support. You might want to glue and screw a facing board to each shelf to add some stiffness. I have 46" shelves in my family room that are stiffened with a 3/4" X 2" X 46" facings. They are loaded with books, hi-fi speakers and other assorted stuff and have sagged very little if at all over the last 30 years.

[Cian]

If the combined thickness of the cleat and bookshelf side are 3/4 + 3/4, then total thickness is 1.5".  I'd use 1-1/4" screws.  Don't countersink the screw too much.  Just get it flush or just under flush to the surface.  I think a No. 8 screw is the size that would work.

In general, the screw needs to penetrate into the bottom piece of wood at least half the thickness of the bottom piece of wood.  The No. 8 size is recommended for 3/4" plywood.  So, in other words, a 1-1/4" long No. 8 screw.  Make sure it's a woodworking screw and not a drywall screw.  Drywall screws can be brittle and break.  Drill a pilot hold for the screw to mitigate the chance of wood splitting.

Another vote for 1 1/4" screws. These are my go to for 3//4 to 3/4 construction. I am partial to the square drive #8 screws. I probably go through as many of these as the rest of the screw sizes combined.

What they both said.  And Welcome to Woodnet!

[iclark]

Welcome to WoodNet.

Please keep in mind that the recommendations above are based on your saying that you are using 3/4" plywood for the sides.

Unless that plywood is something that you have had in stock for a long time, that 3/4" plywood may be significantly thinner than 3/4".

No offense, but please measure the plywood and the cleats before you buy the screws.

Also, I am not sure whether or not some of the recommendations might change a bit if the cleats are plywood.