Bow in 3/4 plywood lumber cart

putttn · Post by **putttn** » Sun Oct 07, 2012 12:21 pm

I built a small lumber cart and used 3/4" plywood as the base. Width is measuring 42" with large casters on all 4 corners. I was suprised to see a small sag in the middle of the base. Not that much lumber in the cart so it's not a weight issue. Thought about putting a board on the leading edge to suck the sag back up...any help here?

JPG · Post by **JPG** » Sun Oct 07, 2012 12:51 pm

putttn wrote:I built a small lumber cart and used 3/4" plywood as the base. Width is measuring 42" with large casters on all 4 corners. I was suprised to see a small sag in the middle of the base. Not that much lumber in the cart so it's not a weight issue. Thought about putting a board on the leading edge to suck the sag back up...any help here?

42" x ??"

holsgo · Post by **holsgo** » Sun Oct 07, 2012 4:48 pm

42 inch across? Yup, that will sag even with nothing on the cart. Over time the plywood, just through moisture and gravity will summon the center to the floor. Take the cart, flip it over and add bracing across the cart in the form of 2x4s or solid stock. Just one piece of 3/4 ply...or even 2 built up will still sag.

putttn · Post by **putttn** » Mon Oct 08, 2012 8:20 am

Added a 2x4 to the top and ran a couple of bolts to suck it back up but can see that it will need some more "beef" to keep it from sagging.

JPG · Post by **JPG** » Mon Oct 08, 2012 10:11 am

putttn wrote:Added a 2x4 to the top and ran a couple of bolts to suck it back up but can see that it will need some more "beef" to keep it from sagging.

I think a 'lip' on each edge would be desirable anyway.

holsgo · Post by **holsgo** » Mon Oct 08, 2012 5:22 pm

If you do it right now you won't wish it was right later.

videobear · Post by **videobear** » Tue Oct 09, 2012 9:18 pm

42" is a long span for 3/4" material. Even bookshelves will tend to have shorter spans, and/or support for the shelves at least along the back edge, and probably on the front edge as well. A stiffening lip UNDER the shelf will do more to prevent sag than a ledge along the top edge of the shelf.

JPG · Post by **JPG** » Tue Oct 09, 2012 9:30 pm

videobear wrote:42" is a long span for 3/4" material. Even bookshelves will tend to have shorter spans, and/or support for the shelves at least along the back edge, and probably on the front edge as well. A stiffening lip UNDER the shelf will do more to prevent sag than a ledge along the top edge of the shelf.

How's zat?? Easier, but stronger???

putttn · Post by **putttn** » Tue Oct 09, 2012 9:49 pm

Thinking about doing a "honeycomb" affair under the base. Have had good luck lately working with FastCap glue so this project will be another good test for the strength of this glue.

JPG · Post by **JPG** » Tue Oct 09, 2012 10:48 pm

putttn wrote:Thinking about doing a "honeycomb" affair under the base. Have had good luck lately working with FastCap glue so this project will be another good test for the strength of this glue.

a.k.a. torsion box.