Newbie alert: Rolling shop cart question

[Bill Schmitz]

My wife and I have done some simple woodworking projects, i.e. a bench in our mudroom, but have recently upgraded our power tools with an eye towards some furniture building (new table saw, jointer and biscuit joiner). Before jumping into really big, complicated and expensive projects, we thought we would build a rolling shop cart that would double as an out-feed table for our table saw. It seems like a nice way to get some practice and add a functional piece to our shop.

We are planning on a three-sided cart with a couple of simple shelves. The top will be solid wood (an inch thick) and the shelves, bottom, sides and back will be made from 3/4 inch plywood. The way I've planned it, the sides would be set into dadoes in the top and bottom, and screwed in from underneath. The back will be set into rabbets in the top and bottom, and screwed in from the back. Then the two shelves will be dadoed into the sides, and then screwed in. We do have a Kreg pocket screw jig, that we were planning on using for the screws into the top, at least.

Here's the issue: do the shelves add enough lateral support for this cabinet? It's going to be on casters and pushed and pulled around the garage, so I want to make sure it's structurally sound. I'm thinking I need to add some other bracing/support, but not sure what or how. Any advice?

Thanks,
Bill

[Jamie Buxton]

The shelves provide little lateral stiffness. However, the back provides a great deal of it.

[Jamie Buxton]

Another thought: don't cheap out on casters. Cheap ones don't roll well, and they die if you load them up with everything that's going to be on a shop cart. Woodcraft offers some which are sturdy enough: http://www.woodcraft.com/family.aspx?FamilyID=1989 .

[Rod Sheridan]

Hi Bill, if you set the sides into dadoes in a solid wood top, you're going to have an issue with wood movement as the top changes sizes with humidity.

My suggestion would be to make the top and sides of a good grade of plywood ( I like Baltic Birch), then the dado joint won't be an issue.

As well I'd rebate the back into the top/bottom and gables as you've planned, and I would rebate the bottom into the gables. This will give you a flat bottom, ideal for casters.

I would simply glue it together, it will be plenty strong and will give you some practice with glueing and clamping.

Regards, Rod.

[Bill Schmitz]

Thanks, Jamie. Good suggestion on the casters. I went ahead and ordered a set.

Rod: The top is going to be a jointed panel (6 - 4" wide pieces glued together), rather than a single piece or sheet. Will we still have issues with humidity and and wood movement? We are planning on doing that as a practice piece for some other projects we have in mind . . .

Thanks,
Bill

[Rod Sheridan]

Thanks, Jamie. Good suggestion on the casters. I went ahead and ordered a set.

Rod: The top is going to be a jointed panel (6 - 4" wide pieces glued together), rather than a single piece or sheet. Will we still have issues with humidity and and wood movement? We are planning on doing that as a practice piece for some other projects we have in mind . . .

Thanks,
Bill

Yes Bill you will have serious problems.

The solid wood panel will change dimensions based upon humidity, and the plywood will not.

If you imagine the top as fixed, and then shrinking, it will split as it gets smaller.

Same scenario, however it's expanding as the humidity increases, and the glue joint is ripped apart.

If you're going to join wood that moves in different ways, you need a method that allows them to slide in relation to each other.

I suggest that you use ply wood for the box, and if you really want a solid wood top, glue up a solid top, then attach it to the plywood box from the underside with a few screws.

Make sure that the holes in the plywood box are slots layed out at right angle to the solid wood grain direction.

Now as the top expands and contracts, it won't split apart since the screws can slide sideways a bit.

Regards, Rod.

[Bill Schmitz]

Thanks, Rod. That's something I never would have thought of . . . BTW, why doesn't plywood have the same issues? Yes, I'm a real newbie. LOL

Bill

[Rod Sheridan]

Hi, the plywood is made out of thin layers that go in alternate directions, held tightly together by the glue.

The expansion forces aren't strong because the wood is so thin.

With solid wood pieces you always have to consider expansion issues.

Regards, Rod.

P.S. If you make the entire cabinet out of solid wood, and the expansion directions of the pieces in the joint are the same, you don't have an issue since all the joint pieces are changing dimensions by the same amount.

[Lee Schierer]

Hi Bill, if you set the sides into dadoes in a solid wood top, you're going to have an issue with wood movement as the top changes sizes with humidity.

If you make the dado in the top piece a dovetail slot and put the tails on the plywood sides, the top will slide onto the side pieces and be free to move with humidity changes if it needs to. No glue or screws would be required to hold it in place.