Dado in large plywood sheet

[Dave Hasson]

I'm getting ready to build a sewing desk for my wife. It will basically be 3/4" plywood base with a cabinet and 4 drawers on each side The base piece of plywood is 60" x 22" and I need a 3/4" wide x 1/4" deep dado around 3 of the sides (so the cabinet sides have something to sit in during construction). I'm guessing I could run the long dado on the table saw, but 60" of plywood hanging off the side doesn't seem safe for the shorter ones. Would you just clamp a straight edge and use a router for this? Any suggestions?

http://www.pbase.com/blucrsr/image/118257086.jpg

http://www.pbase.com/blucrsr/image/118257007.jpg

[Brian Kent]

In a word - Yes. A Router.

[Von Bickley]

In a word - Yes. A Router.


I agree.......

[Tony Bilello]

I would use either, I'm just more used to my dado blade. Also, my outfeed table is long enough to handle it.
I have a few questions.....
1) Why do you need something for the sides to rest on?
2) Why not build each 'box' separately, Then make the top and middle section as one piece and the rear panel as one long piece? This would allow for easy construction, easy installation and easy moving
3) Why not build the sides as frame and panel, the front as a face frame and make separate rear panels, and thenattach the long rear panel behind it during assembly?
4) As for something to rest on, I save large pieces of cardboard in my shop, I also buy sheets of 1/2 thick rigid foam for this purpose.
As the foam gets beat-up, I break it into smaller pieces and use to rest of the pieces when spraying.

http://www.pbase.com/blucrsr/image/118257086.jpg

http://www.pbase.com/blucrsr/image/118257007.jpg[/QUOTE]

[Myk Rian]

Router. I used one with a guide to make my RT a year or so ago. Works great.

[Dave Hasson]

Tony, the front is a face frame. I've attached a picture showing the top off. I decided to do a bottom like shown because the whole thing will be on casters. I was going to make 2 cabinets with face frames and then overlay some 1/2" or 3/4" oak to hide the plywood edges and make it look a little more "furniture like". Since I currently only own a table saw, I thought this construction would work best. I will look a little more into some of your suggestions. Thanks!

http://www.pbase.com/blucrsr/image/118258699/large.jpg

[glenn bradley]

+1 on a router for this task.

[Tony Bilello]

David

The frame and panel can easily be done on a table saw if you have a dado blade. I quite often use a lap joint as opposed to cope and stick. I make the lap joint, then brace the doors to shape on my work table and use a router spline bit to hollow out the recess for the panel whether it be plywood or solid wood. I sometimes use my table saw/1/4" dado to make the reces instead of a router.

[Joe Jensen]

As others have suggested, a router is better for this task. One key reason is that it's hard to ensure the dado is full depth when running a large sheet on the tablesaw.

[Michael Schwartz]

Yes a router and guide is the best option for your situation. A shop made guide works but you might also want to look at a number of the commercially made guide systems out there.

Do yourself a favor too and buy a set of undersized plywood bits. 3/4" plywood is not 3/4" thick so a 3/4" router bit would produce a dado thats too wide. Otherwise you need to take a bit that is smaller than the desired width and creep up on the final width with a few passes.

[Josiah Bartlett]

If you decide to use a table saw, cut the dado/rabbet before you cut the middle piece out of the sheet. Then you don't have to worry about the whole piece twisting when you are sawing. It shouldn't matter with a router.

[Dave Hasson]

Thank you for all the replies. Tony, if I went with the frame and panel method, would that be assembled onto the 3/4" plywood sides or would that replace the plywood sides? I do have a dado blade. I like your idea of making each side and then making a back piece to tie everything together. Thanks!

[Tony Bilello]

Thank you for all the replies. Tony, if I went with the frame and panel method, would that be assembled onto the 3/4" plywood sides or would that replace the plywood sides? I do have a dado blade. I like your idea of making each side and then making a back piece to tie everything together. Thanks!

The sides would be directly attached to the front and rear. No plywood sides.That saves weight and material. I would build each box separately with their own rear panel (1/4" luan should work nicely) and bottom (3/4" ply) to stiffen them. The bottom would actually be a solid shelf just below the bottom drawer and dadoed in place. Then when the unit is assembled, another rear panel is added that will spread across and include both boxes and tie everything together.
Keep in mind that overbuilding is not always a good idea. Things can fall apart under their own weight.
I havent figured out sketch-up yet so excuse my lousey sketch.

[Sarit Sotangkur]

Having rabbets and dados in the top is going to restrict the expansion/contraction of the wood.
You can install corner blocks that go inside the cabinet flush with the top and use those along with elongated screw holes to attach the top.

[Tony Bilello]

Having rabbets and dados in the top is going to restrict the expansion/contraction of the wood.
You can install corner blocks that go inside the cabinet flush with the top and use those along with elongated screw holes to attach the top.

Huh? Where?
I didnt notice anywhere I suggested dadoes or rabits for the top.

[Sarit Sotangkur]

Sorry, my bad. I thought that first image was the top not the bottom.

[johnny means]

Ditch the bottom, it adds nothing to your structure (imagine how weak that piece will be once cut and dadoed) and will complicate your assembly (imagine working in between the two cabinets). Two separate cases with firmly attached top and back will be plenty rigid and easier to build.