Rabbets when joining 3/4 plywood

[Joe]

Hi 

I wish to joining 3/4 inch baltic birch plywood to make an 18 inch square box. If I rabbet one piece  3/8 inch deep for gluing purposes what size screw should I use and will i get a stronger joint? 

Thanks 

Joe

[Joe]

Hi John, Interesting you just glue the bottom into a rabbet at the bottom of the sides then instead of using a groove in the sides? I think that's what you mean as that would give more depth.

joe

[John Schaben]

Hi Joe. I pic up the depth because I glue the tongue into the groove and cut the tongue along the top edge of the bottom. I also use the same joint for the front and back to the sides. Interesting assembly. You start with one side, install the bottom then the front and back and the last side locks everything together. I suppose, theoretically, you wouldn't even need glue if you had tight fitting side mount slides. Personally, I wouldn't go that far.

[Joe]

Hi John,

Yes I have been making drawers this way also, but i have been sliding the bottom in the side groove w/o a rabbet. Your way gives a bigger drawer and strong too. 

I was thinking of the pocket joinery as the availability of the table saw I use is coming to an end and iI wanted to build the bench's cabinets.  Everything else is done. I was originally going to use finger joints on the drawers, but i am running out of time. 

[John Schaben]

Like has been pointed out so many times, way more than one way to skin a cat in this business. Loosing a table saw can put a crimp in your action though. I make those joints on either the table saw or the router table, just depends on which is easier to set up a that given moment. In a pinch, you could cabbage together a usable router table. Just need a hunk of ply with a hole in it to stick the bit through and another straight board to clamp on as a fence. Not terribly elegant but serviceable.

[Joe]

Thanks John, I'll et you know how I make out.

Joe

[Gary roofner]

John you're more experienced than I making these drawers . If you are using 1/2 inch plywood do you use 1/4 inch dadoes and rabbets? For the bottom do you use 1/4 plywood or rabbet the 1/2 plywood to 1/4 inch? My other question is the difference in price between 1/2 and 3/4 plywood is only 3 to 5 dollars a sheet the added strength of the 3/4 is so much more doesn't it make sense to use 3/4 ? One of the reasons I picked up a Radial arm saw was to cut these rabbets and dadoes quickly. I was practicing this evening on some 3/4 scraps and the dado did a good job but it was solid lumber plywood I expect tear out in plywood? Will I need to make the cuts in 2 or 3 passes or am I worrying about nothing?

[Ken Darga]

Gary,

To minimize tear-out or chipping in plywood, make the first pass, with a depth cut setting of 1/32 - 1/16''---

just enough to break thru the top layer of material.

A shallow cut will shear thru the top layer of the plywood.

Then followed by the next pass to the desired depth for the rabbet or dado.

When making multiple passes, with a saw blade, small ridges in the bottom of the cut, will need to be made smooth, for a stronger glued joint.

Smoothening the bottom of the cut, can be accomplished by using a chisel or shoulder plane.

A dado blade will provide a smooth bottom in the depth of cut.

A dado set is very handy to have, if doing lots of rabbet or dado cuts.

Tape, pressed firmly in place, can be applied over the area to be cut, to reduce chip-out.

(Apply tape, press firmly in place with a wood roller---akin to a roller used smoothening wall papering joints).

An alternate method---make a ''knife'' cut into the verneer of the plywood.

The knife cut will break thru the top layer of wood fibers.

Then followed by making the saw cuts.

A straight edge is required as well as a scribing knife, to make the scribe line.

This process is more tedious, and may be necessary for some tasks, to avoid chip-out.

[John Schaben]

Hi Gary - Actually, I just use 1/2" for all of it; front, back, sides and bottom. If I'm not using false fronts I sometimes use 3/4 for the front just for cosmetics. I use 1/4" tongues and grooves and with plywood end up with about 7/32" left over. All of it being interlocked and glued together, I haven't been terribly concerned about strength. I did have a couple of 12" deep drawers I was concerned about and reinforced the corners with aluminum angle but in retrospect, that was more of a "belt+suspenders" move than anything else.

You should be able to make all those cuts in one pass with a RAS. I generally just use one pass with the router using either a slot cutter or a straight bit. Depending on the quality of plywood I get some to none on tearout. That's what I like about those joints... lots of ways to make them and maybe just a depth of cut or fence change to go from rabbet to dado.
 
Gary roofner said:

John you're more experienced than I making these drawers . If you are using 1/2 inch plywood do you use 1/4 inch dadoes and rabbets? For the bottom do you use 1/4 plywood or rabbet the 1/2 plywood to 1/4 inch? My other question is the difference in price between 1/2 and 3/4 plywood is only 3 to 5 dollars a sheet the added strength of the 3/4 is so much more doesn't it make sense to use 3/4 ? One of the reasons I picked up a Radial arm saw was to cut these rabbets and dadoes quickly. I was practicing this evening on some 3/4 scraps and the dado did a good job but it was solid lumber plywood I expect tear out in plywood? Will I need to make the cuts in 2 or 3 passes or am I worrying about nothing?

[David Dean]

Here's another way to build drawer's with 2 pice of 3/4" and two pice of 1/2" and a dado cut 3/8" from the buttom

[Gary V Morris]

My guess is that you have completed the box by the time this is posted. But, just a note for future reference. The ingenious approach of the Kreg Jig removes the need to add rabbets or dados, saving time and setup. Those cuts help to align, square up the box, and are great ways to assemble things, but are not absolutely necessary. Kreg has made the diagonal approach of fastening materials popular and the holding power of the screw is highly effective, even without glue. Some discussion pointed out weaknesses with using screws on end grain; however, the Kreg jig's pocket holes are not into the end grain. They are on a diagonal and have great holding power as a result. The key is make sure all your material is squarely cut and that the opposite sides are exactly the same length. You can readily assemble the box sides with a Kreg clamp. Just be sure to use a square to check before you drive the screws home and attach the bottom last. When using the Kreg screws, the need to clamp the assembly is gone. The screws act as your clamp. If in doubt about using glue, just glue away. It will add to the strength of the assembly. There are a number of tests for screws and glue joints showing that, when pressure is applied to wood, the wood is more likely to break than the joint sections for glue or screws. Titebond was recommended in one reply and is a good choice. I would use Titebond II if this is staying in the garage since is is more water/weather resistant.

You mention using 3/4" and in another comment 1/2" BB is mentioned. If it is 3/4" you could hold an elephant in the 18 x 18 box, half and elephant in the 1/2" material would be OK at that size box. I have seen "professional drawers" of 1/2" BB that were rated at 100 lbs. that were twice the size you are using. If it is 1/2" you might think about using the Kreg Micro Jig and the appropriate screw size for it. It cuts a smaller diameter pocket hole, but the regular jig will also cut 1/2"; it just looks better using the micro jig when using 1/2" material. 

[Joe]

Hi Gary

I made the rabbets. I was wondering if the kreg Jig would make a strong enough joint on its own in this application . Now I know it would have. I should have been more clear in my question. I still have to assemble them. I suppose I could screw it from the inside with the kreg screws and a setting that accounts for the 1/4 inch rabbet. 

Joe

[Joe]

I used the kreg screws from the inside faces of the boxes to hold them together after i applied glue to the grooves and rabbets.  I set the kreg jig on 7/8 of an inch ( to compensate for the rabbet in the 3/4 ply) which gave a  just under a half inch penetration into the joining piece . It turned out very strong, and the rabbet really made joining everything up easy. 

Anybody wishing to do this make sure to take Ken's advice on how to avoid tear out.

Thank you friends for your help.