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

[Joseph A. Marotti]

If you glue the joint and us 1 1/2 #8 screws and pre-drill them first  your joint will be solid.

[Rick]

Yes, of course.

Rabbet do a few things. First, they align the intersecting boards which helps assembly. Second, the joint has more glue surface which makes it stronger.  Third, the joint locks it in one direction.

It also helps to use extra glue on the end grain.

[John Schaben]

If you don't want the screws showing, I wouldn't use any. A good quality glue like Tightbond will give you a quality joint. A 3/8" rabbet will only leave you with 3/8" of stock to grab if you come from the inside of the box. IMO, screws don't buy much going into the edges of plywood. A couple of brads to hold it together while the glue sets would be all I would use.

1-1/2" screws going into a 3/8" rabbetted joint using the pocket hole jig are a cinch to come out the other side.

I agree with extra glue on the edges.

[Joe]

What about pocket screws , glue but  no rabbett then? It doesn't sound like the pocket screws are strong enough on their own.

I was thinking of using a 1 inch screw with the rabbet idea. 1 1/2 half is too long according to the kreg chart.

http://www.kregtool.com/prodimages/ScrewChart.pdf

[John Schaben]

1" screw might work with the rabbet, and, you can always go with a shallower rabbet, 1/4 or 5/16".  I think you want to stay with the rabbet for the extra glue area and mechanical interlocking. Like I said before, a good glue and baltic birch ply is hard to improve on. Just how much weight did you expect this thing to contain?

[Joe]

It is going to have 3 drawers made out of 1/2 inch ply in it for tools and be installed under a workbench.  I haven't thought about the weight specifically but no more than 40 pounds I suppose. I will be using accuride draw slides which I have. There are actually two boxes I am making so Ill have 6 drawers. 

[John Schaben]

Hi Joe - From my experience, tool drawers tend to gain weight pretty rapidly. To beef it up a bit, some plywood corner blocks would add considerable strength. They would just need to be glued in, maybe some short screws there to hold them while the glue sets. About 3 up each corner (12 total) would do it and you can just make them from scrap ply.
 
Joe said:

It is going to have 3 drawers made out of 1/2 inch ply in it for tools and be installed under a workbench.  I haven't thought about the weight specifically but no more than 40 pounds I suppose. I will be using accuride draw slides which I have. There are actually two boxes I am making so Ill have 6 drawers. 

[Ken Darga]

Joe,

Since you plan to make these drawers for holding tools,

and as John mentioned, they will gain weight fast---

I'd suggest making the drawer front, sides and back from 3/4'' stock, and

the bottom from 1/2'' stock.

Install the bottom panel in a grooved (dado) joint.

You can use Kreg pocket hole joinery and the screw Kreg suggests---

periuse the chart you posted above.

You wrote:  >>>...1 1/2 half is too long according to the kreg chart./span>

Use a ''shorter'' screw!

[Joe]

Thanks for the suggestions on the beefier drawers. That will probably be best. Right now I am focusing on wondering if I can use the kreg joinery to make the drawer boxes instead of biscuits, etc. 

From what I gather:

Kreg joining 3/4 ply face to end grain and glue is not going to make a strong enough joint to make the boxes. 

 I can add a 1/4 inch rabbet, but then I have use 1 inch screws in the pocket holes. I'll make the holes on the 1/2 inch setting. I tried that on scrap and the screws stick out 7/16 of an inch, so that works. It just doesn't seem like much screw, but the glue makes up for it.

The corner braces add strength as long as I don't let them interfere with the drawers. Trying to picture that. 

[Ken Darga]

Joe,

Drawer boxes can be assembled using pocket holes and screws.

The screw points should face ''inward'', from the outside edge.

When the screw point is directed toward the outside edge, the wood is subjected to fracturing.

There are some photos, somewhere, that show drawer construction with the outside corners butted, when using pocket hole joinery. 

For corner support---

install 1-1/2" angled cleats vertically on the inside corners of the drawer box---

butt to drawer bottom and make flush with drawer top---

glue and clamp in place.

Add this feature after the drawer box has be assembled.

Angular cleats can be made by ripping 2x2 stock, across corners, at 45 degrees.

 

[Joe]

Hi Ken,

Thanks for the tip on the screw points and the cleats for the drawers. I might make the drawers with the kreg screws as well then  and see how that goes.

I just found this "chapter 13" 90 degree panel joints with the Kreg on the net. I bought this thing so long ago I lost the cd that came with it. I've been using the kreg jig for other operations occasionally where I couldn't use traditional joining methods.  I hate to waste a good sheet of BB plywood but I do want to know if the jig can be truly used to save time with sheet good projects. Iv'e been working with solid hardwoods and mortises and tenons,  dowels ad biscuits up to now.

Kreg suggests in the video that making the cabinets (what I am calling the boxes) that hold the drawers with screws alone is plenty strong. But  your suggestions seem to suggest otherwise. I personally can not see joining  panels w/o glue.

Joe

[John Schaben]

Hi Joe - I have been making all my drawers; kitchen, shop, drawerdrawrs, with just drawer lock joints (aka locking rabbets, rabbet/dado and other names). Very quick and easy as well as absolutely solid. With plywood, you don't need to "float" the bottoms so I glue those in with the same joint. End up with an extremely rigid box as well as gaining some depth. I have just made all of them from 1/2" ply and I know some of them have in excess of 50#'s, Don't need any screws as when assembled the parts interlock and just two bar clamps hold everything together. Assembly is also pretty well self squaring so just need a few tweaks when tightening the clamps. Actually, come to think of it, I started using band clamps, one around the top edge and another around the bottom edge which also helped square things up.
 
Joe said:

Hi Ken,

Thanks for the tip on the screw points and the cleats for the drawers. I might make the drawers with the kreg screws as well then  and see how that goes.

I just found this "chapter 13" 90 degree panel joints with the Kreg on the net. I bought this thing so long ago I lost the cd that came with it. I've been using the kreg jig for other operations occasionally where I couldn't use traditional joining methods.  I hate to waste a good sheet of BB plywood but I do want to know if the jig can be truly used to save time with sheet good projects. Iv'e been working with solid hardwoods and mortises and tenons,  dowels ad biscuits up to now.

Kreg suggests in the video that making the cabinets (what I am calling the boxes) that hold the drawers with screws alone is plenty strong. But  your suggestions seem to suggest otherwise. I personally can not see joining  panels w/o glue.

Joe