Dados and pocket screws

[Roger Pozzi]

I've searched everything I can find but can't get an answer. So I thought surely someone here knows.
Can you use pocket screws with a dado ? Such as a shelf set approximately 1/4” into the side panel of a shop cabinet. I'm using 3/4” cabinet grade birch plywood and would like to use dadoes for the bottom, top, and shelves but, I don't want any visible fasteners showing on the outer surfaces. My reasoning for dadoes is for extra strength and to prevent possible racking.
It seems that the decreased thickness at the joint would require either a different depth setting or maybe just shorter pocket screws.
Please help, Thank you

[keith ouellette]

You really won't need the pocket screws if you have dados.. 3/4 inch birch glued into a 1/4in dado won't come apart even if you want it to. the ply's would have to rip off of the inside of the dado.

this is assuming if the dado was done right, which I'm sure you will.

[Richard M. Wolfe]

The jig is made to allow holes to be drilled to set screws as deeply as possible into material without coming through. If you dado a quarter inch into the side of 3/4" material you are in effect using 1/2" material and the jig then has to be set for that. It would be simple enough to check by taking a couple pieces of 3/4" scrap and dadoing one and then pocket screwing the other to it to see what happens. If there is to be a face frame fitted around the carcase opening (as is the case in nearly everything I build) there is an overlap of stiles onto the shelves and when fastened pretty much eliminates racking.

[Jamie Buxton]

Dados don't add much anti-racking strength to the cabinet. The wall has only a teeny-tiny grip on what's a long lever arm -- the shelf. However, the dado does nicely establish the position of the shelf during glue-up. One issue I've occasionally had with pocket screws is that when you tighten the screws down, they slightly move the parts sideways. A shallow dado prevents that.

A good thing about using pocket screws is that they can provide clamping pressure while the glue dries. There are areas -- for instance the middle of a middle shelf -- where it is difficult to get standard clamps. Screws do a great job there.

[Tony Shea]

Shorter screws is all that should be required. If you change the setting on the pocket jig for thinner material then you will be drilling a hole in the wrong position of the shelf. Instead of the screw coming out near the center of the board it will end up closer to the edge. I'm having trouble explaining this. But the thickness of the peice not being drilled has no weight in what the jigs' depth setting should be. The peice being drilled is what needs to be adjusted for.

[keith ouellette]

I have been thinking about this since I last replied to your post. If the side panel is 3/4" thick and the dado is 1/4" that leaves 1/2" (I'm sure you know that) so then you subtract, say, 1/16" to make sure you don't poke through the other side and that leaves 7/16". then there is the first 1/16" of the tip of the screw that has no threads so now we are down to 3/8"

I don't know a lot about screw mechanics and holding power but I would have to ask is 3/8" of a bite going to help much compared to the strength of the dado? I doubt it could hurt any. But still it got me curious enough to ask.

[sean m. titmas]

I don't know a lot about screw mechanics and holding power but I would have to ask is 3/8" of a bite going to help much compared to the strength of the dado? I doubt it could hurt any. But still it got me curious enough to ask.

good point Keith.

the advantage with using pocket screws is that you have clamping pressure without clamps. with such a short screw shaft i doubt that you could get sufficient clamping pressure from just the screws alone so you would need to apply clamps, thereby negating your original objective. if speed is your desire than i would forget the dado and use a few dowels to align the shelf and a few pocket screws to clamp the assembly.