Pocket Screws for Building Cabinet Boxes

[George Bokros]

I will be building some cabinet boxes our of 3/4 maple ply. I am considering pocket screwing the sides to the bottoms, will that build a strong box? What screws would you use? I am guessing the coarse thread like you would use for soft wood. The screws will be on the outside of the boxes and will not be visible.

Thanks

[Prashun Patel]

I used pocketscrews on several cabinets. They work wonderfully. Use proper pockethole screws. i like the Kreg ones or the ones from McFeely's. The washer head holds better than the pan head. Proper pockethole screws have self-tapping tips, so they don't split the mating piece.

Yes, coarse thread for soft wood and plywood; fine thread for hardwoods.

[Phil Thien]

Add glue to the joint and the combination of pocket screws and glue will be rock solid. If you have any doubt, build a test joint and then destroy it. You'll get a good feeling for the strength of that combination.

[Rich Engelhardt]

Coarse thread & some TBII will make a real strong carcass.
I did the screws on the bottom and into the sides on the kitchen cart I made - which is essentially nothing more than a bottom cabinet base without a back.
There's face frames on the front and back - functional doors on front and back - drawers that open only on the front and dummy drawer faces on the back.

[George Bokros]

Thanks for the responses. The maple ply is pre-finished so glue will add little to the strength. I have used pocket screws for many times just now with ply. I have plenty of Kreg pocket screws, bought two boxes (one fine thread and one coarse thread) when I bought the jig and have plenty left especially of the coarse thread,

[Peter Quinn]

Take some sandpaper, sand the joint line with a little sanding block to scratch off the finish, glue will add plenty. I'll be doing it today.

[Phil Thien]

Take some sandpaper, sand the joint line with a little sanding block to scratch off the finish, glue will add plenty. I'll be doing it today.

I agree.

If the OP has any doubt, he should try a joint using Peter's technique with some glue, and another one with no glue. Now test them and he will see what Peter does (sandpaper, glue) is many times stronger than screws alone.

[Brian Tymchak]

I built my shop wall cabinets 7or 8 years ago using 3/4" ply and Kreg coarse pocket screws. My intention was to glue and screw the joints but I tried a test with just screws first. It was so strong that I decided to forego the glue to simplify the assembly process. I won't recommend against glue, just that I don't think it's required.

[Larry Fox]

Others with more experience might be thinking of something I am not with the glue advise but I have built quite a few cabinets myself using 3/4" pre-finished ply and done all the joinery with pocket-hole screws and they are rock solid. If they are for a kitchen or other type of (relatively) permanent installation I don't see why the glue is necessary as the boxes are not subject to too much stress and gluing will likely add quite a bit of time to the build process with little to no perceivable payoff. For base cabinets the force is mostly straight down. For uppers it is a combination of pulling on that top cleat and straight down. I think if you do a mockup without the glue by the time you attach the face-frame (if you are going that route) and the back that you would have a hard time destroying the resulting box with a baseball bat. As I said though - the experts might be aware of something I am not.

[john davey]

I am doing this now myself for my basement. I watched the video on Kregs site just for the heck of it. they put the pocket holes on the top and bottom. Inside on one side and outside on the other to best hide them. I think this would depend on if they are mounted high or low.

[Phil Thien]

Adding a bead of glue shouldn't add more than a few seconds per joint. Like five seconds per joint.

And I sure wouldn't want to go through all the trouble of building something like kitchen cabinets and try to save five seconds per joint by skipping the glue. After a few seasonal changes you may find some joints aren't as strong as they were initially.

In fact, I have "high-end" Wood-Mode kitchen cabinets and they used production machinery to fasten the corners of the face frames, no glue. And sure enough, after just 1-2 seasonal changes some of the corners have opened up. Never would have happened if they had used glue.

I have made face frames joints with Kreg screws and no glue. I can grab a rail and twist it back/forth quite a bit. Same joint, with glue, no way.

[Prashun Patel]

+1 on skipping glue in favor of speed. For my cabinets, the tops and bottoms overlapped the sides. This means the pocketscrews were all in the sides. My cabs were on the ground, which means they were resting on bases. The pocket screws weren't there for load bearing, just to prevent lateral movement. Removing the finish on the pre-finished ply will be more effort than it's worth. If the ply were raw, I'd still counsel against glue only because it means you have to clean up any squeeze out on the inside.

If it's one, I suppose it's worth adding suspenders to the belt. But I had only 3 cabinets, and every extra operation felt like drudgery, so I appreciated any little marginal improvement in the speed.

[Peter Quinn]

For lowers I see little value in glue, load path to ground is direct, stress is minimal. For uppers I prefer glue. Grandmas china gets heavy over years, doors get slammed, a little glue helps me sleep better at night. If it's adding more than 20 minutes to an average kitchen build you as doing it wrong. A little sanding, a bead of glue, good to go. Quick wipe of interior squeeze....if that's heavy, use less glue. That said if he cabs are FF and the frames are glued and well secured to the plywood the china is probably safe. Still cheap insurance on a 25 year basis.

[Chris Padilla]

Pocket screws ROCK! However, I look at them as strong, permanent, convenient clamps to hold plywood together while the glue dries. Each to their own but I would go through the trouble/time/effort/etc. of sanding the finish at the butt joint and adding glue for anything I plan to use in my home. For jigs and quick stuff or for 2x stuff, I don't bother with glue. And with this stuff being prefinished, wiping up squeeze out is a breeze--just go at it with a damp sponge.

[Phil Thien]

You don't need so much glue that you're getting much squeeze out. Just a thin bead is all you need (said in Johnnie Cochran's voice).

[Dave Zellers]

I don't understand why in this application, you don't just screw down (and up) into the ends of the sides. I use 2" deep thread screws, no glue, and they are rock solid. I pre drill for the screw so it sits flush or below the surface but even so it seems much simpler than using pocket screws.

[Mark Bolton]

Another advantage to the glue, if you do allow for a little squeezeout, it acts as a very nice gap filler if you ply or dados/rabbets arent super tight.

I do all PF carcass' but another shop I know finishes their own interiors and while the customers really dont care in my opinion, a dry assembled box will have some gaps/dark lines at the joints. The glue eliminates that. If they are kitchen or vanity cabs that may ever have a bit of water in them (sink base) its a great thing.

I dont bother sanding any finish off but I am using PF 1 side so I have the edge and one face of the ply in a dado and just the edge on a rabbet. Its very fast and not worth skipping in my opinion.

[roger wiegand]

I guess I'm missing something, why would you use a pocket screw rather than just going straight in from the top or bottom into the sides?

That said I cut dados and use glue, with a couple finish nails to hold things together while the glue sets. It's fast, strong and easy. The cabinets I made 40 years ago are still going strong.

[Rick Potter]

When using prefinished ply, don't forget that TiteBond makes melamine glue for that application.

Rick P

[Mark Bolton]

I guess I'm missing something, why would you use a pocket screw rather than just going straight in from the top or bottom into the sides?

That said I cut dados and use glue, with a couple finish nails to hold things together while the glue sets. It's fast, strong and easy. The cabinets I made 40 years ago are still going strong.

Roger,
My assumption was that that was what the OP was talking about. It was just a discussion as to whether pocket screws were a good choice of screw. He is not talking about pocket screwing, just using the pocket screws themselves (which are very nice screws)

[George Bokros]

I guess I'm missing something, why would you use a pocket screw rather than just going straight in from the top or bottom into the sides?

Screws from the bottom into the plys of the side is not a strong joint. The plys will separate, the screw is then loose and the joint is weak. I learned this from experience.

Pocket screw from the side into the bottom is a strong joint with or without glue.

[scott vroom]

I don't understand why in this application, you don't just screw down (and up) into the ends of the sides. I use 2" deep thread screws, no glue, and they are rock solid. I pre drill for the screw so it sits flush or below the surface but even so it seems much simpler than using pocket screws.


Pocket screws would enter the plywood at an angle and thus provide a far superior grip vs screwing straight into a plywood edge. Screwing into plywood edge grain may feel rock solid initially, but over time that joint will be more prone to separation, particularly if you are driving screws into a hidden void.

[Peter Quinn]

I should have mentioned that generally I won't bother to pocket screw cabs with sides that are blind. I'll either use dados and screws or just butt joints and screws depending on the price point. If it's for my house it gets dados. It's quicker and fairly strong just to come through the sides into the ends of the horizontal shelves and stringers. I'm doing a lot of boxes now where the designer wants plywood finished ends, frameless, can't come through the sides, pocket screws are perfect. My main use of pocket screws is in FF cabinetry to attach the frames to the boxes, quicker than clamping and waiting for glue to dry. You can certainly make cabs with all pocket screws. I took a class some years ago that was pitching all the ways to use pocket screws, we made same boxes using only pocket screws, mine is still in use in my shop, never glued it. It's been a lot of things, router table, tool storage, presently a scroll saw stand. Just seems like a waste of time and effort to run in all the pocket screw holes. Get some good assembly screws and you get to the same place quicker building boxes.

[Gene Davis]

We have built a lot of carcases using butt joints and Hafele Zip-R screws. Fast, easy, and strong.

Always frameless, many in melamine-faced particleboard, some in plywood. Carcase stock always of 19mm material.

No predrill necessary. The only thing we would pocketscrew is the 5/8 nailers that go onto the backs.

[Dan Neuhaus]

++++ on skipping the glue. We use a lot of PF maple. Pocket holes in the top and bottom screwed to the sides. I usually add a couple 5mm dominos on each side mostly for registration but I do glue the dominos. 1/4" back stapled on. Rock solid.

[Fred Heenie]

+1 for a thin glue line, an acid brush is great for a thin spread without starving the joint. For a moisture resistant joint PVA-II, and for a harder glue line PVA-1. For this application, I like !-1/4" screws if both parts a 3/4" thick, course thread is good and the washer head in ply is better than a pan head. I would scuff the glue line first for better adhesion, sandpaper over a finger will do the job and it doesn't take much.
JMHO

[Dave Zellers]

Pocket screws would enter the plywood at an angle and thus provide a far superior grip vs screwing straight into a plywood edge. Screwing into plywood edge grain may feel rock solid initially, but over time that joint will be more prone to separation, particularly if you are driving screws into a hidden void.

Well I drill a pilot hole into the plywood end so there is little wedge action from the screw, only the deep threads bite into the wood and I can tell when I hit a void and just reposition the screw. And you have the same void issue with pocket screws since the most bite you get is about 5/8" even though it is cross grain.

The larger point is not really which approach is stronger since I believe either method is more than strong enough. After assembly, which usually involves screwing base cabinets to each other and to the wall and maybe the floor, and then screwing or gluing a countertop on top, all they do is sit there on the floor. I stopped dadoing and gluing years ago when I decided it was a total waste of time.

But I do see the mention that maybe the OP was asking about using pocket hole screws and not necessarily drilling pocket holes.

[Phil Thien]

Well I drill a pilot hole into the plywood end so there is little wedge action from the screw, only the deep threads bite into the wood and I can tell when I hit a void and just reposition the screw. And you have the same void issue with pocket screws since the most bite you get is about 5/8" even though it is cross grain.

The larger point is not really which approach is stronger since I believe either method is more than strong enough. After assembly, which usually involves screwing base cabinets to each other and to the wall and maybe the floor, and then screwing or gluing a countertop on top, all they do is sit there on the floor. I stopped dadoing and gluing years ago when I decided it was a total waste of time.

But I do see the mention that maybe the OP was asking about using pocket hole screws and not necessarily drilling pocket holes.

Screws in the face of the plywood have greater holding power than screws in the edge.

[Dave Zellers]

Screws in the face of the plywood have greater holding power than screws in the edge.
I agree.

But there are variables such as screw length of the edge screw that change things.

I'm just saying it's much faster for me to edge screw with 2" deep thread screws and there is no way it will fail. None.

[jack forsberg]

Maybe it just me but if the screws are on the out side why pocket hole?

[John TenEyck]

As was said, if you won't be able to see the screws afterwards, why use pocket screws? Just use 2" coarse thread screws at 90 degrees. It's a lot faster to predrill a screw hole than a pocket screw hole. With some of the new self drilling screws you might not even have to do that when using plywood.

John

[George Bokros]

I didn't intend to stir up this much controversy with my post.

Thanks for all the interest.

[Phil Thien]

Maybe it just me but if the screws are on the out side why pocket hole?

Because the edges of plywood are 50% end grain and don't have terribly good screw holding power.

If you have to drill a hole anyhow, why use the method that results in a weaker joint?

It seems we all bemoan the lack of quality goods these days, and here we are discussing ways that save little to no time and yet sacrifice quality.

Go figure.

[Phil Thien]

It's a lot faster to predrill a screw hole than a pocket screw hole. With some of the new self drilling screws you might not even have to do that when using plywood.

John

May as well just use a pneumatic stapler and no glue.

[Dave Zellers]

I didn't intend to stir up this much controversy with my post.

Thanks for all the interest.

Hey! That's the fun part!

:)

[Peter Quinn]

I didn't intend to stir up this much controversy with my post.

Thanks for all the interest.

LOL, For some reason, this topic is a hot button among those that build cabinets. Not sure why. Its very close to being one of those "can't discuss" topics....like sawstop or politics. And I don't understand why. For my money once you have cut up a sheet of plywood, and you are preparing to screw it together, who cares how you do it? Some have hard and fast rules, I like to mix it up, sometimes to suit the build parameters as I see best, sometimes just for a change of pace. Biscuits, pocket screws, confirmats, square in from the outside.....makes little difference to me.

One thing I would add is that when attaching horizontals to verticals with pocket screws, that angle thing works against proper alignment IME. ITs difficult to clamp the middle of a 24" deep carcus, and that little angle of the pocket screws adds just enough wedge action to knock off the flush alignment as the screws tighten and torque. You can generally clamp the snot out of FF butt joints and pocket screw them, and the FF to cabinet connection can easily be clamped, but those carcus connections are challenging. And the last thing I want when screwing large sheets of plywood together is an additional challenge. Screws at 90 degrees tend to pull straight down and in my mind act as both clamps and steel dowels. Having bashed apart a few cabs on occasion, I'd say neither screw has much advantage over the other, they are both pretty tough once you get beyond the theoreticals.

[Fred Heenie]

The movement of parts when driving pocket screws is a real concern but very controllable. Clamps or a pin nail will insure proper alignment of the mating parts.. The pocket screw will not separate the plies in veneer core sheets because of the entry angle, 6° in the case of a Kreg jig. It's that angle that causes parts to move and there are lower angle pocket screw systems. Staples may be OK for kitchen cabinets but not in my house!.

[Mark W Pugh]

Let me just add these videos: https://www.youtube.com/watch?v=-7jSVtoMbOk This is how I built mine, sturdy, no problems. I went to the end of the internet, and this is what I decided on. Everyone has to pick their own technique.

I didn't use the screws he used. So, I predrilled, and screwed it together. I combined numerous techniques from others also on other aspects.

[Dave Zellers]

The movement of parts when driving pocket screws is a real concern but very controllable.
Yep- same is true with screwing into ply edges. Clamps are essential with precision cabinet assembly. After pre drilling the top or bottom piece you must clamp it tight, drill the pilot and sock the two together.

Unless you hit a major void, it's never going anywhere. Shoot, if you screw about 4" OC, it's not going anywhere no matter what.

[mreza Salav]

Why pocket screws?! slowwwwww
Use GRK screws from the top/bottom to the edge, 2" ones, no need to pre-drill. best scews I've used (pricy but have never split plywood).

[Peter Quinn]

The movement of parts when driving pocket screws is a real concern but very controllable. Clamps or a pin nail will insure proper alignment of the mating parts.. The pocket screw will not separate the plies in veneer core sheets because of the entry angle, 6° in the case of a Kreg jig. It's that angle that causes parts to move and there are lower angle pocket screw systems. Staples may be OK for kitchen cabinets but not in my house!.

My experience causes me to disagree with you. Pin nails aren't holding anything except very small moldings while the glue dries. 18ga will hold a box together temporarily but won't even resist the screws torque if they are right next to it. 16 ga has a fighting chance if right on top of the screw location, but that's pretty hard to align on the 5 or so screws that go into a lower cabs connection per corner. K bodies will do it, but that's a lot of moving of clamps, and for some styles of boxes like integral toe kicks some spots are very hard to reach with clamps.

I predrill everything. I use some of the best auger tip assembly screws available, the screws are not the problem, it's the plywood. I think they took all the good stuff out of the glue.....so when you shoot through the side of a case into edge grain of the bottom shelf or stringers, 20% of the time it splits the layers if it lands on a glue line. Or it bulges. All the wood the screw displaces has to go somewhere.....the plyes have already been steamed and squeezed hard not much compression left in them. I find predrilling also eliminates the tendency for screws to side shift things too.

[Max Neu]

It seems like this thread is more about pocket holes in plywood,which I agree is strong enough.But, what about melamine?I am more of a dado/faceframe shop,but occasionally build some frameless melamine cabinets for garages.I typically use my Lamello Zeta with clamex fittings,but I would consider using pocket screws for my own shop cabinets (melamine boxes) if I thought it would last,I just don't want any of my expensive tools hitting the concrete because I was being cheap.:)

[Jim Andrew]

It is just not that hard to set up a router table with a plywood sized bit, and make a groove for the bottom and top to set in. I just make my grooves 1/4" deep, and it aids in aligning the tops and bottoms of your box. If you want to use screws to hold the box together, that is fine. I use pocket screws to build the face frames, fast and simple.

[Chris Padilla]

Plywood thicknesses seem to vary weekly and even within the plywood itself!! I gave up going the dado route and just domino everything now. Anyway, sorry to veer off-topic here. I, too, was a bit confused if the original topic was about pocket SCREWS or pocket HOLES. I'm still confused! :p

[Peter Quinn]

It seems like this thread is more about pocket holes in plywood,which I agree is strong enough.But, what about melamine?I am more of a dado/faceframe shop,but occasionally build some frameless melamine cabinets for garages.I typically use my Lamello Zeta with clamex fittings,but I would consider using pocket screws for my own shop cabinets (melamine boxes) if I thought it would last,I just don't want any of my expensive tools hitting the concrete because I was being cheap.:)

My admittedly limited experience with melamine and pocket screws has been negative. MDF not great either. It's the substrate. The screws displace a lot of material that must go somewhere. Plywood and solids have the courtesy to compress and yield as the screw forces it's way in, man made material not so much. So the stuff bulges , or splits, or worse. Not always, but enough to be a problem. I suppose you could pocket screw, then clamp, then predrill through the pocket screws into the receiving end.....lot of work for not much gain. I'm thinking dowels, confirmats, butt and screw with hi-lows, anything but pocket screws is probably better.

[Mark W Pugh]

Plywood thicknesses seem to vary weekly and even within the plywood itself!! I gave up going the dado route and just domino everything now. Anyway, sorry to veer off-topic here. I, too, was a bit confused if the original topic was about pocket SCREWS or pocket HOLES. I'm still confused! :p

The ORIGINAL question was about what screws to use and would it be strong. One would have to ASSUME if one mentioned using pocket screws, they were referring to using the pocket holes, at least in my world. Everything else was added by the spectators.

[Jim Becker]

I've done that many times. Remember, it's the glue that's actually doing the work!

[Fred Heenie]

"What about melamine"
Max the question is somewhat more complex because melamine is available as a stock standard as an overlay on either MDF or particle board. After that there are different thread forms for each and pocket screws typically have drill points to remove excess material. A pocket screw in a 90° joint in MDF has the advantage of the dense hard face to contain the threads. The shank is in the mush of the vertical component. Melamine particle board is less durable. An aside as to particle board, as to ability for a screw to cinch up and hold two pieces, will be effected by screw size. The builders of waterbed pedestals, vast quantities of particle board, learned in the 70's and 80's that a screw smaller than a # 10 left a lot to be desired in any joint.

HTH