Seeking cabinet construction opinion

[Jacob Canady]

(First off, if I'm in the wrong section please let me know/move the post. Second, I hope my pics are too big...I'll try to resize if so.)

Hello everyone,

Long time reader, first time poster. I've learned quite a bit from several threads and people here and I'm very grateful for all the great information here.

A little backstory as to why I'm seeking opinions on cabinet construction: I just wrapped up a pretty big job for a well-respected contractor I've never done work for before. The remodel was a "squeeze in" type of remodel and called me needing cabinets pretty fast. Knowing his reputation, I couldn't say no. He wanted all prefinished plywood for the boxes, and since he wanted them fast, we just used pocket screws.

We had everything built for him in 2 weeks. Then things went sideways with 2 month delays, changes, etc. We started installing, and after everything got painted, the GC comes in and starts picking apart all sorts of things on the install. Hard not to be devasted when a GC with a reputation like his is picking apart your work. He told me I was making everyone look bad and that really got inside my head!

SO...I'm second guessing every single thing I've done on this project. The upper cabinet construction is keeping me up at night, worrying things will fall apart and come off the wall. Below is a picture of how we build the boxes. We use a 1/4" back with 4" nailers across the top and back. Two pocket screws on each side of the nailer connect to the sides, and the top/bottom are pocket screwed into the nailers as well. No glue, just butt joint pocket screws. Face frames are glued and pocket screwed onto the front.

https://i.imgur.com/aXpHyF2.png

We've never had a box fall apart with pocket screws but I wanted to get the opinion of whoever on here is willing to contribute. Do you guys thing 2 pocket screws on each side of a nailer will be strong enough to keep the box together?

We also had to build a hood last minute, on site. We used a similar technique, except the front of the hood has a solid piece of plywood so we could nail shiplap to it. This one has 6" nailers and I think we did 3 pocket screws on each side of the nailer. Below is how it was built (we needed to leave space for 2x4 blocking for the hood insert:

https://i.imgur.com/nwMSxF0.png

Anyways, sorry for such a long first post. I'm just feeling pretty bad about everything because of the GC, even though the final result turned out pretty good in my opinion. Below are some pics of the finished cabinets, for those interested.

https://i.imgur.com/0gQBj4N.jpg

https://i.imgur.com/Z5zZcZW.jpg

https://i.imgur.com/tW5Fwb4.jpg

https://i.imgur.com/1jTejt0.jpg

https://i.imgur.com/yNK649A.jpg

https://i.imgur.com/3KjwD5U.jpg

https://i.imgur.com/m4chjF8.jpg

[mreza Salav]

SO...I'm second guessing every single thing I've done on this project. The upper cabinet construction is keeping me up at night, worrying things will fall apart and come off the wall. Below is a picture of how we build the boxes. We use a 1/4" back with 4" nailers across the top and back. Two pocket screws on each side of the nailer connect to the sides, and the top/bottom are pocket screwed into the nailers as well. No glue, just butt joint pocket screws. Face frames are glued and pocket screwed onto the front.



We've never had a box fall apart with pocket screws but I wanted to get the opinion of whoever on here is willing to contribute.
Do you guys thing 2 pocket screws on each side of a nailer will be strong enough to keep the box together?

Jacob, I feel sorry to say this but I would personally never trust 2 pocket screws from each side holding an upper cabinet. A pocket screw from the nailer board into the sides?! that has a maximum of 5/8" depth into the side!!!
For my own house I used solid backs and screws from the sides to the back (2" screws). I tried grabbing the bottom of an upper and swing myself without any worry about the cabinet falling.

[Jonathan Jung]

I completely know where you're coming from. I too have lost sleep over such worries about jobs. My gut tells me you don't have a lot to worry about. That said, I can't really see, since your pictures aren't coming through for me. What ply did you use? The weak point will be the laminations of the nailer, unless you used solid wood, then the weakness is the screw into the sides, which is quite strong, being a lateral force. Are the backs set in a groove? This changes the situation. Also remember that the majority of force on those screws is vertical, because the cabinet wants to slide down the wall, not away from it.

All the cabinetry in my work trailer has been held together just with pocket screws, no glue, for 4 years and nothing has fallen apart. It was more of an experiment. I thought it wouldn't hold up, but years later and I haven't had a reason to rebuild any of it, it still works.

[Bryan Hall]

How is the top/bottom secured to the sides? I dado the sides and slot the top/bottom in, glue, pocket screw, then the nailer is pocket screwed in while also being secured to the top and bottom of the cabinet so it's connected in several ways.

I wouldn't feel good about it either, but TBH I continue to be shocked by what doesn't collapse in use. I just ripped out some old particle board cabinets and there wasn't a spot of glue on them, no screws either. I was legitimately able to just pull the faceframes off and pull the boxes apart piece by piece while they were on the wall. Scary, but they had been functioning for a very long time like that without issue.

[Jacob Canady]

Thanks for all the replies! It's horrible losing sleep over something like this for sure. Had I known I would have had a 2 month delay I would have spent more time on the box construction.

Anyways, sorry the pictures aren't coming through. To answer your questions Jonathan, I used 3/4" birch plywood for the sides, top, and nailer. The 1/4" backs are set in a groove. The backs connect to the nailers via the 3" installation screws.

Bryan, there are technically two bottoms on these uppers. The GC had a weird request to have a finished 3/4" bottom, and then a 3/4" void, and then a 3/4" panel that the dishes will sit on. So, the finished bottom panel is pocket screwed into the sides. But the other bottom panel where the dishes sit is glued and dadoed into the sides. The bottom nailer is pocket screwed into that bottom panel. On the cabinet sides that are not visible, I drove screws in as well. The top is pocket screwed into the sides and the nailer. So the whole system is pretty well screwed together I guess.

Mreza, interesting you mention the depth of screw into the plywood. We've done a fair few modular cabinet installations and those suckers are built with a handful of brackets and tiny screws into 1/2" plywood! And lots of people around here have this style of cabinet.

[Kevin Jenness]

The boxes could be stronger, but I don't think you have anything to worry about with the back dadoed into the sides, top and bottom screwed to the sides and nailers, nailers screwed to the sides and (presumably) screws through the back and nailers at least 1" into the studs. If you're losing sleep go back and put a couple more screws into the studs. When you are fastening through a reasonably solid back as well as the nailers the boxes are not going to fall off the wall. Chin yourself on one of your standard boxes and settle the issue for yourself. If you honestly feel the way you did it is too weak, pull the uppers and beef them up or rebuild them.

Is the GC questioning your construction methods or other issues? Did you get paid? Was he familiar with your work prior to signing you up? What is he comparing your work to? If he is really down on your workmanship you may not be able to salvage the relationship but you should at least get a detailed punchlist and work it out as best you can. In the future, make sure the specs are understood and agreed to on both sides before starting work. Rush jobs that lead to cut corners don't help anybody's reputation.

[Jacob Canady]

The boxes could be stronger, but I don't think you have anything to worry about with the back dadoed into the sides, top and bottom screwed to the sides and nailers, nailers screwed to the sides and (presumably) screws through the back and nailers at least 1" into the studs. If you're losing sleep go back and put a couple more screws into the studs. When you are fastening through a reasonably solid back as well as the nailers the boxes are not going to fall off the wall. Chin yourself on one of your standard boxes and settle the issue for yourself. If you honestly feel the way you did it is too weak, pull the uppers and beef them up or rebuild them.

Is the GC questioning your construction methods or other issues? Did you get paid? Was he familiar with your work prior to signing you up? What is he comparing your work to? If he is really down on your workmanship you may not be able to salvage the relationship but you should at least get a detailed punchlist and work it out as best you can. In the future, make sure the specs are understood and agreed to on both sides before starting work. Rush jobs that lead to cut corners don't help anybody's reputation.

I definitely have at least 1" into the studs. It should be closer to 1.5", I went with 3" screws to be safe.

Regarding the GC...that's a can of worms for sure, but he never questioned the construction methods. It was more questioning layout/design type stuff. I had to bid based on someone else's drawings, which were pretty much already OK'd by the homeowner. Since everything was so rushed and last minute, I didn't get much of a chance to redesign. So for example, the GC didn't like that I used "modular" type dimensions. One wall of uppers worked out to have 3 36" wide cabinets in a row. One base cabinet didn't have a big enough spacer (according to him) between the wall and the door, so it "messed up his baseboard." I had to go back and reskin the toekick after the floor guys were done, because they didn't get the floors right up to the cabinets. So he just continually made me the fall guy, even though he had an extra 2 months to look over the drawings and ask me to make changes. He was comparing the work to other cabinet guys he uses who do lots of work for him and know exactly what he wants. I've been paid and told the owners to just call me if they want anything adjusted and to not get the GC involved. It's all been worked out with the GC and he really does do nice work, but I had no idea he was so hard to work with. Oh, and no, he wasn't familiar with my work because signing me up. All in all just a really wild project.

Ultimately, if he were to call again and ask me to bid on a job, I'd have to think pretty long and hard about it. We had headaches with this GC that we've never had before.

[Bryan Hall]

The questions begs to be asked, what happened to his other cabinet team, why did they vanish, why did no other cabinet team he worked with want to step up and take the project? Why did they need everything done immediately, and then the project fell apart?

From the outside looking in it sounds like there's more issues with that GC than their reputation would make you think. As such, I wouldn't beat yourself up over it.

[Jacob Canady]

The questions begs to be asked, what happened to his other cabinet team, why did they vanish, why did no other cabinet team he worked with want to step up and take the project? Why did they need everything done immediately, and then the project fell apart?

From the outside looking in it sounds like there's more issues with that GC than their reputation would make you think. As such, I wouldn't beat yourself up over it.

Well, I'm more concerned about the structure of the upper cabinets, but you guys have eased my mind a bit regarding that. Not the best way to build a cabinet, but certainly not the worst. I actually installed some Home Depot cabinets earlier this year and was pretty surprised they even sell them the way they do. They're basically cardboard.

Regarding those questions, I can answer most of them. His other cabinet team was never involved. I guess the owners ended up going through 3-4 construction companies for their remodel but they all ultimately bailed on the project because it was "too small for them." (For reference, I had to build about 110 feet of cabinet. Not a small job for me at least.) So they finally went with the GC in question because they knew he'd take the project on. So, I'm not sure where the initial cabinet drawings came from or why that cabinet company vanished. I assume they were tied to one of the other construction companies. I don't know why the other cabinet team this GC uses didn't step up and take the job, but after picking up the deposit check and seeing the GC's whiteboard, he has about 10 other jobs going right now. I have to assume his other cabinet team is tied up with all those jobs. As I understand it, everything needed to be done immediately because of timing with the permit. Something to that effect, I'm honestly not sure what the rush was. All I know is the owners are NOT happy that there was such a big delay where nobody from the GC's crew was working on the house. I had everything built and ready to install according to the timeline I was given, and then I sat for 2 months, continuously getting install dates pushed back.

I had to push back 4 other jobs because I kept getting told "next week." He doesn't really operate on written contracts so there was a lot of scope creep. I finally buttoned up the install and told the GC I needed a check because I'd given him my full attention for 4 months and I have other people who need work done.

Anyways, the owners are very happy with their cabinets and I'm feeling better about them not falling apart.

[Bryan Hall]

Well, I'm glad you got paid and it sounds like there are some good lessons learned here. I hope you never go through that again!

[Jacob Canady]

Thanks Bryan! And I agree, lots of lessons learned. Lots of growing pains!


I have to admit though, I don't quite understand how having a dadoed 1/4" back on a cabinet adds much strength to the box. I get how the top screwed to the nailer and the sides adds strength, as it basically ties all those components together into one, but when you guys say having a dadoed 1/4" back changes everything, I don't see how. I've got modular cabinets in my house and they have 1/4" backs and I can push on the backs and flex them! What am I missing?

[Bryan Hall]

Thanks Bryan! And I agree, lots of lessons learned. Lots of growing pains!


I have to admit though, I don't quite understand how having a dadoed 1/4" back on a cabinet adds much strength to the box. I get how the top screwed to the nailer and the sides adds strength, as it basically ties all those components together into one, but when you guys say having a dadoed 1/4" back changes everything, I don't see how. I've got modular cabinets in my house and they have 1/4" backs and I can push on the backs and flex them! What am I missing?

I personally don't rely on the 1/4" back to add anything of measurable value. Especially since I screw the top and bottom nailer off which are married to the top and bottom. None of my shop cabinets have ever had backs, I didn't dado any part of them (to test strength) and just butted, screwed, glued. I have beat the heck out of them for years and never had even a hint of failure.

[Jonathan Jung]

Glad you got paid and can have some breathing room! Cab backs in dados in all 4 sides means the dados would have to give out before the cabinet would come off the wall, if the screws are secure to the wall. I never use nailers, I think they look cheap. I use 1/2" ply backs in dados for upper cabs and that's it. Screw through the back into the wall, finish with a recessed fastcap.

[andy bessette]

Because of the design it gives the overall appearance of a low budget, DIY job.

[Kevin Jenness]

"He doesn't really operate on written contracts so there was a lot of scope creep."

That's a recipe for trouble. If the builder and client signed off on the drawings that you built to I don't see any grounds for complaint, but it's important to get that all on paper and keep track of any changes.

"I don't quite understand how having a dadoed 1/4" back on a cabinet adds much strength to the box."

If the back is fitted tight it will keep the box square. A bead of hot melt or some pins, staples or screws would increase the rigidity further. The dadoes and nailer screws would have to blow out for the cabinet to come off the wall.

For simplicity I use 1/2"backs without nailers. If you don't mind the weight you can decrease waste by making the backs and sides the same thickness.

[Jim Dwight]

I think you already know this due to comparison to stock cabinets from big box stores but your cabinets will not fall apart or cause the homeowner issues based upon your construction. I paid extra for my cabinets to get plywood instead of particle board and it is 1/2 inch at best. It is pretty nice plywood, just thin. Construction is not better than pocket screws. I don't like to look at pocket screws but they are really strong, just ugly.

My classic example of how strong cabinets need to be will probably always be an upper cabinet about 3 feet wide that held all our day to day dishes in Pittsburgh. I built a new kitchen cabinet by cabinet. When I took the subject cabinet down I found it was hanging by two screws. The installers had put the other two screws into the waste stack from the bathrooms above the kitchen. They had rusted off after weeping dirty water into the sheet rock. The cabinet was very cheap particle board construction. But it lasted for a decade or more before I replaced it holding over 100 lbs of dishes. It worked because the cabinet was tight to the wall and friction held it up and together.

My replacements were 3/4 plywood without a face frame with overlay doors of solid oak. They were plenty strong. Yours are stronger due to the face frame. I don't know why the GC wanted to criticize you for the design work you did not do. It may have had a lot to do with other frustrations he was having at the time.

Your cabinets look great to me. I can understand why the homeowners like them.

[Jacob Canady]

Thanks for more insight guys, I really appreciate it. Jim, to be honest I hate how pocket holes look as well, but we only use them where they won't be seen. We cut most of our panels with CNC, so going forward I think an improvement to the design is to have the CNC barely remove the finish where the nailer goes so glue can be used, and make the nailer wider to accept more pocket screws. During the manufacturing stage, I never even considered these changes because I was so worried about getting everything out the door.

Also Jim, thank you for the kind words! It isn't a cabinet style I'd put in my house, but the homeowner pulled all of her design ideas from pinterest and it ended up looking nice. I'm not a pinterest fan myself, as I don't care for a lot of the kitchen designs on there, but this turned out better than I expected.

I came across this video last night which I think is interesting:

Kreg Jig® Wall Cabinet - Part 2 - YouTube (https://www.youtube.com/watch?v=JqpwNCZGQLY&t=619s&ab_channel=KregTool)

Seems like Kreg is willing to put their reputation on the line with almost the same exact way we built these cabinets, only Kreg doesn't have the 1/4" back. They seem pretty confident in that construction technique.

[Andrew Hughes]

Have you thought about making up a cabinet using the same construction mock it up in your shop and see how it holds.
I bet you’re going to be surprised how much it takes to rip it off the wall.
Im a big fan of testing and hold on to what’s true.
Good Luck

[Kevin Jenness]

If you are cutting out panels with a cnc you can save a lot of time by boring construction screw pilot holes through your sidewalls or milling for kd elements like Cabineo fasteners. If you are set on pocket screws a Castle type low-angle machine, even a manual one, is far better in my opinion than the Kreg system.

I have never seen the point of nail rails as opposed to a thicker back except to save a bit of weight at the expense of more labor.

[Bryan Hall]

I came across this video last night which I think is interesting:

Kreg Jig® Wall Cabinet - Part 2 - YouTube (https://www.youtube.com/watch?v=JqpwNCZGQLY&t=619s&ab_channel=KregTool)

Seems like Kreg is willing to put their reputation on the line with almost the same exact way we built these cabinets, only Kreg doesn't have the 1/4" back. They seem pretty confident in that construction technique.

This looks like my shop cabinets and is why I don't put much belief in the NEED for a 1/4" back. I can definitely believe the point that the back gives shape/rigidity, but so does locking it down with screws. I'm not as sold on it helping prevent the cabinet from peeling off the wall. In my mind it's a downward shear force that is critical to build for, not outward pull (which I just experienced on that last demo where I was able to pull out on the cabinet and piece by piece it came apart, but it held all the dishes just fine).

At the end of the day I think it's clear that cabinets aren't consistently falling off walls around the world due to misc. techniques. We can try to build the best of the best of the best but the two week rush job kitchen probably doesn't need that.

[Tom M King]

I took an 8' long upper cabinet down once in a 1920 house. It was over a peninsula, that had a full width pass through under it into a small dining area called a Breakfast Room. There were glass doors on both sides to see through, and also display all the nice china stored inside it.

It wasn't original to the house, but probably added in the 1950's. This was in the early '80's.

It was very easy to take down because it was only held up by two 10d cc nails, straight up into a ceiling joist overhead. Those two nails had held it up, along with easily over a hundred pounds of plates, glasses, etc., for over 30 years. It was solid wood construction. The top board that the nails were through was a 1x12 Yellow Pine.

[Shannon Brantley]

Jacob, I use pocket hole screws on my nailers as well, but in addition to 2 on each end, they are also pocket screwed to the top, bottom, or fixed shelf (whichever is applicable). Plenty of strength there.

I just severed ties with a good (but slow) contractor a few months ago. On more than one occasion, as soon as soon as the home owner would put any heat on him, he would start deflecting that heat to me. Took me a few jobs to see his pattern, but it wasn't worth working with him. I always have an open dialog with the home owner and let them know up front that their satisfaction is my main priority. The last owner was the one that let me know what was going on. GC called midway through the job all upset about something that gets done at the end. I called the home owner to make sure they knew it would be handled and he said "I know. Don't worry about it. I just crawled GC's tail about taking so long and he was looking for someone to throw under the bus." I've got another project coming up with that home owner and the old GC doesn't...

[Ken Combs]

An example of hanging techniques. One I had not encountered anywhere but where I now live. The house was built for my Dad and Mom in 67/68. Done by Dad's brother who was a highly skilled carpenter. Back then it was common for one crew, or in this case, one guy to do everything. Uncle Perry built concrete forms, framed, roofed, trimmed and built the cabinets. Those were the days when cabinets were commonly assembled by the trim carpenter(s) on site from the raw material. So, nailers were common practice. But not for uncle Perry. He chalk lined the walls where the shelves were going to be and placed the 1x12WP shelf material on the line. Then toenailed, one top, one bottom, on each stud with 8d finish nails. The the face frames were assembled with toenails on the edges directly to the shelves.

The cabinet where most of our plates, cups etc is 8' long and I'd guess has 250 lbs of stuff in it. That is in addition to the microwave I installed a few years ago. That's when I discovered the toenailed shelves as I had to remove the bottom for about 22" to insert the microwave.

First thought was 'how did that stay up'. Then I realized, 4 shelves, spanning at least 5 studs was a LOT of nails in shear, so it'll hold way more than I could ever stuff in it.

[Jacob Canady]

I'm glad to hear more and more stories from everyone here. I know there are lots of ways to build and install shelving, cabinets, etc., and it sounds like most of them are just fine. I've actually only seen cabinets fall off a wall one time. A good family friend has me do some handyman type work here and there, and they recently added on to their house. Lots of new cabinets with one bank of old cabinets from before the addition. I got an urgent call from them one night saying 3 cabinets just came crashing down off the wall. I was pretty surprised to hear it, so I went over and sure enough, the cabinets had fallen off the walls. Upon further inspection, none of the screws along the top of the cabinet made it into studs. The bottom screws hit studs, but as you can imagine, the weight of the cabinets bent those screws as they fell off. I put them back up and made sure each box had about 6 screws into studs!


Jacob, I use pocket hole screws on my nailers as well, but in addition to 2 on each end, they are also pocket screwed to the top, bottom, or fixed shelf (whichever is applicable). Plenty of strength there.

I just severed ties with a good (but slow) contractor a few months ago. On more than one occasion, as soon as soon as the home owner would put any heat on him, he would start deflecting that heat to me. Took me a few jobs to see his pattern, but it wasn't worth working with him. I always have an open dialog with the home owner and let them know up front that their satisfaction is my main priority. The last owner was the one that let me know what was going on. GC called midway through the job all upset about something that gets done at the end. I called the home owner to make sure they knew it would be handled and he said "I know. Don't worry about it. I just crawled GC's tail about taking so long and he was looking for someone to throw under the bus." I've got another project coming up with that home owner and the old GC doesn't...

Shannon, that GC sounds a lot like the guy I won't be working for again. There were quite a few things that went wrong well before I started installing and the homeowners actually would complain to me about him...they even told me they felt like I was the only guy who cared about their project. But like the GC you severed ties with, whenever this guy felt pressure, someone else was getting blamed. Not healthy for anyone!



SO...update. I built a cabinet box this afternoon from the same materials in the same construction method. Even the same size...42" tall, 30" wide. No glue, only pocket screws. The only difference this time is that the bottom panel is pocket holed into everything instead of dadoed in, since I didn't have two bottoms (which, funny enough, the GC didn't even use for under cabinet lighting..). I didn't glue the face frame on because this was just a basic test. I was pretty surprised by the results.

I did a few chinups from the upper panel of the cabinet as well as the lower panel. No issues. I weigh about 150lbs. So then I hopped up in the cabinet and sat there for a while, bounced around a bit, tried to make it break...didn't budge. So then I added 40 pounds and did it all again. Nothing. I added another 50 pounds and did it all again. Still nothing. I added another 50 pounds and did it all again. At this point, I'm out of weights to add. I can comfortably say that 2 pocket screws into nailer strips and no glue, with everything else pocket screwed together, can easily support 300 pounds and not fall apart. At least, not fall apart in the 30 minutes of testing I did. But I expect that long term, there won't be issues. Dishes don't dance around and try to make the box fall apart. And to be honest, I wouldn't expect more than probably 150 pounds of weight per cabinet anyways. At least in a 30" wide cabinet.

[Jon Barnett]

I'm a construction super, working on very high end homes for 24 years; before that I worked as a carpenter, making millwork, and eventually furniture.

One of my biggest frustrations is designers and or contractors who pay cursory attention to detail at the start of a project, then come up with a never-ending list of complaints once the finished product is installed. Clients are not immune to this either (I didn't realize it would look like that.......).

While you my have learned some valuable tips on casework from the posts above, and are obviously conscientious, try not to take the comments personally. Many of these people can be very derogatory about things they know virtually nothing about. And blaming trades is a standard method of deflecting blame :).

[Jacob Canady]

I'm a construction super, working on very high end homes for 24 years; before that I worked as a carpenter, making millwork, and eventually furniture.

One of my biggest frustrations is designers and or contractors who pay cursory attention to detail at the start of a project, then come up with a never-ending list of complaints once the finished product is installed. Clients are not immune to this either (I didn't realize it would look like that.......).

While you my have learned some valuable tips on casework from the posts above, and are obviously conscientious, try not to take the comments personally. Many of these people can be very derogatory about things they know virtually nothing about. And blaming trades is a standard method of deflecting blame :).

Jon, you hit the nail on the head. The owners were already pretty happy with the design, and since it came from another company they already had a chance to look over it. But I spent several hours redrawing the design into my software (so I could translate it into CNC work) and when I gave the drawings to the GC, I got nothing back from him. No "hey let's give an extra inch here for clearance" or "make this opening xyz for the fridge." I think even "cursory" is being generous with him. He saw everything a couple times during installation, but talks about making changes AFTER everything got painted and then blames me for things being wrong. Once it's painted I really hate taking tools to it.

Funny enough, when the cabinets went in raw, the owners kind of had a "I didn't realize it would look like that" moment (even though I generate a full 3D model for them because I begin any fabrication) but once it was painted they were over the moon, and it looks pretty dead on with the 3D rendering.

[Steve Rozmiarek]

You would be shocked at the way some commercial cabinets are built. I've actually had a commercially sourced wall cabinet begin to fail, the homeowner had crammed a 36" wide upper FULL of canned goods. It pulled a mounting screw through the 1/4" mdf core back and chincy glued and stapled nailer was coming off. Luckily I saw it and fixed before it came down. Your cabinets are far better than that construction, you will be just fine. They look nice, good work!

I personally do my boxes with dados, but mainly because I'm charging a little more and I like how they go through my shop faster. Dedicated dado saw is always set up and its a lot faster to use it for my shop than screws ever are. Both are structurally fine. You've probably smashed an old cabinet to get it to fit in the roll off. Lots to be learned by that.