I'm planning on using GRK Cabinet screws to fasten cabinets to the walls, but plan on using GRK trim screws to secure the cabinets to each other, like these.
Are these appropriate? The heads seem a little small, but I figured drawing force wasn't so critical on securing cabinets together, and these heads will hide nicely when countersunk into the cabinet frame.
In most cases those will work nicely. At times, though, drawing force is substantial. The world isn't flat and level and hardwoods can be stubborn.
Feel free to use those screws, properly piloted and countersunk, but be prepared to use conventional flute-head screws (gold construction screws) behind hinges or in other hidden locations to do some heavy lifting.
For clarity, I'm assuming a faceframe configuration:
______________________________ ______________________________
| _____________________________| |______________________________|
| | | | | | | |
\ \ \ \
| | | | | | | |
| | | | | | | |
|___| |___||___|<-- screws here |___|
If you're dealing with frameless cabinets I'd consider sleeve bolts as suggested in other answers, but only if you have a tough situation. 1-1/4" drywall or gold screws behind the hinges are usually adequate.
I've had good luck with so-called "connecting screws". They are a two-part design, with both sides having a head. One end is like a machine screw with a pan head, the other part has a pan head, but the shaft is hollow and threaded for the opposing end to screw into. They are designed specifically for this purpose. You can get them in various lengths and colors. Colored ones tend to be plastic, while you can buy all metal ones as well.
Screws are a bad idea. A #8 IMHO isn't thick enough. And 2" long is about 5/8" too long if you are using the standard 3/4" melamine coated chip board. I think you need to distribute the load over more surface, or use a lot of fasteners.
Remember Murphy. If you have a wall that is half an inch out of flat, you are going to try to uses these screws to bend the cabinet. This won't happen, but it will try. I have a house where the center of the kitchen, and the wall separating it from the dining room settled 2 inches over 20 years. And another wall that has a 1 inch bow in it over 12 feet.
The head distributes the load over more cabinet. I don't like the particular style with the slot connectors.
You can also get plastic covers. Drill a 1/16" deep hole with a bit 1/16" larger than the overall diameter of the head. (Experiment on scraps) The covers snap into place.
Spax makes screws that work exceptionally well for this application if they're frameless cabinets. They're called rear panel screws, 1.25" length #8s, but the head and thread is made to work well in MDF/particle board. They also make some MDF-specific threaded screws in other sizes, but the wafer head on the rear panel ones makes a nice, clean finish with melamine.
If you have face frames, make sure you find something with no thread for a good part of the screw. It'll make it much harder to get a tight join and you'll be creating expansion/contraction issues down the line. Finish screws are not a good idea...you're relying on the strength of the head for your joint holding power, not the threads. Invest in a good countersink bit, predrill, and use ones with a nice bugle head. Or alternatively use a small forstner bit (slightly larger than the head size) and use washer head screws.
Also, regardless of how thick the joined materials are, you don't need more than 3-4 threads engaging, usually around 1/2". Never go more than 2/3 the thickness of the adjoining material for your embedment.
Source: architect, woodworker, former custom kitchen installer.
M6 connecting screws mate perfectly with 5mm shelf pin holes in EuroStyle cabinets. Using these screws, I typically join cabinets together thru the shelf pin holes. It makes for perfect alignment every time in comparable cabinets. Hafele, among others, has these screws in their catalog.
