Countersink and Screw Size

Question

I have been googling this for a few hours now and I really can't find a direct answer. This is a stupid question to validate my logic, however I like firm answers instead of assuming.

I need a countersink bit to install my cabinets. The size of the counter sink is:

• DEWALT DW2569 Style#10 Countersink with 3/16-Inch Drill Bit

Knowing it is a size 10 and 3/16in drill, should I buy the same size screw 10#? I assume this to be correct.

Or, is it best to use a size #8 countersink with a size #10 screw?

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This is the desired result:

http://www.rockler.com/how-to/difference-countersink-counterbore-screw-holes-usage/

Part 2 - Installing Wall Cabinets, start at 2:56

Answer 1

A standard #10 screw has an outer thread diameter of 3/16". The #10 countersink you are referring to is a combined tool designed for applications where the screw is to pass completely through the material without digging the threads into the wood and have the head sit flush. If you wish to use a screw that is actually going to grip the material, such as a wood screw or self-tapping screw, do not buy the item. Instead you will need an appropriately sized #10 pilot drill (3/32" for soft wood, 7/64" for hardwood) and a separate countersink bit designed for your chosen screw size.

So, the answer depends on the application. If you intend for the screw to pass completely through the first work piece with nothing but the head securing it (no threads biting into the wood) then the combined #10 drill/countersink is great. If you intend for the screw to bite the material, you need a separate pilot drill and countersink bit.

Answer 2

When it comes to installing cabinetry the only time you would counter bore is if you plan on plugging the hole, its pretty rare that you need to use lags to install a cabinet. All you really need to know is that the countersink needs to be at least as big as the head so it doesn't have to crush the fibers the go flush, the hole in the first piece has to be bigger than the screw threads (called a through or body hole), the hole in the second piece (pilot) should be the size of the diameter of the shaft of the screw. For clarity's sake here's a diagram: This way the screw pulls the two pieces together like a clamp. If you don't have a through hole there will always be a portion of the threads creating space between the two so to suck them together you have to actually strip the first piece out.

The best countersinks I've ever found are these: Fuller Countersinks, because they countersink, through, and pilot with one bit. Having said all that, when it comes to screwing face frames together the standard practice is to use trim head screws. In this method you clamp the two frames together, drill the first piece to just under the size of the head, then drive the screw home. Its head is so small it needs no countersink and because trim heads are self piloting you (usually) don't need to pre-drill the second piece.

Answer 3

A #8 countersink will not only drill too small a hole, it'll also leave a #10 screw's head protruding slightly above the surface (assuming flat-head screws, since countersinks aren't used for any other screw head style). Use a #10 countersink for a #10 screw.

From your description of the screws you intend to use, though... I don't think you want to countersink at all, only predrill. If you need those heads to be below the surface, you'll need to "counterbore" instead of countersink; counterboring leaves a flat-bottomed hole instead of a taper-bottomed hole, and it's done with the appropriate size Forstner drill bit... BEFORE drilling the clearance hole.

You may or may not be satisfied with the tapered drill included with that countersink for drilling both the through hole and the blind hole (the one the screw bites into). A #10 wood screw starts and seats very well into a 9/64 blind hole made with an ordinary straight-shanked drill bit.

Since you're driving into hardwood, you'll do yourself a big favor if you go pick up a "toilet wax ring" from the hardware store and use that wax to lubricate your screws before you drive them. The difference in driving effort is amazing, and the screws are far less likely to split the wood. Don't use soap as a screw lubricant - it contains water and will rust the screws (unless they're brass).

Answer 4

It does not matter what the screw size is, only the angle is important. You have to determine the angle of the head of the screw you are using:

Your countersink should be of the same angle or you will not get a clean result. Most flathead screws are 82 degrees, but you have to check to make sure.

Also, there is an art to boring the chamfer. Due to various complicated factors it is very easy to tear up the chamfer and make a ragged seat. The first thing is to make a pilot hole, very important. The second is to make sure you are holding the drill absolutely perpindicular to the surface.