Shank pilot hole?

graywings123March 16, 2010

I want to enlarge a hole in a piece of steel so that a #6 wood screw will go through it.

I found a chart on the internet that indicates a shank pilot hole of 9/64 for that size wood screw. And it says, "The shank pilot hole is one which will clear the thickest part of the screw body."

So, does this mean that I should use a 9/64 drill bit to drill the holes in the steel to accommodate the #6 wood screws?

And if I also wanted to bevel the holes with a countersink bit as Randy suggested, is it a two step process - enlarge the hole then go at it with a countersink drill bit? Or could I just start with a 9/64 countersink drill bit?

Here is a link that might be useful: Chart

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What you read was the process to use to drill a hole in wood so a wood screw can make its own threads in the wood.

What you want to do is make a hole the size of the diameter of the screw threads, not the shank(which is the center part of the threaded length.)

The easiest way to select the correct sized bit for that is to hold the screw in front of a drill bit. If you can see a tiny part of the bit on either side of the threads of the screw, that bit should work. You can double check that by inserting the screw into the hole in the drill bit holder. If the bit is too small, you will have to begin turning the screw to get it into that hole.

Countersinking a hole in metal can be done two ways. First, you must have bits built for drilling metal. Wood countersink bits will not work. Second, the metal has to be at least as thick as the head of the screw. (Sheet metal is too thin)

You can use a metal countersink bit(pretty expensive) or simply use a twist drill bit the size of the head of the screw. You can size the bit for that the same way as above.

    Bookmark   March 16, 2010 at 11:00AM
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Thanks, handymac! I am sooooo glad I asked.

    Bookmark   March 16, 2010 at 12:26PM
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Fir putting a wood screw through metal and into wood you need a shank hole in the metal, with the appropriate countersink for a flat head screw.

A wood countersink and pilot bit will not drill the metal without being destroyed, if it can even cut.

For countersinks in metal a single flute with the correct angle for the screw head is the easiest tool to control.
Multi flute countersinks for metal require the metal to be tightly clamped down and a rigid tool like a drill press or milling machine to be used.

The angle for a wood screw is 82 degrees.
This gets more important in metal.
many wood tools are made at 90 degrees since the wood will easily compress for a tight fit.

When countersinking for a wood screw in metal you ned the correct angle.

Below are sets from MSC.
You may be able to find singles.

The pilot hole should be tapered for conventional wood screws, but you can compromise in most woods and use a shorter but straight pilot hole.

If the screws are brass, be sure to drive the same size steel screw in the hole first to form it before driving the softer brass screw.

Here is a link that might be useful: pilotless countersinks

    Bookmark   March 16, 2010 at 1:10PM
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Eeeeek! Thanks for the info Brickeyee. I think I'm going to skip the countersinking and just use round head screws.

    Bookmark   March 16, 2010 at 1:46PM
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The Fuller chart I consulted also had the shank clearance diameter for #6 wood screws being 9/64"

    Bookmark   March 16, 2010 at 7:18PM
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Conventional wood screws are designed to have the shank in one piece of material being fastened and the threaded portion in another.

By drilling a shank hole in the piece closest to the screw head and the pilot hole diameter in the other the pieces are pulled together tightly.

If you cannot find a screw with the correct proportions, you can still screw the pieces together. Make sure to clamp them to pull them tight before driving the screw.

Modern screws with a uniform thread diameter have the same issue. A larger hole in one piece provides clearance for the threads. If the threads will be in both pieces of wood they need to be pulled together before driving the screw.

For fastening metal to wood round heads eliminate the need to countersink metal, but you still need a shank size hole for part of the depth and a pilot for the rest.

If you use a modern wood screw with no taper the same size hole works since the shank is smaller than the threads anyway.

The metal just need a hole to clear the threads.

    Bookmark   March 16, 2010 at 9:41PM
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Drill some test holes of different sizes in a scrap piece of wood.

    Bookmark   March 18, 2010 at 12:58AM
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