Re: Rules on pre-drilling sizes for screws

On Wed, 31 Oct 2007 13:34:52 GMT, "Thomas G. Marshall"
<tgm2tothe10thpower@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

Top posted for your convenience.

(In other words, you can look at the earlier text by scrolling down if
you *want* to, but you're not forced to wade through dozens of lines
of unedited material to get to the meat of THIS post:)

**************************************************************

There is an article at WoodCentral which has the correct sizes of
drill bits for screwhead, shank, and root diameters of common sizes.
There's also drilling and tapping information for metal work.

http://www.woodcentral.com/articles/shop/articles_713.shtml



I'm never quite sure what the best practices are for pre-drilling holes for
screws.

What I have been doing is holding the drill bit in front of the screw at eye
level and trying to sight it to see if I can still see the shaft of the
screw behind it. If I can just /barely/ see it, then I know that the
screw's shaft will be a smidgeon larger than the hole it's teething into,
and that's what I'm aiming for usually.

Note, I'm not talking about the case where I need a hole large enough in a
board for the threads to spin freely to pull the board down to something
underneath. I'm talking about the underneath business, but perhaps there
are rules for the board here too.

Fundamentals:

1. Does pre-drilling generally create a stronger hold, because presumably
there is less wood pushed to the side of the screw? Or does the stress of
the wood split to the side add to the hold against the threads?

2. Should a pre-bore be large enough to only grab the threads? Or is this
only necessary for the harder of the hard woods?

Thanks!


--
LRod

Master Woodbutcher and seasoned termite

Shamelessly whoring my website since 1999

http://www.woodbutcher.net

Proud participant of rec.woodworking since February, 1997

email addy de-spam-ified due to 1,000 spams per month.
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