Leon wrote:
"Jon Danniken" wrote in message
...
J. Clarke wrote:

It's in "Wood As An Engineering Material", Page 7-11. What they say
is:

"For low-density softwoods, such as the cedars and white pines, 40%
to 70% of the shank diameter; for Douglas-fir and Southern Pine, 60%
to 75%; and for dense hardwoods, such
as oaks, 65% to 85%. The smaller percentage in each range applies to
lag screws of the smaller diameters and the larger percentage to lag
screws of larger diameters."

Excellent reference, J. Thank you for posting that, it is very much
appreciated!

The lag bolt which snapped off had an average shank diameter of
0.182". Sixty percent of this value is 0.1092, while seventy five
percent of this value is 0.1365, which puts a pilot bit of 1/8"
right in the middle.

Jon


BUT Jon,,,,,, While it is a kewl reference that agrees with what you
were using as a pilot hole, how did that work out for you?

The information could be out dated for readily available fasteners
today. If might be a new publication using old data.

The numbers are based on maximizing holding power, not making a crap
fastener survive being driven. They state the assumptions, which are 35,000
PSI yield and 77,000 PSI UTS, slightly higher than required for a Grade 1
bolt.