lagging steel items to wood beams

Well, f'sure both methods beat no pilot hole at all, and I can see a logic to both. I've done it basically your way, a hole slightly smaller than the root diameter, as wood is compressible, and about 1/2 short.

Kevin Gallimore

Grant,

I suspicion that the "Wood Butcher" you did the work for was used to using lag bolts that were only threaded part way up, so he (rightly) would drill a pilot hole of the diameter of the body... He just (wrongly) didn't drill the rest of the pilot to thread root diameter...

I was taught to drill a pilot hole the root diameter (or *SLIGHTLY* under) to full depth, and then if the bolt wasn't threaded all the way up to clean up the beginning of the hole to body diameter...

--. Dave

Lag screws, like wood screws, require prebored holes of the

proper size (Fig. 7-6). The lead hole for the shank should be

the same diameter as the shank. The diameter of the lead

hole for the threaded part varies with the density of the wood:

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. Soap or similar

lubricants should be used on the screw to facilitate turning,

and lead holes slightly larger than those recommended for

maximum efficiency should be used with long screws.

In determining the withdrawal resistance, the allowable

tensile strength of the lag screw at the net (root) section

should not be exceeded. Penetration of the threaded part to a

distance about seven times the shank diameter in the denser

species (specific gravity greater than 0.61) and 10 to 12 times

the shank diameter in the less dense species (specific gravity

less than 0.42) will develop approximately the ultimate

tensile strength of the lag screw. Penetrations at intermediate

densities may be found by straight-line interpolation.

The resistance to withdrawal of a lag screw from the endgrain

surface of a piece of wood is about three-fourths as great

as its resistance to withdrawal from the side-grain surface of

the same piece.

I think he might have been lucky using green beams. I suspect an aged beam might be a different story. I have turned the heads off lag bolts. I use a bar of soap and soap down the lag screws. That helps a great deal.

Martin

Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net TSRA, Life; NRA LOH & Endowment Member, Golden Eagle, Patriot"s Medal. NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member.

Grant Erw> Anyone know the *right* way to use lag bolts? What I have done most often

That is my method also. ( another vote for that ) ...lew...

I will add to this a caveat that you should seek a supply of good quality lag screws. I bought a bunch that were outright junk and the heads would shear even though I was setting them in douglas fir with a pilot hole just slightly less then the body diameter of the screw.

It appears that unlike cap screws, lag screws have no quality standards so you are subject to a lot of failures with the cheap junk import crap.

Shouldnt use soap. It will "sort of" attract water and cause rust. Use bees wax instead. Or from McFeeleys Ackemputty (?sp). :-) ...lew...

Personally I use wood glue on the threads. Works as an OK lube while it's wet and fills in any inconsistencies left by variance in threads.

And authoratative, i.e. based on laboratory testing rather than just theory or folklore.

David Merrill

I've been using the wax used on bandsaw blades to good effect. The wax is quite sticky, and stays on the threads.

Joe Gwinn

I quite often use wheel-bearing grease (because it is inexpensive, on hand and easy to get out of the tub) and sometimes Vaseline. In the long term the grease hasn't caused me any known troubles so far.