What size drillbit to predrill for lag bolt?

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I need to predrill holes in a board plus a tree for lag bolts. Should I use a drill bit the same diameter as the solid part of the bolt (minus the threads), so just the threads bite into the wood, or should the drill bit be smaller than that? I'm hanging a board between two trees to hang a child's swing from; is that the best way to fasten the board to the tree?

Many thanks,

-- Elizabeth in E TX (kimprice@peoplescom.net), July 17, 2001

Answers

I forgot to ask if a 2x6 board is sufficient to hold the weight of two small boys whose weight together is 90 lbs? The span is a bit less than 7'.

-- Elizabeth in E TX (kimprice@peoplescom.net), July 17, 2001.

Elizabeth, the 2x6 will be plenty strong enough for the job. I'd drill the holes in the 2x6 the same size as the lag screws including the threads. No reason to have resistance in the 2x6. Be sure and use some fender washers on your screws. You are using screws aren't you? You won't need bolts unless your tree is small enough to drill completely through and attach the nuts on the other side.

Your idea to allow just enough room for the threads to "bite" into the tree is good. Hold your lag screw up and hold your drill bit in front of it. Choose a bit that will allow you to see all the threads on your screw. You could even use one a size smaller if your screws are large. I would put two screws in each end of the 2x6.

-- Jim (catchthesun@yahoo.com), July 17, 2001.


Elizabeth. The ideal hole will depend somewhat on the type of tree! For hard wood you will need a larger hole and of course smaller hole for soft wood tree. Try a small hole and if it is too hard to put the lag bolt in then drill the hole larger.

Incidently, I am not sure what a 'lag bolt' is but I assume it is like a big wood screw with a square head?

It is not really the best idea to bolt or screw things to trees as (disregarding whatever distress it might cause the tree) the tree will move a little in the wind and weaken whatever you have attached to it this would be less of a problem with mature trees but I am guessing you dont have two giant redwoods 7' apart! :-)

Cheers.

-- john hill (john@cnd.co.nz), July 17, 2001.


Elizabeth, I think the advice given to you is good, and I agree a 2x6 would support 90 lbs. You might want to consider a 2x8 or even a 2x 10 instead so it will still be suitable when your children are bigger. I think the 2x 6 will eventually sag with a 7 ft span.

Down here I've always heard giant wood screws called "lag bolts". Anything which passes thru the wood and gets a nut is called a "thru- bolt". I had always assumed they were called lag-bolts because you have to wrench them in. Is this the same as a "lag screw"? Maybe a case of regional termology. Good luck wth your project!

-- Mark M in NC (MagicMark85@aol.com), July 17, 2001.


These are giant wood screws (5" long) with a hex head. I used a ratchet wrench on them and had a lot of trouble; evidently I hadn't drilled the holes deep enough into the tree, so there was quite a bit of resistance, and the torque broke two of the screws off about 1" from the head, level with the surface of the wood. The board feels rock solid and I let the boys swing from it this afternoon, but I'm going to see if my husband wants to redo it when he gets home (he's a carpenter). This was my first project on our new land, so the boys can swing and play while I work on the place. It looks good and I know they'll have fun on it but what's really great is that they were more interested in helping me work! Thanks all, for your advice:o)

-- Elizabeth in E TX (kimprice@peoplescom.net), July 17, 2001.


What size tree are you trying to lag into? If its small a good size lag bolt could kill or damage it.

-- gary (gws@redbird.net), July 18, 2001.

Elisabeth,

If these are smaller trees, you may want to use a "u" bolt (ask at a HW store) and some washers to go around the tree, instead of into it. That way, you won't be damaging the tree as much. As the tree grows, it'll actually grow around the board and bolt (several years) and will be an interesting conversation piece.

-- Dave (peasedj@sparc.isl.net), July 18, 2001.


Dave: FWIW, I had some experience with a similar situation a while back. A TV antennae was strapped or wired to the top of an old white pine by the squatter who lived here prior to our buying this land. The tree is about three feet in diameter. Anyway, a couple years ago we had a storm, with strong winds, and the top of the tree snapped right off where the antennae was wired to it. It had started to grow around the tie wire as you suggested it might, but the rate of growth was noticably different and it obviously jepordised the strength of the tree.

-- john (natlivent@pcpros.net), July 19, 2001.

The advice you were given sounds like it would work but, I would use stainless steel bolts rather than galvanized (poison)or zink. If you are going to harm the poor trees, please be gentle with them. Oak

-- Oak (StrugglingOak@aol.com), July 20, 2001.

I don't want to harm the trees, but, truth is, these are trees that will probably have to come down when we build our cabin--this land has never been lived on and the trees are growing too thick and close. There is no way to build without cutting some trees! The only clear space is where the driveway comes up the hill. Thanks for your ideas, everyone!

-- Elizabeth in E TX (kimprice@peoplescom.net), July 22, 2001.


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