apprehensive newbie and lag bolt cantilever limits (outside the stud)

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post #1 of 6

10/19/09 at 11:54pm

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i am mounting a 60 pound 42 inch plasma on 2 2*4 studs with 3.5 inch long 5/16's and predrilled holes of 3/16 diameter which are 3.25 inches deep (0.25 would be used up by the frame and washer). i have proceeded gingerly with a socket wrench and am currently at this stage :
0.75 outside (ie the shank)
0.75 in drywall
2 in the stud

here comes the newbie part:-). the socket wrench is pretty hard to turn and i fear the bolts might snap if i continue. i am minimising sideways movement by applying pressure on the socket wrench head while turning in small increments of 20 degrees.

if i use some spacer for the 0.75 on the outside, would it provide adequate strength for my 90 pound = 60 pound tv + 30 pound frame load.
or i should just continue tightening the bolt? slowly!

post #2 of 6

10/20/09 at 2:28am

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I can only tell you I snapped one bolt head of three (the first one) when mounting my 37" on a tilt/swivel panel mount. I was able to remove the still-protruding bolt with a pair of 'Vice-grip" pliers. Then I went down to the local hardware store and bought 3 good quality lag bolts to replace the 3 in the mount. Cheap Chinese hardware was my diagnosis.

post #3 of 6

10/20/09 at 9:51am

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i am using home depot bought unmarked(grade 2, i guess) lag bolts.

so is my current setup -2inch in stud bite with .75 inch in dry wall and 0.75 inch packed with washers- capable of providing a secure mount for a 100 pound load

post #4 of 6

10/20/09 at 9:53am

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Quote:

Originally Posted by muddypaws

i am mounting a 60 pound 42 inch plasma on 2 2*4 studs with 3.5 inch long 5/16's and predrilled holes of 3/16 diameter which are 3.25 inches deep (0.25 would be used up by the frame and washer).

The correct pilot hole size for a 5/16" thick lagbolt is 7/32". Your pilot hole is only a little smaller so it sounds like the wood is very hard. I would remove the lagbolts and re-drill that pilot hole to 7/32". I'd also make that hole another half-inch deeper. You need a little void area ahead of the point of the lagbolt's point for the excess wood to move into.

You should also open up the clearance hole in the drywall to 5/16" to match the shank of your lagbolt. Drywall is dense and lagbolts will bind on it if the clearance hole is smaller than the shank of the bolt so that could be adding to the friction when you're tightening it.

Quote:

the socket wrench is pretty hard to turn and i fear the bolts might snap if i continue. i am minimising sideways movement by applying pressure on the socket wrench head while turning in small increments of 20 degrees.

if i use some spacer for the 0.75 on the outside, would it provide adequate strength for my 90 pound = 60 pound tv + 30 pound frame load.
or i should just continue tightening the bolt? slowly!

I wouldn't bother with spacers on the outside, just install the bolts properly and use the supplied flat washers between the bolt head and the wall bracket.

When the bolt head contacts the washer, you only need to snug the bolt down a little beyond that and stop when it starts to resist your turning. There is no need to crank it down tight, and doing so will only start to tear the wood away from the threads on the bolt and will result in less strength and possibly snap the lagbolt. Just snug it - it ain't gonna go anywhere.

post #5 of 6

10/20/09 at 10:50pm

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