I don't have my wood design books at home but I think a 1/4" diameter
lag bolt is good for several hundred pounds of pullout. If I do this I
will use 4 of them. I'm a licensed professional engineer so I can
figure out the safe load capacity of this type of connection.
I installed a ceiling fan in my old house many years ago. This was one
of the 50 pound Hunter fans so I wanted to make sure it was properly
attached. The ceiling in our den had fake wood beams and I didn't want
to connect directly to them. I found where the actual roof joist went
over the fake beam, and drilled a hole in the bottom of the fake beam so
I could reach the real joist. I used a long drill bit to drill a pilot
hole in the rafter. I bought a lag bolt that has lag bolt threads on
one end and 1/4-20 machine threads on the other end, and joined it to a
piece of 1/4" threaded rod with a sleeve nut. I screwed this long bolt
all the way up into the rafter. On the bottom end of the threaded rod I
had formed it into a hook to match the hardware normally used for that
fan model. After I put the long J-bolt in I hooked my screwdriver
through the hook and picked up my weight with it. I figured if it would
hold my 175 pounds it would hold the 50 pound fan.
> I don't agree. Lag bolts pulling straight down are relying on the
> threads that's less than 1'8" bearing pulling to hold up to 300 lbs
> and the strain of pushing it sideways. Not a good idea. Not the same
> as holding the top of a rafter, or better bridging 3 floor joists.
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