CurtPalme.com Home Theater Forum

Cube · Joined: 06 Dec 2009 Posts: 77 Location: IL, USA

I'm trying to mount a Sony 1272 in my basement (roughly 140 lbs). The joists are single 2x10s I think, so it seems like 3/8x4" bolts (as suggested in another thread) would damage the tensile strength of the joists if I drill straight up into them. Would it be safer to drill sideways through the joist further up, say 1/3 from the top? I guess I could attach angle brackets then and bolt the strut into that.

The screen's already mounted with the center between two of the joists, which run perpendicular, so I figured I would run struts parallel to the screen spanning four rows of joist and attach the projector mount to that. Any thoughts? Am I being paranoid?

greg_mitch · Joined: 03 May 2006 Posts: 5321

4" lag bolts in 2x10's here for at least 2 years now.

Just pre-drill your holes and lubricate the bolts as you HAND turn them in. Otherwise you will snap them...I know...I did it to two of them.

rod · Posted: Fri May 14, 2010 5:04 am Post subject:

let me qualify this comment by saying I am not a structural engineer.

but, I did speak with an engineer that indicated that the stronger option is to drill horizontal holes thru the 2X10 and use the angle iron. I used 2" aluminum angle iron and 1/2" bolts and lock nuts (ie. with the nylon sleeve inside the nut), and large washers. I also sourced the highest grade bolts. All entirely overkill but for the extra 40 bucks it's worth it to me.

Driving lag bolts vertically into the joists will always have pressure exerted on them and overtime may come loose. Especially if you do not drill the proper size hole. Be careful not to make the hole too big (hence losing the grip), or too tight causing the joist itself to split. I also thought that if the PJ was subjected to horizontal shock (ie someone hitting their head on it) this would also be more stress applied to the lags as opposed to and angle iron setup.

my 165lbs barco has been hanging since 2003.

**AnalogRocks** · Posted: Fri May 14, 2010 6:21 am Post subject:

Over-engineered there Rod. That one's not coming down until you want it down

JustGreg · Joined: 07 Mar 2006 Posts: 3098 Location: Kenosha, WI

Well one thing to always consider when drilling into wood is it's age. If the joists are older than say 10 years there's no way in hell I would drill horizontal holes in it. Look at it this way...you ever see wood age normally with a bow along the spine? Nope...it's always along the widest face because as the wood ages the fibers undergo increasing tension due to loss of moisture. Cracks in old wood are just about always caused by the tensile forces that exist on the OPPOSITE side from the crack. Which side cracks is a crapshoot for the laymen but anybody good with wood can tell you at a glance which side will crack or split...or if it will at all.

You also have dead loads upstairs including unsupported load bearing walls (not supposed to be unsupported but you'd be surprised how many homes were 'modified' over time), non load bearing walls, stoves, refridgerators, marble or ceramic flooring, furniture, etc. etc.

If it makes you feel better just drill through the spines like we all have and then add a length of aircraft cable to the 4 corners and THEN add your plates to anchor those to it. EDIT: as SAFETY BACKUPS NOT FOR MOUNTING!!!!

The only concern I could ever see with hanging a pj was what and how much of a dead load is already on the other side of the real estate location you plan to work with. If you have a Wolf stove or a fridge in the spot...brackets hung horizontally have the potential to hurt integrity more than they would be the safest option IMO. You just have to do what you're doing and research it a bit and then be comfortable with what you settle on.

Personally, I put more time into thinking about a hassle free mount that could be lowered and raised by one person than I did the actual mounting method. Wink

WanMan · Joined: 19 Mar 2006 Posts: 10273

And what if this discussion included joists fabricated with Boise-Cascade I-Joists with rather narrow stiles? The stiles on mine are about 1" to 1-1/4" wide and less than an inch high. The webbing is about 1/4" to 5/8" at best. I'm regretting haven drywalled (and trimmed and painted) the room before I had devised a projector mounting solution.

garyfritz · Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO

zaphod · Joined: 16 Jun 2006 Posts: 2002 Location: Cloverdale

Sparky015 · Posted: Fri May 14, 2010 3:57 pm Post subject:

Ok, so horizontal lags are overkill, lags from the bottom will work (unless you have manufactured I-beams), just be smart in the size hole you pre-drill and use soap on the threads to avoid snapping heads or splitting the joists. Does that about sum it up?

garyfritz · Joined: 08 Apr 2006 Posts: 12026 Location: Fort Collins, CO

That's what 95% of us here have done, and so far no projectors or ceilings have come crashing down. Or if they did, nobody survived to come tell us about it. Laughing

ecrabb · Posted: Fri May 14, 2010 4:32 pm Post subject:

Don't worry about it. A properly drilled lag screw installed in a standard lumber joist probably has a wicked pull-out strength... I don't remember the exact numbers, but for a 5/16" lag, it was something like 250 pounds per inch of threads. So, if you properly drill and install even a 5/16" lag screw with 2" of threads in the center third of a lumber joist, you're talking around 500 pounds of pull-out strength on each screw!!!

Even a G90 is only going to put maybe 60-70 pounds on each of the four mounting points, so you're talking about a safety margin somewhere in the 8x neighborhood... Way WAY safe.

SC

ecrabb · Posted: Fri May 14, 2010 4:35 pm Post subject:

Oh, and don't over-torque... That stresses the grain in the wood and reduces pull-out strength. The threads interfacing with the wood makes the strength. Just snug it up and you're good to go.

SC

Cube · Joined: 06 Dec 2009 Posts: 77 Location: IL, USA

Thanks for all the suggestions... I guess drilling into the spines wouldn't be too bad for a 140-lb. projector, but I figured the horizontal method would be the safest for little extra effort. JustGreg's comment surprises me, but I guess I don't know much about the material physics of wood. The house is over 20 years old, so maybe I should have a professional come take a look at the joists and advise.

JustGreg · Joined: 07 Mar 2006 Posts: 3098 Location: Kenosha, WI

rod · Posted: Sat May 15, 2010 12:33 am Post subject:

I don't disagree with the vertical lags. you're right, I'm sure you can hang 2-300lbs off of one bolt. What I never was able to determine was what is the proper torgue? the proper hole size? So I simply asked an engineer which was stronger and went with that. I can't remember the reasons but he was definite and he did say either would suffice. I don't see any extra effort with either method really except for drilling holes in angle iron. I had access to a machine shop

JustGreg · Joined: 07 Mar 2006 Posts: 3098 Location: Kenosha, WI

rod · Posted: Sat May 15, 2010 1:06 pm Post subject:

No worries Greg, never took it that way at all. As you say, we are not all experts (but sometimes some think they are). This is why threads grow because us "half-bakes" need to challenge the other 'half-bakes". You take from the discussions what you can get - for what you pay. For me that's the whole point of these forums. If you REALLY REALLY want to make sure, hire a structural engineer and have him stamp it. That'll be safest bet, but will cost you more that the PJ is worth Wink

So..... speaking of extra metal (if you are referring to the angel iron) that's why I went to aluminum to reduce the magnetism effect. I did it only because of the slight possibility of magnetic interference AND because I had free source of aluminum AI. but that's a whole other thread on convergence drift (somewhere in these forums) that I'll leave alone.

WanMan · Joined: 19 Mar 2006 Posts: 10273

I guess my concern is that drilling into the webbing from its edge, something the I-Joist manufacturers would highly disagree with, when the lag bolt's diameter is on the same order of the of the webbing's thickness could potential compromise the structural integrity.

If one looks at the allowances for making changes to the I-Joist's webbing, they do not want anything on its edges, usually within 1/4" of the webbing-stile contact. But using 3-4" long lag bolts would surely project well into the edge of the webbing and a bolt with diameter on the order of the webbing's thickness would act like a saw cut rather than a drill.

I guess I'll need to tear into the ceiling drywall in order to hang something.

zaphod · Joined: 16 Jun 2006 Posts: 2002 Location: Cloverdale

is there a way to get some 16" 2X10 on hangers between, and perpendicular to, a pair of I-beams? then you have some "real wood" on which to attach the unistrut.

ecrabb · Posted: Sun May 16, 2010 3:56 pm Post subject:

Wan, I don't think anybody is suggesting you drill through the stiles into the webbing on your engineering joists... This thread is about dimensional lumber. I think you should talk to somebody that knows what they're doing if you're going to tear into your engineered joists.

What I'd probably do is glue some OSB stiffeners onto both sides of the webbing, then through-bolt some lumber or steel members to hang the projector off on some all-thread. Unfortunately, I don't see how you'll be able to do anything without tearing into the ceiling to do it.

No biggie, though.. Drywall is cheap. Find your joists and cut open a nice clean rectangular hole big enough to allow you to do everything you need, then have somebody put a new piece back and re-texture, prime and paint.

SC