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-   -   Toggle bolt through stud? (http://www.diychatroom.com/f14/toggle-bolt-through-stud-117703/)

djgrant 09-19-2011 12:50 PM

Toggle bolt through stud?
 
For attaching a heavy TV to a wall, what do you think is stronger, a long Toggle bolt like this:
http://www.toggler.com/products/snaptoggle/overview.php
behind the stud, or a 3/8" x 3" lag bolt screwed into the stud itself? Just curious. Usually people put toggle bolts in drywall and screw into studs, but I've never heard of a toggle bolt behind a stud. In most cases there is probably another piece of drywall or something behind the stud, but in my case, there is empty space behind this stud.

djgrant 09-19-2011 01:00 PM

FWIW, this guy (http://woodgears.ca/joint_strength/index.html) showed wood screw thread failure at 210lbs applied at 20cm from joint. He really should have calculated the force at the point, which is fairly trivial to do. I'm guessing the force at the point where it is screwed in is about 3 times 210lbs, since it is about 3 times closer to the pivot point (7 cm?). So maybe 610lbs. I'm guessing a 1/4-20 machine screw screwed through 1/4" of threads in the toggle can hold way more than that.

Clutchcargo 09-19-2011 01:03 PM

Are you talking about drilling all the way through a stud to install a toggle bolt?
Why would you bother with a toggle bolt if you have access to both sides of the wall?

In any case a through bolt would be strongest, followed by lag screw. The toggle bolt would be the weakest.

djgrant 09-19-2011 01:11 PM

Quote:

Are you talking about drilling all the way through a stud to install a toggle bolt?
Yep.
Quote:

Why would you bother with a toggle bolt if you have access to both sides of the wall?
I don't actually have access from behind, but there is a big void space in that wall, it's 45 degree angled wall in the corner of the room with an unused metal fireplace pipe inside.
Quote:

In any case a through bolt would be strongest, followed by lag screw. The toggle bolt would be the weakest.
By "through bolt" do you mean a through bolt with a nut screwed on? Those toggle bolts I hyperlinked too are basically just a nut. Not the same as those cheap toggle bolts that are a 2-piece toggle design.

djgrant 09-19-2011 01:20 PM

Another slightly related question...the mount I am going to buy comes with 4 3/8" x 3" lag screws. Since I am screwing through 3.5" of stud + 0.5" of drywall (4"), if I use fully threaded 4" long lag screws do I get 40% more strength out of it? (3.5" in stud vs. 2.5" in stud). Is there any problem with drilling/screwing deeper into the stud? Will it make it weaker or anything?

josall 09-19-2011 04:28 PM

Just use the bolts supplied by the manufacturer and be done with it. The mount will fail long before you pull 4- 3/8 lags out of the wall.

djgrant 09-19-2011 05:07 PM

Quote:

Originally Posted by josall (Post 731651)
Just use the bolts supplied by the manufacturer and be done with it. The mount will fail long before you pull 4- 3/8 lags out of the wall.

The mount will fail? Really? I thought that would be the last thing to fail.

Actually it's a pull down mount and when fully extended the center of gravity of the 100lb TV+sound bar is about 16 inches away from the wall. The top two lags will be taking all the pull out weight and because my studs are not centered on the wall, in fact, the one slightly off-centered top lag will be taking most of the force while the other one (15" away to one side) will not take as much. The one top lag needs to withstand 200lbs of pull out force (according to my calculations) but the manufacturer of the mount says 400lbs (I trust their calculations). The question is how much force does it take to pull a 3/8" lag that is screwed 2.5" deep or 3.5" deep into a 1/4" pilot hole?

kwikfishron 09-19-2011 05:11 PM

Quote:

Originally Posted by josall (Post 731651)
Just use the bolts supplied by the manufacturer and be done with it. The mount will fail long before you pull 4- 3/8 lags out of the wall.

I bet the TV will fail (not fall) even before that. :whistling2:

djgrant 09-19-2011 05:13 PM

Can anyone answer whether a SnapToggle type toggle would be better than a wood screw? Thanks.

Mr Chips 09-19-2011 05:36 PM

You are correct about a snap toggle being basically a nut and bolt. I'm not sure you can say it's the same thing as a nut and bolt because there is probably fewer threads actually being engaged on the toggle

Snap toggles are stronger in drywall than standard toggles because the wing is one piece, and will not fold back like a standard toggle. In the application you are talking about, a standard toggle is probably stronger because most standard toggles utilize a jam nut ( still fewer threads engaged than a standard nut, but probably more than a snap toggle)

my biggest problem with your application is snap toggles require a much larger hole than a comporable size lag bolt, and it sounds like your plan is to drill into the narrow face of the stud. The larger hole needed for the strap toggle could compromise the integrity of the stud.

djgrant 09-19-2011 06:18 PM

Quote:

Originally Posted by Mr Chips (Post 731718)
My biggest problem with your application is snap toggles require a much larger hole than a comporable size lag bolt, and it sounds like your plan is to drill into the narrow face of the stud. The larger hole needed for the strap toggle could compromise the integrity of the stud.

Awesome, thanks! I was a bit worried about that as well. You're right, the through hole for the toggle would have to be 1/2" wide into narrow face of stud, whereas the pilot hole for the 3/8" lag would be 1/4".

I was also worried about the toggle not engaging as many threads as a normal nut would.

(Also, the toggle would be a 1/4"-20 machine screw. I know machine vs. wood screw is not apples-to-apples, but in addition to needing a larger hole drilled through the stud, the screw is a bit smaller too.)

Mr Chips 09-19-2011 06:44 PM

Another issue you have is the hole you are drilling might violate code.

I think any through hole in a stud has to be 5/8" from the edge of the stud ( people normally drill into the wide face, but i assume it holds true for either)
so there is really NO WAY to drill a 1/2" hole through the narrow face of the stud and still be code compliant. You may not be allowed to drill through the narrow side at all. I'm not sure, but it wouldn't surprise me

havalife 09-19-2011 11:42 PM

My TV is mounted with 3 lag bolts and mounted in a corner so the arm is extended out all the way. TV is still hanging after 4 years. I was more concerned about hitting the middle of the stud. If you want the best way to mount it then put a plate on the back side of the studs, if you can't get to the back of the stud then make sure you hit the center.

djgrant 09-19-2011 11:52 PM

Quote:

Originally Posted by havalife (Post 732024)
My TV is mounted with 3 lag bolts and mounted in a corner so the arm is extended out all the way. TV is still hanging after 4 years. I was more concerned about hitting the middle of the stud. If you want the best way to mount it then put a plate on the back side of the studs, if you can't get to the back of the stud then make sure you hit the center.

Hehe, yeah I'm worried about that as well. Another good reason to use a wood screw with a small pilot hole rather than a large hole for a toggle bolt.

Luckily there is a hole in the drywall for low voltage cables right next to the stud. So I can actually feel and see the stud there. I'll probably try and measure the distance from the drywall opening's edge to the stud, then mark off the exact location of the far side of the stud, then drill right through the exact center. As for the other stud 16" away, I guess I'll just have to rely on the stud detector... but that one won't take much of the load apparently.

Mr Chips 09-20-2011 11:23 AM

if you are really worried about making sure you find center of stud, once you hone in on it with the stud finder, mark the edges with a pencil or painters tape, then use a thin paneling nail or finish nail to poke through drywall a few times until you can feel the edges of the stud and double check that way. do it close to the location where you plan to drill pilot hole so the mount will cover the 5 or 6 tiny holes you'll need to make.

quick and easy, and will give you peace of mind


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