Strength of a 1/2” screw eye?

[Seattlemusic]

I have four 1/2” screw eyes going into 2 x12s which are running perpendicular to 5x12 glulams holding up about 250 pounds total (hanging a cluster in a music studio). It seems rock solid but I have heard some say the break strength of ANY screw eye in wood of any type is 75 pounds. So yes technically it can hold it even with those numbers but not nearly at the safety margin I want. I will be sitting under this cloud/cluster often.

Curious if this is sufficient or if I should open up the ceiling and get up higher with a through hole or something that won’t have a risk of wood + bolt failure.

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[J. Clarke]

On Fri, 21 May 2021 13:45:03 +0000, Seattlemusic
<fe631b6ee051d611...@example.com> wrote:

>I have four 1/2” screw eyes going into 2 x12s which are running perpendicular to 5x12 glulams holding up about 250 pounds total (hanging a cluster in a music studio). It seems rock solid but I have heard some say the break strength of ANY screw eye in wood of any type is 75 pounds. So yes technically it can hold it even with those
numbers but not nearly at the safety margin I want. I will be sitting under this cloud/cluster often.
>
>Curious if this is sufficient or if I should open up the ceiling and get up higher with a through hole or something that won’t have a risk of wood + bolt failure.

Here's a calculator that might be helpful
<https://www.engineeringtoolbox.com/wood-screws-allowable-withdrawal-load-d_1815.html>

[Ed Pawlowski]

On 5/21/2021 9:45 AM, Seattlemusic wrote:
> I have four 1/2” screw eyes going into 2 x12s which are running
> perpendicular to 5x12 glulams holding up about 250 pounds total (hanging
> a cluster in a music studio). It seems rock solid but I have heard some
> say the break strength of ANY screw eye in wood of any type is 75
> pounds. So yes technically it can hold it even with those numbers but
> not nearly at the safety margin I want. I will be sitting under this
> cloud/cluster often.
> Curious if this is sufficient or if I should open up the ceiling and get
> up higher with a through hole or something that won’t have a risk of
> wood + bolt failure.
>

I found this:
1/2" diameter x 3-1/4" shank length, Hot Dipped Galvanized Screw Eye Bolt

Screw eye bolts are designed for screwing into wood. And because of
this, do not have a working load limit assigned to them because it is
not possible to determine the various densities and conditions of the
wood the eye bolts are screwed into.

If I was sitting under 250# I'd probably use a thru bolt

[k...@notreal.com]

When I put in my hoists, I didn't trust screw eyes so added 2x8 beams
across the room, sitting on the walls to take the weight. My jousts
are "engineered" so can't take any suspended weight at all. The 2x6s
allow me to put a 2x across them and use an eye-bolt and washer.

Whatever you do, make sure the fastener is rated for *lifting*. Most
aren't.

[dpb]

On 5/21/2021 8:45 AM, Seattlemusic wrote:
> I have four 1/2” screw eyes going into 2 x12s which are running
> perpendicular to 5x12 glulams holding up about 250 pounds total (hanging
> a cluster in a music studio). It seems rock solid but I have heard some
> say the break strength of ANY screw eye in wood of any type is 75
> pounds. So yes technically it can hold it even with those numbers but
> not nearly at the safety margin I want. I will be sitting under this
> cloud/cluster often.
> Curious if this is sufficient or if I should open up the ceiling and get
> up higher with a through hole or something that won’t have a risk of
> wood + bolt failure.

A screw eye is more like a lag screw thread than an ordinary wood screw.

The maximum direct withdrawal load of lag screws from side grain of
seasoned wood is

p=8100 G^(3/2) D^(3/4) L

where

p = Max withdrawal load, lbf
D = Shank diameter, in
G = Specific gravity of the wood based on oven dry weight and volume
at 12% moisture content
L = Length of penetration of threaded part, in.

For SYP assuming it is 1/2" shank (not clear) and 1" penetration, it's
about 3,500 lbf for each.

If it is symmetrically-shared load, each is only about 60-65 lbf loading
presuming your estimate of the total load is approximately correct.

Again, the above also presumes a properly-sized pilot hole and installation.

<https://www.engineersedge.com/calculators/lag_screws_in_wood_pullout_resistance_15390.htm>

Can't really envision the physical arrangement of these 2x12 with
respect to the glulams; are they inserts and if so, how are they being
supported? There _might_ actually be the weak point, depending...

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