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Old 06-08-2007, 08:48 PM   #1
Chris Solar
 
Default Best anchors for heavy cabinets on steel studs

I'm looking for suggestions for a hollow-wall anchor sytem.

I'm building a set of wall-mounted bookcases. These will be quite heavy when
fully loaded.

I plan to use a French cleat system to hang the cases, but need suitable
fasteners to attach the wall-side cleat to the wall, which is drywall over
steel studs, 16" oc.

The wall cleat is a strip of 3/4" plywood, 9" wide, with a 45 degree bevel
on the top edge. I plan to fasten this to the wall with some kind of anchor
that goes through the flanges of the studs, grabbing them from behind. I'll
use two rows of anchors on this cleat, top and bottom.

So far the default choice are the standard toggle bolts with the
spring-loaded wings. My only objection with these is that the hole drilled
in the wall is much wider than the diameter of the bolt, so it doesn't seem
like there's a really good bearing surface for the bolt to resist the
downward pull of the cabinets.

Does anybody have any suggestions?

Thanks,

Chris.


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Old 06-08-2007, 08:49 PM   #2
BobK207
 
Default Re: Best anchors for heavy cabinets on steel studs

Chris-

I've mounted plywood strips to steel studs with the toggle bolt method
& I was not satisfied with the result. Too much slop in the drywall
hole, postion of strip & subsequently mounted unit is totally dependent
on clamping force.

I have switched to very large coarse thread sheet metal screws (like
#12 or #14). I drill the steel studs just slightly less than the
screws' root diameter, drive on low speed & push like hell. The method
forms a "thread" in the stud. Be careful not to overdrive/strip out
the screws.

What gage studs do you have? Hopefully they're not less than 20 gage,
which pretty thin.

cheers
Bob

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Old 06-08-2007, 08:50 PM   #3
Chris Solar
 
Default Re: Best anchors for heavy cabinets on steel studs

Thanks for the reply...that confirms my suspicions.

I guess the other option is the E-Z Toggle
(http://www.itwbuildex.com/ezprod.htm). I'd still have to drill a fat hole
in the drywall and stud, but at least the body of the anchor is the same
size as the hole.

(I assume that the teeth on the end of the anchor are only capable of
drilling through drywall, and not the steel stud.)

Using sheet metal screws sounds appealing from a cost/convenience
perspective, but I worry about the pullout resistance. Last thing I want is
to have a few hundred pounds of book/shelf coming down on someone's head.
Have you used this for heavy loads?

-Chris.


"BobK207" <rkazanjy@gmail.com> wrote in message
news:1109450218.846983.208770@l41g2000cwc.googlegr oups.com...
> Chris-
>
> I've mounted plywood strips to steel studs with the toggle bolt method
> & I was not satisfied with the result. Too much slop in the drywall
> hole, postion of strip & subsequently mounted unit is totally dependent
> on clamping force.
>
> I have switched to very large coarse thread sheet metal screws (like
> #12 or #14). I drill the steel studs just slightly less than the
> screws' root diameter, drive on low speed & push like hell. The method
> forms a "thread" in the stud. Be careful not to overdrive/strip out
> the screws.



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Old 06-08-2007, 08:51 PM   #4
BobK207
 
Default Re: Best anchors for heavy cabinets on steel studs

Chris-

Yes I have used this technique for heavy loads (magnetic white boards),
however there are few loads as heavy as a loaded book shelf.

I used to figure about 2 pounds per running inch of bookshelf when
designing bookshelves.

How tall are the shelves? How close to the top edge would the strip be
mounted? How deep (~10")?

So if your studs are 16" o/c that's 32lbs per shelf per stud.

If you're talking about a 4-shelf unit (~40 to 48" high & about 10"
deep). The CG of your book load is about 6" off the wall, the total
(per stud) book load is about 130 lbs.

If the line of action to resist the shelf pulling away from the wall is
~3" from the top & the bottom edge of the shelf bears against the wall
you have a resisting "couple" of about ~36" minimum.

If my way of looking at it makes sense; we've got 6" x (130lbsof books
+ 25 lbs of shelf)

Or (torque yanking bookshelf off the wall) 930 in-lbs resisted by a
36" couple>>>>>

Need ~25lbs of safe allowable withdrawl per stud location. We also
need 155lbs of safe allowable shear resistance per stud location.

I'm was concerned about shear loading than withdrawl but that's just
my point of view.

I'm talking about burly #12 or #14 SMS not POS drywall screws. Should
be able to get a lot more than 25lbs withdrawl safely out of a #12
unless your studs are paper thin.

btw any idea stud gage? anything less than 20 & I'd get worried.

Anybody willing to verify / correct my assumptions & calcs? The are
just "seat of the pants" but they seem reasonable.

Chris, I guess we should also consider the "unanticipated" load, extra
125 lbs point load; painter using the shelf as a foot hold. I've done
that dsort of "extra" loading.

You could whip up a small frame out of plywood, sawn lumber or MDF & do
a quick experiment. Screw it the to wall with the bottom ~4" off the
ground & then stand on it.


Or you could install a SMS thru a piece of 3/4" ply, leave the head
proud & see if you can pry bar it out. Figure you mechanical
advantage on the pry bar (10 or 12 to 1?)

One good test is worth 100 expert opinions.

cheers
Bob

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Old 06-08-2007, 08:51 PM   #5
BobK207
 
Default Re: Best anchors for heavy cabinets on steel studs

Better yet, checkout

www.toolbase.org/docs/MainNav/
SteelFraming/4298_Hybrid_Steelguide_2.pdf -

page 6 of the pdf; page 24 of the "paper" document

looks like you'd have capacity to burn even if the struds are only
33ksi material

If you counter bore your plywood big enough & deep enough to accept the
driver socket & screw head; you could use self-drilling screws &
really scream through it.

Bob

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Old 06-08-2007, 08:55 PM   #6
Chris Solar
 
Default Re: Best anchors for heavy cabinets on steel studs

The largest section of shelving is 65" wide, 37" tall, and 9" deep. It has
three rows of books (183 linear inches of bookshelf), so almost 300 pounds
for a fully-loaded unit based on my measurements. It's hanging up near the
top of a 9' ceiling, so I don't think it will make a convenient step-stool
for painters...but then again someone reaching to get to that top shelf
could fall off their chair/ladder/pile of phone books and attempt to use a
shelf as a grab bar on the way down.

The mating surfaces of the French cleat will be about 3" below the top of
the unit, as you guessed.

I don't know what gauge the studs are; this is not for my house.

The wall cleat will span five studs, so there's 60lbs (shear) per stud, and
at least two fasteners per stud.

In addition to the French cleat along the top, I was going to fasten a 3"
strip of the same 3/4" plywood along the bottom, and the cases will be
screwed to these through the backs. The upper cleat is what's really meant
to take the load, though.

I suppose I could go with a hybrid approach: put a row of EZ-Toggles along
the top of the main cleat (where the pullout loads are greatest), and put
another row or two of fat sheet metal screws lower down to finish the job.

Thanks,

Chris.

"BobK207" <rkazanjy@gmail.com> wrote in message
news:1109474051.114975.62680@z14g2000cwz.googlegro ups.com...
> How tall are the shelves? How close to the top edge would the strip be
> mounted? How deep (~10")?
>
> So if your studs are 16" o/c that's 32lbs per shelf per stud.
>
> If you're talking about a 4-shelf unit (~40 to 48" high & about 10"
> deep). The CG of your book load is about 6" off the wall, the total
> (per stud) book load is about 130 lbs.
>
> If the line of action to resist the shelf pulling away from the wall is
> ~3" from the top & the bottom edge of the shelf bears against the wall
> you have a resisting "couple" of about ~36" minimum.
>
> If my way of looking at it makes sense; we've got 6" x (130lbsof books
> + 25 lbs of shelf)
>
> Or (torque yanking bookshelf off the wall) 930 in-lbs resisted by a
> 36" couple>>>>>
>
> Need ~25lbs of safe allowable withdrawl per stud location. We also
> need 155lbs of safe allowable shear resistance per stud location.
>
> I'm was concerned about shear loading than withdrawl but that's just
> my point of view.
>
> I'm talking about burly #12 or #14 SMS not POS drywall screws. Should
> be able to get a lot more than 25lbs withdrawl safely out of a #12
> unless your studs are paper thin.



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