LumberJocks

Z Bar/French Cleat conundrum

  • Advertise with us

« back to Designing Woodworking Projects forum

Forum topic by newwoodbutcher posted 11-12-2018 11:03 PM 448 views 0 times favorited 12 replies Add to Favorites Watch
View newwoodbutcher's profile

newwoodbutcher

777 posts in 3052 days


11-12-2018 11:03 PM

I’m not a professional woodworker and this is my first ever “commission”. I’m building an unusual (for me) project for a very good friend, I’m about four months into the project and almost ready to glue up all the parts, and now at the 11th hour, I have a big concern. The project is a headboard and two nightstands hanging from the wall, no legs, hanging from a French Cleat. For ease of delivery and installation I’m making it in four modules, two pieces for the head board and two nightstands. The whole thing put together is 111” long and 30” tall. All together it will weigh about 260 pounds. The headboards are 12’ Deep with a flip up lid to store pillows out of sight. It’s a Modern Monolithic design. The night stand table (top) surface is 18” wide and 24” deep. Here’s a picture of the plan. Sorry if it’s hard to read. The project is made of Baltic Birch Plywood with Mahogany veneer covering and Solid Mahogany frame and panel Trim. It’s been a challenge but I’m almost there. Here’s two pictures of one of the almost completed Nightstands. Before I started I made a prototype of ¾” construction plywood hanging on a plywood French cleat to test for strength. I was able to stand and slightly bounce up and down and it was rock solid. As you can see in the attached photograph I utilized through tenon and tusk on the table top surface to strengthen that connection. The plan is to laminate another layer (Thickness TBD) on the ½” thick Baltic Birch back of the tall board for added strength. The whole project weighs about 260 pounds, I was planning to hang it all from a single Z bar or French cleat. I ordered a Z Bar that is rated for 300 pounds. It’s a bit concerning as they rate a little 16” Z bar for 300 pounds and the same sized Z bar 48” long is also rated for 300 pounds. I’m not an engineer but I don’t believe both of those ratings can be true. It seems to me a longer Z Bar with more screws into more studs would be stronger. But I digress. I received the Z bar yesterday and it seems way too flimsy for this job. Top half of the Z bar (where it overlaps is 3/32” thick aluminum and bottom half is 1/8”thick. This doesn’t seem to be strong enough to hold up the weight of the parts as well as the torque and strains of human interaction. So, I’m looking at these flimsy Z Bar parts and wondering if I need to change the design to a 4-6 inch wide, ½ inch thick wooden French Cleat. Or perhaps go to a local metal shop and have a custom Iron Z bar made. Any opinions will be appreciated.

-- Ken


12 replies so far

View lumbering_on's profile

lumbering_on

574 posts in 692 days


#1 posted 11-12-2018 11:21 PM

Do you have a link to the Z bar? That would be very helpful.

It is possible that the rating is the same as it wold be based on the type of material and size. However, it’s impossible to tell without seeing the specs.

View newwoodbutcher's profile

newwoodbutcher

777 posts in 3052 days


#2 posted 11-13-2018 04:31 AM

Lumbering, the site is
http://www.zbarhanger.com/
The product is: Large Zbar Hanger ,5    CZ12         1  41.50  sizes: = 72inch pair

-- Ken

View lumbering_on's profile

lumbering_on

574 posts in 692 days


#3 posted 11-13-2018 05:01 AM

Maybe, I’m just looking at the wrong product, but from what you describe in your original post the 16” bar is only rated at 30lbs

http://www.zbarhanger.com/16lazbhahaha.html

However, the 48” bar is rated at 300lbs, as you describe.
http://www.zbarhanger.com/48lazbhahaha.html

This seems to make perfect sense, and you’d be surprised at how much some things can support. I have about 150lbs of lumber resting on three cantilever shelves with only 3 #8 screws per shelf. This may not seem like a lot, but each #8 screw could support the weight of the wood by itself.

However, if you’re worried, you could double up the cleats, but I’d contact the company first. If it’s anything like most things that support weight on a wall, it’s likely that the actual weight it can support is 2-3 times higher. Going back to the #8 screw, I calculated it’s ‘safe’ support at ~95lbs. However, this is at 40% of it’s max shear weight, and I doubt that this company would just give the weight the bar would hold before tearing off the wall.

View GrantA's profile (online now)

GrantA

736 posts in 1610 days


#4 posted 11-13-2018 02:13 PM

First keep in mind the zbar weight rating isn’t dependent on length, the thickness and height determine its strength. Looking at what you’ve got there I’d run 2 sets of cleats though, one at the top and another midway or so, as close to the bottom as you can.
In case you weren’t already planning on it you’ll probably need to scribe to the wall and it looks like you have enough meat around the edges to do so

View ChefHDAN's profile

ChefHDAN

1193 posts in 3052 days


#5 posted 11-13-2018 02:27 PM

I get that it’s supposed to float, but most of the underside will never be seen. If it were me, I would bring along some lengths of 6” 3/4 ply painted to the wall color. Hang the entire unit on the Z-bar, and then measure supports from the bottom edge of the unit to the floor and then install them on studs to transfer much of the load to the floor.

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

View clin's profile

clin

956 posts in 1198 days


#6 posted 11-13-2018 10:36 PM

I don’t see several hundred pounds across the Z bar as an issue. It’s going to be more or less spread evenly across the bar. I too would be more comfortable with steel than aluminum for these.

This design and discussion seems very familiar to me. OP, did you start a thread don this a while back? Regardless, I know my concern in that other thread, and for this, is the “floating” nightstands. But if I understand what I’m seeing in the photos, the nightstand has a back extending up about 2 feet.

I agree with the idea of strengthening that back. It needs to be an integral part of the nightstand and resist the loads on the nightstand trying to pry the nightstand from the wall. I would run ribs from top to bottom rather than double up the sheet material. I would make these full depth (same as the frame). Glue and screw from the back side.

As this is, it will hang from a cleat near the top. But the weight and load on the nightstand will be pulling at this back, at your tenon location, as you obviously know. This will be trying to pull the back out and I think that back may start bowing. The added ribs would help resist this. 2 or 3 full depth ribs would add a lot more stiffness than doubling with a layer of 1/2” ply.

You could add another cleat near the tenons to help hold the back to the wall and resist the force trying to bow it. If it were me, I’d screw the thing to the wall with screws inside the night stand. located as high as possible. This would pull the night stand tight to the wall.

Your total weight really isn’t much of an issue. In many ways, what you have is just a bank of wall cabinets. And it’s going to hold pillows not heavy plates. The night stands are the issue becasue they stick out 2 feet and will want to sag under their own weight and of course, someone will put their weight on the front edge of these someday for some reason.

I like what you have and I think in the end it’s going to work out well.

-- Clin

View CWWoodworking's profile

CWWoodworking

184 posts in 381 days


#7 posted 11-14-2018 02:10 AM

The Z bar weight limit will depend on if you hit studs or not. A 16” piece with pre drilled holes will likely miss all studs.

If you want to use them, ignore the predrilled holes, and drill where the studs are and hit everyone. Buy the longer lengths and run them the full length. if you do that, weight will never be an issue.

Kind of a waste of money though, as you can acomplish an even stronger system with a hardwood french cleat.

And by the way, “torque and strains of human interaction” is an awesome quote and will forever be saved in my repertoire. :)

View newwoodbutcher's profile

newwoodbutcher

777 posts in 3052 days


#8 posted 11-15-2018 11:15 PM

Lumbering,
Thank you. I must have seen the specs on a different site. The Z bar I received seems pretty flimsy, It is however rated for 300 pounds. If I use two Z Bars each holding up 1/2 of the 260 pounds (130 Each, it would seem strong enough. Still, I’m one of those people who always over builds. Perhaps it’s not necessary. Thank you for your input.

-- Ken

View newwoodbutcher's profile

newwoodbutcher

777 posts in 3052 days


#9 posted 11-15-2018 11:20 PM

Grany A, Thank you for your input. I considered using two rows but I am not confident about getting them installed exactly where the can share the load equally. Also there may be some scribing but the owner said the builders used a laser to line the the studs when building the wall. I checked the wall with a straight edge and surprisingly it’s pretty darn flat.

-- Ken

View newwoodbutcher's profile

newwoodbutcher

777 posts in 3052 days


#10 posted 11-15-2018 11:22 PM

Chef, Good idea. I can do that, and will under the headboard but it would show under the nightstands

-- Ken

View newwoodbutcher's profile

newwoodbutcher

777 posts in 3052 days


#11 posted 11-15-2018 11:29 PM

Clin, The “backer boards” on the nightstands are 29” tall Made of 1/2” Baltic Birch. My thinking on reinforcing it with another layer of BB is to make it thicker (more layers). I like your idea about using ribs though. Perhaps I will do ribs glued to the two sides of the frame and plywood between them. You have given me great ideas, and more to think about. Thank you

-- Ken

View newwoodbutcher's profile

newwoodbutcher

777 posts in 3052 days


#12 posted 11-15-2018 11:31 PM

Cw, I have a feeling you are right about hardwood cleats. instead.

-- Ken

Have your say...

You must be signed in to reply.

DISCLAIMER: Any posts on LJ are posted by individuals acting in their own right and do not necessarily reflect the views of LJ. LJ will not be held liable for the actions of any user.

Latest Projects | Latest Blog Entries | Latest Forum Topics

HomeRefurbers.com