91' Hallmark Bed Sag Fix

[flysar]

I removed the 1/8" luan top piece of my bed area expecting to find severe dry rot causing the center of the bed to sag on my recently purchased 91' Hallmark Cuchara.

I was surprised to see no wood rot but the sagging center supports were only 1x2's over a span of 54" with 24" between each board.

I have a Kreg Jig system so I can easily glue & screw new supports like what is there but would expect them to eventually sag again.

- I could epoxy & screw some 3/4 x 1 x 1/8 aluminum angle along the 2 center boards reducing the chance of sag

or

- Put more center boards in, maybe 4?

or

- Install 2x2's in the center & add another 1x2 on the edge boards to match center boards height

What makes sense and will best minimize sag?

I'm 205 and would be the primary user with my wife joining me occasionally.

[steve68steve]

What you're trying to make is called a "torsion box". The skin must be rigidly attached to the frame tying it together as one structure.

Think of an "I" beam: the I shape (would be handy if this font had serifs on the I) is really about the two horizontal surfaces held together at a distance apart by the web. If you support both ends of a beam and add a load to the span, the beam tries to bend under the load. That means the top horizontal surface is in compression - it's trying to get shorter; and the bottom horizontal surface is in tension - it's being stretched. The further apart those two surfaces are, the stronger. The separation of the horizontal flanges influences strength more than their size - this is whey a 2x4 is stiffer on edge than laying flat.
The center of the web has no load at all on it - you'll sometimes even see I beams with large holes in the web to reduce material and therefor weight/ cost.

Ok, so for a TC cabover, you want the web as tall as possible, and you want the skin (plywood) glued/ screwed to the frame rigidly. Even foam insulation board in this scenario - if continuously attached to a skin on each side - adds significant structural strength. That's why airplanes, boats, etc. are often made of a tough, strong skin (carbon fiber) sandwiching some lightweight honeycomb material. It's an I beam in sheet form... like the floor of a TC cabover.

I worked the math out for a platform bed span I made years ago: Click for math.
I was frustrated by very seasoned pro woodworkers not really having any idea how to CALCULATE or ENGINEER the structure... they all just guessed and used their intuition, recommending a structure which would have been a LOT heavier and more expensive to make. From the date on that blog post, I can tell you that bed platform has been in service for 5 years now, no problems.

[Tarkin75]

If it helps... on my Pastime solid wall camper it had a "checkerboard" type support structure. Where you have two long 1x2's, my pastime had them running the front to back length just about every 8" or so. I didn't measure, so might be 6". Then it had smaller sections cut out and inserted/stapled between the full length front to back 1x2's.

Later
C

[flysar]

JoeChiOhki wrote:

flysar wrote:

JoeChiOhki wrote:
Tear it all out and start from scratch using a frame that uses a 2x3 every 12" on center from front to back, then add stiffeners glued and clamped between.

Using weights, glue and screw luwann to new floor assembly.

Lift new floor into place, set a good bead of glue along the perimeter, screw into place. Fill all gaps with tight fit foam board, lay down glue on frame members, install 3/4" plywood floor.

Should hold up solidly to future weight.

If still concerned, have metal shop fab tubular steel frame to replace wood.

I imagine it is possible to overbuild the cabover creating to much weight therefore causing other frame/structure issues down the road.

I don't think Hallmark built it this way to be cheap, maybe the previous owner stored heavy items in the center of the bed?

Thanks for the input.

No, it's a Hallmark, much like Palomino, their old stuff was built about as flimsy as it comes. There's not enough lateral integrity in that floor to support a large load (more than a hundred pounds) without sagging in the current structure. A cabover floor needs to be built at least as strong as the floor that you walk on and that right there is about as half-@ssed as they come.

Given that the cabover on a pop up has no full size sidewalls to give it much larger truss to bear the load, the short side walls are usually built to be able to withstand the load of is occupants by it's own.

If you're concerned about the weight, use 1/2" plywood instead of 3/4". Remember your floor just hangs from the side walls and it's those two little 2x3s that are all that's supporting you and your wife.

Nothing like learning the hard way... after the fact!

I just got off the phone with Hallmark and discovered that until 99' Hallmark's focus was not on campers and they were quickly thrown together with bare minimum construction, hence the bed construction... glad I only paid $400 for it.

So if you're looking for a used Hallmark Popup Andy recommended 99' or newer.

[JoeChiOhki]

flysar wrote:

JoeChiOhki wrote:
Tear it all out and start from scratch using a frame that uses a 2x3 every 12" on center from front to back, then add stiffeners glued and clamped between.

Using weights, glue and screw luwann to new floor assembly.

Lift new floor into place, set a good bead of glue along the perimeter, screw into place. Fill all gaps with tight fit foam board, lay down glue on frame members, install 3/4" plywood floor.

Should hold up solidly to future weight.

If still concerned, have metal shop fab tubular steel frame to replace wood.

I imagine it is possible to overbuild the cabover creating to much weight therefore causing other frame/structure issues down the road.

I don't think Hallmark built it this way to be cheap, maybe the previous owner stored heavy items in the center of the bed?

Thanks for the input.

No, it's a Hallmark, much like Palomino, their old stuff was built about as flimsy as it comes. There's not enough lateral integrity in that floor to support a large load (more than a hundred pounds) without sagging in the current structure. A cabover floor needs to be built at least as strong as the floor that you walk on and that right there is about as half-@ssed as they come.

Given that the cabover on a pop up has no full size sidewalls to give it much larger truss to bear the load, the short side walls are usually built to be able to withstand the load of is occupants by it's own.

If you're concerned about the weight, use 1/2" plywood instead of 3/4". Remember your floor just hangs from the side walls and it's those two little 2x3s that are all that's supporting you and your wife.

[recycler]

you could add 1x2's so they are on 12" in centers and glue down a layer of 1/4" plywood while supporting from the bottom till the glue sets...strongest stuff you can get would be best..

[popeyemth]

Let me add mine is a Shadow Cruiser pop top but I believe they are similar

[popeyemth]

Mine has the one by three behind the crank system, one by twos on edge as " joists " and the luan deck is framed and hinged to lift for storage between the joists.
If I'm understanding you I believe yours has been modified to make room for the foam. Insulation that I don't have.

[flysar]

popeyemth wrote:
Aren't you missing the plywood (luan) deck and frame in the pic?
Do you have the original innerspring mattress?

I removed the 1/8" luan deck and white foam core between the frame. What you see is the frame of 1x2's running front to back and there is a 1x3 laying left to right that the lift system is attached to & under the storage boxes in front.

I have what I believe is the original (fabric matches the dinette) cheap foam core mattress.

1x2's in edge make more sense than the way this is set up.

The only thing I can thing of is if the top/bottom luan pieces were still glued to the luan maybe it wouldn't flex?

[popeyemth]

Aren't you missing the plywood (luan) deck and frame in the pic?
Do you have the original innerspring mattress?
Can't say about yours but our plywood deck is framed and the 1X2 ribs are on edge not on their sides like the pic. I think it's a case of all the pieces working together to function
I can get a pick of mine tomorrow if it would help
Good Luck, Mike

[flysar]

JoeChiOhki wrote:
Tear it all out and start from scratch using a frame that uses a 2x3 every 12" on center from front to back, then add stiffeners glued and clamped between.

Using weights, glue and screw luwann to new floor assembly.

Lift new floor into place, set a good bead of glue along the perimeter, screw into place. Fill all gaps with tight fit foam board, lay down glue on frame members, install 3/4" plywood floor.

Should hold up solidly to future weight.

If still concerned, have metal shop fab tubular steel frame to replace wood.

I imagine it is possible to overbuild the cabover creating to much weight therefore causing other frame/structure issues down the road.

I don't think Hallmark built it this way to be cheap, maybe the previous owner stored heavy items in the center of the bed?

Thanks for the input.

[JoeChiOhki]

Tear it all out and start from scratch using a frame that uses a 2x3 every 12" on center from front to back, then add stiffeners glued and clamped between.

Using weights, glue and screw luwann to new floor assembly.

Lift new floor into place, set a good bead of glue along the perimeter, screw into place. Fill all gaps with tight fit foam board, lay down glue on frame members, install 3/4" plywood floor.

Should hold up solidly to future weight.

If still concerned, have metal shop fab tubular steel frame to replace wood.