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Split headboard

3/27/15       
Russ Member

I recently built this solid cherry bed. After delivery (bout 2 weeks) the client called said the headboard had split in the upper right corner. The picture primarily shows the footboard, but the headboard is built the same way just taller. See areas indicated. I cant figure out why the wood would split like it did-even if expanding it doesn't explain why it split in this location. Any insight would be great. thanks.


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3/27/15       #3: Split headboard ...
rich c.

What's the joinery to the leg? Hopefully not glued mortise and tenons top and bottom. I'm guessing that headboard is solid wood, grain running opposite of the leg. Solid panel shrinks in the winter, leg does not shrink in length, headboard cracks. Woodworking 101 on what not to do with solid wood. Crack looks to start at the tenon? Either that or you did not allow enough slop in the mortise for the wood to shrink. That's a lot of width in that panel, probably shrinks 1/4 to 3/8 from season to season. Looks like to get to make another one with allowance for wood movement this time.

3/28/15       #4: Split headboard ...
Russ Member

Mortise and tenon as you surmised, but I did leave some slop at the top and bottom edge of the tenon cheeks, drove a single peg through the leg and center of the tenon (drawbored) on the back side (not shown) to keep in place. We're in SF bay area so not too much variation in humidity...perhaps they had the heater turned up. Either way its gonna take some redoing. Any suggestions on joinery at the leg? thanks.

3/28/15       #5: Split headboard ...
Gene Wengert-WoodDoc

Wood shrinks and cracks like this for only one reason...it has lost moisture. Do you know the humidity in your shop and in the bedroom, as well as the actual moisture content when you made the piece?

3/28/15       #6: Split headboard ...
rich c.

Did you draw bore top and bottom? Glue top and bottom? One of those mortise and tenon joints has to be able to slide. That means no glue in one of them. You can pin the dry joint, BUT, you must elongate the hole in the tenon. Dry fit, transfer the location of the pin hole to the tenon, take it back apart, and make that hole in the tenon with a router. It has to be at least 3/4" wider in the vertical direction so that wood can slide back and forth when it changes. I would have made that panel float, and had a frame around it. Then you can glue up the m&t solid into the legs and the panel has room to expand and contract in the grooves of the rails.

3/28/15       #7: Split headboard ...
David R Sochar Member

I see the panel as a mock frame and panel, but one piece of wood, and agree with the others that this is shrinkage.

Had you made the piece as a a true frame and panel, floating a solid wood panel within a frame that is securely fastened to the legs, then there would be no problem .

3/28/15       #8: Split headboard ...
Gene Wengert-WoodDoc

If you float the panel, but finish the panel in place, it is possible that the panel will shrink, pull away from the frame a little bit and some unfinished wood will be exposed (a white streak). So, oftentimes it is best if the panel is finished before finally assembly.

3/29/15       #9: Split headboard ...
mark

Just an additional note to point out that this sentiment:
"We're in SF bay area so not too much variation in humidity..."
is completely absurd.
If there were no variation in RH, then it would be either raining all of the time or never raining at all. Likely, it would have to always remain exactly the same temperature as well.
Making any piece of furniture out of wood which necessitates a fixed humidity level will result in failure.

3/30/15       #10: Split headboard ...
markbattles Member

Website: http://v-dubfurniture.com

I'm guessing that headboard is solid wood, grain running opposite of the leg. Solid panel shrinks in the winter, leg does not shrink in length, headboard cracks. Woodworking 101 on what not to do with solid wood.

3/30/15       #11: Split headboard ...
Gene Wengert-WoodDoc

The monthly change in OUTSIDE average humidity for San Francisco is very small, with an average of about 14% EMC at the airport, with a monthly average high of 15.1% and low of 13.6% EMC. This is not much change, but many locations in the U.S. change even less. However, right now it is 51 F at the airport, so many folks would have the heat on in the bedroom. Heating damp air by 20 F will create about 7% EMC INSIDE the home. A shop that does not develop such warm temperatures and that also has the heat turned off at night and on weekends in the cooler time of year will likely average around 10% EMC, so the wood will be 10% MC. (Lumber stored outdoors, even if kiln dried to a low MC, will be trying to get to 14% MC.). In a bedroom with the windows open in the warmer season, the air coming in will be around 14% EMC, so the furniture will be moving toward that high MC.

The bottom line is that although the OUTSIDE humidity is fairly constant in SF, as it is in many places, the interior environment does indeed vary, plus the shop may not be as dry as in a home. MC changes in wood furniture can be expected and must be accommodated in the design and in manufacturing.

To minimize moisture changes, lumber should be dried to 7.0% MC or a bit drier, stored at the same low value, and the shop should maintain the same low values at all times. In practice, a little too dry is many times better than a little too wet. Finally, to CYA, a shop should use a MC meter to check (and then record) the MC of lumber riot, during and after manufacturing. Lumber that is too wet should not be processed.

A rule of thumb, but see my earlier posting about wood shrinkage for details, a 1% MC change results in about 1/4% size change. In this case, a 24" wide panel that changes 4% MC will try and change its width by 1/4" and if restrained from shrinking will try and make a 1/4" wide crack.

3/30/15       #12: Split headboard ...
snugthejoiner

The area of the split looks like very short grain to me, and bear in mind that this is a bed. As a furniture design book I read early in my career delicately phrased it: "Beginning designers should bear in mind that beds are subject to active as well as static loads."

Not strong enough and it broke during use.

3/30/15       #13: Split headboard ...
Gene Wengert-WoodDoc

Indeed, parts of a bed or other furniture can be under high stress. Such stress can crack the wood, but an open or wide crack indicates shrinkage.

3/30/15       #14: Split headboard ...
Glen

We are in Arizona and have done wood samples many times to measure expansion and contraction. Even in a low humidity area it will move up to 3/8" over time across the grain. We use veneered mdf panels with solid trim pieces for headboards and solid posts and never had a problem.

3/30/15       #15: Split headboard ...
B.H. Davis Member

Glued or not the bottom tenon is significantly wider than the top tenon. Combine this with what appears to be 24" to 30" of width and you are looking at a significant amount of movement being applied to the smaller top tenon.

To be honest I'm surprised it split as little as it did. I would think that other than a quarter sawn, known for stability species, over that width you are going to see enough movement to result in failure unless the top tenon is significantly oversized.

BH Davis

3/31/15       #16: Split headboard ...
Russ

Thanks to those who provided the constructive critique and good advice, its really appreciated. I had a chance to repair the damage and as suspected, some of the glue in the drawbore worked its way into the mortise on the right side where the crack occurred (left side looked good, but redid anyway) and the rest is history as thoroughly explained by Gene. I did check the MC at the home and on other cherry stock at my shop and it was between 6 and 8%. I estimate EMC is about 11% +/- 0.5 between shop and home (per table at http://www.csgnetwork.com/emctablecalc.html) but I suspect the home heater didnt help and perhaps weakness in the grain. The customer asked for solid cherry, but I like Glen's approach-something to keep in mind. I ended up remaking the top mortise and included an elongated bore and was careful to not get any glue in the mortise or on the tenon, its pretty solid and movement shouldnt be an issue-I'll hang on to the piece a bit to see if I can record any movement.


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