Wood Movement - Cabinet Door - Need Advice

[Ken Frohnert]

Okay. I made my first cabinet door. Nothing fancy but it coming out okay so far. I used 3/4" by 2.5 inch white pine for the frame. There is a 3/4" by 2.5" brace across the center. I used two 1/4" dowels at each joint and yellow glue. The door is for a jewelry cabinet and it is 20" wide and 37.5" tall. I plan to route a 1/2" dado in the backside of the 2.5" frame and put in a 16x16 plywood panel in the top and bottom.

Here is my question - can I glue the 1/4" birch plywood in place. Since plywood is pretty stable or do I have to float it because of the white pine frame?

Thanks.

[Bill McNiel]

Yes, you can glue the plywood in place, the movement of 2 1/2" styles and rails is minimal.

[Adam Herman]

i would float it.

[Lee Schierer]

Your frame will not get longer or shorter along the length of the pieces. The pieces may change width slightly which shouldn't cause any issues.

Here is an interesting article on wood movement (http://workshopcompanion.com/KnowHow/Design/Nature_of_Wood/2_Wood_Movement/2_Wood_Movement.htm). You can calculate the amount of change your wood might have using this calculator (https://www.popularwoodworking.com/tricks/how-to-calculate-wood-shrinkage-and-expansion).

If you purchased your Pine from a construction wood supplier, it may not be fully dry as construction grade lumber is not dried to the same level as cabinet grade lumber.

Be sure to apply finish to all sides of your finished doors to reduce the moisture changes and to insure they even out to some degree.

[John TenEyck]

I almost always glue in plywood and MDF panels, whether in a rabbet or dado. Never had a failure in over 30 years.

John

[J.R. Rutter]

Very dependent on moisture content of the frame wood. It can definitely shrink along the grain, normally 1/3 up to 1/2 as much as cross grain. It is rare, but I have seen doors crack at the cope because the ply panel held the stiles in place while the rails got shorter. On floating panel doors, I have seen the entire door get narrower from highish mc stock drying out indoors with very cold winter weather. I agree that it is not common though, because most of the time there are not large enough sustained humidity swings to notice it. Something to be aware of but not obsess over...

Here is another helpful calculator: http://www.woodbin.com/calcs/shrinkulator/

[John TenEyck]

JR, your comment that wood shrinks along the grain seems contradictory to what Hoadley says. He says on page 117 that "total shrinkage along the grain is normally only about 0.1%..... and is normally considered negligible". I typically work with wood with a MC between 6 and 9% and live in an area where the indoor RH ranges from maybe 30 to 75%. I've seen plenty of door failures, but never one in a door I made with a glued in plywood/MDF panel. What conditions caused the problems you described?

John

[Ken Frohnert]

Thanks guys. I am going to try glue based on the general opinion here.

[Bill Adamsen]

Unless I'm doing a glass door, I typically cut a groove (dado) in stiles and rails for the panel not a rabbet after the assembly. Typically it is part of the stick and cope operation. Assumption is that with a wood panel, the panel is installed at the time of assembly. I undersize panels since assembling a door (or drawer) and finding you can't close up the joints because of 1/100th of an inch is frustrating. But still, you have the option of gluing or floating and I think either would work in your situation with the rabbet as well. I've seen many posts here of folks cutting the rabbet after assembly and using mold to fix the panel in place, and obviously that works too.

[J.R. Rutter]

JR, your comment that wood shrinks along the grain seems contradictory to what Hoadley says. He says on page 117 that "total shrinkage along the grain is normally only about 0.1%..... and is normally considered negligible". I typically work with wood with a MC between 6 and 9% and live in an area where the indoor RH ranges from maybe 30 to 75%. I've seen plenty of door failures, but never one in a door I made with a glued in plywood/MDF panel. What conditions caused the problems you described?

John

Ah man, I cited numbers for radial/tangental, sorry.

The batch of doors that I saw shrink was the result of sitting in the customer's shop during a couple weeks of sub zero weather. Being in the northwest, that meant an unusually big swing in RH. Thinking about it more, it could have just been the stiles losing width, and cracked door being caused by the stub tenons in the copes bottoming out as the sides of the groove got shallower.

[John TenEyck]

Ah man, I cited numbers for radial/tangental, sorry.

The batch of doors that I saw shrink was the result of sitting in the customer's shop during a couple weeks of sub zero weather. Being in the northwest, that meant an unusually big swing in RH. Thinking about it more, it could have just been the stiles losing width, and cracked door being caused by the stub tenons in the copes bottoming out as the sides of the groove got shallower.

Thanks JR. That seems more likely.

John