plywood panels and glue

[vernonls]

I frequently build projects which use plywood cut to fit in dado slots so that the plywood is surrounded by rails on the top and bottom and stiles on the sides. In the past I have always been careful not to glue the plywood into the slots, but I am wondering if it is really necessary to not use glue to secure the plywood in the slots.  Typically it would be 1/4 inch plywood inserted into a 1/4 slot and might be anywhere from a 10x10 panel to an 18x20 inch panel.

I know that wood moves and if it was a glued up panel I was inserting I believe my caution would be necessary, but I am wondering if that is really the case since the plywood is not subject to much expansion/contraction due to weather/humidity/temperature.

What do other woodworkers think? 

Vern

[Phil Thien]

The question is whether the plywood, if glued, will prevent the solid-wood rails and stiles form expansion/contraction.

For example, in the case of a typical cabinet door, the expansion of the solid wood, would be across the width of the rails/stiles, so gluing the plywood in place will not prevent expansion/contraction and will only make the assembly stronger.

[ianab]

Agree with Phil. 


The movement of plywood should be negligible, as should the Length-ways movement in the frame components. The individual pieces  of wood in the frame may get very slightly wider (or narrower) but the inside of the frame where the ply is glued shouldn't be moving, and because those boards are only a few of inches wide, it's not enough to affect anything much. 

Now with a solid wood panel, it's a very different scenario.

[fredhargis]

One more vote for glue the ply panels in. That goes for drawer bottoms as well as frame and panel doors.

[Cooler]

I glue about 3" of length in the middle of the rail or stile.  That allows expansion/contraction and still keeps everything in place.  The expansion and contraction over the 3" length will not be of consequence.

[Hank Knight]

I always glue in plywood drawer bottoms. The result is a bombproof drawer box.

[Woodshop]

I frequently build projects which use plywood cut to fit in dado slots so that the plywood is surrounded by rails on the top and bottom and stiles on the sides. In the past I have always been careful not to glue the plywood into the slots, but I am wondering if it is really necessary to not use glue to secure the plywood in the slots.  Typically it would be 1/4 inch plywood inserted into a 1/4 slot and might be anywhere from a 10x10 panel to an 18x20 inch panel.

I know that wood moves and if it was a glued up panel I was inserting I believe my caution would be necessary, but I am wondering if that is really the case since the plywood is not subject to much expansion/contraction due to weather/humidity/temperature.

What do other woodworkers think? 

Vern

fully gluing the panel in will cause the door to warp.  I learned my lesson over 30 years ago in two kitchens . I only glue a dab top and bottom in the center to secure the panel from sliding around.
That is my advice . why take the chance. Drawer bottoms are a different story because the board is not lying flat like a door, don't confuse the two.

[Alan S]

fully gluing the panel in will cause the door to warp.  I learned my lesson over 30 years ago in two kitchens . I only glue a dab top and bottom in the center to secure the panel from sliding around.
That is my advice . why take the chance. Drawer bottoms are a different story because the board is not lying flat like a door, don't confuse the two.

I don't understand this answer.  Could you explain why gluing in a plywood panel would encourage warping? 

I agree that the structure of a drawer is better oriented to resist warping of the bottom than is the frame of a door, which I think you are saying in your last sentence.  But I don't see how leaving out glue in a plywood door panel would help resist warping.  Stock selection is important for that.

[John Mihich]

Been doing it for years - never had a problem.

[Woodshop]

I don't understand this answer.  Could you explain why gluing in a plywood panel would encourage warping? 

I agree that the structure of a drawer is better oriented to resist warping of the bottom than is the frame of a door, which I think you are saying in your last sentence.  But I don't see how leaving out glue in a plywood door panel would help resist warping.  Stock selection is important for that.

I don't understand how it happens. but I can tell you 15 of the 46 on one kitchen job the doors warped.   I used a steam iron to break the panel lose and get them straight. that was oak with 1/4" ply panels. on the next flat panel job like 1 year later,  I forgot and glued maple flat panels. doors 6 of the 35 warped.
I say maybe it was the climate in the new homes.  possibly winter and freshly plastered, don't know. I remember many times installing cabinets after new homes have been freshly plastered, seeing the windows dripping with water. that's usually when the customer wants the cabinets so they can move in. The Maple job that wasn't the case. I only know for sure it happens, and it's not worth it to me to take the chance. It isn't necessary to do in the first place. if you are getting away with it good for you, I learned my lesson.  I have been doing kitchens and baths for over 35 years and at 62 I'm getting pickier about what I want to build now days.
BTW I always glue my drawers all the way around.
Don