Joining Poplar and Red Oak - wood movement

Hi,
I am building a pass through that will have a narrower piece of poplar below a wider piece of red oak. I want to join the pieces together so they are solid, but am concerned about differential wood movement causing problems.
I'm new to woodworking, and this is the first time I have used multiple species that will be joined together this way, so any comments would be appreciated.
My initial thought was to put in a couple of screws in elliptical countersunk holes so that the wood can move independently, but I don't know if this is really needed.
Thanks for any help, Jeff
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If the grains of both pieces are in the same direction and the length is <10 feet glue them together. To be a truly strong joint, consider making a grove. If you are serious about woodworking use metal fasteners as a last resort.
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"Jeff" wrote in message

And correctly so.

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch12.pdf
Table 12-5

You more than likely do need to do something. It is hard to tell what without a better description.
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More information:
The pass through is 4"x4' and currently has a 40 year old piece of countertop on it. We wanted to keep the thickness of the countertop (~2") and wanted a distinctive feature, so I had thought about a stepped or scalloped edge. So, we bought a 1"x10"x8' piece of poplar and a 1"x12"x4' piece of red oak, both plainsawn.
The kitchen side of the pass through will be straight edges about 1" into the kitchen. Once through the wall, the poplar will be curved with a routed edge, maybe a cove. The red oak (the top) will have the corners rounded but otherwise be full. Since someone could pull up on the oak without pulling up on the poplar, I need to make sure they are secured.
Thanks for the info. I am going to look at the pdf now.
Jeff
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I built a butternut table (http://www.frontiernet.net/~toller/table.doc ) that had oak for all the internals for strength. The two were glued up directly. I was warned by more experienced woodworkers that the two would blow apart. It is now 3 years old, and nothing has happened. I think that with modern climate, and modern glues, control wood movement just isn't the issue it used to be.
Frankly though, I am not sure it ever was. I mean, the joints are only a half inch wide; how much differential expansion can occur over a half inch? Interestingly, I made a bowl of wenge and ebony. I thought the ebony was dry, but it wasn't, so over a couple weeks the ebony shrank noticably; but the glue (polyurethane) crept rather than breaking. I sanded the top down to make the two surfaces even and no one would notice my screw up. So, even if there was major differential expansion, the glue might be able to accomodate it.
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