Joining plywood to 40mm MDF "Worktop"

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SimonStevensCanes

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I'm building a desk for the home office and have an off cut of 40mm MDF that we used as a worktop for another project. Unfortunately it's not quite as deep as required, but as it will be built-in this gives me an opportunity to add a "cable trough" along the back edge. I have made this from plywood (a simple U shaped profile) and now face the task of affixing one vertical face to the endgrain of the MDF.

I have a large span that will have minimal support (i.e. not a leg) so I would like to make this joint as still as possible for stiffness. Whilst I would typically trust wood glue and minimal mechanical fastenings, I suspect that it will get absorbed into the MDF endgrain too quickly to be effective, is this correct?

I have had unpleasant experiences with using screws with MDF in the past and had hoped that deep pocket holes in the worktop would be a good solution, but test pieces faced the same splitting that is common with fixings and MDF.

A supporting piece could be easily secured to the plywood trough to create a "shelf" to support the MDF and allow fixing into the face would do the job, but unfortunately I don't have the room to do this along the full length.

If the word picture I'm attempting to paint above is clear as mud, please let me know and I'll try to cook up some photos.

Any suggestions, most welcome.
 
For all intents and purposes MDF has no grain and being the cable trough is at the back, not likely to see much stress. I wouldn’t hesitate to just glue the plywood to the MDF. If you are worried about glue starvation, coat the MDF, then the plywood and then add a little more to the MDF just before clamping.

Pete
 
Yes as Pete says with the glue, another thing you can do with MDF particularly as yours is so thick, is to drill a hole partway through from the bottom and glue a piece of 1” dowel in, you can then screw in to the side of the dowel.
The last time I used this method I was turning a mirrored front wardrobe door (near enough 8 x 4 ) into a pocket door. Now let me see if I can find a picture of it. Ian edit The whole weight of the door and the mirror was hanging from eight of these dowels, planed flush after glueing.
9820120D-7BDA-4DEE-A888-40AC3F462402.jpeg
 
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Would using equally spaced hidden dowels,just as in a biscuit jointer, help? Then you don't see a screw or anything on the outside and it might look neat?
 
Once installed I assume the only way to see the join between MDF and plywood will be with a mirror if the tray is at the back of the desk.

Only you will know the compromise you have made to get it fixed securely!
 

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