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Mdf rail coped to hardwood7/8
I do a lot of large wood vent hood enclosures that have a large (48x54) five peace cope and stick front. Many have a large bottom rail up to 12 tall to allow for a mantle/shelf detail and an arch below. Always hard maple with a mdf panel. Would an mdf rail coped into the maple styles work to avoid the movement of that large rail? Have lots of cracks in paint at that cope and stick joint. Is there a problem joining mdf to hardwood that Im not seeing?
The hardest thing is painting the joint. MDF and hardwood take the paint differently. I've noticed this when I did Classic Core with the 1/8" outer layer of MDF. When I joined it with a Maple face frame the difference between the Maple and the MDF stood out. 2 coats of primer and 2 coats of paint and I could still notice it.
When I was doing mantles I would split up the large rail and have the mantle cover the joint.
Leo is right. You'll see the joint, there's no sensible amount of paint (or wood glue in the joint) that will make it disappear. The hardwood and MDF just expand/contract at different rates and you're not going to defeat that.
That's not to say that it's a fail. The market you're in may consider seeing a line there OK. My market would not, but I have worked in places where the price point and expectations were both less than what I'm selling now.
The other problem we had when we tried running MDF into Solids was the issue of sanding at different rates. Even with hard block sanding the joint it was an issue.
Make the arch below the shelf a slab, no cope. Use the shelf to hide the seam.
Thanks for all the responses. I was afraid competing mdf into hardwood might have issues. My crack is always vertical along the cope and stick. We battle it on the doors (3 rails) and can minimize it by making sure we get total glue squeeze out at assembly but those larger 10-12 tall rails move so much
While not a perfect solution whenever we needed to make a 12" wide rail we would glue three 4" rips together to net the 12".
I will caution against allowing illogical statements making for shop policy. 3-4" sticks, randomly chosen, will not make expansion/contraction worse or better.
I sympathize with the attempt to find solutions, but they still must past the most rigorous test - reality. Hope is nice, but better used in other situations.
Mixing wood & mdf rails is a no go for all of the reasons mentioned.
If the glue joint is the problem, try fixing it. Use an epoxy glue. It allows for more slop and more flexural movement.
Put it on the end grain of the rails. Let it soak in for a moment or two. Then a bit more before assembly.
Using epoxy on exterior doors effectively stops most joint issues. Its occasionally worth the extra 1 minute of time for interior work as well.
It does help on end grain work. If you look under a microscope the endgrain is saturated and is technically now fiber reinforced epoxy. The bond is much stronger than a typical pva joint.
Completely irrelevant when edge gluing.
Keith, we found to let the doors remain in clamps for 24 hrs helps the joint lines.
Is it possible to just use MDF for both stiles and rails?
Sorry Dave, a little bit of mis-speaking and misinterpretation of the problem on my part. I agree that the method I was talking about would do little to nothing in terms of wood expansion and contraction. The issue we were trying to deal with was eliminating any cupping of the wide rail. When would make a rail like that all three pieces would be ripped from one wider board.