When building flat panel (solid wood) doors, must the panel be finished prior to assembly? These doors are cope and stick hard maple with 2 1/2" stiles and rails. Widest door is 24". Can't outsource, as customer is supplying birdseye boards to use for some of the panels.
From contributor W:
I'm going to venture a guess that you are concerned about the panel shrinking and showing an unfinished edge. If the wood has a higher moisture content than should be, and you can't wait for it to dry completely, then finishing the panel first would be a good idea. If already at a good MC for your location, it probably won't shrink any further. Since it is birdseye, they might be willing to let you dry the wood out some, which would be the right thing to do anyway.
The wood will shrink and expand seasonally. It will shrink and expand whether or not it is finished, since the finish will just slow the moisture exchange between the air and the wood, not stop it. (That's why 5 piece doors are built, to accommodate seasonal wood movement.) Maple actually expands and contracts quite a bit, seasonally.
It won't hurt to finish the panels before assembly, but it does slow the door-making process. I'm not sure if it would help anything. What are you trying to avoid with pre-finishing the panels?
I'm getting a bad feeling from somewhere in my memory when you mention solid birdseye panels. You know, when a customer says "can we do it this way?" and you get a bad feeling, but you don't know why? Until you start fabrication, then the reason comes back. I think if a customer asked me to build birdseye panels I would use the AWI premium style for building them, not solid wood. I kind of remember experiencing some pretty wild movement with birdseye. I could be wrong, though.
When I finish after assembly I use air to push the finish into the hard to reach areas. I've had good success using both methods. Either way, don't forget the space balls.
Contributor W has the correct idea, but your shop's conditions (EMC of the air) may be equal to the MC of the wood, so everything is happy, but the problem comes when the customer has drier conditions. Shrinkage will result. There is no finish that stops drying and shrinkage. Due to the difference in movement of the frame and the panel, it is not a good idea to glue the panel to the frame; rather use a floating panel and space balls, as indicated. Therefore, as the tenons (panel edges) will not be glued, I am not sure why you need to protect them when finishing.
I have built raised panel wet bars for exterior and painted them and just used this technique and not had a problem. I have made 48 wide panels raised over hearths and not had a problem. It all moves and some more than others. Period.