Cupped Raised Panel Question

[Don_M]

I may be over thinking this a bit – but I am building several frame and panel cabinet doors. I have made slabs for the panels. They are approximately 12 x 24 x ¾” th. (made from two book-matched 6” wide pieces). After glue-up they slightly cupped about 1/32” in the middle of the slab. I am getting ready to shape them into the panels.
 
Question: which orientation would work best for the raised panel to reduce further “cupping”? Cupped side down (top picture) or cupped side up (bottom picture) - see sketch. Or does it even matter. My gut tells me that cupped side up (bottom picture) would resist further cupping because I would be eliminating material along the edges of the cupped material – just not sure.
Thoughts?

[MichaelMouse]

Have the prettiest side out.  The groove trapping each end of the panel will take the cup out for you when you tap it in.

[jteneyck]

I agree with MM.  If the frame won't pull the cup out than you should toss it and make another panel.  Happens.  Next time, though, you can reduce the potential for cupping by making sure your wood is at EMC with your shop before using it, or milling off equal amounts from both sides if it's not.  It's best not to mill it all at once either.  Rough mill it to maybe an eighth of an inch thicker than your final thickness and then let it sit on edge or end so that air can circulate all around it overnight, then re-joint/plane it to final thickness.   

John

[Routerman]

Panel cup probably from inaccurate jointing and/or no stickering.
Panel should be assembled on a flat frame that won't bend.
I'd cut the panels thinner, 9/16 - 5/8. A 1/32 on your 3/4 panel is not
an insult; not bad for a foot wide panel. Thinner panel will exert less
force on your frame. And I'd put the convex (wide) side out; it will see more
air than the inside of the panel, may flatten.
Bottomline: 1/32"/12" is correctionable x the frame alone.

[Steve N]

If they are just cab door inserts, there is nothing that says they must be 3/4" thick. In your pic that top piece would sit on the jointer just like that, with edges down, so it won't rock. Start taking small passes and when you are getting closer to flat (those pics are pretty severely cupped for my taste) then you can count on the frame to help keeping it flat. If they were cupped like that on wide stock, I would rip, joint a much smaller cup, and glue it back up.

[rwe2156]

1/32 across 12" is not enough to worry about.  After its assembled you will never see even a 1/8" cup.

Worry about the best face, not the direction of cup.

Use a hand plane to fine tune the bevel and it will fit fine.

[Steve N]

On your cupped pieces check your end grain, and see if it isn't oriented much like that in your pic, rainbows.


When you source stock, especially for uses when you want stability like door panels, sides of cases, tops. Try to source wood with an end grain that looks more like this. You will see a lot less movement, and cupping.

[jteneyck]

Steve, QS is the end grain at 90° to the faces, as in your middle photo.  The top and bottom photo, with the grain running at about 45° is known as rift sawn. 

With respect to raised panels, they are traditionally made with face grain, where the grain runs parallel with the face or 0°.  The frames are usually made with QS stock.  You are right that a QS or rift sawn panel will move less than one made with face grain, but frame and panel construction allows the use of the often more visually pleasing face grain panel to ride in a stable QS framed w/o problems. 

In the end, you can use any grain orientation you want for the panels if you mill the stock carefully and accommodate it's yearly expansion/contraction swings in the frame.  I prefer to only use stock that is fully acclimated to my shop before milling it, but I know others are successful by taking equal amounts off both faces, letting it rest overnight, etc.  

John

[MichaelMouse]

You read the original post?  If the panels are "book-matched", I assume that was done for visual effect.  With a book match, the annuals will run opposite on each side of the joint.  Most likely cause of cup is moisture differential.  So all your fine advice about quarter, flat/rift is not applicable.  The man wants to put the pieces to rest and equalize, once a couple weeks have passed, he can joint the faces if the problem is too great for his sensibility and put them into their frames, where any cup should be invisible, unless he's foolish enough to finish only one side.  That would give the panel the "washboard"  effect that the smile alternating with  frown hacks recommend.

[Don_M]

FWIW – IMO the pieces were properly acclimated (sat in shop for about a month), jointed and planed. I generally “rough” mill the stock – leaving it a bit oversized; wait a few days (even up to a week) – before milling to final dimensions. I checked each individual piece on the jointer bed before assembly and they were dead flat. I used a digital angle gauge to set up the jointer to 90 degrees and even reverse jointed the glued edge(s) to account for any slight variation in the jointer set-up. The material (Makore - which was actually closer to rift sawn than flat sawn) was assembled on a flat surface (a slab of granite) and that is why I was a bit surprised by the (slight) cupping of the overall panel (the pictures are exaggerated just for illustration purposes).  But I agree 1/32” of “cupping” is small – so I may be overthinking this a little.

Did not see a response to my basic question – but I did a little research on wood movement and came to the conclusion that the cup up (bottom illustration) is the way to go to minimize or perhaps relieve further cupping. My thought is that by removing material along the convex side (i.e., closer to the outer radial growth ring) would reduce some of the strain on the inner radial growth ring and reduce further cupping.