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I am making a frame for a heavy antique mirror that is 54" by 16" by 1/4" thick. Currently, I have glued up the frame. It consists of four lap jointed 2x4's. Mirror Frame

After the glue had dried, the frame did not sit flat on the bench. When I held one corner down, the adjacent corner rose 5/8" off the bench. This indicated the frame was not square, so I investigated further with winding sticks. winding sticks

The frame is indeed out of square. It is twisted. twisted frame The next step in the in the build process is to use a router to cut a 1/4" rabbet that will accept the mirror. This rabbet will be cut with an upcut bit spun by a plunge router with an edge guide. router Before I proceed with cutting the rabbet, should I fix the twist in the frame? I have identified several options, but as I have never dealt a work piece that is this far out of square, I am not sure what to do.

My options:

  1. Do nothing, force the mirror to flex to adapt to the twisted frame.
  2. Use a router and jointing plane to remove material until the winding stick are parallel.
  3. Cut the rabbet deeper in the corners that are twisted up to accommodate the mirror.

What is the best option, is there an option that I have overlooked?

Edit:

I decided to proceed with this twisted work-piece. The next step was to cut a rabbet for the mirror to sit in. After cutting this rabbet, the frame was noticeably less twisted. Lots of material was removed, apparently some internal stresses in the wood were twisting the frame:

rabbet in frame

After cutting the rabbet, I gave the mirror a test fit. It looked pretty good. The mirror weights around 40 lbs, and after test fitting the mirror, I decided that the frame needed a brace. When gluing the brace, I warped the frame a little past level:

brace on frame

Checking again with the winding sticks, the frame looks like it's nearly perfect: level winding sticks

In retrospect, I definitely recommend trying to salvage a twisted glue up.

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    It's not the best way to go (I think remaking is the right call here if this twist remains stable after further drying) but if you route a standard rebate into a twisted frame but want the panel not to be flexed you can simply use small packing pieces as needed. These can be slivers of wood or cardboard, in either case they're hidden from view in the finished mirror. You will have a larger gap in certain places along the reveal but perhaps not that obvious. You can always try it, put the frame upright to see how it looks and if not acceptable then you know you have to go a different route. – Graphus Oct 14 '18 at 15:24
  • @Graphus, I think I'll give this a try. Cutting the rabbit a little deeper and using shims, may work pretty well. – Stephen Meschke Oct 14 '18 at 15:29
  • Yep, nothing to lose really other than the time trying it. Even if it doesn't work it teaches you something. BTW one other thing I realised I was seeing just now, are there four screws per corner in addition to glue? Corner overlap joints like this can be fine glue-only, but if you want to reinforce one dowel or screw per corner is fine. There's a chance the large number of screws could actually have contributed to the problem (especially if there are no clearance holes in the uppermost piece). So one other thing you might try is withdrawing all the screws, see if the frame relaxes somewhat. – Graphus Oct 14 '18 at 15:41
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A flexed mirror, even if it doesn't break, will distort the image one sees in the mirror, generally in an way that is not pleasing.

Given the size of the twist, I'd say the best course is to salvage what you can and start over. Otherwise it's good money (time) after bad.

The wood appears to be construction-grade, you might consider upgrading or otherwise being very selective in the pieces you choose. I see at least one knot; that's a no-no for stability. What you're looking for is straight grain and the absence of reaction wood. That's the bits where the grain goes curvy around a knot or other discontinuity in the tree, like maybe a fork or whatever.

If you can't find full-sized pieces with those characteristics, consider gluing up from narrower sticks. In my Home Depot, the 2x2s tend to have tighter, straighter grain than the 2x4s, possibly because they would go all wonky with a big knot in the middle.

Once you have the blanks, make sure they are jointed dead flat and brought to a consistent thickness such that front and back are perfectly parallel. After milling them like this, leave in an environment similar to their ultimate home for a week or so and make sure they don't move as they acclimate moisture-wise. If the pieces aren't dead flat before joining, they won't be flat after.

Finally, your joints (lap joints here it looks like) need to be dead true so they don't introduce twist. Definitely clamp in a square/flat position while the glue is drying.

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    ^^ all this... but just to note, a week indoors isn't enough to dry out some of the swamp bottom crap that comes forth from the big box stores. I'd only buy straight dry wood. Sometimes they stock framing lumber that's actually dry-ish; otherwise, head to the 'fine' wood section where stuff will be markedly more dry. You could save yourself some lap cutting time by using two-ply 1x4. – Aloysius Defenestrate Oct 13 '18 at 21:21
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    If you're looking for construction lumber at the big box with straight grain, skip the 2x4's. Go to the 2x10 or 2x12 bins and search for portions of the board that are clear. Those wider boards tend to be taken from sections of the log that have a lot less knots. – Ashlar Oct 14 '18 at 1:08
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    @AloysiusDefenestrate, "a week indoors isn't enough to dry out some of the swamp bottom crap that comes forth from the big box stores" very much so. Acclimation can easily take longer than two weeks even for thinnish stock. Many pros wait at least a month or two, and much longer where they can and that's even with them buying properly dried material from legit yards. – Graphus Oct 14 '18 at 15:27
  • 2x4s, especially from big box stores, are pretty much the worst wood commercially available. The only exception might be furring strips, but then at best they're tied for last place. Even 2x6 are better. – aaron Oct 15 '18 at 12:14
  • @scanny Thanks for the great suggestions, I choose to continue with the warped work-piece and I have made lots of progress. I detailed how I fixed this in an edit to my original post – Stephen Meschke Oct 17 '18 at 20:18

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