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I just built two bookcases to line the wall of a room in my house and apparently didn't build them square enough so, when I put them next to each other, I get this giant gap. (I think the one on the right is pretty square but the one on the left appears to lean to the left at the top.)

Any suggestions on how I can make this look better? The shelves are going to be sanded, spackled, caulked, and painted. One thought I had would be to remove the vertical strips of molding where the two bookcases meet (there is 3/4" square molding on all the edges) and make one custom piece that attaches to both. This piece would be wider at the top and taper at the bottom. Maybe that would look bad--I don't know. It also wouldn't address the gap on the top horizontal surface.

enter image description here

Any suggestions would be appreciated!

dotancohen
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jevron1984
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    Is it possible that some portion of the gap is due to variation of the floor? – Michael Karas Apr 07 '19 at 14:15
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    You should get a tool called a framing square so that you can check squareness rather than guess. Maybe it is possible for you to remove the back of one unit and spring the shelves into square and reattach the back to hold it in the square shape. It is not quite clear how the backs are fabricated and the worst could be that you would have to make a new back. – Michael Karas Apr 07 '19 at 14:19
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    @MichaelKaras -- Your comments would make a good answer. – Jasper Apr 08 '19 at 00:45
  • @MichaelKaras: This is good advice, but I would add: check the framing square for squareness! I once spent a frustrating hour trying to figure out why no matter how I tried, the jig I was building would not come out square. I realized eventually that I was not crazy, it was the square that was wrong. A solid steel square presumably made by professionals was 89 degrees. – Eric Lippert Apr 09 '19 at 00:57
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    Now that you've fixed it, please post an updated picture so we can all sleep at night. – DavidS Apr 09 '19 at 16:58
  • @EricLippert .. or had warped or become bent. – whiskeychief Apr 10 '19 at 12:01
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    Note that you don't need a square tool to check for squareness - if you measure the diagonals, and they are the same, then it is square. – AnoE Apr 10 '19 at 14:59

6 Answers6

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Swap their positions.

Place the bookcases so that they lean into each other instead of away from each other. This will eliminate the gap between the tops.

Bookcase contents are usually quite heavy. Once the cases are filled, you will probably find that you can force the bottoms together and the weight of the contents will distort the shape of the cases so the gap disappears.

If an unsightly gap remains visible then you will need to resort to a decorative molding.

A. I. Breveleri
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    Another benefit to swapping them is you can see if the problem is actually caused by an uneven floor. – bitsmack Apr 08 '19 at 06:39
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    It's funny that the best solution (in my opinion) is a quick bodge. – Ismael Miguel Apr 08 '19 at 18:03
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    Or flip them upside down, they look like they would go either way – undefined Apr 09 '19 at 09:09
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    @LukeMcGregor even if they go either way, flipping them will either point the opening against the wall or rotate them so that the long diagonal is in the same position it was before. Right now the long diagonals look like this: `[\][/]` Flip them 180 degrees and they look exactly the same. – candied_orange Apr 09 '19 at 17:38
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Thanks everyone; I figured it out and came back here to update my post and noticed that Michael Karas said the same thing I realized (although it was a comment, so I couldn't mark it as the correct answer): I had to pop the back off the left unit (which was actually quite easy because it was just 1/4" plywood attached with brads and no glue), re-rack the unit into square, and then reattach the back. Thanks for the input!

jevron1984
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    Yes - this is certainly the correct answer. It is not a huge gap and the force required to push the backless bookcase into a cuboid is unlikely to be too great to be held by a few panel pins once you put the back back on. They look like nice bookcases, and good luck! –  Apr 07 '19 at 23:51
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    Still, it is often the case in older houses (and sometimes in new ones) that the floor is not flat. You need to level them with a spirit level and some kind of shims so they are perfectly level. Then you could consider screwing them together top and bottom. – RedSonja Apr 08 '19 at 07:00
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    So you had frame square or went and bought one? – Solar Mike Apr 08 '19 at 07:49
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    I didn't buy a framing square (although it's on my list--I used to have one but it's disappeared). But I used my smallish rafter square on the corner of the left bookcase and it looked out of square. I then made an ad-hoc plumb line and used that to verify that the left bookcase was indeed racked to the left. The right one was square. – jevron1984 Apr 08 '19 at 20:52
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You don't have to buy or get a framing square : just measure the diagonals... That will tell you if either or both units are out of square.

If they are both ok, then look to the floor - small change in the floor will make a large gap at the top... Then you need some adjustable feet of some sort.

Solar Mike
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  • Would,'t measuring the diagonals only help in the case of a general quadrilateral? If this is a parallelogram or a symmetrical trapeze the diagonals will be the same. making sure that $height^2 + length^2 = diagonal^2$ would check for right angles – WoJ Apr 08 '19 at 13:07
  • @WoJ well if you want a bookcase with a sloping side then use Pythagoras... – Solar Mike Apr 08 '19 at 13:09
  • I do not understand your comment. You suggest to measure diagonals instead of using a framing square but I think it will only cover a subset of the cases. Am I missing something? – WoJ Apr 08 '19 at 13:19
  • @WoJ diagonals won't work for a rhombus... – Solar Mike Apr 08 '19 at 13:21
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    Well, yes they won't. That's my point. Neither for a parallelogram, a trapezoid, ... The diagonals will be equal, like for a square. – WoJ Apr 08 '19 at 13:24
  • @Woj so how do you measure a "square" angle of 90 degrees on your trapezoid with the framing square? Or are you assuming that a framing square is adjustable? – Solar Mike Apr 08 '19 at 13:26
  • @Woj do your shapes represent what the OP shows? – Solar Mike Apr 08 '19 at 13:28
  • You put the framing square inside the shelf. If it fits everywhere, then the angle is square. Repeat for all angles. If you measure the diagonals, you will only catch some shapes where the angles are not square. You will miss parallelograms, trapezoids, etc - which are not what you want to have. – WoJ Apr 08 '19 at 13:28
  • *do your shapes represent what the OP shows* yes, why not? How would you know that they are not parallelograms for instance? Not by measuring the diagonals (they will be equal, like for a square/rectangle), but by using something else (a framing square for instance) – WoJ Apr 08 '19 at 13:30
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    @WoJ a parallogram does not have equal diagonals, but they **do** bisect each other... So, the method I suggested is still valid. You may find this helpful : https://www.mathplanet.com/education/geometry/quadrilaterals/properties-of-parallelograms – Solar Mike Apr 08 '19 at 13:31
  • yes, of course you are right for a parallelogram (sorry). An isosceles trapezoid is the right example. Sorry for the confusion. In that case the diagonals will be the same (you could check their intersection, though, to see whether it falls in the middle but this requires a measuring process more complicated than just two length measures) – WoJ Apr 08 '19 at 13:35
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    *(a parallelogram having equal length diagonals ... pfff ... the shame ...)* :) – WoJ Apr 08 '19 at 13:37
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    @WoJ I think we can assume that the top and bottom are the same length, and the left and right sides are the same length, so it is a parallelogram and the trick with the diagonals works. – David Richerby Apr 08 '19 at 14:55
  • If yo aren't sure the opposing sides are equal, you can measure 3X length from a corner one way and 4X length the other way and mark. Then measure between the points. If it's square, the hypotenuse will be 5X length. – JimmyJames Apr 08 '19 at 15:01
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    @WoJ - "a parallelogram having equal length diagonals", yeah, I've heard of them, they are called rectangles. – Glen Yates Apr 08 '19 at 21:57
  • If the shelves aren't racked (which the OP's were), shim at the floor and cover with 1/4 round. – Mazura Apr 09 '19 at 00:40
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I have used interscrews (e.g. from screwfix) in the past to join units together to make them line up nice and tight.

Doris
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If the shelves are sturdy, just get some molding and cover the junction of the two units. Nail the molding to only one unit so they can be easily separated if you want to move them.

Jim Stewart
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I would turn the left bookcase upside down. If the other side of the left bookcase is more square, or slants to the right, this will fix your problem.

spacetyper
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