hinge trouble

[Dave Tesch]

i'm having some trouble with hinges on a current project. now keep in mind the amout of hinges i havent had trouble with is far greater than the number i have had trouble with; most of the time it works fine and the hinges are true.

not this time. this is the second time i have had this particular problem, and i cant quite put my finger on it.

the project i am working on is an instrument case, 5/8" ply approx 32.5" x 9" x 17"

hinged side is 32.5"

a simple 6 sided box cut down near the middle to create two halves that should fit together, kind of like a toybox.

before i cut the box in half (not really in half, its just easier to say. lets say 3/4 for real) i mark it with lines so that i can match it up after the cut. i also use inside corner blocks to align the box while i cut out the latch holes and install the hinges. everything went well until i removed the corner blocks, and the lid twisted against the body so it appeared racked.

a long series of investigations while checking the lines revealed that when i removed the hinges i could position the lid so that it was true. installing the hinges caused the lid to rack. i can not find anything wrong with how i installed the hinges nor the hinges themselves.

i finally gave up and used a piano hinge, and this works fine - no racking or twisting of the lid. i would prefer to use the hinges i bought originally as they are a stop hinge; allowing the lid to only open just past vertical and then stopping just past where gravity will hold the lid open. without the stop hinges i will have to use a strap, which is fine, i would just prefer the stop hinges.

i have a couple other cases with the stop hinges that turned out well without racking or twisting.

this is the second box i have had this trouble with - am i doing something wrong?

the way i have been installing the hinges is to use a square, scribe a line for each hinge and mark the holes with the square before drilling. this usually works, and i cant find anything wrong with my measurments on this box.

here is a pic of a case that turned out well. the current project is a little bigger, but not much.

http://inlinethumb28.webshots.com/48091/2124462900026985969S500x500Q85.jpg (http://entertainment.webshots.com/photo/2124462900026985969UTkIIF)

http://inlinethumb45.webshots.com/19052/2905896610026985969S500x500Q85.jpg (http://entertainment.webshots.com/photo/2905896610026985969ZcZSWB)

http://inlinethumb16.webshots.com/5071/2742474170026985969S500x500Q85.jpg (http://entertainment.webshots.com/photo/2742474170026985969PWqqxK)

[Jon van der Linden]

Sounds like one of those things where something is being overlooked (don't ask how I know about that, because I'm not telling). You've established that it's not the box/case, because it lines up fine without the hinges. There are only two other things that could be an issue, either the hinges, especially if they are not exactly identical, or the placement/installation of the hinges might be just enough off to create a problem.

If the hinges are identical and I couldn't see the problem, removing some or moving them around might indicate where the problem is.

I don't think there's any way to solve this without seeing the problem item, although you probably could look at the hinges you removed and see if there is any variation there. (Hope you didn't reuse hinges from the previous "bad case" on this one.)

[Dave Tesch]

no, these are new hinges. the previous bad case is still funny, i never fixed it. the lid is off by 3/32" on either side of the front.

i did swap around the hinges as well as try 1 , 2 and 3 hinges in the different spots. no change.

my best guess is that the ply is warped at the hinge area enough to throw off the alignment, and adding the piano hinge is enough to bring it back into shape; this is a guess only - i have no proof.

i agree i may be overlooking something, thats why i am asking. i assume that when it works i may have gotten lucky.

[Jon van der Linden]

Kinda reminds me of a contractor working on the house of a friend where they were replacing the double front door. The supervisor couldn't figure out why there was a 1/4" gap at one of the corners. He laid his 4' level on the sill and it was "dead on." Lifted up one end until the bubble was exactly in the middle and said "that's your 1/2" right there."

Based on your reply I'll have to add that the case may be off as well!!! I'd check the case against a long straightedge and use winding sticks to check for twist.

Regardless, it's one of those things where you probably have to be there to see it.

[Harvey Pascoe]

Those narrow strap hinges are the likely source of your problem. Any distortion in the case will telegraph to the the top. Make sure the case is perfectly square. If it is not, try shimming the hinges with strips of clear plastic cut from packaging until the top sits square.

Next time I'd choose a larger, wide hinge.

Also if those are rivits or bolts holding them on, are your bolt holes perfectly aligned? If not, when you tighten them down it will cause the top to skew.

[Dave Tesch]

i found something today;

i spent some time looking at the box and the way the lid fits on it, and concluded that if i removed some material off the rear of the lid where the hinge mounts i could straighten out the lid. i sanded a slight slope into one half the lid totalling around 1/16" off the far edge and easing that into the rest of the lid.

after i did this the front of the lid straightened out (i did three passes/fits). it was then i discovered that the inside of the lid doesnt match with the inside of the base - i removed the latches (see pic in OP) and by using my fingers i could tell that the insides dont match anymore. the lid is on crooked. i'm not sure how this happened, but it seems to happen sometimes. i suppose i could blame it on the wood moving after i cut the lid off the body and that is my best guess at this point.

i think i can salvage this project, but my heart sinks knowing its not "right". i have plenty of boxes that fit right, if i had one wish it would be to understand how this happens and if its just the nature of the wood or if i am doing something wrong.

[Jon van der Linden]

Based on your last post, my guess is that there may be some stress from how the plywood box is assembled/glued. Need to know your assembly process to have any particular thoughts on that. I'd still check any offcuts lying around just to verify that the plywood isn't warping. 1/16" over 32" is a fair amount.