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Thread: Best way to squash down rigid foam in a case?

  1. #1
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    Default Best way to squash down rigid foam in a case?

    I bought a SKB-80A A mandolin case at a good price as an 'open box' deal. It's ABS outer, hard polysterene foam interior with the usual nylon fur. My Eastman 305 with a ToneGard on fits - only just, no room for spare strings and the strap is only just in - whew. Originally the case would sit open about 1-1.5 mm before the clips went on, which meant there was nothing to spare on the case depth, and probably some pressure on the bridge top when closed. It seemed like I needed a little more depth in the area where the middle of the mandolin back touches. I got a soft face hammer and applied it to the case in that area, then I got my heel in it with hard shoes on and stomped around some. That squashed the foam down just enough that now the case closes completely before I put the catches on. Will that do it, or do I need a bit more clearance than that in case someone bumps the case? If so what's the best way to compact the foam down a few more mm?

    Thanks, Max

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    Default Re: Best way to squash down rigid foam in a case?

    Sounds like the Gator ABS-outer Styro-inner cases commonly available here in the US for around $100 new. I've been using them for a number of years now, they are relatively inexpensive and protect well, but in the act of protecting during a serious accident the ABS outer will commonly fracture as impact pressure is absorbed, so replacing the case becomes the worthwhile expense of having an accident. I've replaced my Gator mandolin case twice over the course of about 10 years, after having (rather stupid) accidents that would have resulted in serious damage with a standard plywood case... Since observing how well my mandolin has been protected I've gotten similar cases for my main-playing banjo and my wife's main playing guitar, and we've both been happy with their protection too.

    And yes, my method for compressing the styrofoam inner to fit the instrument better is similar to yours, basically holding a blunt and heavy, somewhat round shaped object -- like the head of a hammer -- in my hand and pressing that object hard against the styrofoam until the material is sufficiently compressed. It works pretty well, sometimes I'll repeat the process a few times to get more appropriate compression. The compressed styrofoam "remembers" the compression pattern pretty permanently.

    Edit: It's worth mentioning, the styrofoam in these cases has airspace between the ABS-outer and the styrofoam-inner, in various locations, especially around the large top and back areas. The only reason I'm aware of it is that I've had fractured cases which have allowed me to inspect them in areas that are not normally visible. In other words, the styrofoam-inner is not a solid styrofoam fill, by design. The styrofoam is shaped and glued in place so it won't move around, but if enough compression energy is applied in order to properly fit an instrument, it's possible that the styrofoam inner could be cracked in various locations inside the case. I don't know if that would represent a problem, since the styrofoam is still present to absorb impact, but it's worth being aware of.
    Last edited by dhergert; Oct-22-2021 at 7:54am.
    -- Don

    "Music: A minor auditory irritation occasionally characterized as pleasant."
    "It is a lot more fun to make music than it is to argue about it."


    2002 Gibson F-9
    2016 MK LFSTB
    1975 Suzuki taterbug (plus many other noisemakers)
    [About how I tune my mandolins]
    [Our recent arrival]

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    Default Re: Best way to squash down rigid foam in a case?

    Thanks for that Don - the SKB case is probably very similar structure to the Gator case, so should respond similarly. It's a bit like a bike helmet - if it gets a good hit, it loses protection so you thrown it away and buy a new one. I'd have liked a Hiscox case, but that costs 60% more than the SKB and is bigger and probably heavier. Some ABS guitar cases aren't bonded to the foam liner all over, it just sits inside by friction or is tacked with a glue gun in a few places - I've taken two old cheap ones (free cheaper Fender cases) apart.

    What I don't know is whether it's better for an instrument to fit in its cases exactly (so it doesn't bounce about inside the case), or have a little space for compression in case something heavy squashes the case - there may be no answer to that. I once had a cello with a fiberglass flight case made by Alan Stevenson, the British guy whose flight cases many professionals use. Those are lengendary protectors for falls out of cargo holds etc - the instrument is held in place with many pads that hold it away from the case skin. However a friend of mine got her cello case off a transatlantic flight to find a 1/2" hole punched straight through one of those cases. Fortunately whatever did that missed the headstock by 1". Just shows you can't cover everything

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    Default Re: Best way to squash down rigid foam in a case?

    By definition, accidents are almost always going to happen randomly, unexpectedly, it's part of life...

    My first mandolin related Gator case accident was caused by opening the back hatch of my SUV which was slightly aimed downhill, and having the case shoot out as if it were fired from a canon. It hit a curb and shattered the case at that point, but the mandolin was completely unhurt. This accident won't happen again, since I now routinely put up the cloth fence, plus I tie the mandolin in with a safety belt.

    My second accident happened late one night when lighting was poor and I was tired after a gig... I was unpacking the instruments out of the car -- I had gotten my wife's guitar and my double bass into the house, and was in process of getting my banjo and mandolin... In the dark I tripped over the mandolin -- actually kicked the poor thing -- and then fell onto my banjo case over the neck. What a mess, the mandolin case fractured at the impact point into a number of pieces, but the banjo case was left completely intact. Both instruments were completely unhurt. This accident also won't happen again as I've installed sufficient automatic lighting so I can see where things are when it's dark there.

    In both accidents the mandolin case fractured at the impact point, pushing inward into the airspace between the ABS and the styrofoam. The styrofoam appeared to be untouched and was basically left completely intact, cradling its precious cargo. I suspect the springiness of the ABS as it fractured soaked up the majority of the impact pressure in both accidents, and this is probably by design.

    Having seen this happen twice now seems to be like some form of crash-test-dummy experience. It may not happen exactly this way all the time, but I suspect there's been some real testing involved and the springy, breakable ABS has proven itself to be the life-saving influence for the instrument inside, at least with accidents like I've experienced.

    All and all, I'd gladly pay for the cost of replacing these cases in exchange for having the instrument unharmed.
    -- Don

    "Music: A minor auditory irritation occasionally characterized as pleasant."
    "It is a lot more fun to make music than it is to argue about it."


    2002 Gibson F-9
    2016 MK LFSTB
    1975 Suzuki taterbug (plus many other noisemakers)
    [About how I tune my mandolins]
    [Our recent arrival]

  6. #5

    Default Re: Best way to squash down rigid foam in a case?

    Your analogy of the bike helmet is proper, but the reason you throw it out is because, being compressed, the foam is harder and less compressible, which means two things; it can absorb less energy and also is actually harder. (I was involved with bike helmets in the early days at what was the National Bureau of Standards, since I had started the first, and probably last, employee club, and very recently, got attached to a helmet startup and wound up duplicating the test setup at home.)
    So, the issue, I think, without actual numbers, is that since a mandolin weighs very little, and the foam is probably more like what might be in other packaging, it’s way too stiff to deform in a typical accident, like a drop of a few feet, and is therefore not functioning as an energy absorber between the instrument and the case. The case, though, is much heavier, and that kinetic energy of hitting the ground has to be dissipated. The mass of the object to be protected, mandolin or cranium, enters into designing the padding, so if I got involved with a design, there would be a very much softer padding, or just more open structure to it.
    I would be surprised if anybody in the business spends time thinking about this.

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