Thursday, November 09, 2006

Bulletin board threads, crumple zones and suspension system

[I've had to remove some live links from this post as they have resulted in so much spam]

There have been some trenchant comments about the Calder case and some interesting suggestions on this Acoustic Guitar Magazine bulletin board;f=7;t=007019;p=2 . Invigorating for me to read positive and negative feedback as well as some good questions.

Out of this discussion I've done some more work on the suspensions system needing a 'crumple zone' to protect instruments from the shock of a severe impact. I had planned to use a high density closed cell foam but now I'm researching potential alternatives.

The trick is to find a materials that is soft enough to cushions the instrument from shock and at the same time firm enough to stop the instrument being damaged from making contact with the side of the case.

Expanded Polypropylene EPP seems a good candidate - a very tough shock absorbing material used in crash helmets, car fenders and other high impact applications. I've been had good support from JSP one of the leading manufacturers of EPP - I'll be running tests on their product ARPRO.

Canadian company Godin manufacture an EPP guitar case for their acoustic guitars called TRIC.

Another interesting contender for the suspension system is a new UK developed materials called d3o which is causing a stir in the sports world.

And for those of you who are interested in more bulletin board stuff on suspensions systems here's a thread on Maestronet I contributed to recently -" .


Calder blog homepage
Calder website homepage


Anonymous Anonymous said...

A few notes:
1. You're not going to support the neck at all? Consider that the most common catastrophic failure for a packed guitar is headstock fracture at the neck. It may be difficult to account for all teh different shapes and sizes, but it's the most vulnerable part of the instrument: a 14 inch+ long, thin strip of wood with over 100 lbs of tension and significant torque across it. Frank Ford, master repair luthier of fame, highly recommends padding the hell out of the headstock/neck when traveling so it's completely immobile. Which brings me to my next point...

2. One thing I have considered in my own case designing (not building, yet) is the idea that padding as shock absorbtion might be, unintuitively, worse for the guitar than a truly rigid shell which allows nearly no internal guitar movement. Guitars do not contain small shock-damagable internal components like a laptop might, but rather they are essentially a single object. As such it might be that if you treat it as an oddly shaped, monocoque object which is NOT shock sensitive you get better protection from a very close fitting and rigid case that does not flex.

Imagine you are really just trying to protect your favorite 4x4. If you machined out the center of a steel block to perfectly fit your board, screwed it shut, and shot it, dropped it off a tall building onto concrete that was on fire and covered in broken glass and nails it would come out unscathed as long as the steel did not deform.

Similarly I might assume a perfectly fit case would be just as useful, that immobilizing a guitar while ensuring the guitar itself cannot be LOCALLY damages (i.e. don't puncture the case or bend it into teh instrument) would be just as good for drop protection as wrapping it in it's own Nerf factory. Making a huge solid case with just enough padding to protect the guitar primarily from users putting it in and taking it out, which never could locally damage the guitar and would distribute the g-forces from a drop evenly across the whole body and even better across the case itself, would be ideal.

You want a case that is ultrastiff, moves the shock around the guitar, and prevent the guitar from being shocked by the case itself.

3. d30 can't actually be bought just yet, and it has to be hit pretty dang hard to be useful. I had the same thought when it first started making headlines, but the G-ratings are pretty high, high enough that if you don't buy the loose logic in argument #2, you don't want to use it. Check the spec sheets.

Anyhow, that's just my $2 opinion and ramble, so keep up the good work. No point in getting too dragged down by nay sayers, you'll never get anywhere at all if you try to please everybody or indulge every cry for "crumple zones" to be installed in boutique guitar cases.


11:11 PM  
Blogger Nick Comer-Calder said...

Hi Dave - I enjoyed reading your comments and suggestions - it is a real pleasure to get such thoughtful input.

Here's my take on your points -

1. I've read that the headstock is vulnerable. And it figures that if the body of the guitar is held rigid and the whole thing then subject to massive shock there could be a whiplash-like stresses placed on the neck/headstock. So I agree that there needs to some restraint up at that end.

The big issues is (and this applies to the whole guitar) that the restraint which protects from impact can become a hazard when the case is subject to crushing forces. This is especially an important at the headstock where any pressure will be hugely on the headstock will be magnified by the neck acting as a long lever.

2. I've been researching the physics behind this for some time and your way of putting it is a good deal more common-sensical that much that I have read.

My original plan had been to make suspension units of high density foam. These would hold the guitar very securely at just three points where it is strongest.

Now with a better understanding of the need to spread impact shock over a larger area I'm considering a system that has more contact with the guitar - along the base and around the heel.

The system would still hold the guitar away from the top and bottom of the hard shell so that there to minimise the possibiity of crushing pressures being transmitted to the guitar.

I'm getting samples of EPP to see if offers better rigidity/impact protection than closed cell foam. I'll post the results of my test.

The ultra-stiffness of the carbon fibre offers an excellent container for the suspension system - the trick will be making sure the hard shell and the suspension and the guitar all fit perfectly together when the case is closed.

I had understood that d3o was available - in any event I suspect it is better suited to applications where flexibility is essential - as in sports wear.

Thanks for your closing remarks about not listening to negative comments. I like to be in touch with people who are interested in the process - but it is my journey and I must find my own road.


9:35 PM  
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Anonymous Anonymous said...

Check out Akton polymer has the consistency of fatty tissue and acts as a good shockabsorber. Material is used in gun recoil-pads among other things. I'll be glad to send a sample for testing if you let me know the dims.

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V.P. Business Development

1:35 AM  

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