Powerband Static Testing

[fernandezh]

You guys have to check out this website for Powerband static testing. He turned it into rocket science. . .


http://rocknfish.com/Rubber_Test.html


It makes my head hurt just thinking about it.


Hector

[richhermes]

Some people have entirely too much time on thier hands.

[fernandezh]

Originally posted by richhermes
Some people have entirely too much time on thier hands.



That was the first thing that came to my mind when I saw the site.


That quote on your posting. Isn't that from Oddball in Kelly's Heroes?

[richhermes]

Hell yeah. You gotta like Kelly's Heroes.

That movie is on almost every weekend on HBO. I can't help but watch it over and over--Donald Sutherland is FUNNY as hell.

[Kasshia]

I just put the gun butt down on the edge of the kitchen counter hook the scale on a band and pull. Then check the reading on the scale when the band stretches back to the tabs on the shaft. I'm sure there's a better way to do it, I just don't do this often enough to bother setting up anything else.:)

[FredT]

Rubber works by stretching bonds, the first few times you stretch a band you break a few of the weaker bonds. The more times the band is stretched the fewer weak bonds remain to break.

The guns I use require the bands to be built on the gun as the gun has no "band loading" slot to weaken the muzzle. This can be a pain, but it means we are always ready to instantly adjust the band length.

History shows that new bands have the most punch. As the band ages it rapidly goes into a plateau on the stress strain curve where little is lost each time the band is stretched. One method used around here is to "pre-stretch" the bands by loading the gun and let it set overnight, then trim the bands down to the desired stiffness the next morning. Band strength is a bit under new, but the strength changes VERY slowly after that treatment, so your impact point also changes very slowly. When the bands are once again "easy" to load, it's time to trim them again. Normally we'll get 3 trims on a band set before they weaken to the point they need to be replaced. "Trimming" simply consists of re-tying the band with the wishbone ball pushed 1/2" or more farther into the rubber, then trimmng the excess.

Note that ANY visible weakness at the muzzle end of a band means it's time to replace it! Anyone who has had a band break up there while loading it knows EXACTLY why this is so, and will NEVER forget the lesson. Being slapped by a sledge hammer has notheing on that pain!

BTW I did a hydraulic tension tester a few years ago for a buddy by placing an oil chamber in a JBL sized SST tube and a guided but otherwise unrestrained muzzle as the active piston. With a trigger assembly on the other end it's possible to load a band and instantly get it's tension simply by reading the pressure gauge and knowing the tube inside diameter. Strangely enough the area inside a JBL heavy tube is really close to 1 square inch so even the math is easy. :D

FT

[f94gator]

I'm pretty sure it's not, but doesn't that guy kinda look like Genesis? Writing style fits and he'd be the kind of anal bastard to do something like this.


Hmmmmm...

[Spear One]

I found that site to be informative but mostly it just validated what I have known for years.... speargun tubing breaks down rather quickly. The farther you stretch it and the more often you stretch it, the faster it breaks down / loses power!

What that means for most divers, especially those who don't know how to tie their own bands is, if you expect your gun to shoot at optimal power and range, you better be willing to change your bands at least 4 to 6 times per year, and possibly more often if you shoot a lot.

The only alternative to this is to do what Fred T said and cut the band down a little on both ends before the next trip. If you don't know how to tie a band, you cannot do this. In my opinion, if you are trying to achieve a higher level of skill and accomplishment in spearfishing, it is gonna be a tough road if you cannot tie or make adjustments to your bands.

In order to "become one" with your speargun, you must totally understand the propulsion of the shaft and therefore be able to recognize when something is "not right". Then you can make the necessary adjustment between dives or certainly before the next trip.

If you are striving to get better or simply become the best spearfisherman you can, you MUST start paying attention to DETAIL. Even as mundane as some of you may find this topic, I personally think this is the single most important, and usually the most overlooked DETAIL in spearfishing.

[201proguide]

wwwooah. this has gotten way over my head. informative, and hepful, but way over my head. i just gotta keep telling myself: baby steps young grasshopper...baby steps...

this brings up a question that i have for you spear one: since i dont know yet how to tie my own bands, should i just be changing them regulary when it dosent feel "right", or should i wait till the next dive to see if it wasnt my shooting that wasnt on key, and the bands are fine?

[Kasshia]

When I make my own bands, after I figure out the diameter and length I want, I just shove the knotted end of the wishbone line up into the hollow band, saliva makes a good lubricant for this, then close the end of the tubing by cinching a plastic zip-tie down on it. I like to leave ~1/2" between the end of the tube and the closest edge of the zip-tie.:)

[subdude]

Originally posted by Spear One

The only alternative to this is to do what Fred T said and cut the band down a little on both ends before the next trip. If you don't know how to tie a band, you cannot do this.

and can't be rocket science but like everything else it is very difficult if you don't know how. I use a JBL gun for now.

Where can I get bulk rubber?

Can I reuse wishbones? (I don't think so 'cause I have had them break on me ... OUCH)

What do I use to tie them off? I have heard zip-ties and no zip-ties. I would think no zip-ties. When I was in the USAF, we used to tie off wire bundles with wax string. That shit is STRONG. Is that what someone said in another thread you use S1?

What do I need to know that I don't know I don't know?

subdude

[greyface]

That was one topic I really wished Kevin could have covered at the Orlando seminar...he may have afterwards, but I had to get back to St. Auggie. If I knew how to tie my own, I'd buy all the materials from SS. hint hint;)

[richhermes]

SpearOne,
Your band tying method is quite simple yet effective. Would you happen to have a graphic or diagram showing how this is done?

[subdude]

Originally posted by greyface
If I knew how to tie my own, I'd buy all the materials from SS. hint hint;)

Absol****inglutely.

subdude

[Spear One]

All good questions.... as a general rule, as soon as you can see any minor cracking around the ball of the wishbone, the band is done. However for me, the band is done long before any cracking occurs.

If you shoot mostly with one band, the snap or power of the band is very critical. That one band must be as "punchy" as possible without causing "erratic" shaft flight. If you have sat through one of my seminars you know how I feel about "shaft flutter" and the adverse problems it creates.

The more bands you shoot, 2 to 6, the less "critical" the freshness
of the rubber can be up to a certain point. I would assume that a big time Tuna shooter can tell when his 6 band bazooka just ain't got it, just as well as I can when my one band gun ain't got it. But as a whole, multiple band guns, especially 3 & 4 band guns and up, are more forgiving of "lazy" bands.

For instance, if you shaft weighs 1 1/2lbs and you are using one 24" long 5/8 dia. band that at optimal 4 time stretch produces 130lbs of pull. Lets assume that you are happy with the way that band shoots. Now, your buddy is powering his gun (which is identical in length) with the same weight shaft but decides to use 3 bands for extra power and distance.

Lets assume he is using a 26" long 9/16"dia. band that is stretched 3 times its relaxed legth and produces 80 lbs of pull.
Multiply 80 X 3 = 240lbs of combined pull. You are using 140lbs to throw your shaft with a single band and your buddy is throwing the same weight shaft with 3 bands @ 240lbs.

The three band gun is obviously more effecient at throwing the shaft a greater distance with more power than the single band gun. This factor increases as you increase the number of bands on your gun (4 to 6 bands). However as a general rule, the more bands you put on the gun, the longer you make them, and the shorter distance you stretch them. Shaft "flutter" becomes a big factor when you get into 3 to 6 band shooting if your bands are too short.

If the info gain from that web site and Fred T is correct, we know that tubing loses its inherent power just by loading the bands. If you are shooting one band, you cannot afford to lose 20 to 30% of its initial power after one trip and expect the gun to be shooting correctly. When you are shooting multiple bands this becomes a little more forgiving.

The moral of the story is: once you band loses 20 to 30% of its initial power (regardless of how old the band is) you only have two choices... shorten the bands or replace them! If you choose to shorten them be careful. You can usually get away with this one time with a freeshaft "single band". If the band gets too short it can also cause accuracy problems. 1/2" on each side is about all you can take on a freeshaft band.

As for using zip ties... I have never been able to get them to work. Kashia must be using some type of "nuclear" zip tie. Plastic zip ties stretch too much and usually allow the ball to eventually pull through.

As for selling direct... this obviously creates problems for us. We rely on the dive stores to sell our products and it would be unfair for us to work around them. We have been working to find stores which are willing to believe in our system and stock the products. The stores we do the seminars at are some of these stores.

If you want bulk items to make your own bands just order them from the store and I will make sure they get sent ASAP. If you are a good distance from one of our stores, call and place the order at the store and usually we can arrange convenient shipping options.

I don't have any diagrams of how to tie a band. We usually show folks at our seminars if they want to learn. I will be posting very soon about the final seminars we will be doing before the busy season arrives in mid April.

201 Grasshopper... Be Patient, there is no substitute for underwater time.... just keep that band fresh.

[FredT]

Originally posted by subdude
Where can I get bulk rubber?

Most Riffe dealers can get it from them up to 3/4" (amber only)
Kevin at SS sells it up through 5/8"

Originally posted by subdude
Can I reuse wishbones? (I don't think so 'cause I have had them break on me ... OUCH)


No sweat, but inspect them closely before reuse. Cable bones generally shouldn't be reused due to fish hooks in the cable, but they are easy and cheap to make with a crimp tool and stop buttons

Originally posted by subdude
What do I use to tie them off? I have heard zip-ties and no zip-ties. I would think no zip-ties. When I was in the USAF, we used to tie off wire bundles with wax string. That shit is STRONG. Is that what someone said in another thread you use S1?


I use 2 wraps of 304 stainless steel safety tie wire. It's hard on rubber, but the band is going to get trimmed before the rubber is hurt too bad anyway. Be sure to crimp the tail in so it's buried in the rubber aft of the tie of. Sharp edges hurt. The waxed nylon string also works well. It's what is used on Riffe bands and I think on SS bands as well, but it's a bit harder to do properly in the field and more importantly it's quite a bit slower if reworking bands in the field.

Originally posted by subdude
What do I need to know that I don't know I don't know?


Probably a bunch, but that is what life is for. The lessons learned keep it interesting.

Be sure to minimize contact of rubber with copper, rubber with SST is no where near as bad but is still "not a good thing." Insulaton of metal with a high shrink ratio adhesive heat shrink is good too.

NOTE: Adding a couple drops of hot glue to the bead on the sides of the wish bone will do the same thing during the shrink process if you don't have access to 4:1 adhesive heat shrink tube. It's not cheap stuff and radio shack doesn't carry it.

Riffe solves this "problem" by using a totally non-metallic wishbone and tie assembly. The "floppy wishbone" does however require a slightly different loading technique.

If you dive often the bands will wear out before the SST contact is an issue.

FT

[subdude]

I use 5/8" bands and am very familiar with safetywire from my off road motorcycle (I have a trophy on my mantle and 2 screws in my knee) and avionics maintenance days. Hell, I even own a pair of no-shit safety wire pliers.

I think I will give this a shot in the not too distant future.

Thanks Fredt and S1,

subdude