Cutting paddle to change feather - strength lost? - Mountain Buzz
 



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Old 07-17-2009   #1
V for Victory
 
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Cutting paddle to change feather - strength lost?

Let's say you cut a 45 deg carbon paddle to have an insert put in and reglued in order to change the offset to 15. Is this seriously going to compromise the strength, or is that insert going to be about equal?

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Old 07-17-2009   #2
 
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First issue is if it's a Werner or any other paddle that has hand indexes. The shaft goes from a circle to a oval at the hand position. Changing the feather will change how that is supposed to sit in the hand. For strength it's probably weaker than the original but not a big difference. Most paddles that I've seen have issues are in the hand area and out to the blade. Most of the strain on the paddle when boating is in this same area.
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Old 07-17-2009   #3
 
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not a materials expert, but have a mech. engineering degree collecting dust somewhere--I would have to say that the shaft is not designed to withstand the loads that would be placed on the cut end once you cut it and install the insert--I believe you would incurr stress concentrations at the cut, that could propagate and fail

perhaps if you wrapped the joint with fiberglass it might resolve that issue though...

I say do that if it's just for playboating--but would you want to trust it in any type of extended or difficult runs where paddle failure would be unwelcome at best?
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Old 07-17-2009   #4
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Quote:
Originally Posted by sbratt View Post
First issue is if it's a Werner or any other paddle that has hand indexes. The shaft goes from a circle to a oval at the hand position. Changing the feather will change how that is supposed to sit in the hand.
No, if you cut in the center where it is a circle, the indexes do not rotate independently of their associated paddle blade. It'll still be appropriately aligned.

Quote:
For strength it's probably weaker than the original but not a big difference. Most paddles that I've seen have issues are in the hand area and out to the blade. Most of the strain on the paddle when boating is in this same area.
JayH makes an excellent argument for stress concentration, but your point here overrides it I think. The paddles, especially bent shafts, tend to break at the bend or hand area, not the center. Everyone agree here?
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Old 07-17-2009   #5
 
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We are thinking the same thing on the indexes, just look at is closely and make sure you are happy with the position the oval will be in your left hand. I'm assuming it's a straight shaft. I have one of the 6" tubes to make a break down lying around, if that's what you are using it should be fine.
Do be careful cutting the shaft, makes sure it's wrapped tight with tape to reduce splintering. Though I have no idea how I would measure a 15-offset when gluing it together.
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Old 07-17-2009   #6
 
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the center of the paddle is where the torque will be greatest with a technical stroke top hand stationary. no matter what stroke you take the integrity of the product will not be the same. fixed to broke paddles to make one good one. not very strong. worked my ass off and after a hard core round on the wave or 2 rounds its jacked. i would save the paddle as a spare and buy one with the degree you are wanting. after all gear is cheap.
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Old 07-17-2009   #7
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I'd think you could make the insert of a stronger material than the shaft and then if it is long enough, you'd have minimal compromise, yes? (though it might make it heavier)
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Old 07-17-2009   #8
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Most paddles seem to use two manufactured pieces bonded together in the center anyway. Anybody know what they use to bond it? I would think you could do something similar and if you cut it where the original bond was you're not introducing anything new.
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Old 07-17-2009   #9
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Here are the problems and how to go about it:

1. The internal diameter of the shaft can vary from manufacturer to manufacturer -- sometimes as much as 2 mm. You cannot make this up with extra epoxy -- it will still oval out or not line up correctly and you can create a stress riser. If for some reason the shaft is aluminum, you've got a mess. I'll assume it's glass/carbon, etc.

2. The "spigot" (name for the internal sleeve) should be about 8 inches long, depending on the length of the paddle. Longer = more weight (but they're made out of carbon, usually) and more strength so you shouldn't need an external wrap of glass/kevlar/carbon on the shaft. If the spigot is too long, it'll interfere with the ovaling/indexing on the shaft, provided it's not an add on such as a shrinked wrapped indicator (then no issues). So measure the distance between the ovals -- I'm assuming since you said nothing about shortening the stick, you should be fine.

3. So, other materials. You need real epoxy. I prefer West Systems since it is very hard. System 3 is fine as well, but their product is a little softer and really works best on top sheets and sidewalls of skis. Do not use Devcon or Gorrilla Glue. Devcon can break down in constant water use and Gorrilla Glue expands. You're looking for something to hold it together and won't slip. There are other products out there, but West Systems is best for this one. (I was once teaching in Parkdale after assembling my paddle 3 days prior. A blade fell off while my entire class of 200+ pound guys were swimming through 3 rocks at 2000 cubes... Kind of embarassing)

You'll need spigot (sleeve, ferral, whatever your local shop wants to call it).
You'll need an epoxy thickener, such as resothix. You need some sort of template (other paddle at 15 degrees) or a protractor (to measure angle). Lastly, electrical tape and rubbing alcohol to clean up.

Hopefully the cut is clean. Rough up the inside of the shaft. Rough up the outside of the spigot. Fit together. Mark a halfway point on the spigot so you know how far to put it in. With epoxy on it, it's like KY so expect some more slippage. With the spigot in the shaft, set you angle (make sure the control hand it correct!) and mark the shaft with lines (3 or so) from one side to another. If you want, use 3 different colors so you don't think about which line it which.

Mix epoxy per instructions and add thickener (some people add thickener before the hardner is added, your choice.) The consistency should be like a peanut butter. Use enough thickener -- other wise the spigot will slip on the shaft.

With latex gloves on, lube up the inside of the shaft -- both halves. Put the spigot in about 2/3 of the way to your half way mark. (with how much epoxy in the shaft, blob it up and I twist the spigot on the way in to make sure it is covered.) Put some epoxy on the spigot coming out of the shaft. Carefully get the other half of the paddle on (watch the spigot so it is not excessively going into on shaft half or the other) and line up your lines. Do a quick couple of wraps (don't twist the shaft) w/ tape. Wipe down any stray epoxy.

Leave it alone. If you put it in the sun (heat is good for epoxy, it crosslinks it and makes it stronger) make sure there is no way for the blades to twist.

After a day, so if you can twist it in your hands -- I doubt you will but if you have epoxy failure, now's the time to find out.


Have fun, it's really not that hard.

So most spigot's are much thicker that the original shaft. If it's long enough, centered and put together with good epoxy you're fine. I have even used a hot glue gun with no issues.
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Old 07-17-2009   #10
 
San Juan Islands, Washington
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I've had several paddles cut by Werner and made into 2 pc. paddles, I never noticed any difference in shaft strength or had any extra play.
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