so, I need to attach a couple of cheek blocks to a carbon fiber spin pole and am alittle bit leary of using Stainless steel rivets since I think it could damage the CF on the inside of the tube. What's the consensus here on attaching items to carbon?

Riveting into carbon seems to be done fairly often however, based on my experience, I would only do so as a last option. I have found that pop rivets are not a prefered method of attaching fittings to carbon fiber unless you are able to put a backing plate on the underside of the rivet. When you use a rivet, it point loads the piece and basically tries to split open the hole in the carbon piece. I have had fittings pull out that were riveted in to carbon. If you are unable to use a backing plate, I would consider through bolting (with a compression sleeve if possible). Otherwise, reinforce the area to be riveted with additional carbon before riveting if necessary.

sm

Rivets holding a simple and not heavily loaded fitting on our carbon spi pole did not last long. The rivets pulled trough the carbon and kevlar layers. Trough bolting with a backing plate have been rock solid.

Todd - I take it that this for the self-tacking jib blocks?

AHPC, Fiberfoam, and Hall Spars routinely use pop rivets for fittings on their A-Class carbon masts. The masts are all pre-preg auto claved carbon uni and bi directional materials which might be a better fit for pop rivet attachment. I think they also use a different pop rivet than what you would use for attaching a fitting to an aluminum spar or pole. I believe the pop-rivet body has like a knurled finish for better grip. We also learned you should mix up a batch of West Expoxy (mix it with a little hi density filler) and goop the body of the rivet to add more holding power and to act as an insulator between the rivet and the carbon.

Suggest you call Hall Spars and Rigging in Bristol, RI and ask for their rigging department. I'm sure they would be happy to share their methods with you.

Bob Hodges

All of the mast fittings on the Stealth carbon mast are rivetted. I don't know of anyone with major problems as a result. On the other hand, being new to the class at the time, I took the precaution of through bolting the upper and lower diamond tangs <img src="http://www.catsailor.com/forums/images/graemlins/smile.gif" alt="" /> (it does no harm!)

If I were going to rivet into carbon, I'd drill the hole, paint it with epoxy to seal the ends of the cut fibres, and then pull up the rivet. Ideally I'd want to get a backing plate on as well.

You got it right Keith. I see you guys attached your blocks the same way I did. It works, but is less than ideal because of the geometry of the loads. I want to move the blocks to the pole, but am a bit nervous drilling into a nice clean carbon pole. looks like I have alittle more work than just drilling and riveting.

I have riveted stuff onto my carbon N20 spin pole before. I have never had any problems in the last 2 or 3 years I've had the boat. I think you'll be fine.

Hi All

I've done some work in the fibreglass industry and there was a special rivet we used in water tanks and they were stainless, when the rivet pulls up, it splits off into four instead off balling up, it looks like a cross on the inside when your finished, and spreads the load of the rivet.

Regards

Todd,
If concermed you could always glue them to the pole.
Layer of glss around the pole to insulate the stainless from carbon. Bed them into glue and then wrap a couple layers of glass around the stainless tags on the cheek blocks.
If concerned about appearance you can colour the glue black with a picgment in the resin when mixing up the glue and we can now buy epoxy resin with a hardenner that does not discolour due to UV. So the glass can remain transparent.

So if concerned, with a bit of care and planning, you can probably make the attachment almost invisable.

Regards,
Phill

I prefer to thread self-tapping screws into carbon in place of rivets. They hold very well and don't squash the laminate.

Mike.

Drilling a hole in carbon goes a lot smoother with an abrasive cone shaped dremel bit. The one i use is just over 3/16 at the fattest part of the cone. a drill bit breaks away fibers and leaves a mess on the inside wall just as drilling a hole in plywood without a sacrificial backing board would do.
i know aluminum and carbon + salt water almost makes a bomb and thinking you can do a barrier with some glass is overly hopeful in many cases. It's news to me that good stainless would react at all with carbon. It's stainless and not supposed to react with most other solids.
Also do rivet sleeves like they use on Hobie cats help?

Stainless does indeed react with Carbon. The following image shows the galvanic relationship of particular materials (graphite = carbon). Monel is one of the Cu-Ni alloys on that scale. To avoid galvanic corrosion between dissimilar materials, you want to choose materials that are close to each other on this chart. As you can see, Aluminum Alloys are almost as far away as they can get from graphite...the aluminum, being the more active of the two will act as the anode and will corrode at a high rate. 316 series stainless steel is what's usually used in marine application and most common stainless fasteners but even it is a bit far away from the graphite - it will rust if in contact (stainless is not impervious to everything...soak it in concentrated bleach for 24 hours and then water for a few hours and you will see!). 304/302 Stainless steels are the poor man's version of stainless (we typically build machine frames from 304 because it offers similar corrosion resistance at a reduced price from 316).

What you really need are platinum rivets...they'll stand up well with that carbon.

I used to be a cathodic protection system technician for a gas company....I would watch over the systems and methods used to slow down the corrosion of steel and cast iron gas pipelines... so I got a pretty good education on these things.

What the guys are talking about with the fiberglass is for it to act as an electrical insulator. All of this galvanic corrosion takes place when the materials start swapping electrons - this leaves the less noble material unbalanced and oxygen atoms step in and start to make new materials from it (oxidation!). If you can keep these two items electrically isolated (for instance, with a patch of fiberglass cloth and resin) or charged with a small current (as we did in some pipeline systems), they won't swap electrons as readily and it helps the less noble material keep it's molecular crap together. When they're in the process of corroding you can actually measure a tiny electrical current. This also explains why salt water accelerates the problem - there are other things involved but the salt water will carry electrical current better than fresh water so when you get salt water mixed between these materials, it accelerates the corrosion because it increases the electrical conductivity allowing the different materials to swap more electrons.

Jake,

you had me at "I used to be a cathodic protection system technician for a gas company..."

And this paraphrased section " salt water will carry electrical current better than fresh water"

Fresh water will carry a current, pure water will not, but you knew that.

You post above is very informative.
I just kinda knew the basics, of what you have down to a science.

Nice post btw

That chart is worth saving. Never have heard of this alloy 20 stainless. probably, titanium is what the highest level guys use with carbon.
Mostly, all my s.s. rusts a little already, and i hadn't noticed that the bolts in the carbon were any more rusty than usual.
You can make your own cheek block and fasten it with epoxy and carbon using an existing sheeve. My policy is; getting rid of as much metal as possible is the way to go.

Pure water has a resistance of 18 meg-ohms.