Ganzi

imbed stainless steel in a carbon laminate - should I ?

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I am rebuilding the 2 flanges/cheeks that attach the tiller to my cassette rudder. They are made of carbon fiber. The helm is attached to those flanges with bolts, and the corresponding holes in the flanges became  oval (this cassette has an history of abuse,  dont ask). I would like to reposition precisely those holes  and make sure that they stay true The flanges are not very thick - 5 mms maybe - so I am thinking of inserting a stainless steel washer in the middle of the laminate  (therefore they will be sealed with carbon on both sides when I am finished).

Any reason not to do that ? Better solutions ? I thought of G10 1/4 inch but it seems much more work  to integrate in cleanly in the schedule.

thks

 

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I don't think stainless likes to be deprived of oxygen, although in this application it probably doesn't matter much. How about a titanium washer? Not sure what the wear characteristics are compared to stainless, but it'd be cooler.

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No.

Every example I have seen of metal embedded in plastic has ended badly.

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No. Stainless washers are sloppy out of the box. Likewise I wouldn’t bury a piece of metal inside composite unless it was a chunk of aluminium like they do on high-end bikes.

The more typical way would be to have a couple of bushings made up. The holes are enlarged as the bushings have larger external flanges. If it’s a 1/4” bolt the bushing would be 1/2” the flange would be 3/4”. 
 

It distributes the load. Limits the damage to the composite. Gets rid of washers. 

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You might be able to have them turned by a machinist with a lathe. Delrin(acetyl) plastic might be better with carbon vs metal. 

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Does the tiller need to be separated from the rudder?  If not what about gluing G10 rod where the bolts went and going over the whole thing with carbon. Seems like it's sticks close to the original setup without alot of rework or added weight and should be stronger.

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5 hours ago, PaulinVictoria said:

I don't think stainless likes to be deprived of oxygen, although in this application it probably doesn't matter much. How about a titanium washer? Not sure what the wear characteristics are compared to stainless, but it'd be cooler.

Titanium is very bad in cyclic bearing.

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Can you close the tiller flanges at the aft end to make a continuous structure?  Then slide it over the cassette and try to make it as tight a fit as possible, if needed put shims at the corners to make a snug fit.  Then the loads get directly transferred into the composite much more spread out instead of a very concentrated bearing stress at the bolt.

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instead of flanges on both sides can you add a top and bottom so it is a box the the tiller slides into? Would make things less prone to flex. Could still use bolts. Add G10 tubes in the tiller for the bolts too. 

 

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 thks all,

tiller needs to flip up  when I remove the cassette (which I do as soon as the boat strays docked for some time). so, no permanent bonding of the axis.

titanium, I dont have. 

closing the flanges + shims,  yes but no, as it would be in the way of the pin.

bushings ... Got some nylon bushings today from hardware store, and then looked at this interestign chart - thks Diamond Jim - and now it seems that SS will actually have good bonding (wat’s nylon on this chart ? PPE ?)  Still, I think I ll go this way - if it fails I wont have to destroy the flanges to replace them ... 

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Don't do it. Carbon + s.s. = electrolysis The s.s. gets eaten, the carbon is more noble. You isolate the s.s.with a thin layer of regular fiberglass. If you look at composite chain plates, you'll see the thin glass layer between carbon and the s. s. Bushing. 

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Stainless is used against carbon all the time.   I'll have to go tell my gooseneck 316 stainless pin to begin rusting as it's lazy ass is still like knew 12 years later.   As well as my t-bar fittings, as well as my backstay pin, sheave pins, sheave boxes.....   all stainless....   all rust free a decade plus later.  

Yes of course you can encapsulated stainless in fiberglass first for any application you can't inspect or replace like in a rudder tube insert, etc.

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It's true that stainless doesn't get along with Carbon. Sometimes you have to use stainless fasteners with carbon because titanium fasteners are so cost prohibitive, but replacing them at intervals is kind of important. Titanium plate and rod are not cost prohibitive and it's not the worst stuff to work with. Makes bright white sparks when grinding. Watch out for breaking taps when tapping titanium. It's kind of sticky and rubbery. Allied titanium is a good place to buy from and they have metric and imperial stock.

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On 7/4/2020 at 11:19 AM, Ganzi said:

(wat’s nylon on this chart ? PPE ?)  Still, I think I ll go this way - if it fails I wont have to destroy the flanges to replace them ... 

Nylon is very slippery. It’s got one of the lowest coefficients of friction. Comparable to polyethylene. Same problem as a bearing material. Soft.

Delrin(Acetal) is the go. Strong easy to machine.

Nylon is a great material when reinforced with glass fibre. Harken & Ronstan use it for the cheeks on their blocks. 
 

http://www.dotmar.com.au/propertiestables.php

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I’d be surprised if you got ohmic contact between ss and carbon unless you drill or machine the composite after cure. Casting in place with epoxy should be insulated. Any evidence to the contrary?
 

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If consolidated well, fibers will touch the s.s. I have always thought of it as "best known practice" for 18 years or so. 

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Have you ever measured it with a meter?  Ohmic contact to carbon nanotubes is not simple.   But I readily believe a fastener or machined surface would conduct. 

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Some of my older carbon sails have very visible corrosion on the stainless grommets and cringles.

Sailmakers have since learned that the stainless needs to be better isolated from the carbon to prevent corrosion. 

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I would guess crimped cringles are similar to mechanical fasteners with pressure between fibers and metal as opposed to bonded

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It's simple to avoid - a single layer of fiberglass between them is normal/best practice.

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On 7/2/2020 at 9:08 PM, Ganzi said:

I am rebuilding the 2 flanges/cheeks that attach the tiller to my cassette rudder. They are made of carbon fiber. The helm is attached to those flanges with bolts, and the corresponding holes in the flanges became  oval (this cassette has an history of abuse,  dont ask). I would like to reposition precisely those holes  and make sure that they stay true The flanges are not very thick - 5 mms maybe - so I am thinking of inserting a stainless steel washer in the middle of the laminate  (therefore they will be sealed with carbon on both sides when I am finished).

Any reason not to do that ? Better solutions ? I thought of G10 1/4 inch but it seems much more work  to integrate in cleanly in the schedule.

thks

 

9BE04483-EF72-462A-98A1-B26811E29C72.jpeg

No problem with stainless 

 

the photo is a carbon mast , built Switzerland 1993 

the gooseneck saddles  are stainless 

 

the halyard exits are stainless 

 

the Swiss have a habit of using a layer of eglass  between metal hardware  and  carbon  

This is a very old carbon spar, you might contact the west guys for current best practice 

I believe the gooseneck saddle bonding surface is sand blasted 

 

resin system was Gurit 

 

 

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"the Swiss have a habit of using a layer of eglass  between metal hardware  and  carbon "

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I have two through bolts holding my tiller to the rudder stock, the holes were slogged in the stock.

I heated some long bolt shafts and coated in wax, wiped off and cooled. Set these in place and poured epoxy to fill the gap. Bolts easy pull out when set.

Tiller solid now.

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