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Old 08-03-2015, 13:04   #16
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Re: Removal of stainless screws from aluminum and corrosion

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I watched an outboard mechanic deal with stainless screws stuck in aluminum many times. He would use a torch to heat the aluminum and the screws came out with no problem. Yes the aluminum expands much more than the stainless.

When he reassembled it, he would coat the screws with Permatex 3. If the engines came back again, the screws would come right out with no corrosion.
Isn't Tefgel the go-to stuff for preventing the dissimilar metal corrosion problem?
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Old 08-03-2015, 18:50   #17
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Re: Removal of stainless screws from aluminum and corrosion

Poiu, TefGel hadn't been invented when I was hanging out in an outboard shop. I have heard good things about TefGel in that application. Permatex smells better than TefGel
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Old 09-03-2015, 06:22   #18
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Re: Removal of stainless screws from aluminum and corrosion

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I have had a lot better results using a manual impact driver rather then the cordless/electric kind. They are able to deliver far more downward force/holding power/shock then the electric kind ever can. Along with oil and heat as mentioned above, I would say thats your best bet.
This will certainly get them out but you'll be beating on your window frame with a hammer.
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Old 09-03-2015, 09:39   #19
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Re: Removal of stainless screws from aluminum and corrosion

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I use all the expletives and macho death threats I can come up with. Doesn't always work but I get the last word and feel better about my efforts. when they do come out use a tap or thread chaser to clean the female threads and recoat with teffgel or similar.
If that fails, barking out "You can be replaced you &%$#@*!" often yields surprisingly good results. It's weird, but it works. Maybe boats really do have souls.
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Old 09-03-2015, 10:09   #20
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Re: Removal of stainless screws from aluminum and corrosion

Heat the aluminum. The hole is what you want to increase in size.

Use Tef-Gel to eliminate corrosion when you screw the fastener back in. The riggers where I haul out, KKMI, are all using Tef-Gel. This is a high end boat yard that hauls very high end race boats...so they know what they are doing.

Lanocote is old school, dries up over time and overall is less effective.
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Old 09-03-2015, 10:16   #21
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Re: Removal of stainless screws from aluminum and corrosion

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Isn't Tefgel the go-to stuff for preventing the dissimilar metal corrosion problem?
Absolutely!
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Old 09-03-2015, 11:36   #22
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Re: Removal of stainless screws from aluminum and corrosion

Tef Gel or Forespar Marine Lube TEF 45 Corrosion Blocker & Anti-Sieze.
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Old 09-03-2015, 12:51   #23
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Re: Removal of stainless screws from aluminum and corrosion

My Question would be why use Stainless Steel Screws if it is a know fact they will turn up this way. Would it not be wiser to use Aluminum Screws? One the other side of the issue, would be a system that prevents the SS SCREW from direct contact with the Aluminum Hull, not an easy order I admit, but we Americans made it to the moon and back, certainly our Engineers ought to be able to design a SS BOLT or SCREW that has a shield built around it preventing direct contact of SS with Aluminum. I am only presenting this as a MAYBE, and just MAYBE it cannot be done.

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Old 09-03-2015, 16:28   #24
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Re: Removal of stainless screws from aluminum and corrosion

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My Question would be why use Stainless Steel Screws if it is a know fact they will turn up this way. Would it not be wiser to use Aluminum Screws? One the other side of the issue, would be a system that prevents the SS SCREW from direct contact with the Aluminum Hull, not an easy order I admit, but we Americans made it to the moon and back, certainly our Engineers ought to be able to design a SS BOLT or SCREW that has a shield built around it preventing direct contact of SS with Aluminum. I am only presenting this as a MAYBE, and just MAYBE it cannot be done.

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Aluminium is very soft. If you went a hard, heat treated aluminium alloy screw (which would need to be a machine screw) then the corrosion problem would still be present due to the alloys used. I believe monel is the metal to use, although is expensive. The poor mans fix is to use a galvanised steel screw. The screw corrodes then and not so much the aluminium.

For perfect compatability where the load is suitable, aluminium rivets dipped in tefgel before use are the best solution if electrolysis corrosion prevention is the priority.
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Old 09-03-2015, 16:54   #25
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Re: Removal of stainless screws from aluminum and corrosion

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Start soaking them with penetrating oil for a while in advance. Like daily, or several times a day for a week+ before you go near them with tools, if you can. Well, other than perhaps giving them a light tap with a mallet, to assist the penetrant in getting into the threads more effectively.

When it comes to tools, & pulling out seized screws in aluminum, I prefer the non powered variety. That way you can feel when you're on the edge of too much resistance/about to tear the head off of the fastener. Even if it means going to vice grips on the head of the screw or bolt, to get a better grip than a screwdriver alone will provide.

Also, of course, leaning on top of the handle of the screwdriver while turning it (or trying to) helps. As does doing anything you can to relieve pressure on the fastener/metal interface. Ditto on sometimes seeing if you can tighten a frozen one 1/8th of a turn @ first, prior to trying to extract it.

I've even used blocks of dry ice, or set stubborn parts in big freezers, in order to get the stuck metal bits to contract a bit. Just watch the bare skin on metal thing, if you go this route.

Also, given that you're talking about removing fasteners around a window, is there something heavy which you can lean up against it, so as to reduce the pressure of it's gasket against the frame & fasteners?

Plus when undoing screws or bolts on the perimeter of something like this, at the outset especially, you only want to loosen each one only a little. As if you totally pull one, a lot of it's load is taken up by it's nearby neighbors... making them even tougher to pull.
And if you can undo the fasteners in something resembling an X pattern, that'll generally help to mitigate this kind of issue also.
Good advice.

A short screwdriver will feed impact loads from a hammer well. A long screwdriver will twist. Sometimes a few taps can help and this may crack the screw free.

Make sure you have a good fit. Either flat blade or phillips. Both are less than ideal as they carry so little torque. If you replace them with internal wrenching the job will be easier next time.

Unfortunately the aluminum oxide (the corrosion) expands and really hangs on. Drilling out is often the only practical way. To make sure you drill concentric use a dremel and carbide burr to fashion a dome in the center. Then use a center drill, not a normal drill bit to get started.

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Old 09-03-2015, 17:02   #26
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Re: Removal of stainless screws from aluminum and corrosion

If you're planning on drilling out broken screws on a regular basis, these gizmos are the tool to use for marking the centre....



They're called "transfer punches".
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Old 13-03-2015, 00:51   #27
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Re: Removal of stainless screws from aluminum and corrosion

Guys, when it comes to drilling out fasteners, first try a left handed bit. Sometimes the torque from the drill, plus a bit trying to bite into the fastener in the opposite direction from it's threads is enough to get it to come out. Sans having to truly & fully drill it out... so then, too, if you're lucky & this works, odds are, you can just clean up the threads a touch, & you're good to go.

And... aluminum sucks (relatively speaking) when it comes to withstanding shock loads on fasteners. So if you're well & fully @ the point of being ready to drill out the offending screw or bolt, first give it a few good solid whacks with a hammer, & then try unscrewing it with the aid of Vise-Grips.
If it works, you'll likely still have to tap for new threads, & or install Heli-coils, but you wont be there for 1/2hr smoking bits, & getting cutting oil everywhere.


Also, I'm not knocking Tef-Gel, but I think that a lot of folks on here's drunk the Kool-Aide a bit much regarding it. As there are plenty of things which you can put onto threads, which provide galvanic isolation. Plus...

More importantly, there are items & places where you DON"T want the screws to be super easy to extract. As in some applications, if such is the case, then they may loosen up/fall out on their own. Due to thermal stresses, vibration, tens of thousands of work cycles, etc.
And them self loosening/falling out can lead to situations which are truly Bad Juju.

For example, you don't want to use Tef-Gel on a critical fitting on your furler, way up at the masthead. I mean who wants to go up there & try & fix things in a storm (at night, of course), or even in just a solid breeze with lumpy, & confused seas... After you've just spent 3hrs un-f**king the jib, & getting it stowed below decks. And then hoisting some other, inferior sized, canvas on your inner forestay.

In such an instance, you would want to use something such as an application appropriate type of thread locker, such as Loctite or similar. Usually Blue, but like I said, it varies with the application.
That said, they provide both galvanic isolation, and also ensure that the fasteners stay put.
- And the perk. There are varieties of thread sealants, & thread lockers (of various strengths) which will wick down into the threads & seal/cure, AFTER you get things adjusted perfectly. A handy trait from anyone's purview.

Just "a think"/something to make you choose your thread coating "tools" as selectively as you do, or more so, than the tools which you use to work on the project at hand.
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Old 13-03-2015, 01:04   #28
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Re: Removal of stainless screws from aluminum and corrosion

On the topic of galvanic corrosion, Skylark is having a new anodized aluminum mast step built to replace the original iron step. I asked the machinist to set up the step so I can use a retaining pin or bolt at the base of the mast. Maybe it is overkill, but I would like to use two short bolts of substantial diameter, one from each from the port and starboard side of the mast. There will be "ears" welded to the new step that will be inside the mast when the mast is on the step. I want to tap the "ear holes" and don't want to use S/S bolts.

Looking at the galvanic scale, I see that Indium is next to aluminum, but Indium is too soft for making bolts.

I am thinking ordinary steel for the bolts and , Loctite, Permatex or teflon tape on the threads. Any suggestions about bolt material?

I have learned the hard way that S/S straight slot or phillips head machine screws are not the best to use in connection with aluminum. I replaced all the retaining screws on my cast aluminum boom caps with bolts that use a hex wrench. I also turn these screws on the boom yearly, to keep 'em moving.
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Old 13-03-2015, 04:45   #29
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Re: Removal of stainless screws from aluminum and corrosion

On your mast step, if it's not already being machined, you might consider going with G10, if said material gets the nod from the engineer who's designing it. And I say as much due to the quantity of water, especially the salty type, which tends to eat many aluminum mast steps over time.

Also, with your idea for pins, to "bolt" the mast to the step. What are the odds of having the step come up far enough inside of the mast, so that pins can be run transversely through the (reinforced) tube & the step? Or that just the extra height of the step itself is enough to secure the mast in place. Like say a 4" vertical protrusion or so.

On bolts, I wouldn't overly sweat using stainless ones, actually they're a decent choice. It's the engineering/design behind how they fit into things that's the kicker.
What you want is things to be setup so that any holes in the mast which they pass through are oversized, & fitted with isolator sleeves.
Much the same way that Monel keel bolts are used to attach lead keels to an aluminum hulled boat.

Thus, anywhere the 2 electrically different metals would meet, there's a high modulus "plastic" (or similar) isolator. Pardon the expression, but think of it as a condom for bolts. They (the isolators) act like Tef-Gel, only on a bit bigger scale.

So in this case, you could have an oversized compression tube (or two) welded transversely through the base of the mast, & the tabs welded over the ends of the tube on the outside of the mast tube.
- Much in the same fashion as cross bolts mounting reinforcements are done for shroud tangs.
Then run an isolator & bolt through the base of the spar. And use isolating washers under the heads of the bolts which pass through the mast, as well as underneath of the heads of the bolts securing the tabs to the step.

FYI, in a lot of alloys used in marine applications, welding them causes a strength loss of 50% give or take. So it's worth thinking on/factoring in.

Also, on your current step, isn't there a flat, rectangular plate, with fore & aft slots for bolts on both sides of the spar, welded to the base of the mast at the moment?
They're often done that way on a lot of boats so that the heel of the spar can be moved fore & aft slightly in order to tune the rig. And once the heel is in the correct place, then the bolts in said slots are cranked down, to secure the mast to the step/ring frame.
- I don't have any pics of this kind of setup handy, but it's VERY common on racing boats, in all varieties of sizes. A rigger could show you all kinds of examples. As might a Goggle search.
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Old 13-03-2015, 05:21   #30
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Re: Removal of stainless screws from aluminum and corrosion

PS: On types of mast steps. If you look very closely at the pictures in the linked listing, where the base of the mast is shown, you can see the rectangular plate @ the base of the mast, on top of the (molded fiberglass) step as I described, just above.
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