Screwing into aluminum - SailNet Community
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post #1 of 39 Old 09-18-2017 Thread Starter
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Screwing into aluminum

Sailheads!

I'm preparing to mount a Raymarine Rotavecta onto the top of my mast (pictured) and I need to know how this is done. The Windex that is there was secured with what looks like a wood screw (pictured) and Raymarine included two screws (also pictured) that to me look like just plain old wood screws.

So should I just drill some pilot holes and screw the base into them? Is it really that easy? Doesn't the kind of metal that the screws are made of make a difference? Should I line the holes with some sort of sealant? Or do I need to get out the tap and die set and prepare more formal holes?

Any tips would be appreciated!

Thanks!
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post #2 of 39 Old 09-18-2017
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Those are panhead sheetmetal screws. Usually you drill a pilot hole a little smaller diameter than the screw. I would guess that it's a good idea to bed the screws with butyl tape.
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post #3 of 39 Old 09-18-2017
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Re: Screwing into aluminum

Agree those are sheet metal screws. But the top of your mast is much thicker than typical sheet metal. You should be able to drive them into an undersized hole there, but it isn't going to be easy. A better installation would be to tap the holes and use machine screws.

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post #4 of 39 Old 09-18-2017
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Re: Screwing into aluminum

I would tap the holes and use machine screws. Also coat the screws with Tefgel, Duralac, or similar to prevent corrosion, and use a locking washer to prevent backout. Maybe use Locktite instead, which will provide some corrosion resistance and lock them in. I don't see any need to bed it with butyl tape, as it isn't a leak concern.

The problem I always have with sheet metal screws is that if the pilot hole isn't almost the same size as the threads, then driving them through that much aluminum tends to snap them before they sit fully. Then you have a real problem. And if you make the hole large enough to prevent this, then the holding is marginal. The cheap quality screws provided with most things make the problem worse.

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post #5 of 39 Old 09-18-2017
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Re: Screwing into aluminum

You could use self-tapping screws. If the mast head has any depth to it you need to drill and tap which is not easy in aluminum, go slow back and forth a lot.
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Re: Screwing into aluminum

Chances are you will not be removing that bracket any time soon. I would just use aluminum rivets. Much simpler and a better mount.

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post #7 of 39 Old 09-18-2017
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Re: Screwing into aluminum

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Originally Posted by Skipper Dan View Post
You could use self-tapping screws. If the mast head has any depth to it you need to drill and tap which is not easy in aluminum, go slow back and forth a lot.
Anything is better than nothing on a Tap, Kroil, any tapping compound, I used to use this pink stuff kinda thick I don't remember the name now and in a pinch lithium grease will help a bunch.
+1 on tefgel I have a small tube that will probably never run out, it was cheap too.
SS self tappers will work good I would pre-drill which kinda defeats the purpose but they hold better than a sheet metal screw IMO.
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Re: Screwing into aluminum

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Chances are you will not be removing that bracket any time soon. I would just use aluminum rivets. Much simpler and a better mount.
I have had way too many aluminum rivets corrode and fail, even when just connecting aluminum parts to aluminum. If you go with rivets, get monel rivets.

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post #9 of 39 Old 09-18-2017
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Re: Screwing into aluminum

I predrill self tappers. They are just better than sheet metal screws. Either will break when going into aluminum that is thicker if not drilled.
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Re: Screwing into aluminum

As has been stated, drilling and tapping for a machine screw is far better than using a panhead sheet metal screw in aluminum thicker than 1/8". I would use a 10-32 machine screw and apply removable threadlocker (blue) when installing it. A tapping fluid such as Tap Magic would be good to use for aluminum but you could also use plain old mineral spirits, just remember to keep the tap perpendicular to the axis of the hole and back it out a quarter turn or so for every half turn. Rivets, especially aluminum pop rivets come loose and there is no way to tighten them. I would use an Allen head screw although a 5/16 hex head would be fine also.
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