Machine screws instead of Rivets?
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- Rank: Lubber
- Registered: May 09, 2012
- Last visit: May 13, 2012
- Posts: 6
Posted: May 13, 2012 - 09:28 AM
I need to reattach some hardware that is riveted on, just wondering if anyone has ever drilled and tapped for machine screws? Or are rivets the way to go? -
- Rank: Lubber
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Posted: May 13, 2012 - 10:12 AM
Most of the time on a cat there is not enough material to have enough threads for proper strength. Also you can't tap fiberglass. So that's why rivets are used.
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ALLEY CAT 1984 RED LINE HOBIE 18 MAGNUM
Sail # 10505 or 277
San Diego, Ca
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- Rank: Mate
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Posted: May 13, 2012 - 12:08 PM
Machine screws need at least three threads to develop any kind of strength in the joint. Better if they have at least five. If the screw is going to be subject to a lot of radial load that is likely to wallow out the material the screw is fastened to, you want more than that.
You can use something like nutserts or rivet nuts (two names for the same beastie) to add threads to thin material. These show up a lot in sheet metal work like you'd find in computer cases and electronics enclosures. They work great with sheet steel and sheet aluminum. But I doubt they'd work with fiberglass. They rely on plastic deformation of the base sheet material when they're installed. Glass won't do that.
If you have access to the back side of the fiberglass (if that's what you're talking about riveting into) you can glass in threaded metal inserts. This actually works quite well, though I don't think I've seen it on a boat before.
Likewise, if you have access to the back side of the material you're attaching your hardware to, you can always use machine screws and nylock nuts. When I rebuilt my trapeze bungee hardware I did this for the rear padeyes. There was an option to get a reinforcing plate with the padeye, which goes on the inside of the fiberglass. Once the screws and nuts are on, the glass is essentially sandwiched between the padeye and the reinforcing plate. Makes for a tough joint. Massive overkill for a bungee padeye, but it sure put a smile on my face.
Tom
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Tom Benedict
Island of Hawaii
P-Cat 18 / Sail# 361 / HA 7633 H / "Smilodon"
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Posted: May 13, 2012 - 12:28 PM
What are you re-attaching?
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Dustin Finlinson • Magna, UT
Member: Utah Sailing Association
1982 Prindle 18
1986 Hobie 17
1982 Prindle 16
1980 Prindle 16(mostly)
1976 Prindle 16(mostly)
Check out "Prindle Sailors" on Facebook.
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Posted: May 13, 2012 - 02:54 PM
If it was originally put on with rivets, put it back on with rivets. All Prindles and Nacras were assembled with either Stainless Steel or Monel rivets, and all but the earliest Hobies as well. Using anything else is a planned failure. Aluminum rivets are soft, wear quickly and then allow other parts to wear excessively.
The parts on your boat were designed to be held by good rivets. You are weakening the engineering of your boat by using weak parts.
Getting away with using aluminum rivets is just that - an attempt to cheat your safety and enjoyment of sailing to save some effort or money.
Don't mean to be preachy, I just don't want to read about how you were dismasted because you used aluminum rivets on your mast horn or a crossbar fitting and somebody got hurt.
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Sheet In!
Bob
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Prindle 18-2 #244 "Wakizashi"
Prindle 16 #3690 "Pegasus" Sold (sigh)
AZ Multihull Fleet 42 member
(Way) Past Commodore of Prindle Fleet 14
Arizona, USA
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Posted: Sep 03, 2012 - 03:26 PM
Were do you get long rivets to hold cleats on the mast of a h 16 -
- Rank: Mate
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Posted: Sep 03, 2012 - 04:33 PM
I always use self tapping phillips head stainless screws (obtainable any hdwe) with screw body diameter about 3/16" same as rivit. Pete
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