Coarse or Fine thread?

thinwater · May 16, 2011

FWIW, rivies are not hard to drill out. If the wall is less than 1/8", go with the rivets.

Course threads in such a soft material, in my expereince, though I have used both with success. Don't forget the tef-gel or equivalent.

Ron20324 · May 16, 2011

Coarse is better, but obviously you don't get as many. Fine you get less bite depth and more threads but the reaction will make the fine threads usless quicker than the coarse. It's a toss up, and may depend on if there is much load on the fitting. I like fine.

bria46 · May 16, 2011

It really depends on the size of the machine screw that you plan on using - #6, #8 and #10 with plenty of curve on the boom = 32 Threads per inch. #12 or 1/4" - 20 - 24 tpi or 20 tpi. Use a drill bit a couple of thousands smaller than the recommended size for the tap. Make sure that you use a sharp/clean tap, removing the aluminum chards often by backing/reversing out the tap.

dscribner · May 16, 2011

I mounted an eye to the top of my mast but I thru bolted it. I epoxied nylock-nuts in a channel at the same spacing as the eyes holes. I drilled the holes in the mast, then I taped the channel to three lengths of PVC pipe and slid it into the bast with the holes facing down. Once I located the channel over the holes, I started both screws. Since they were contained in the channel they couldn't spin and I could tighten them to my hearts desire. The nylon keeps them from spinning out. It worked well on the mast. If you can open on end of the boom, it would work well there too.

Merlin Clark · May 16, 2011

I generally use aluminum pop rivets (with aluminum mandrels) but was just last night reading (somewhere on SBO forums) about rivet nuts and will pick up one of these on my next trip accross the bridge
http://www.harborfreight.com/45-piece-threaded-insert-riveter-kit-1210.html

Lee Thompson · May 16, 2011

I agree with Thinwater go with the rivets. Lee

kenn · May 17, 2011

Another vote for pop-rivets.

Joe11688 · May 18, 2011

Ted said:
I am planning on mounting some new fittings on my boom. I want the ability to remove them in the future so I don't want to use rivets. Is it better to use coarse or fine threads when tapping thin walled aluminum? My guess would be to use fine threads but I don't want to guess here? All expert advice welcome. Thanks

I would use coarse thread machine screws and coat the threads with Lock-Tite thread cement, red.

Timo42 · May 19, 2011

Screws aren't going to hold very well in thin aluminum, if you can't reach the back to add a nut or nutplate, rivets are a better choice. I would go with SS rivets fo anything structural or highly loaded, but there are high strength aluminum rivets out there. Rivnuts work ok but the shoulder of the rivnut is going to leave your hardware a little proud of the surface, unless you use some sort of gasket it could wobble loose or bend.

Steve Dion · May 19, 2011

I would also go with rivets. If you use ss screws in aluminum you will eventually get corrosion between the two metals. Rivets are easy enough to remove in the future and save a lot of aggravation.

Joe11688 · May 19, 2011

Timo42 said:
Screws aren't going to hold very well in thin aluminum, if you can't reach the back to add a nut or nutplate, rivets are a better choice. I would go with SS rivets fo anything structural or highly loaded, but there are high strength aluminum rivets out there. Rivnuts work ok but the shoulder of the rivnut is going to leave your hardware a little proud of the surface, unless you use some sort of gasket it could wobble loose or bend.

I disagree. The mast on his boat has thicker Aluminum than my Z-Spar mast on my 1986 O'Day 222 but that's beside the point. Three years ago I installed a Jib sheave block on my mast and I drilled and tapped it for four machine screws. My CDI Roller furler has it's own halyard and the only time I use my Jib Halyard is when I need to raise/lower my mast with my Gin Pole. So you can imagine the strain that I'm putting on this Jib sheave block. I mounted a horn cleat on my mast for my flag halyard back in the 1980s the very same way and it's still holding strong. I use it to tie off a "pig stick" at the top of my mast with our club pendant attached to it.

Three weeks ago I mounted a pad eye on my mast for a Forespar whisker pole that one of my friends gave me last year. I drilled and tapped the mast. I used thread lock cement on the screws.
Rivets are OK to use. I have nothing against using rivets, but in most cases stainless steel machine screws will also work fine as well. Anyway, it's his call and I'll let him make it.

Joe11688 · May 19, 2011

Steve Dion said:
I would also go with rivets. If you use ss screws in aluminum you will eventually get corrosion between the two metals. Rivets are easy enough to remove in the future and save a lot of aggravation.

This is true. You can get corrosion between the two metals and this is why I mention using the thread lock cement which will not only keep the screws from backing out, but will also insulate them as well.

esterhazyinoz · May 20, 2011

I have used both screws and rivets to mount various hardware to my mast. Even with a small boat, if using rivets on hardware that will take some decent amount of load, I used large SS rivets that required a really large rivet gun like the one pictured. You have to use these with some caution as they can take a slice off you fingers or nipple if you stray too close when compressing the handle.
Whichever I use, screws or rivets, I always coat the area and connector with sikaflex 291 to stop any corrosion due to dis-similar metals.

kenn · May 20, 2011

Trinkka said:
in most cases stainless steel machine screws will also work fine as well.

Your experience confirms that screws can work, but if the question is 'which is better?', I still think rivets are the better choice.

Joe11688 · May 20, 2011

esterhazyinoz said:
I have used both screws and rivets to mount various hardware to my mast. Even with a small boat, if using rivets on hardware that will take some decent amount of load, I used large SS rivets that required a really large rivet gun like the one pictured. You have to use these with some caution as they can take a slice off you fingers or nipple if you stray too close when compressing the handle.
Whichever I use, screws or rivets, I always coat the area and connector with sikaflex 291 to stop any corrosion due to dis-similar metals.

I think I'd be afraid of using that thing myself, being a guitar player.

I think that one has to use some discretion when it comes to using rivets or screws. When I bought my CDI Roller Furler, I needed to change my fore stay connection from a T Ball fitting to a marine eye. Actually, you're supposed to install regular toggle fittings at both ends of the fore stay for the furler, but I came up with a Mickey Mouse type of toggle fitting that makes it easier to remove my fore stay from the tang on the mast when I'm trailering my boat with the fuler attached to the mast. I ran it by a guy who is a top authority on O'Day sailboats first, and he said it was OK.

I needed to convert the T-Ball plate on my mast by adding a Dwyer tang to my mast which I did. I spotted where the tang needed to go on my mast, and I drilled the holes for the rivets. Then I had to trailer my boat with the mast on it to D&R Marine where my friend Rudy had his pneumatic rivet gun at his shop, and I had him install the six rivets to the tang.
For things like tangs and pad eyes that will take a lot of strain, I can see using rivets over screws.
This sidaflex 291 is similar to most marine caulking and will do the trick at insulating against electrolysis.
Years ago when I lost my first mast out off of Newport RI, I had a new Z-Spar mast made up with a Kenyon hinged tabernacle. The rigger used Stainless steel threaded machine screws to secure the plug of the hinged plate to the inside of the mast. Years later, the metal around the screws started to deteriorate. I wound up bring my mast to a guy who does Heliark welding and he straightened it out along with a couple of cracks in my mast. I use West System Epoxy for an insulator when the two metals come in contact. I let it dry and screwed it back together. Hopefully I won't have a problem but some guys have used the plastic from milk jugs as an insulator. Anything that you can apply between these metals is better than nothing at all I think.

esterhazyinoz · May 20, 2011

I was fitting a spinnaker pole mast ring using large SS rivets when I used that monster rivet gun. I borrowed it from my local chandlery. Even with all that mechanical advantage I still had to lean into it. Being a guitar player also, I kept my fingers out of harms way.
Re electrolysis prevention, there are a lot of products out there that will achieve that, I like the gooey stuff that will coat all contact surfaces and create a watertight connection by squeezing some in to the middle of the rivet.

Joe11688 · May 20, 2011

esterhazyinoz said:
I was fitting a spinnaker pole mast ring using large SS rivets when I used that monster rivet gun. I borrowed it from my local chandlery. Even with all that mechanical advantage I still had to lean into it. Being a guitar player also, I kept my fingers out of harms way.
Re electrolysis prevention, there are a lot of products out there that will achieve that, I like the gooey stuff that will coat all contact surfaces and create a watertight connection.

I'm a huge Chet A and Jerry R fan myself. I think that Tommy E from down under is phenominal. I have a CD with he and Chet together.
Have a great sailing season!

Joe

esterhazyinoz · May 21, 2011

Is it warm enough yet to sail off your beautiful coast? I visit that area of the world often as my sister has a house on Martha's Vineyard. That New England coast is just a beautiful part of the universe.

Joe11688 · May 21, 2011

esterhazyinoz said:
Is it warm enough yet to sail off your beautiful coast? I visit that area of the world often as my sister has a house on Martha's Vineyard. That New England coast is just a beautiful part of the universe.

It's been cold and rainy for about a week now. May has been a terrible month this year and it's usually a warm month. I've had my boat in the water for about two weeks now and I've only used it once for an overnighter in one of my favorite coves on the river. Next week should be pretty good. We're having our opening day today at our yacht club with free hamburgs and hot dogs on the barbie with a pot luck dinner.
http://www.shawometyachtclub.com/
Martha's Vineyard is one of my favorite islands. We used to sail over there from Mattapoiset Harbor on Buzzard's Bay back in the 1990s and anchored in Vineyard Haven Harbor near the beach. Another nice place to visit in that area is Cuttyhunk Is. at the end of the Elizabeth Is. It's like going back in time. I don't get out to those areas much anymore. My area is Mount Hope Bay Ma., and Narragansett Bay RI., particularly the Bristol area.
Smooth Sailing!
Joe

Coarse or Fine thread?

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