Rivets: simple question
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Don't even think it, with SS rivets in an aluminum spar. It will ruin the hole.
As others have said, drill the old rivets out. Most are 3/16", but check. Use the same diameter drill as the rivet. I've done this up the mast many times, it's not hard. Sometimes the rivet starts to spin; if it's that loose either grab it with vise grips or wedge a scraper under the lip and continue drilling. Take a 3/16-inch punch with you; often they don't quite let go and a tap will finish them. New rivets are fast, but take some care; everything must be pressed tightly together as the rivet expands.
If the holes are still 3/16-inch, go back with rivets. Never self tapping screws. Not withstanding the good reasons given, eventually they will snag a halyard or nick a wire.
It is also possible that there simply were not enough fasteners. Don't drill too many holes close together, but one or two more fasteners might help. Can't tell without seeing it.
I don't mean to be a pest about this, but the instructions for intalling the mast and boom fittings for the Spinlock Powervang, says "drill and tap", though it does not say what kind of screw they have in mind. From what I am reading here, a rivnut would be a far better fastener for a device that will be subjected to the forces normally visited on a topping lift, vang, and jibe limiter.
If you are going to drill & tap be sure the mast section is at least as thick as the wire diameter of the machine screw you're using & use fine threads.. Personally I would rivet that with SS rivets and call it a day.
Hey MS
I was not trying to say that sheet metal screws are the end all be all in boat construction. They do work though, albet with some reduced saltyness to the eye. After trying to attach the SS bail that controls the halyard to mast angle on the roller furling jib with rivets while up the mast I'm of the opinion that my sheet metal screw solution was both eaiser and holds the bail more firmly than the rivets I initally tried. The only down side I could possibly see it the head may catch on the sail. My solution was above the jib so not an issue for me.
I was not trying to say that sheet metal screws are the end all be all in boat construction. They do work though, albet with some reduced saltyness to the eye. After trying to attach the SS bail that controls the halyard to mast angle on the roller furling jib with rivets while up the mast I'm of the opinion that my sheet metal screw solution was both eaiser and holds the bail more firmly than the rivets I initally tried. The only down side I could possibly see it the head may catch on the sail. My solution was above the jib so not an issue for me.
Did a search on Tefgel and it's a teflon gel . It eliminates dissimiliar metal corrosion.
(DUH!!for me). LOL
How is it applied when using stainless steel rivets in a 1/8" thick aluminum mast and is it necessary??? I'm just asking to learn so please be kind. I dont really understand what the risk of galvanic interaction with stainless and aluminum is and where strength of SS would be a "significant" requirement over aluminum rivets. Again just asking so that going forward I can do the right thing. Understanding why helps me to remember the correct way to do something.
If you are going to drill & tap.....machine screw you're using & use fine threads.. quote]
Some replies are drifting over to saying "sheet metal screws", and then there machine screws. To the OP, he might not pick up on what the replies are really saying. Or, Bill, are you REALLY saying 'sheet metal screws' as opposed to 'machine screws'
For jfmid
TefGel does two things, first it is an anti-seize agent which help deter stainless threads from galling and second it helps prevent galvanic corrosion between dissimilar metals (typically stainless and aluminum). It is a white semi-solid (think warm creamy peanut butter) and you apply it by any method that works; dip, brush, spatula, etc.
If you have ever tried to get the end fittings off of a 10 year old boom on a salt water boat you will know about galvanic corrosion as the stainless screws will be locked into the aluminum and after you twist the screw head off you will find a hard white layer of corroded aluminum locking the screw in shank in place.
My suggestion is to spend the outrageous price of about $30.00 for the 2 oz. tub (I'm on year 9 with mine and think it will be a lifetime supply) and use it on all the stainless/aluminum spots on your boat.
TefGel does two things, first it is an anti-seize agent which help deter stainless threads from galling and second it helps prevent galvanic corrosion between dissimilar metals (typically stainless and aluminum). It is a white semi-solid (think warm creamy peanut butter) and you apply it by any method that works; dip, brush, spatula, etc.
If you have ever tried to get the end fittings off of a 10 year old boom on a salt water boat you will know about galvanic corrosion as the stainless screws will be locked into the aluminum and after you twist the screw head off you will find a hard white layer of corroded aluminum locking the screw in shank in place.
My suggestion is to spend the outrageous price of about $30.00 for the 2 oz. tub (I'm on year 9 with mine and think it will be a lifetime supply) and use it on all the stainless/aluminum spots on your boat.
Thanks for all the discussion. I reported what was said to my friend, but he was definite that he wanted to replace the rivets with machine screws. He said that's what the rigger he'd talked with recommended. I had to drill the rivets out with a pretty large bit (1/4") so I had to go with larger machine screws. No, I didn't use self tapping sheet metal screws - I tapped and used machine screws, using the blue Loctite and a rubber gasket type of material between the ss mounting plate and the mast.
I don't understand some of the bias against rivets. I've certainly tapped for machine screws too, so I do understand their merits. They are stronger in thicker masts (read "larger boats") but weaker in thinner masts (read "trailer boats and beach cats"). You MUST use Tefgel on screws you intend to remove someday, though with rivets it makes less difference.
a. I don't understand why you would drill oversize to remove a rivet. I have removed hundreds over the years, in both marine and industrial settings, and never had to do that. Drill the exact size, hold it if is spins, and tap it through with a punch. Drilling over size was most likely a mistake born of fatigue; we all make them.
b. Machine screws and self-tapers can sieze, rivets cannot. They always drill out.
c. Drilling out seized SS machine screws is really bad. Not something you want to do up a mast; most likely it would have to come down. Not much fun in the shop, though reasonable with good attention to detail.
d. I wouldn't use a gasket in general (depends on the geometry--acceptable if there are multiple bolts on the same plate); that simply allows for increased movement, loosening, and eventual failure. Tefgel is enough.
e. Aluminum rivets arn't a great idea. I've seen them used on sailing dingies (rare), but they are generally too soft to hold up under high load. Best limit those to gutter repairs.
Rivets are NOT some cheap production trick; they are the right answer in many circumstances. Perhaps not in this case, since the mast is thick enough to take threads and because the radar is likely to come down someday. If you ask me to replace the hounds on a beach cat, it's rivets every time. If you ask me to add a block to the boom on my PDQ (did that a few months ago) I'll be tapping machine screws.
Horses for courses.
a. I don't understand why you would drill oversize to remove a rivet. I have removed hundreds over the years, in both marine and industrial settings, and never had to do that. Drill the exact size, hold it if is spins, and tap it through with a punch. Drilling over size was most likely a mistake born of fatigue; we all make them.
b. Machine screws and self-tapers can sieze, rivets cannot. They always drill out.
c. Drilling out seized SS machine screws is really bad. Not something you want to do up a mast; most likely it would have to come down. Not much fun in the shop, though reasonable with good attention to detail.
d. I wouldn't use a gasket in general (depends on the geometry--acceptable if there are multiple bolts on the same plate); that simply allows for increased movement, loosening, and eventual failure. Tefgel is enough.
e. Aluminum rivets arn't a great idea. I've seen them used on sailing dingies (rare), but they are generally too soft to hold up under high load. Best limit those to gutter repairs.
Rivets are NOT some cheap production trick; they are the right answer in many circumstances. Perhaps not in this case, since the mast is thick enough to take threads and because the radar is likely to come down someday. If you ask me to replace the hounds on a beach cat, it's rivets every time. If you ask me to add a block to the boom on my PDQ (did that a few months ago) I'll be tapping machine screws.
Horses for courses.
Main, I never planned to use screws in the installation of the Spinlock Vang. I only pointed that out because it seemed odd that the Spinlock's installation instructions mentioned only screws and not rivets at all.
That still leaves two questions: (1) Why do you prefer rivets to rivnuts for this very high stress installation, and (2) For this install, is there a reason to consider aluminum rivets over SS in an aluminum mast and boom?
That still leaves two questions: (1) Why do you prefer rivets to rivnuts for this very high stress installation, and (2) For this install, is there a reason to consider aluminum rivets over SS in an aluminum mast and boom?
First of all screws have a slot for removing them as well as installing them. Rivets are considered permanent. Before they welded ship's plates together they riveted them. Rivnuts allow you dis-assembly. Rivets are just as strong but are for a one time use. Tef Gel does not isolate the parts but it prevents the electrolyte from entering the joint. You can't have electrolytic corrosion without an electrolyte. A perfectly dry zinc to steel joint will last forever if it stays dry.
why oversized
As for replacing the rivets, the issue was this: the plate for the radar mount is flat, fitting onto the curve of the mast. The result is that one part of the plate isn't snug up against the mast and the rivet didn't seem to be really tight. I must say, when I shook the radar side to side at first it had a fair bit of play. After replacing the rivets it didn't.
By "oversized" I meant larger than I'd intended. I was going to use a 1/4-20 tap, but I had to use a 1/4" bit to drill out the rivets, leaving a hole too large for that tap. (A smaller bit wasn't large enough to drill out the rivet.)
As for replacing the rivets, the issue was this: the plate for the radar mount is flat, fitting onto the curve of the mast. The result is that one part of the plate isn't snug up against the mast and the rivet didn't seem to be really tight. I must say, when I shook the radar side to side at first it had a fair bit of play. After replacing the rivets it didn't.
OK, I am definately zeroing in on this now. So, Ross, I believe rivnuts are the way to go for the vang installation. The mounting holes are 1/4". The only remaining question is SS or aluminum rivnuts. I assume alunminum is easier to install with a lighter duty tool, easier to find, and the flange is more likely to conform to the shape of the mast . Probably less durable and not as strong. Is there any reason to favor an aluminum rivnut in an aluminum mast?
That is the main weakness of rivets; if you can't press everything flat and tight before expanding the rivet, the result is wobbly. A bolt, on the other hand, will pull up. Good choice.
But isn't that issue resolved by using rivnuts, which also eliminates the inadequate "bite" when screws of any kind are put into thin-walled material?
thin walled
by the way, this was on a Jenneau 46, so the mast was relatively thick walled.
The mast on my Hunter 31 is not that subsantial, nor that wide. I worry about threaded pointy objects inside the mast to catch unwary wiring or rigging. The rivnut has a pretty short smooth profile inside the mast.
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