Rivet question

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eddystone

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Just trying to rivet end cap back onto boom. I have some 4.8mm and 6.2 mm monel rivets - the smaller are pretty loose and the larger won't fit. I can get a 5mm drill bit in with room to spare and a 5.5mm bit is a very tight fit. Would you use the smaller size or drill out to accommodate the larger ones? No-one seems to sell anything in between. I have seen 3/16" rivets advertised as both 4.8mm and 5mm and also "stainless steel monel rivets"!
 
As you are clearly aware Monel and stainless are quite different, though monel rivets could have a stainless mandrel. In an aluminium boom you should use monel rivets, however in 6.4mm size they are a tough job to pop. The end cap in a boom is not subjected to forces trying to pull it out so it might be perfectly acceptable to fix it in with aluminium rivets, which are a good deal easier to pop. I would drill out the holes to fit the larger size, making sure that the end cap was fully pushed home into the boom when I did so. The important issue is to make sure your rivets are correct length as well as diameter. The standard rivet size now seems to be 6.4mm not 6.2, and the former are probably effectively quarter inch rivets as a quarter inch equals 6.35mm.

Before drilling the holes just make sure your rivet gun is man enough for the big rivets. I have lazy tong one, which is a struggle to use and would certainly need a second person to hold the boom. The best rivet gun I have is a big long arm one, but it still needs quite a lot of effort to pop the largest rivets.

There is a table on the e-bay listing that gives guidance on rivet length. http://www.ebay.co.uk/itm/6-4mm-x-C...hash=item3a7395c6db:m:mTb4OqkcVuvbwDRI3ImbpgA
 
Assuming there is nothing else attached to the boom end plug, yes use ali rivets even small ones will be OK. Given that you may occasionally need to remove the plug for access to internal ropes and sheaves you might even consider drilling and tapping small screws into the plug so it can be removed easily. My little boat boom has a cloth cover attached with velcro mainly to keep the birds out. good luck olewill
 
My boom end caps were originally retained with aluminium pop rivets. There is no force on them as all the compressive loads are taken by the land on the end casting. When I installed in-boom blocks for single line reefing I drilled out the rivets and replaced them with Rivnuts in case I ever needed to service the blocks (which turned out to be very useful when my crew pulled all the reefing lines right out). However, I would have replaced aluminium rivets if this was not an issue.
 
In theory tapping into a mast section is a poor idea, in practice it seems to work quite well. I have retained the end of my boom like this for over 10 years with no problem.
I have fixed light duty cleats in the same way.
 
Been doing a lot of research on rivets recently as rebuilding my mast and have come to the conclusion if its structual i.e. part of the rigging then always use monel and if not aluminium is perfectly acceptable. Aluminium rivets still have a shear strength of several hundred kilos and are stronger than most people credit them. Stainless ones are not recommended as you need professional pullers to set them properly as the material is so hard.
 
Final thought - is there a risk M6 machine screws without a securing nut could work loose? is there anything that would secure them without making them impossible to remove - Loctite? Varnish?
 
eddystone said:
Final thought - is there a risk M6 machine screws without a securing nut could work loose? is there anything that would secure them without making them impossible to remove - Loctite? Varnish?
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The machine screws on the boom end fittings (gooseneck and boom end) on my boom haven't loosened in years. Bear in mind that the alloy casting of the fitting is what carries the tap, so there's a reasonable depth of metal for the tap, not just the thinner metal of the boom tube, which could present a problem. If you're really worried about things working loose, then a drop of Loctite would keep things together.
 
duncan99210 said:
The machine screws on the boom end fittings (gooseneck and boom end) on my boom haven't loosened in years. Bear in mind that the alloy casting of the fitting is what carries the tap, so there's a reasonable depth of metal for the tap, not just the thinner metal of the boom tube, which could present a problem. If you're really worried about things working loose, then a drop of Loctite would keep things together.
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I agree with this. Modern end caps are made for attachment by screws into tapped holes in the castings. My old ones pre-date this, which was why I used Riv-nuts instead. The screws have never moved in years.
 
Think I'll have to revert to rivets; the existing holes are a v.tight fit for a 5.5mm drill bit but 5mm is loose so probably 5.3-5.4ish. However the table I have says with ISO the correct hole is the tap size (6mm) less the pitch (1mm) i.e 5mm so already too big to make a clean thread.
 
eddystone said:
Think I'll have to revert to rivets; the existing holes are a v.tight fit for a 5.5mm drill bit but 5mm is loose so probably 5.3-5.4ish. However the table I have says with ISO the correct hole is the tap size (6mm) less the pitch (1mm) i.e 5mm so already too big to make a clean thread.
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Then why not use 8mm fasteners; or 6mm fasteners with thread inserts?
 
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