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Old 10-10-2018, 13:24   #1
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Filling Old Rivet Holes

I pulled my mast for painting, and took off most of the hardware. This includes mast steps that went up to the first set of spreaders that were attached with rivets. If I choose to not re-install them, what would be the best course of action regarding filling the holes? I would think filling/closing off the holes would be the way to go, but I am unsure of how to go about it. JB Weld, thickened epoxy, re-rivet?

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Old 10-10-2018, 14:07   #2
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Re: Filling Old Rivet Holes

There are "closed end blind rivets", pop rivets that leave a piece on the mandrel inside the rivet so it has no hole after installation. That would be the easy way.

You could use short self-tapping screws, but the pointy ends might chafe wires or halyards inside. Or tap the holes and insert machine screws, which would be a lot of work but leave you the option of reinstalling steps at a future date without more drilling.

Or chamfer the edges of the holes a bit with a wider drill bit then fill with the epoxy of your choice. (JBWeld just being a filled epoxy.) You could probably fill epoxy with aluminum dust so it looked more like the mast metal when set. If you're painting the mast, epoxy filling might disappear the old holes.

Or even put a neat circle of "roof and gutter" stainless steel metal tape over each one. Reasonably permanent, really cheap and fast.
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Old 10-10-2018, 14:58   #3
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Re: Filling Old Rivet Holes

I'd avoid use of any stainless (screws, rivets or tape) in making what is a cosmetic repair, for these would inevitably lead to corrosion. I would lean towards blind aluminium rivets: no corrosion issues, easy to install, and if steps are ever retrofitted, easy to drill out.

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Old 10-10-2018, 15:54   #4
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Re: Filling Old Rivet Holes

And stick each rivet shank into a tube of some sort of sealant or glue. That will keep the stem from maybe falling out and really stop corrosion.
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Old 10-10-2018, 16:06   #5
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Re: Filling Old Rivet Holes

Any harm in leaving them unfilled?
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Old 10-10-2018, 16:13   #6
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Re: Filling Old Rivet Holes

None of which I am aware.

Ann
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Old 10-10-2018, 16:35   #7
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Re: Filling Old Rivet Holes

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Any harm in leaving them unfilled?
No, this effort is completely cosmetic. None of the methods proposed add any strength to the tube. Possibly welding and grinding might restore some of the lost strength, but then the welding can alter the heat treatment state of the alloy and actually weaken it further.

But, the losses involved with the series of small holes is too small to be of interest... but it does leave the mast looking like termites had been at work!

Jim
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Old 10-10-2018, 16:52   #8
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Re: Filling Old Rivet Holes

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No, this effort is completely cosmetic. None of the methods proposed add any strength to the tube. Possibly welding and grinding might restore some of the lost strength, but then the welding can alter the heat treatment state of the alloy and actually weaken it further.

But, the losses involved with the series of small holes is too small to be of interest... but it does leave the mast looking like termites had been at work!

Jim
That's ok. I also had a colony of bees living in the column beneath the main halyard sheaves, so it's used to insects of all sorts.

Kidding aside, (truth about the bees though) welding and grinding is not gonna happen. Good to know I can just leave them alone if I want.
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Old 10-10-2018, 17:30   #9
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Re: Filling Old Rivet Holes

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Any harm in leaving them unfilled?
Sure, it's sloppy. At least put some sealant in the holes. At best ream and chamfer each hole both inside and outside and then treat for corrosion. Every one of those holes could grow into a crack and your mast could break off.
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Old 10-10-2018, 17:43   #10
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Re: Filling Old Rivet Holes

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Sure, it's sloppy. At least put some sealant in the holes. At best ream and chamfer each hole both inside and outside and then treat for corrosion. Every one of those holes could grow into a crack and your mast could break off.
Aww, come on...

Ream? why?

Chamfer INSIDE? How to do that twenty feet up the tube?

These holes are small, not concentrated on one area and in general, not likely to "grow into a crack" causing mast failure. In a typical alloy mast there are dozens of other holes, many concentrated in high stress areas; these are inconsequential in comparison. Don't frighten the horses or the OP with needless worry.

Using a sealant will help keep water out of the mast, and as such might be a good idea, but again, comparing their area to all the other holes, not a big deal.

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Old 10-10-2018, 17:52   #11
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Filling Old Rivet Holes

Jim, what he is saying is best practice in a highly stressed tube. Iíd want it done in a racer maybe, but in truth most cruising boats I donít expect to see that kind of stress, or Iím hosed, the holes that were put into my mast by Mack Sails would make any A&P sick, and they are supposedly Proís, so Iím assuming sail boats masts just really donít see much repetitive stresses.
Believe it or not, but drilling a nice round hole without any stress risers is an art that not many can do, most of us normal people have to ream to get there.

The rivets that have a lock ring to contain the stem are either Cherry Max, which has a steel stem and is as strong as a solid rivet, or Cherry Lock http://www.cherryaerospace.com/product/blindrivets
Riveting I see on boats is by aircraft standards horrific, in both materials and workmanship, but it obviously works doesnít it

Of course the average Cherry Max pneumatic gun runs about $1,500 too, but you can hand pull the smaller ones
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Old 10-10-2018, 18:55   #12
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Re: Filling Old Rivet Holes

I was also thinking about the corrosion around a hole in an anodized mast. All of the holes in my mast have corrosion growing from them. The only way to get things under control would be to ream the hole to fresh metal and then corrosion proof it. As for chamfering a hole on the inside, at any height, it's about tooling, pretty simple actually.
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Old 10-10-2018, 19:03   #13
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Re: Filling Old Rivet Holes

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Aww, come on...

Ream? why?

Chamfer INSIDE? How to do that twenty feet up the tube?

These holes are small, not concentrated on one area and in general, not likely to "grow into a crack" causing mast failure. In a typical alloy mast there are dozens of other holes, many concentrated in high stress areas; these are inconsequential in comparison. Don't frighten the horses or the OP with needless worry.

Using a sealant will help keep water out of the mast, and as such might be a good idea, but again, comparing their area to all the other holes, not a big deal.

Jim
I am not scared of the mast corroding where these small holes are, nor the mast creasing/breaking. The wall thickness is pretty robust, and the mast hasn't been used much. Lots of food for thought here. Thanks for the input, and keep it coming if there are any new ideas.

I should mention where the mast is in the refit process. The paint was barely starting to craze, but definitely still good. I stripped everything and sanded down. Applied 3 coats of awlgrip 545, but ran out of time in the yard to finish it up. Headed back down in a few weeks to sand again, a few more coats of primer, and three to four finish coats of Awlcraft 2K.
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Old 10-10-2018, 19:14   #14
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Re: Filling Old Rivet Holes

Well, I'm sure you airplane guys live by a different standard, but I've looked at a hell of a lot of masts and don't recall seeing stress cracks around holes like those from mast steps. After all, the holes were already there and putting a rivet or epoxy in them does not restore strength.The OP does not report any cracking around the subject holes so far.

As to the corrosion issue, not so many masts are anodized these days. Dunno about this one... But on my now 28 year old painted mast, I don't see corrosion around empty holes. Those with s/s attachments or screws are not so lucky!

I'm curious about the means of chamfering the inside of such holes. How do you do that on airplane spars? And the idea of reaming a drilled hole to eliminate stress risers... well, I've not seen this practice in marine usage. Perhaps in top end racers (if any are using alloy spars these days), but despite hanging around rigging shops and spar manufacturers shops, never encountered the reaming practice.

I'm pretty sure that the mast on a Skookum 47 is more of a telephone pole than a bendy noodle and can likely suffer the crude marine standards without much risk... been standing for a while now!

Jim
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Old 10-10-2018, 23:15   #15
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Re: Filling Old Rivet Holes

I have repaired them using an aluminium rod which I used a thread die to put a thread on, then tap the hole the same size thread. Screw enough threaded rod into the hole to reach right through and cut the rod off with about 1 mm projecting then peen it until it swells tight in the hole and file it back flush. If you get it right and polish the scratches out the repair can be almost invisible.
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