An alternive to pop rivets.

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William_H

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An elegant (perhaps not elegant) solution for attachment of things to a boom.
I had a saddle pop riveted to the top of my carbon fibre boom for the reefing line. I don't like the idea of tieing the tail right around the boom. Anyway with a bit of dissimilar metal corrosion and the ali pop rivet let go under load.
The solution was to fit a bolt (screw) and nut from inside but it was all out of reach up the end of the boom.
I got a 3/16 inch ww screw (4mm to you folks) and ground down 2 flats on the thread ends of the screw. I then drilled a tiny hole through the thread sideways. Put a nut on the thread first to clear the threads after this brutalisation.
I tied a piece of whipping line to the screw through the hole. Put a washer on the screw head.
First a stiff wire as a messenger from the open end then tied the whipping twine to the messenger. Thus when I pulled the messenger then the twine and eventually out came the thread end of the screw. I placed the saddle end over the screw by feeding the thread through the saddle hole then fed the nut on again over the thread. Got the nut started. Once the nut was screwed down far enough I cut the twine and used an open ended spanner on the nut while holding the flattened thread with pliers.
Now this was easy to get the screw out through the hole as I was lifting the screw vertically however it may work for a horizontal hole just a bit more fiddly to get the screw end to emerge. Might be an idea for some situation. The down side is that the nut is on the outside. If you cut off the cut end of the thread you may not be able to get it undone again.
olewill
 
Ingenious. Sounds like it's time for my spiel on self tapping screws into sheet metal. I used this tactic over 30 years ago to attach a lower front apron to the bodywork of my MGA roadster. I happened to get just the right sized pilot hole and was amazed at the grip that the screws achieved. It appears that if you get it right the sheet metal bends itself into a spiral shape around the screw thread with minimal actual cutting of metal. Still have the car.
 
Ingenious solution.
Could also use rivnuts from the outside and only have the heads of the fixing bolts on the outside. The advantage is that you do not need an open end through which you feed the line. You don't need the 'special' tool to collapse the rivnuts if you use a temporary bolt and a nut from the outside.
 
DO NOT USE Monel or aluminum rivets on Carbon fiber, They dissolve at a rapid rate in a salty environment. Stainless steel rivets I understand work much better if you can get them
 
Last edited:
seumask said:
DO NOT USE Monel or aluminum rivets on Carbon fiber, They dissolve at a rapid rate in a salty environment. Stainless steel rivets I understand work much better if you can get them
Click to expand...

Stainless is OK, aluminium will corrode very quickly.
I have used a variation of the op's technique.
Use fine copper wire for the mouse line, or even just the last bit. You can wind it around the threads of the machine screw with a bit of sealant (maybe superglue would be better?) and pull the screws through without needing to drill them. Once they are through, you can put the nuts on, then hold the threads with vice grips (mole grips), no need to file flats.

For thin carbon sections though, a better technique is to pull a backing piece with a tapped insert into place, then insert the screw from the outside.
 
A splice around the spar would still be stronger, though :)

Lots of traditional techniques start to make sense again when done with dyneema and carbon instead of hemp and wood.

Pete
 
lw395 said:
Stainless is OK, aluminium will corrode very quickly.

For thin carbon sections though, a better technique is to pull a backing piece with a tapped insert into place, then insert the screw from the outside.
Click to expand...

I used that technique with blind section fittings where I consider the load greater than I would like with a pop pivot fitting.

My main sheet boom fitting is done like that on am aluminium boom and I have fitted pram canopy fittings to my GRP dingy into a sealed section.
 
"DO NOT USE MONEL" ?
Is this correct? I've seen lots of recommendations for using monel and have therefore used them for attaching bits and pieces to boom and mast
 
I think, instead of filing a flat on the thread end and using that to tighten against. I would put a couple of nuts lock nutted together.. But hey ho if it works dont knock it.

For a horizontal hole then you might need to get real sneaky....
Find some flexible tube that is the same o/d as the bolt, reduce the bolt end so it slides into the tube, file 2 flats on the reduced section and drill hole for your ferreting line. Pull the ferret till the bolt is at the hole, slide the tube down the ferret, through the hole and let it push the bolt back a bit. with a bit of push and pull you should get the bolt tip into the tube then out the hole.
 
Was described in a book by Ian Nicholson, I think he used a similar method to attach all the fittings to his mast. Forget the title now but certainly worth a read for his accounts of solving technical issues during fitting out.
 
Hi Vic yes stainless steel rivet would have worked OK. I should have used SS in the first place instead of ali when the boat was home last winter. This was a bit of a rush repair for next Sunday's madness. (race) I had also forgotten that there was in effect a backing plate in the form of the flange mounting of a sheave box on the inside.
Anyway with the boat on a swing mooring my only tool for setting SS pop rivets runs on an air compressor so not practical in the dinghy.
Incidentaly the cuts in the side of the thread were not just to provide a grip but also to provide room for the string in the case of a neat fit hole. (Which it wasn't as it turned out.) olewill
 
Spuddy said:
"DO NOT USE MONEL" ?
Is this correct? I've seen lots of recommendations for using monel and have therefore used them for attaching bits and pieces to boom and mast
Click to expand...

Monel is the right thing for alloy masts.
Not so good with carbon, but it's much better than aluminium.
 
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