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Old 15-02-2015, 10:27   #16
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Re: Rivets in Mast Cleat Question

Originally Posted by MarkSF View Post
However, the choice is not simply between cheap rivets, and screws. How about using GOOD rivets? McMaster Carr have high strength SS rivets, rated for 2200 lbs each in 1/4". That means you could lift my boat by the boomvang, as 6 of them hold that on.

Bristol used rivets to hold my boom to the mast, and it's been working for 35 years.

Finally, here is the incredibly exotic piece of equipment you need to install 1/4" rivets. Hardly out of the reach of the ordinary mortal, is it? :

Astro Pneumatic 1/4 Hand Riveter -

It fail no matter monel or ss in those specefic áreas, gooseneck, vang ...
They usually have 2 pan head screws in the midle holding the fitting and rivets in the sides but they work loose with time, cleats to, mast steps, etc... i dont recomend it unless is a light load aplication or there is enough rivets holding the hardware, with a cleat there is usually 2 , i see some of this cleats working loose in a dangerous fashion, goosenecks wrecked , hell even we splice a Jeaneau mast with rivets, but we dont have choice since the mast maker insist in use rivets and warranty isues in between.

This is the pneumatic gun we use and this is the 2 halves joined by rivets.
Each in their own , after the ARC each year we replace hundreds of broken rivets and damaged hardware...
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Old 15-02-2015, 10:32   #17
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Re: Rivets in Mast Cleat Question

Thanks, very handy info. I are a injineer too but I studied how to move electrons around. They did force feed me a little bit of mechanical knowledge, statics and dynamics but only enough to be dangerous. It was enough however to help me more or less understand what the other guys are trying to tell me.

Originally Posted by leftbrainstuff View Post
Choosing the thread form is a simple engineering calculation. The limiting factor is the shear strength of the base material. In reality we pragmatic engineers rarely do the math.

Some rules of thumb are:
1) use coarse threads in soft materials (eg aluminum) and fine threads in harder materials (eg ss)

That totally makes sense.

2) thread length at least as long as the thread is wide for pure axial loads. Use a backing plate wherever possible.

In the specific I'm working on IE to capture the jib halyard and prevent wrap around the roller furler, the load on the screw will be mostly axial but since the halyard is only held a few degrees from straight should not be much.

3) if the joint is subject to a radial load then you either need a much larger diameter thread or thread depth greater than 2 x thread width. Also see 7).

Going through the mast so thread depth is what it is.

4) for coarse threads you need at least 4 or more threads. This limits in how big a diameter you can go to.

Diameter was set by the min size threaded insert I could use to repair the hole where I had to drill out a SS fastener that welded itself into the Al mast. $#@!$#!@!!!!

5) threads need to be full depth. Most taps are tapered. You need a finishing tap for blind holes.

Fortunately could tap all the way through but adding a set of bottom taps for blind holes is on my list. Just hasn't made it to the top, yet.

6) the 55 degree whitworth thread form is generally the strongest.

They still make Whitworth stuff? I thought that went out with antique British cars and Royal Enfields.

7) select bolt diameter so that you can sufficiently torque the fastener. Yielding of the fastener in the elastic region is required for dynamically loaded fasteners. This typically leads to a minimum diameter fastener. This opposes 4)
8.) to the experienced eye 'what looks right is right'.

Eyeball engineering. That's my area of expertise. Works most of the time but every once in a great while it does bite me in the butt.

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