Rivets or Machine Screws When Splicing a Mast?

[Dave_S]

Originally Posted by Chotu

Thank you very much, Dave. Thanks for these responses and for saving my bacon as they say.

I just want to point out that the inside plate is 1/4 inch. The regular mast is 3/16. That’s why I came up with 3.25 threads in the 1/4” threaded part. I have 7/16” inch of material total.

So it’s 7/16” minus the countersink, with 3/16” being the depth of material available for countersink with 1/4” of material available inside the mast for threads to grab into.

That should change things quite a bit because it’s almost twice as thick as what you are calculating with.

So doesn’t that bring me back to almost half an inch? I have 7/16” of aluminum in total.

I think we are miscommunicating, I'll draw it up tomorrow.

[Chotu]

Originally Posted by s/v Jedi

I did the math: your mast is 3/16” which is 0.1875” a 1/2” flathead bolt has a head height of 0.223” so it’s way too big.

Edit: socket head height is even more… over 1/4”. Even at 5/16” it is more than 3/16”.

1/4” head height for a socket machine screw is 0.127” so will fit.

So, the head height doesn’t work on any of these. 5/16 doesn’t work. 3/8 doesn’t work.

So this is no good. Now what?

Doesn’t 1/4 of an inch seem wrong? Diameter too thin?

Do 100 degree heads have a shallower head depth I wonder?

This is now holding up the entire project. The metal guy is not too happy because we don’t have screws.

[s/v Jedi]

Originally Posted by Chotu

So, the head height doesn’t work on any of these. 5/16 doesn’t work. 3/8 doesn’t work.

So this is no good. Now what?

Doesn’t 1/4 of an inch seem wrong? Diameter too thin?

Do 100 degree heads have a shallower head depth I wonder?

This is now holding up the entire project. The metal guy is not too happy because we don’t have screws.

Socket flathead M6 A4-70 would be the best countersink fastener. It has a 90 degree countersink angle and leaves 1mm material. Here is a direct link: https://www.boltdepot.com/Product-De...?product=22677

Even better to use a buttonhead without countersink. Here is a good option: https://www.boltdepot.com/Product-De...?product=22798

I think the DIN A4-70 steel holds up better so I prefer it over 316 (it’s supposed to be the same)

M6 sounds like a perfect choice, but for buttonhead you may be able to go for M8: https://www.boltdepot.com/Product-De...?product=22808

(Just think about how much $$$ you’re saving here ;-)

[neilpride]

Socket flathead M6 A4-70 would be the best countersink fastener. It has a 90 degree countersink angle and leaves 1mm material.


This one...

[col50]

If you end up using the buttonhead screws, you should counter-bore the hole enough to allow the screw head to sit on a flat surface.

[carlosproa]

Don’t forget to take pictures when they do the work in your mast.

[Chotu]

Originally Posted by col50

If you end up using the buttonhead screws, you should counter-bore the hole enough to allow the screw head to sit on a flat surface.

What about this factor? The button heads look kind of silly sticking out of the mast. I lean more toward the flat heads.

[Chotu]

M6 A4-70 it is! Thank you!

[Chotu]

Actually, the 12mm is too short. I got 20mm. That way he can make up for any gap. We decided on three-quarter inch just in case there was a gap to pull in.

[col50]

Originally Posted by Chotu

What about this factor? The button heads look kind of silly sticking out of the mast. I lean more toward the flat heads.

I'm with you on that.

[s/v Jedi]

Originally Posted by Chotu

Actually, the 12mm is too short. I got 20mm. That way he can make up for any gap. We decided on three-quarter inch just in case there was a gap to pull in.

Total thickness is 7/16” which equals 11.11mm. I was thinking any gap would disappear as the screws are torqued?

[Chotu]

Originally Posted by s/v Jedi

Total thickness is 7/16” which equals 11.11mm. I was thinking any gap would disappear as the screws are torqued?

It would disappear as soon as things are torqued. And that’s the idea.

However, just to play it safe and not run into problems at $90 an hour, we decided that it’s good to have them just a little bit longer so that if there is some kind of gap to have to reach, he can reach it.

It has the first reach the threads before it can torque the thing in.

Better safe than sorry here. To use a navigation analogy, we’re going to stay in the channel rather than cutting that nun to shave a few moments off of the trip. Ha ha.

There shouldn’t be any gap at all, but just in case, we will be playing it safe.

[Wotname]

Sounds like 5/8" (16mm) would be the goldilocks length.

[RaymondR]

There are gadgets you can put into adjoining holes to pull the parts together they use them a lot in aircraft fabrication.

[s/v Jedi]

Originally Posted by Wotname

Sounds like 5/8" (16mm) would be the goldilocks length.

Originally Posted by RaymondR

There are gadgets you can put into adjoining holes to pull the parts together they use them a lot in aircraft fabrication.

Exactly, I’m flabbergasted over the decision to double the length which enables bridging gaps of almost 15mm, leading to a finished install with every fastener sticking 9mm (3/8”) into the mast after all the discussion to prevent exactly that.

A couple of longer screws to help if needed until they can be replaced with the short ones would have been enough.

16mm would allow bridging gaps up to 3/16”