Rivets or Machine Screws When Splicing a Mast?

[Breaking Waves]

Originally Posted by Dave_S

1. The optimum machine screw diameter is usually approximately equal to the material thickness.

I believe the 1:1 standard is typically for steel. For Aluminum, I was taught to use 2:1. The objective is to have enough thread engagement for the fastners to break before the threads strip - this will vary between even different hardness aluminum.

In thinner material, often an internal sleeve (or simply flat bar) is used to get desired thread engagement. When you look inside a (typically pretty highly loaded) machine-screwed boom vang lug, you will find (should find) a doubler or a piece of flat bar (or both). OP already has an internal sleeve as part of the design (at least as I understand his plan).

For threaded fasteners, threat engagement is ofc critical. Ofc if you 'test' threaded fasteners with less than suggested thread engagement, you can get arbitrarily low strength. For testing, you either need to follow standard engineering minimum rules or very clearly note that you are not (and why not).

Use of helicoils or threaded inserts increases ease of removal, and typically (although not always) increase thread strength - but at the cost of extra materials and labor. Harken blocks (just for instance) typically go down this route.

[Chotu]

Please keep the conversation going. This is a FANTASTIC thread. Learning lots. Thank you!

[AKA-None]

I think your biggest issue will be keeping the two in column while you do the fastenings irrespective of what you use to tie them together

[ItDepends]

Originally Posted by Cheechako

The Pro's use rivets and structural epoxy on assembly between the sleeve and the two mast sections. I had one done years ago by Chesapeake Rigging. They did a lot of this type of custom work for expensive racing yachts etc.. The sleeve should fit closely.

Anything threaded will become threadless in short order anyway from corrosion.

That last comment is ONLY true if the treads are applied dry and unprotected. It’s the kind of silly statement made a lot. think about it. IF it was true, there would be bits and pieces falling off masts everywhere.

A good acrylic thread locker will isolate the metals and prevent corrosion. I have removed screws from a mast that I installed 10 years earlier with nylon washers and blue locktite, and they came out neat and clean and all threads were perfect.

Here is the GENERAL rule:

• Production operations tend to used rivets because they are quick and easy to install once you have the right tooling. The right tooling for the right rivets for high load application in not trivial.
• DIY workers and small shops tend to use screws because the tooling is widely available and cheap, but takes a lot of extra time.

It actually make very little difference in this application. The loading on the individual fasteners is quite low as long as the mast stays in column. If the mast is not in column, well SOMETHING else just broke anyway.

[Chotu]

Originally Posted by AKA-None

I think your biggest issue will be keeping the two in column while you do the fastenings irrespective of what you use to tie them together

Thankfully, I’m not doing it. But hopefully he will be able to keep them in column

Edit: I think the two pieces have to lineup. The piece in the middle makes it impossible for them to get out of alignment. That’s what it’s all about.

If you think about it, if the mast is out of column, that piece in the middle is bent and broken. Otherwise it Has to be in alignment. Because that’s what the piece does. Keeps it in alignment.

[Chotu]

Originally Posted by ItDepends

That last comment is ONLY true if the treads are applied dry and unprotected. It’s the kind of silly statement made a lot. think about it. IF it was true, there would be bits and pieces falling off masts everywhere.

A good acrylic thread locker will isolate the metals and prevent corrosion. I have removed screws from a mast that I installed 10 years earlier with nylon washers and blue locktite, and they came out neat and clean and all threads were perfect.

Here is the GENERAL rule:

• Production operations tend to used rivets because they are quick and easy to install once you have the right tooling. The right tooling for the right rivets for high load application in not trivial.
• DIY workers and small shops tend to use screws because the tooling is widely available and cheap, but takes a lot of extra time.

It actually make very little difference in this application. The loading on the individual fasteners is quite low as long as the mast stays in column. If the mast is not in column, well SOMETHING else just broke anyway.

This makes a lot of sense. My guy is not cheap. At least I don’t think so. $90 an hour. That makes for some pretty expensive tapping and machine screwing.

Hey, where is that jerk from yesterday telling me that I get what I pay for by hiring homeless members of the forum ? Ha ha ha.

Maybe my metal guy could buy the structural rivet guns cheaper than his labor?

And yes. Those rivets don’t do anything really. They just hold the inner piece together with the outer shell. I’ll explain the process for those that aren’t sure how it’s done.

When you splice a mast, you are creating a butt joint. Think about a little wooden dowel stuck in between two drinking straws the old plastic ones. Press the straws together over the dowel so that they come in contact with each other and they are tight against the dowel.

Now if you press both ends of both straws, if they will act as one straw.

This is exactly how a mast splice works.

So instead of the dowel, inside we have another section of mast inside the two parts being joined. The job of the rivets or screws is to hold the outer sections, the plastic straw, to the inner section, which is like the dowel.

That’s all they do. There is no force on them from the top or bottom. They function to keep the two outer sections in alignment with each other. And that’s what’s critical. Those two sections you are joining have to mate perfectly all the way around the perimeter of the section. That’s what carries the compression load from the top of the mast down through the splice all the way to the deck.

The function of the piece inside the mast is just to keep those two in perfect alignment. Because if they get out of alignment, then you’re all done.

[Baby tug]

I realize you guys like to overthink things , I started wondering why are you extending the mast to begin with , creates a lot of extra work rigging has to be redone everything has to be redone , Most likely the mast is extruded and is not uniform in shape , How are you going to Find a sleeve , I own a 36 foot aluminum trawler everything is welded Everything railing, Cleats, Drum winch, hand hold’s, Radar arch , antenna brackets , on and on and on , a few things are bolted on , stainless tender davits,A latch or two , Anywhere there is Dissimilar metal there will be corrosion. Doesn’t matter if you isolate it with plastic or whatever it will corrode ,As to welding making it weaker whatever you do will make it weaker , I have outriggers with paravanes guess what aluminum , Pretty strong , I would have to have a pretty good reason to extend the mast , And if I did I would most likely weld it providing the metal is thick enough, Anything less than 1/8 inch I would probably rivet, Which is why most airplanes and truck bodies are riveted , metal to thin can’t handle the heat , I would never use screws , I’m not trying to convince anybody just my opinion that’s what I would do

[thinwater]

Originally Posted by Chotu

...
...

I am puzzled by why the rivets are in nice neat rows, rather than staggered to spread the force? I suspect it is related to the shape of the section, the shape of the plug, and minimizing distortion. For example, you would rather place a fastener on the flat than on a move curved area.


Boilers and tanks are usually, but no always, staggered. But when they are on square pitch, it is evenly spaced, not in rows. Of course, the purpose here is both holding stress and to make the seam liquid-tight (pull the surfaces together).




These guys are pros and the rivets are staggered (Annapolis Rigging).




The only reason I can think of is that the section is less likely to be distorted if the rivets are in a row, though a good fit and the epoxy should prevent that.

Mast splicing is common and I have never heard of one failing.

[Chotu]

Originally Posted by Baby tug

I realize you guys like to overthink things , I started wondering why are you extending the mast to begin with , creates a lot of extra work rigging has to be redone everything has to be redone , Most likely the mast is extruded and is not uniform in shape , How are you going to Find a sleeve , I own a 36 foot aluminum trawler everything is welded Everything railing, Cleats, Drum winch, hand hold’s, Radar arch , antenna brackets , on and on and on , a few things are bolted on , stainless tender davits,A latch or two , Anywhere there is Dissimilar metal there will be corrosion. Doesn’t matter if you isolate it with plastic or whatever it will corrode ,As to welding making it weaker whatever you do will make it weaker , I have outriggers with paravanes guess what aluminum , Pretty strong , I would have to have a pretty good reason to extend the mast , And if I did I would most likely weld it providing the metal is thick enough, Anything less than 1/8 inch I would probably rivet, Which is why most airplanes and truck bodies are riveted , metal to thin can’t handle the heat , I would never use screws , I’m not trying to convince anybody just my opinion that’s what I would do

Holy cow it’s frustrating that my posts aren’t all in one place. I should probably have my own sub forum. Lolol.

You are just missing years of knowledge in my quest here. You just don’t have the facts or information behind all of it.

I don’t blame you, I didn’t mention any of it in this thread.

But it’s unfortunate that there’s not a way for people to already know everything going on with the project. Maybe I should’ve done a website or something. But then I would have to spend another 10 years building this thing. Ha ha

I am wondering why not screws? You didn’t make a case for why not screws. It seems like machine screws are the most common thing used for this other than rivets.

Interestingly enough, speaking of welding, everything is welded to my mast. And everything is riveted to my crossbeam.

The tangs for the hounds, various other bits of hardware everywhere, it’s all welded to my mast. That’s how it was built.

But of course, here, we are not adding things on the outside of the mast. We are doing a butt joint and keeping that in line with a piece inside. Fasteners aren’t really doing very much. Just keeping things lined up. Just joining the outer pieces to the inner piece.

[Chotu]

Originally Posted by thinwater

I am puzzled by why the rivets are in nice neat rows, rather than staggered to spread the force? I suspect it is related to the shape of the section, the shape of the plug, and minimizing distortion. For example, you would rather place a fastener on the flat than on a move curved area.


Boilers and tanks are usually, but no always, staggered. But when they are on square pitch, it is evenly spaced, not in rows. Of course, the purpose here is both holding stress and to make the seam liquid-tight (pull the surfaces together).




These guys are pros and the rivets are staggered (Annapolis Rigging).




The only reason I can think of is that the section is less likely to be distorted if the rivets are in a row, though a good fit and the epoxy should prevent that.

Mast splicing is common and I have never heard of one failing.

Yeah. I’m with you. That splice in the first picture that I shared that just came up randomly from Google, I don’t really like it. It doesn’t look like it has much going on inside, very short piece inside, and those rivets all in a row or bolts don’t seem right to me.

I much prefer the pattern that you show in the last picture. And that’s what I’ll be doing. Something that makes a little bit more structural sense. Thankfully, I don’t have one of those square mast sections. It is an ellipse. A beautiful, perfect ellipse. Nothing fancy with weird tracks built into it and stuff. It actually has an external track for the cars.

[neilpride]

The the OP, Chotu, i suspect you dont order the mast from a mast maker? right? If you can provide more info like where is placed the sleeve, over spreaders? your mast rigging setup is diamond triangle spreaders? swept back spreaders? fixed spreaders? mast bend? how much? in mast furling ?

[neilpride]

Originally Posted by MWGDVC

I would tend to agree with this except for the FLAT 82 deg. I would use 100 deg. as less of the wall thickness is removed from the mast for the countersink (most flush rivets are 100 deg).

Right, 82 or 100, probably 100 better, but honestly, dont make any diference, the sleeve purpose is to keep the 2 sections aligned with each other, and to add a bit of strenght in the area, low budget spar makers use SS rivets , regular SS rivets, ej, ZSpar, I believe Selden use Monel, top end Spars makers use screws , i will say that its more important that both sections faces perfectly, without gaps.

[Dave_S]

Originally Posted by Breaking Waves

I believe the 1:1 standard is typically for steel. For Aluminum, I was taught to use 2:1. The objective is to have enough thread engagement for the fastners to break before the threads strip - this will vary between even different hardness aluminum.

In thinner material, often an internal sleeve (or simply flat bar) is used to get desired thread engagement. When you look inside a (typically pretty highly loaded) machine-screwed boom vang lug, you will find (should find) a doubler or a piece of flat bar (or both). OP already has an internal sleeve as part of the design (at least as I understand his plan).

For threaded fasteners, threat engagement is ofc critical. Ofc if you 'test' threaded fasteners with less than suggested thread engagement, you can get arbitrarily low strength. For testing, you either need to follow standard engineering minimum rules or very clearly note that you are not (and why not).

Use of helicoils or threaded inserts increases ease of removal, and typically (although not always) increase thread strength - but at the cost of extra materials and labor. Harken blocks (just for instance) typically go down this route.

I'm happy to be proven wrong but I believe the 2x is for the benifit of thread strength in the tapped hole to suit the fixing torque settings, not for maximum clamping force or for fixings with loads in shear in a soft material. The 2x rule would suggest that a 3/32nd or M2.5mm is the best size in 3/16th material which I don't believe to be suitable for this application.

The correct answer is difficult to calculate for sheet metal because it doesn't follow the design built in to the fixings for torque settings and stretch. Some suggest the thread length should be 2/3rds the fixing diameter for maximum clamping strength and shear loads this is probably theoretically accurate? I'm not completely sure. i.e. that would suggest a 1/4" screw in 3/16th plate. It will depend on the grade and temper of the aluminium but I don't think there would be enough torque available for the screws to hold well enough, perhaps with formed threads (not cut) and no chamfers?

If using machine screws best practice would be to use formed threads, they can be hand formed in aluminium but it requires a much higher standard of workmanship.

[Chotu]

Here’s a question. Do rivets pull both sheets together? I know they kind of clamp down when they install.

If you had a very small gap between a couple of sheets of metal, and you put a machine screw in there, you would retain the gap probably. That’s assuming both are threaded.

Wood rivets pull the sheets together?

[Dave_S]

Originally Posted by Chotu

Here’s a question. Do rivets pull both sheets together? I know they kind of clamp down when they install.

If you had a very small gap between a couple of sheets of metal, and you put a machine screw in there, you would retain the gap probably. That’s assuming both are threaded.

Wood rivets pull the sheets together?

The rivets do pull the sheets together. You can see it happening as you use the tool. The rivet would stretch along the full length of the shaft the clamping force should be even at both ends.

P.S. the rivet will have a working tolerance of thickness which isn't a lot, if the distance, including the gap is outside that you will have problems. I wouldn't want the rivet deforming much before pulling the plates together. If there is much resistance you might run the risk of the rivet deforming into the gap between plates before the plates pull together.