Making a tapered aluminum tube

[deltap]

The video explains a lot. Put 3 stays on the mast.

 

[rons]

Use a good mechanical engineering modeling program to see if your dimensions are going to work.
A thickness of 3mm (.118) is pretty thin for a windy day sucking into a large sail.

 

[boslab]

I went to a place making tapered tube many years ago, there was a round tube with hydraulic connections, they stuffed the tube in and pressed the pedal, it sort of chugged as the dies squeezed the tube, came out pointy or tapered, there was also a home made “lathe” made of 2 girders, it had opposing hydraulic cylinders with rollers, it was for flagpoles I beleive, should imagine a flagpole and a mast are similar, it was fairly thick tube btw, the had an annealing tunnel oven too ( and a bar of soap I noticed even though there were thermocouples )
Perhaps a flag pole company could help, I was told that masts were spiral welded? Never saw it though, sounds interesting, I can sort of see it in my mind, like the ducting stuff but gradually decreasing, most masts are carbon fibre resin composite these days I read, wires included for nav lights and radars/radio etc, I saw some crazy yacht building on YouTube, timber mast, big ol tree,
Mark

 

[BoxcarPete]

The video explains a lot. Put 3 stays on the mast.

Laser don't need no stays, why should he?

But I'm thinking composite as well. Start with a wooden mast of any shape you like which you can make for $50, and with $100 (at least around here) you can get 3 yards of 12k carbon at 50" width, which gives you the length you need at about 25" of width. For a 70mm mast diameter, that would give you about 6 wraps at .023" thickness per wrap. More as you approach the tip. That'll come out to as much carbon around the outside of the wood as your hollow aluminum was going to be, and it will be much stiffer and stronger than 6060. If you find you don't need that much carbon, you can get 6k sheet or only buy 2 yards of the thick stuff, and save 33% on the fiber cost either way. It shouldn't break your budget too much to get yourself some epoxy and shrinkwrap to lay it up.

 

[boslab]

I was always under the impression that carbon fibre composite was part science plus witchcraft and cost massive amounts of money, how much does the stuff cost?
Mark

 

[Milland]

Laser don't need no stays, why should he?

But I'm thinking composite as well. Start with a wooden mast of any shape you like which you can make for $50, and with $100 (at least around here) you can get 3 yards of 12k carbon at 50" width, which gives you the length you need at about 25" of width. For a 70mm mast diameter, that would give you about 6 wraps at .023" thickness per wrap. More as you approach the tip. That'll come out to as much carbon around the outside of the wood as your hollow aluminum was going to be, and it will be much stiffer and stronger than 6060. If you find you don't need that much carbon, you can get 6k sheet or only buy 2 yards of the thick stuff, and save 33% on the fiber cost either way. It shouldn't break your budget too much to get yourself some epoxy and shrinkwrap to lay it up.

The OP is in Lithuania, and has already told us a bunch of times that CF will be too expensive in his area.

We're sort of spoiled, we have easy access thanks to the purchasing power of the aircraft and military demands...

 

[Milland]

I was always under the impression that carbon fibre composite was part science plus witchcraft and cost massive amounts of money, how much does the stuff cost?
Mark

It's not cheap, but not that bad now considering what it cost ~25 years ago. And design is still a little tricky if you're going for maximizing properties, but fab is more tedious than magic. Cleanliness, organization, and patience does wonders for making good parts.

Oh, and a million dollar autoclave.

 

[DDoug]

Simple really...

a 6 pack of empty beer cans, and some explosive forming, and BAM your done....

Easy Peasy.

 

[BoxcarPete]

I was always under the impression that carbon fibre composite was part science plus witchcraft and cost massive amounts of money, how much does the stuff cost?
Mark

It's surprisingly inexpensive if you're willing to get your hands dirty. What you're paying for is the witchcraft and labor for the most part.

As I said, thick sheets (0.023" thick) are only $30/yd at 50" sheet width. Thinner sheets at 0.014" are around $20/yd.

I go to these guys whenever I need any composite stuff.

Soller Composites (no affiliation other than satisfied customer)

Poking around their website a bit more, they sell carbon fiber sleeve with a usable diameter range of 1.4"-3" for $5 per foot. I don't know why OP would do anything other than that before he's tried it on a wood mast.

 

[BoxcarPete]

The OP is in Lithuania, and has already told us a bunch of times that CF will be too expensive in his area.

We're sort of spoiled, we have easy access thanks to the purchasing power of the aircraft and military demands...

Yes, he has said that, but it's hard to imagine that figuring out how to ship a relatively small package internationally would be more difficult than making multiple welds along 6+ meters of aluminum...

Edit to add: I checked on Soller's website, they do ship internationally. Might cost a bit, but I think it's worth looking into. Likely just the fabric, and OP will have to look for epoxy locally.

 

[Scottl]

As I recall most of the better aluminum masts are elongated as well as tapered.

Probably the best bet for the OP would be to progressively round tubing, saw out a tin wedge to taper the other dimension, and then weld the remaining two halves together.

 

[DDoug]

More than $150 worth of Argon will be used on all this "Cut & Weld" orgasm.

BTW doo some test cuts with your plasma cutter on the material, including the welding of said cut edge.

 

[laukejas]

I don't know all that's involved with the flexibility of the mast relative to contributing to the sail shape, but could the sail itself be adjusted such that the aerodynamics were appropriate to the new mast stiffness profile? Surely that's an option, and easier to do some sewing that to make a mast?

You are right: sails are shaped according to the bendiness of the mast. I do that when I sew my sails. However, there is a limit to how much the mast should flex. Too much - and no sail shape can compensate for it.

Another wacko thought - how about going with something like a 50mm mast OD, and using simple linear strips of carbon fiber tape to adjust the stiffness profile over the length? It would take relatively little tape to make significant changes to the bending stiffness.

So you might have three layers along each side of the tube for the first 2M, two layers the third meter, then one strip at four meters. Or taper the width of the strips as you go up, it would accomplish the same thing.

The amount of tape (being just a limited reinforcement) would be so little that the actual cost should be that bad - perhaps under 100 Euro? Add some epoxy and prep supplies, still not that much.

You would need to ensure there's full epoxy coatings over the CF where it touches the aluminum, you don't want a galvanic cell being set up.

That is an interesting idea. All the carbon wrappings I've ever seen have full coverage of the mast, not just reinforcing strips on each side. I'll have to run some numbers on this.

I'm still missing something in all this....a 5.5M long mast that is 70mm at the bottom....if it were even possible to convert those numbers to God's Units, we'd come with about 17 feet long and approaching 3 inches in diameter. The wall thickness of 3 mm is within a few inches of 1/8 inch.

In 2022, we'd figure out the cost of metal using the formula: Metal price + Sales Tax + Shipping + Biden Tax

Assuming you used a round tube to start (as originally suggested) That would equal something like: $200 + 16 + ? + $400 = $616 w/o shipping

I have no idea where you'd get the raw materials for $150...and then any tooling, consumables, and labor would also need to be free. $150 these days? That's a tank of gas and a cheeseburger.

Is aluminum really so expensive over where you live? I thought it is expensive here... Well, in any case, the breakdown is like this. a 70mm tube with 3mm wall weighs 1.74 kilos (3.83 lbs) per meter. Global aluminum price now is $3.37 / kilo ($1.53 / pound). So, 6 meter tube is 10.44 kilos - that should be $35. Unfortunate, Lithuania is an insanely expensive country, so I pay 3 times that - around $100. This is taxes included. We don't have Biden Tax here in Lithuania I only buy locally, so no shipping costs either.

The video explains a lot. Put 3 stays on the mast.

I did. It doesn't help. Mast has to be stiff enough on it's own, even with stays. It might not need to have full strength on it's own, but it must be stiff, otherwise the compression from the stays leads to buckling. Besides, stays are more trouble than they are worth on a small boat.

Use a good mechanical engineering modeling program to see if your dimensions are going to work.
A thickness of 3mm (.118) is pretty thin for a windy day sucking into a large sail.

I did math on this a while ago, I seem to remember that 3mm worked out well for the sail I have. But I'll recheck it.

The OP is in Lithuania, and has already told us a bunch of times that CF will be too expensive in his area.

We're sort of spoiled, we have easy access thanks to the purchasing power of the aircraft and military demands...

I couldn't have said it better myself. Yeah, I am aware that CF would be ideal, but like I said, building a CF mast would cost almost as much as my entire boat - that is not including labor. Simply out of the question, unfortunately.

And in any case, building from CF is extremely labor intensive as well. If pure CF, I would have to build a perfect mold that is possible to pull out from inside the mast once composite cures. I talked to professionals people who deal with composites on daily basis, and when I described this challenge, they said even they couldn't pull this off. Just too difficult to make the mold smooth and accurate enough. There is like a 99% chance that the mold will get stuck. And even if that part somehow goes right, any imperfection in lamination will lead to stress concentrations and cascade failure. CF is totally unforgiving there. Either the lamination is perfect and it all works, or it breaks in two like a toothpick. The risk factor is huge.

And if I go with CF-reinforced wooden mast, then again, it is doubly labor intensive, risky AND expensive at the same time. I did suggest this option when I talked to the CF people. They said the same thing - unless I have a machine that can lay carbon fiber, a resin infusion system and a vacuum to compress it all, don't even bother trying it, as it will end up in failure. And even if I have that, I should expect at least several failures before I get it right. CF is insanely difficult to get right.

 

[Gordon Heaton]

. . .BTW doo some test cuts with your plasma cutter on the material, including the welding of said cut edge.

This is good advise. Aluminum doesn't cut as cleanly as steels, and the slag is a royal mess by comparison. Complete grinding/sanding to a virgin edge is necessary before TIG welding.

 

[Milland]

CF is insanely difficult to get right.

I think that's a little overboard (Hah! Another boating joke), CF is not easy if you're going for the very highest performance to weight properties (as in F1), but as a "generic" composite material It's not horrible. Frankly, the irritation from tiny CF filaments getting in my skin is the worst aspect of it (wear gloves and a respirator if working the material).

It is brittle, and will fail if stressed beyond it's limits, but I think if used as I suggested as a stiffener on a Al mast, that will be less of an issue.

As I think about it, the main complication there might be the very different coefficients of thermal expansion - you'd want to keep the mast from freezing or getting excessively hot to avoid shearing the adhesive.

 

[Kevin T]

Oh, and a million dollar autoclave.

We make canoe hulls out here that are a carbon fiber sandwich around dense foam. Vacuum bag them and have them cure under a row of heat lamps.

 

[EmanuelGoldstein]

This whole project as described is dumb. It's a 15' mast. We're talking a few ounces at most, but he's not even addressing the bigger problem, making it as a circular section. High efficiency masts have not been circular for decades. Many decades.

This is stupid.

 

[Milland]

Vacuum bag them and have them cure under a row of heat lamps.

And then throw all of that in the million dollar autoclave.

I was kidding, I know there's a lot of options for curing CF.

 

[henrya]

Carbon fiber landing gear parts for an airliner are insanely important to get right. That is not whats happening here. You can make a prototype and test it as needed and no one will die.

There are many consumer products made with tubular carbon fiber components. Fishing rods, oars, paddles, tennis rackets, maybe golf clubs, ships masts and spars. This is not new ground.

What is called for here is almost just an oversize fishing rod. But it does not require that much complication. Rods are rolled on mandrels and then stripped off for finishing. This mast can be made from very light weight wood, shaped appropriately and then covered in woven carbon tubing and resin. As I posted earlier, it can be wrapped or bagged. Make one that seems about right and test it. If it works you are good to go.

Its not like you’re in the middle of a jungle somewhere in the Amazon basin. Other than the Russians maybe rolling in, you have no big problem getting modern materials and supplies. You’re in the EU - you can buy this stuff.

 

[BoxcarPete]

And if I go with CF-reinforced wooden mast, then again, it is doubly labor intensive, risky AND expensive at the same time. I did suggest this option when I talked to the CF people. They said the same thing - unless I have a machine that can lay carbon fiber, a resin infusion system and a vacuum to compress it all, don't even bother trying it, as it will end up in failure. And even if I have that, I should expect at least several failures before I get it right. CF is insanely difficult to get right.

I disagree with this. If you get the 1.4~3" tube, you will need only to slide it over your wood mast, lay it up with epoxy, and apply some kind of clamping force around the outside. The fiber has been laid into a tube by machine already, hand-squeezing is plenty good for infusion (wear gloves!) if you do it one layer at a time, and you don't need a vacuum if you go around and around with plastic wrap (test it first to make sure it won't stick to your epoxy). The epoxy should soak into unfinished wood to some extent and give you a very strong bond. It might not look good enough to make a trim piece for a supercar, but it will reinforce your mast. It will take you an hour or less once you have everything ready.

Also note that I found you a source who ships internationally (they also have kevlar and fiberglass sleeves if you want to save a few bucks), and it has been discussed already by several other members that the consumables required to do the amount of welding required are likely higher in cost than the composites I've linked above.