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Making a tapered aluminum tube

henrya

Stainless
Joined
Jun 25, 2008
Location
TN
Look at how hand made bamboo fly rods are made. Starting there, you could likely make a better wooden mast and include carbon fiber into the glue up and make a great mast for not much money. Might be easier than how you do it now.

There are some smart people here trying to help, but I have not seen an idea that won’t cost anywhere near your $150 price target.

What is the purpose of the taper? The mechanical reason for it? If its looks, give up on it. If its some magical bending response that makes the boat sail better, think of another way to get there than tapered metal.
 

laukejas

Plastic
Joined
Feb 27, 2022

Mike, what is it, exactly? It is very difficult to make out from that low-resolution picture. Can you tell us more?

Look at how hand made bamboo fly rods are made. Starting there, you could likely make a better wooden mast and include carbon fiber into the glue up and make a great mast for not much money. Might be easier than how you do it now.

There are some smart people here trying to help, but I have not seen an idea that won’t cost anywhere near your $150 price target.

What is the purpose of the taper? The mechanical reason for it? If its looks, give up on it. If its some magical bending response that makes the boat sail better, think of another way to get there than tapered metal.

Like I said, I want to explore aluminum options only in this topic, because I have well-researched these other methods, including wood and carbon, and I am well aware of them as alternatives.


The purpose of the taper, like I described in the first post in this thread, is to save weight aloft, because load decreases up to, so the mast doesn't have to be as stiff there. Ideally, mast tapering profile should be balanced in a way that distributes loading equally along it's entire length. That also induces some very favorable bending characteristics which are important for safety. But mainly it's about weight. If taper wasn't important, I wouldn't have created this topic - there are plenty of very easy and very cheap ways of having a non-tapered mast... Like just buying an aluminum tube, drilling a hole at the top and that's it. Big boats with ballasted keels can get away with that weight aloft, but for a small boat, taper is absolutely essential. No way around it.
 

Evenglischatiest

Cast Iron
Joined
Nov 22, 2005
Location
Santa Barbara
I'm picturing something like this:
Staff Patrol Expandable Police Batons - YouTube

A series of telescoping tubes, pressed together at the ends. You'd take off the shelf tubing, of whatever length you can work with, and machine both ends to fit the tube on either side. Alternately, use the stock tubes, and machine a series of reducing couplers for the joints. In either case, weld (or bolt, or rivet...) the joints.

Another idea-
Do you actually need a taper? Or do you just need weight reduction as it gets higher? Perhaps you could use a straight 70mm tube all the way up, and drill/mill progressively more holes in a pattern along the length.
 

laukejas

Plastic
Joined
Feb 27, 2022
I'm picturing something like this:
Staff Patrol Expandable Police Batons - YouTube

A series of telescoping tubes, pressed together at the ends. You'd take off the shelf tubing, of whatever length you can work with, and machine both ends to fit the tube on either side. Alternately, use the stock tubes, and machine a series of reducing couplers for the joints. In either case, weld (or bolt, or rivet...) the joints.

Another idea-
Do you actually need a taper? Or do you just need weight reduction as it gets higher? Perhaps you could use a straight 70mm tube all the way up, and drill/mill progressively more holes in a pattern along the length.

I covered the telescoping tubes idea in my initial post. The overlaps required to have enough strength would negate all the weight savings of having this kind of "taper". It would actually weigh even more.

Holes are generally avoided in masts wherever possible because they disrupt the "grain", and also create stress concentrations where cracks start to form... I considered reducing the wall thickness towards the top of the mast, but this would require an insanely large lathe. I can't imagine any makeshift rotary jig that would have enough rigidity to allow me to remove material in a controlled manner. Perhaps possible somehow... But definitely not worth it for a one-off mast. If you have any ideas about that, I'm all ears, though.
 

Rocketdc

Aluminum
Joined
May 24, 2020
I watched the video you linked and if you have a plasma cutter that's even simpler than my saw idea. Fabricate a straight edge using a taught string line and use it as a guide to run the plasma torch against. You could set this up very quickly and inexpensively.

I would still try making the wood or plywood block dies using clamps to draw the tubing back together. Working slowly in sections down the mast, similar to the press in the video, would probably work.

No idea about heat treating, that's above my pay grade.
 

henrya

Stainless
Joined
Jun 25, 2008
Location
TN
Sounds like a router jig is in your future. Start with a straight tube and taper it in a jig where the router slides along the tube, thinning the tube as it cuts on a slight angle.
 

Ries

Diamond
Joined
Mar 15, 2004
Location
Edison Washington USA
your video of the factory uses several of the techniques I mentioned in my "non-viable" response.
Theoretically you could hand cut those tapers with a jig saw, or maybe even a router. Assuming you built a good sturdy jig with guides.
Its not clear in the video, but I believe they are cutting 3 slots on each tube, and only on the top 1 1/2 or 2 meters.
But then, they are, as I said, using a very large press brake, and custom made tooling, to squeeze it.
To get an even taper, and a straight mast, which, I understand, is needed so it will bend predictably under sail, you need a jig like they have built, that keeps it straight.
You could perhaps try crimping a few inches at a time with a hand operated or foot operated press, but you would inevitably get a kinky tube, and you would need to straighten it.
Tubes can be straightened, sure- I have done a LOT of em by hand with a hossfeld bender and tube tooling for it- but thats another chunk of money, and a learning curve.
Then, the welding- again, exactly like I said, the ran a motorized carriage mig welder.
Do you have experience welding aluminum?
Cause I do- 30 plus years of it.
And I dont see how it fits in your fifty dollar window-
A machine to weld that probably needs to be at least 200 amps, shielding gas costs money. Then, you need to grind and then sand it.
Then, figure out how to heat treat it.

Blacksmiths make specialty forges all the time, by stacking fire bricks, building burner heads, and using natural gas or propane to bring the oven up to temp. That vid says 200 degrees (celsius, cause its a british manufacturer) for 10 hours. Its a lot like a kiln for ceramics, and controllers are available with thermocouples.

But all that stuff is gonna be more than 50 to a hundred bucks, especially if anything oddball has to be ordered from Germany or somewhere.

At your target price, wood masts are much more possible.

I assume you are not going to pay for labor, or get paid for your time.
Maybe, maybe, you could make the shape for that amount. But the heat treating is another hurdle, with a failure rate at first before you got it right.
 

Evenglischatiest

Cast Iron
Joined
Nov 22, 2005
Location
Santa Barbara
There's no reason reducing joints would need to add significant weight. On the first joint, for instance, you turn both the ID of the 70mm tube and the first OD of the reducer to 67mm, for the length where they overlap. The reducer would then taper to, for instance, 62mm OD and 59mm ID, over whatever length you can turn. The next straight section would then be 65mm OD, bored to 62mm ID for the length of the overlap. Drill half a dozen holes along each overlap and plug weld them. Maybe butt weld the seams, as well. You'd keep a steady 3mm wall thickness through the entire length. The only weight difference would be the filler material you use, minus the weight of the holes you drilled.
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
You drive a hard bargain, so here's my final offer:

How about a two piece tube of constant OD (70mm), with a 3mm wall base of 3M, then a top of 1mm wall for the remaining distance. Adjust as per loads, maybe you can use 2M and 4M for the lengths.

At the mate, use a "fish tail" (appropriate) notch of two or three tails, which could be laid out with a paper template printed and taped around each end. Either saw, drill holes at the edges, or otherwise cut the notches, use hand files or small right-angle sander to finish notches and adjust for mate and co-linearity.

Weld, and then let it sit for a while to regain some hardness through natural aging [It's worked for me, my arteries are much harder than they used to be!].

About as simple as you're going to get, and with a paper template getting the notches right won't be that hard. It does take more skill to get a good weld with such wall thickness differences, but you can practice with short sections of tube with simple butt welds.
 

rcoope

Stainless
Joined
Sep 25, 2010
Location
Vancouver Canada
I see a carbon 49er mast complete in three sections plus spreaders, is €5700 whereas the tapered aluminum RS200 mast which is more or less the one in the Selden video is a mere £1,056.00 (€1300). But 4.6m carbon windsurf masts are more like US$500 (€450), or even $350 for fiberglass. Meanwhile the two parts of the classic aluminum Laser standard mast (~6m total height) are around US$400. A crucial difference is that the tapered windsturf and straight Laser masts are just plain tubes, whereas the Selden tapered masts for RS have built in mast tracks for the sail, so have to be extruded first and then modified. And of course Selden is buying in sufficient volume that they can get whatever they want from the extrusion mill. To DIY this you would have to start with plain tubes and you'd be making the equivalent of a windsurfer mast with the sail sliding over it like a sock. But I think these prices give some relative idea of the cost of making these parts, so if one was to do it as a DIY project, I'm guessing the costs would scale similarly. And given how much the costs of composites is labour, which we're assuming is inexpensive here, you really could get to that low price point with the right composite design.

laukejas could you give is further insight into the kinds of boats you've built? Are you working on skiffs or even low cost Moth like boats? None of this discussion should dissuade you from trying the cut, form and weld approach, we're just saying it's going to be hard, and in North America or Wester Europe, composite is likely to be easier. The good news is breaking the top of a small boat mast is not generally a disaster, so would be fun to try.
 

petersen

Aluminum
Joined
Dec 13, 2008
Location
minnesota
Laukejas:

If you have the expertise to weld a "longseam" or two as you suggest in your original post,..why not four " longseams"??

You could consider simply cutting tapered strips of sheet or light plate, and bending (brakeing) a 45* crease down the center of each strip and assembling four strips to create an eight sided
tube with four longseams.

Make the strips 4' or 5' or 2 metres long; or whatever is practical to brake. And start with two long strips and two short strips so you can join a next section with transverse welds staggered to avoid a full circumference heat affected zone.

You could use heavier material at the bottom. and lighter as you build toward the top, and taper continuously from bottom to top.

Much less complicated metal forming task, But the welding supplies would probably exceed your unrealistic budget.


petersen
 

HappyWyo

Aluminum
Joined
Nov 30, 2019
A lot of good ideas. I used to hang glide before I got my pilots license. My hang glider tubes had holes all over in it for pins. Aircraft aluminum of course. But the holes never weakened it any. I would think rolling the tube from sheet would be the easiest.
 
Though I suppose there is a minimum amount of force required to overcome the elastic modulus of aluminum in order to get any kind of permanent deformation. It probably goes without saying that this is beyond the scope of a DIY?

If you are determined to make tapered aluminum poles, i think that method is accessible.
The actual rolling stand and rollers are a relatively simple fab and lathe work.
Then a few volunteers to tighten the rollers with screw actuators as the work progresses instead of cnc hydraulics.

Something to grip, and spin the tube such as a collet and plug arrangement.
Some gearing and threaded rod to pull as it spins. All mounted on a big honking W section ("I-beam") perhaps bolted to a concrete floor. If you have good scrap yards and industrial wastelands to cadge the big steel pieces, it could be done for under $1,000 + a scrap motor. I know where the 40' 12" or 14" W pieces might still be mouldering beside a turf runway at a very secluded airport.

The key issue would be to understand what exactly needs to happen before making the rolling stand parts.
For aluminum, you would have to stop and torch-anneal it every "X" number of rotations. (Like others on here, i have annealed aluminum sheet and bar which bashing it into shapes, so as not to crack it). Though that is not my regular work.

RE: your note abotut 7075: Don't even think of it for regular boats, even if you figure out a way to form and weld it. It is extremely susceptible to corrosion, esp. filiform corrosion. Only reason to use it would be for a world class competition where it only had to last a season, and every gram counted.

Good luck - I think the rolling option is accessible since it is essentially simple, & only requires simple, albeit brute force, &rigid, equipment.

smt
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
RE: your note abotut 7075: Don't even think of it for regular boats, even if you figure out a way to form and weld it. It is extremely susceptible to corrosion, esp. filiform corrosion. Only reason to use it would be for a world class competition where it only had to last a season, and every gram counted.


smt

Great, now you're going to disparage my idea for an unpainted pure magnesium boat hull...
 

laukejas

Plastic
Joined
Feb 27, 2022
Thank you for the extensive replies, guys. I like where this thread is going, there are some really great ideas here.

I watched the video you linked and if you have a plasma cutter that's even simpler than my saw idea. Fabricate a straight edge using a taught string line and use it as a guide to run the plasma torch against. You could set this up very quickly and inexpensively.

I would still try making the wood or plywood block dies using clamps to draw the tubing back together. Working slowly in sections down the mast, similar to the press in the video, would probably work.

No idea about heat treating, that's above my pay grade.

I do have a plasma cutter. Never used it on aluminum, but I think it should be pretty straightforward with an appropriate straightedge fixture.

As for clamping, if I were to make more cuts (2 or 4) along the length of the tube, shouldn't it be possible to draw that tube closed again using hose clamps, adjusting them slowly and tacking with a welder once in the right alignment?

your video of the factory uses several of the techniques I mentioned in my "non-viable" response.
Theoretically you could hand cut those tapers with a jig saw, or maybe even a router. Assuming you built a good sturdy jig with guides.
Its not clear in the video, but I believe they are cutting 3 slots on each tube, and only on the top 1 1/2 or 2 meters.
But then, they are, as I said, using a very large press brake, and custom made tooling, to squeeze it.
To get an even taper, and a straight mast, which, I understand, is needed so it will bend predictably under sail, you need a jig like they have built, that keeps it straight.
You could perhaps try crimping a few inches at a time with a hand operated or foot operated press, but you would inevitably get a kinky tube, and you would need to straighten it.
Tubes can be straightened, sure- I have done a LOT of em by hand with a hossfeld bender and tube tooling for it- but thats another chunk of money, and a learning curve.
Then, the welding- again, exactly like I said, the ran a motorized carriage mig welder.
Do you have experience welding aluminum?
Cause I do- 30 plus years of it.
And I dont see how it fits in your fifty dollar window-
A machine to weld that probably needs to be at least 200 amps, shielding gas costs money. Then, you need to grind and then sand it.
Then, figure out how to heat treat it.

Blacksmiths make specialty forges all the time, by stacking fire bricks, building burner heads, and using natural gas or propane to bring the oven up to temp. That vid says 200 degrees (celsius, cause its a british manufacturer) for 10 hours. Its a lot like a kiln for ceramics, and controllers are available with thermocouples.

But all that stuff is gonna be more than 50 to a hundred bucks, especially if anything oddball has to be ordered from Germany or somewhere.

At your target price, wood masts are much more possible.

I assume you are not going to pay for labor, or get paid for your time.
Maybe, maybe, you could make the shape for that amount. But the heat treating is another hurdle, with a failure rate at first before you got it right.

Good points. I think I could handle the cutting with the plasma torch and straightedge jig, I've done similar lengthwise cuts on steel profiles, perhaps it would be possible to do with aluminum as well.

I have space to lay out that tube and clamp it down flat and straight during welding. Perhaps if cuts could be made symmetrically on 2 or 4 sides on that tube, the shape distortion could be kept to a minimum.

I have some experience welding with MIG and TIG - not much, admittedly - but I am pretty comfortable with the process. And I do have the equipment for it (shared workspace). That being said, I am not exactly sure of the gas and filament cost calculations. I didn't think it would be significant here. I will look into this. As for grinding and sanding, I have equipment and experience with that as well, that part is definitely doable.

But the heat treatment might be the deal breaker here. I have no idea how to solve that one yet. Building a furnace/kiln for one mast just doesn't justify the costs. This is definitely something I need to figure out.

There's no reason reducing joints would need to add significant weight. On the first joint, for instance, you turn both the ID of the 70mm tube and the first OD of the reducer to 67mm, for the length where they overlap. The reducer would then taper to, for instance, 62mm OD and 59mm ID, over whatever length you can turn. The next straight section would then be 65mm OD, bored to 62mm ID for the length of the overlap. Drill half a dozen holes along each overlap and plug weld them. Maybe butt weld the seams, as well. You'd keep a steady 3mm wall thickness through the entire length. The only weight difference would be the filler material you use, minus the weight of the holes you drilled.

I don't think I can turn anything... The lathe I have access to can turn 1 meter long objects at best. There is an additional issue of having to purchase aluminum tubes of different diameters - I would have to buy full length tube (6m) for every diameter. No one cuts tubes for retail of such sizes here, especially for rare diameters. Not even scrapyards have anything like that. But the idea you presented is pretty interesting, if I understand it right. Could you perhaps make a quick sketch or something?

You drive a hard bargain, so here's my final offer:

How about a two piece tube of constant OD (70mm), with a 3mm wall base of 3M, then a top of 1mm wall for the remaining distance. Adjust as per loads, maybe you can use 2M and 4M for the lengths.

At the mate, use a "fish tail" (appropriate) notch of two or three tails, which could be laid out with a paper template printed and taped around each end. Either saw, drill holes at the edges, or otherwise cut the notches, use hand files or small right-angle sander to finish notches and adjust for mate and co-linearity.

Weld, and then let it sit for a while to regain some hardness through natural aging [It's worked for me, my arteries are much harder than they used to be!].

About as simple as you're going to get, and with a paper template getting the notches right won't be that hard. It does take more skill to get a good weld with such wall thickness differences, but you can practice with short sections of tube with simple butt welds.

If I understand this right, there would be a sudden change in the wall thickness where 3mm wall and 1mm wall tubes meet... I did consider something like a this a while ago, I actually made a small scale mock up from other materials. Problem is, the sudden change in rigidity doesn't work well at all for bending the sail on such a mast. The taper and change in rigidity must be very gradual. Perhaps this could be smoothed out with more sections, but again, that means buying even more full-sized aluminum tubes that I'm only going to use a little of each...

I see a carbon 49er mast complete in three sections plus spreaders, is €5700 whereas the tapered aluminum RS200 mast which is more or less the one in the Selden video is a mere £1,056.00 (€1300). But 4.6m carbon windsurf masts are more like US$500 (€450), or even $350 for fiberglass. Meanwhile the two parts of the classic aluminum Laser standard mast (~6m total height) are around US$400. A crucial difference is that the tapered windsturf and straight Laser masts are just plain tubes, whereas the Selden tapered masts for RS have built in mast tracks for the sail, so have to be extruded first and then modified. And of course Selden is buying in sufficient volume that they can get whatever they want from the extrusion mill. To DIY this you would have to start with plain tubes and you'd be making the equivalent of a windsurfer mast with the sail sliding over it like a sock. But I think these prices give some relative idea of the cost of making these parts, so if one was to do it as a DIY project, I'm guessing the costs would scale similarly. And given how much the costs of composites is labour, which we're assuming is inexpensive here, you really could get to that low price point with the right composite design.

laukejas could you give is further insight into the kinds of boats you've built? Are you working on skiffs or even low cost Moth like boats? None of this discussion should dissuade you from trying the cut, form and weld approach, we're just saying it's going to be hard, and in North America or Wester Europe, composite is likely to be easier. The good news is breaking the top of a small boat mast is not generally a disaster, so would be fun to try.

You have done your research. The prices you mentioned are exactly what I've seen too. Sail track is not required for me. I had experience with them on factory-made boats, and in my opinion - they suck. Unless they are made with absolute precision and highest quality of materials, they tend to jam at the worst possible moment. Any dent, any debris or dirt in the track is going to make it jam, making it impossible to lower the sail when it's most needed... Like during an approaching storm. This is one of these items that make sense for F1-equivalent racing boats, but not for DIY people. Lashing sail around the mast with rope or using sail sleeve (like on windsurfers) is a far more convenient option.

The reason why I shy away from composites is because they are exceptionally expensive where I live. For example, making such a mast from carbon would be over $600 for carbon alone, not counting in epoxy, mold, jigs, release agents, disposable tools and so on. I guess this material is still too high-tech for where I live.

I do skiffs, yeah. This is my latest boat, built last summer (I'm the guy onboard): Burvaltės "Jumpyra" pirmoji savaitė ant vandens - YouTube

As a matter of fact, the mast we're talking about is for this boat. As you can see from the video, I took a gamble and used a windsurfer mast, the thickest and most rigid I could find, with additional stiffening. Unfortunately, it is a total disaster - it bends way too much and totally ruins the sail shape. Which is why the boat is so slow in this video. This is why I am looking to build a new mast this summer. My default plan is to do a 2-piece wooden mast with fiberglass sleeve as a joint (due to storage and transportation limitations), but if I could do an aluminum one I would much prefer it... Like I said, getting quality lumber is just near-impossible nowadays.

Laukejas:

If you have the expertise to weld a "longseam" or two as you suggest in your original post,..why not four " longseams"??

You could consider simply cutting tapered strips of sheet or light plate, and bending (brakeing) a 45* crease down the center of each strip and assembling four strips to create an eight sided
tube with four longseams.

Make the strips 4' or 5' or 2 metres long; or whatever is practical to brake. And start with two long strips and two short strips so you can join a next section with transverse welds staggered to avoid a full circumference heat affected zone.

You could use heavier material at the bottom. and lighter as you build toward the top, and taper continuously from bottom to top.

Much less complicated metal forming task, But the welding supplies would probably exceed your unrealistic budget.

petersen

Very interesting idea. This sounds a lot like making a wooden mast from wood strips (birdsmouth method). I little idea of how much welding would cost at this scale, I never welded so much in one go. I will have to run some maths.

As I understand, this would end up in a 8-sided mast that I would have to round using the water pressure method?

A lot of good ideas. I used to hang glide before I got my pilots license. My hang glider tubes had holes all over in it for pins. Aircraft aluminum of course. But the holes never weakened it any. I would think rolling the tube from sheet would be the easiest.

But how would I roll a 5.5m long sheet into a cylinder? Is this possible with DIY means? Seems to me like this would require a metal forming roll of 5.5m long working length... How would you do it?
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
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?
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
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.
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
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.
 








 
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