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Making a tapered aluminum tube

laukejas

Plastic
Joined
Feb 27, 2022
Do you build racers or cruisers? High tech materials are more expensive. Metal masts are available from marine suppliers in a wide variety of stock sizes. You can't build one as good. If you are a sailor, a big advantage of metal is lightening protection and it becomes apparent once you experience storm conditions.

I build small racing sailboats (3-4 m in length) for myself, as a hobby, sailing and racing inland. But I do have quite a lot of experience with them already. Most are built on a shoestring budget (<1000$). Definitely no high-tech materials. Seaworthiness, storms and lightning are of little concern. I am trying to explore and work out new boatbuilding methods that are both simple and cheap, to share with the rest of the boatbuilding community in my country - other builders with VERY limited financial means.

I am aware that I can't build something as good as the stuff made in factories for class-regulated sailboats. But I want to see how close I can get to that with simple DIY means.
 

GregSY

Diamond
Joined
Jan 1, 2005
Location
Houston
Ries said it best.

This is one of many examples in modern life where we've grown accustomed to things that have shapes and sizes we take for granted....but in reality they're very difficult to make until you invest a few million dollars in tooling....then they're not too bad.

An automobile fender is a good example.

Most machinist and fabricators have had someone show up with a common item they want made....only to be told by the machinist or fabricator that it can't be made....at least not without lots of suffering, time, and money.


How will you make a decent mast for not too much money or effort? You won't.


If it was me...I'd talk to people who are already making them...or something similar like flagpoles....and spend my time begging their asses to make a one-off for me. They'll give you a 'get lost' price....all that is left is for you to find a way to cover it.
 

Kalispel

Aluminum
Joined
Jan 27, 2021
Location
Ohio
That sounds like a very promising option! I'm just not exactly sure about that first part: why do the halves have to be flat? Wouldn't it be easier to start with a round tube, cut in half with tapering? Starting off with flat plate and making 30 degree lengthwise bend sounds like a very tough challenge...

Also, what kind of water pressure am I looking at for the dimensions I mentioned?


The pressure applied must cause a hoop stress sufficient to overcome the yield strength of the tube causing it to expand. Hoop stress for a thin tube = P*r/t. Depending on the radius and wall thickness, a high pressure washer might do it.

6060 is not a strong alloy. It is a poor choice for this application.
 

Kevin T

Stainless
Joined
Jan 26, 2019
Can a linear array of through holes of increasing size provide enough of a "guide" for your cutting method? Oh yeah I am spitballin but maybe worth a try? I might try a test on a section of this pipe where the drilling would be the largest size and then see if your press can help bring it back into a useable shape for tacking. You can use that lathe of yours to make some female dies for controlling the outside shape at intervals along the axis, but can it be kept straight? I assume you'll be squeezing, tacking and moving up and repeating. If my calculus is tight you are looking at about 1/8" wall tubing. Maybe there is no easy way to control the straightness over that length?
 

Rocketdc

Aluminum
Joined
May 24, 2020
I would try to figure out a way to use the woodworking track saw concept where the saw rides on a linear rail.

The tubing would have to be held in place and secured to keep it straight and the saw rail can be positioned over the tubing to accommodate cutting the slight taper. The saw would either be attached to the rail with a bearing or it would ride on top of it. The rail could be round or flat, the challenge would be accommodating the length. Might have to use a shorter rail and reposition it for several cuts.

To close the tubing for welding I would try to make some dies close to the OD of the tubing, possibly out of wood by cutting holes with a hole saw then splitting the pieces in half for the two dies. Make a bunch and slowly draw them together with clamps along the length of the mast and tack it together once it's closed sufficiently. Would probably create more of a teardrop shape.
 

Gordon Heaton

Stainless
Joined
Feb 19, 2007
Location
St. George, Utah
. . .annealing requires heating up aluminum to ~300°C for hours. How would you suggest I do that on a 5.5 meter long piece? I can't imagine building a heating chamber that big. And how would I perform age hardening?

Common alloys like 6061 don't require soaking at temp to anneal. Simply heat, then cool as soon and as fast as you want. It'll be dead soft. My stuff isn't life threatening in any way and I just use the old-time 'coat it with soot from a rich acetylene flame and burn the soot off' procedure and it always works. Age hardening will take place without any action on your part beyond waiting. It won't get back to the original spec, though.
 

laukejas

Plastic
Joined
Feb 27, 2022
Ries said it best.

This is one of many examples in modern life where we've grown accustomed to things that have shapes and sizes we take for granted....but in reality they're very difficult to make until you invest a few million dollars in tooling....then they're not too bad.

An automobile fender is a good example.

Most machinist and fabricators have had someone show up with a common item they want made....only to be told by the machinist or fabricator that it can't be made....at least not without lots of suffering, time, and money.


How will you make a decent mast for not too much money or effort? You won't.


If it was me...I'd talk to people who are already making them...or something similar like flagpoles....and spend my time begging their asses to make a one-off for me. They'll give you a 'get lost' price....all that is left is for you to find a way to cover it.

Well, for me, guythatbrews said it best, because he actually suggested a very viable idea. Look, I don't mean to be rude, since I'm asking for help, but discouraging and saying "can't be done", when just a few posts above people are actually suggesting good ideas how it could be done, doesn't add very much to the discussion. I am well aware that what I'm asking is difficult, but maybe not impossible with the right approach.

Like I wrote before, I am trying to figure out new cheap and easy ways to build various parts of sailboats for our community. We already had quite a few discoveries that allowed us to build various hardware at 1/10 of the price of the commercial alternatives. So "finding a way to cover the cost" is the very opposite of what I'm trying to achieve here.

The pressure applied must cause a hoop stress sufficient to overcome the yield strength of the tube causing it to expand. Hoop stress for a thin tube = P*r/t. Depending on the radius and wall thickness, a high pressure washer might do it.

6060 is not a strong alloy. It is a poor choice for this application.

Thanks for the formula, I'll run some calculations on this. As for the alloy - yeah, I know it is terrible. But like I said, it is the only alloy available for purchase around here. During my boatbuilding adventures, I spent insane amount of time sourcing materials, so believe me, I looked everywhere. You can get better alloys if you order a truckload of it, so in the end it just doesn't justify it for home-builders.

I would try to figure out a way to use the woodworking track saw concept where the saw rides on a linear rail.

The tubing would have to be held in place and secured to keep it straight and the saw rail can be positioned over the tubing to accommodate cutting the slight taper. The saw would either be attached to the rail with a bearing or it would ride on top of it. The rail could be round or flat, the challenge would be accommodating the length. Might have to use a shorter rail and reposition it for several cuts.

To close the tubing for welding I would try to make some dies close to the OD of the tubing, possibly out of wood by cutting holes with a hole saw then splitting the pieces in half for the two dies. Make a bunch and slowly draw them together with clamps along the length of the mast and tack it together once it's closed sufficiently. Would probably create more of a teardrop shape.

Great advice, thank you. I will definitely try this on the small-scale experiment.
 

henrya

Stainless
Joined
Jun 25, 2008
Location
TN
As soon as you omit the requirement to be tapered this becomes much more manageable. I’d start with a thin aluminum tube in the light side of your needed strength and then pull woven carbon tube over it. Pull it tight, then apply resin and wrap the assembly round and round with shrink wrap. You will need some helpers to make it all happen in order. Alternately, you could vacuum bag the assembly.

You’ve already rejected carbon, but other than buying the fabric and resin its the best method to make a good safe product with limited tools and money. Look harder at this and I think you will see its the cheapest, best, simplest way to get there.
 

laukejas

Plastic
Joined
Feb 27, 2022
As soon as you omit the requirement to be tapered this becomes much more manageable. I’d start with a thin aluminum tube in the light side of your needed strength and then pull woven carbon tube over it. Pull it tight, then apply resin and wrap the assembly round and round with shrink wrap. You will need some helpers to make it all happen in order. Alternately, you could vacuum bag the assembly.

You’ve already rejected carbon, but other than buying the fabric and resin its the best method to make a good safe product with limited tools and money. Look harder at this and I think you will see its the cheapest, best, simplest way to get there.

I already did that on some of my previous boats. Without taper, it is dead simple, but also pointless. If I didn't need taper, I wouldn't be asking here :D Unfortunately, taper is absolutely essential, it's the whole point of this.
 

Kalispel

Aluminum
Joined
Jan 27, 2021
Location
Ohio
As soon as you omit the requirement to be tapered this becomes much more manageable. I’d start with a thin aluminum tube in the light side of your needed strength and then pull woven carbon tube over it. Pull it tight, then apply resin and wrap the assembly round and round with shrink wrap. You will need some helpers to make it all happen in order. Alternately, you could vacuum bag the assembly.

You’ve already rejected carbon, but other than buying the fabric and resin its the best method to make a good safe product with limited tools and money. Look harder at this and I think you will see its the cheapest, best, simplest way to get there.

I have seen this done making specialized radio antenna masts. The inner metal tube was part of the electrical circuit. The carbon fiber adds strength. A non-circular foam form was placed over the tube as the foundation for winding the fiber to form an airfoil shape. The operation was not complex.
 

laukejas

Plastic
Joined
Feb 27, 2022
I have seen this done making specialized radio antenna masts. The inner metal tube was part of the electrical circuit. The carbon fiber adds strength. A non-circular foam form was placed over the tube as the foundation for winding the fiber to form an airfoil shape. The operation was not complex.

Well, theoretically I could wrap a VERY thin aluminum tube (say 1mm wall thickness) with carbo, but I would still need to make that taper in the aluminum tube somehow prior to carbon. And like I said, carbon is way out of budget anyway...
 

laukejas

Plastic
Joined
Feb 27, 2022

Thanks, great videos :) I have no idea of the forces involved in this process, and I wonder if it is possible to substitute a construction as rigid as in these videos with a less rigid jig but making more passes. 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?
 

gary s moore

Aluminum
Joined
Nov 9, 2008
Location
Rock Island Wa USA
rather than tube spiral wrap flat stock around a mandral turned of short sections welded together to get the total length neaded. this would be a lot of welding and hand forming but i think doabl with 6 to 12 inch flat stock.
 

laukejas

Plastic
Joined
Feb 27, 2022
rather than tube spiral wrap flat stock around a mandral turned of short sections welded together to get the total length neaded. this would be a lot of welding and hand forming but i think doabl with 6 to 12 inch flat stock.

Interesting idea. Similar to wrapping carbon, I suppose. I have never seen anything like that done with metal, though. Adding to the list.

What exactly is your target price for this endeavor ?

Well, I build a typical wooden mast of these dimensions (tapered) for around $50. I can buy an aluminum tube of these dimensions (non tapered) for a little over $100. I think the most I could throw in addition to that is another $50 for tapering tools and jigs (so total of $150, three times the price of a wooden mast), after which it would be not worth it anymore the time savings.
 

Turbowerks

Cast Iron
Joined
Nov 9, 2018
Location
Windom
We’ve pretty much beaten the easy cheap ways to death and the expensive ways. Make a wooden die at the taper you need for half your shape, beat sheet stock into the die, trim make another piece and weld together. Time is cheap for the diy person. But right now unless you cut a tree down for the die the wood will cost more than 150.00


When I find it I don’t need it
When I need it I can’t find it!
 

laukejas

Plastic
Joined
Feb 27, 2022
I just found this video on factory-made tapered aluminum mast manufacturing: How masts are made for sailing dinghies : Friday Forum - YouTube

It appears that they are doing exactly what I suggested in my very first post. They are using plasma cutters to make that tapered removal of the material, but mentioned that other companies do it by hand. Then they use press and dies to close up the gap, and weld it straight. So again, just like I intended.

The caveat might be that they are working with pre-treated aluminum, and they heat-treat it afterwards. This is an issue, but Milland said I could anneal aluminum to make it more malleable and then heat-treat it afterwards.

Can anyone check out that video? Having seen this example, I am a bit confused why it wouldn't work with DIY tools. Of course, it would take longer, but is there anything in this workflow that is actually impossible?
 








 
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