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  1. #1
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    Default expanding alloy extrusion

    As far as I know alloy extrusion doesn't want to be bent, much. Or at least not without compromising its strength. But I have a project that requires a sleeve to fit over the top side of a tube extrusion, so I was wondering if a similar section of the tube can be heated and stretched on to make this partial sleeve. I am thinking that the strength isn't that important, but am willing to be corrected. I hope this graphic explains my question a little clearer.





    Fwd beam and a frame.JPG

  2. #2
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    It will depend a bit on the tube diameter and wall thickness, but I think the most likely answer is 'it won't really work'.

    To achieve what I think you want to do I think you will either have to make the sleeves a bolt on arrangement (that is, two halves that bolt together over the tube) or machine up a circular part of appropriate thickness and then weld the (thinner) wall tube into it. Bear in mind that when you weld the Al tube you will be annealling it so making it softer. You might be able to get away with that by gluing the tube in the machined socket (loctite or similar)

    Michael

  3. #3
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    There may be ways to do it, but it could be painful...

    I recently did a turbo upgrade on my Landy, and I needed to expand the end of a 2 1/4 inch aluminium mandrel bend up to 2 1/2 inch to suit the silicon coupler I had room for. I did it by using a "tube beading" die on my bead roller to create a bunch of ribs, and then changed the dies around to bring the lows up. It works by stretching the material, making the wall thickness slightly thinner in exchange for gain in surface area. However, it was painfully slow, and not a very even expansion the way I did it, and some work hardening will occur (although this can be solved, depending on material grade and desired temper etc).

    However, assuming you're using a round tube (the drawing looks a little oval, but that may be the perspective setting in your cad program), what could work for short lengths is to use a slip roller. If you can remove the top roller from the machine, then fit the tube over the top roller, and refit, you could then crank the pressure up. Even better if you can get the lower roller right underneath the upper, so that the tube is being squeezed between the two rollers, to really get the metal to thin out a bit. Won't go very quickly, but should get the job done eventually.

    Of course, if you had access to a slip roller in the first place, you could just roll up your own size of tube anyway, and weld the join since you've got some welding to do anyway :

    Better, of course, if you can just buy a different size of tubing that is a nice slip fit? All depends on the grades of material you're using, looks like this needs to be suited to a marine environment?

  4. #4
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    Default

    Quote Originally Posted by perrycas View Post
    As far as I know alloy extrusion doesn't want to be bent, much. Or at least not without compromising its strength. But I have a project that requires a sleeve to fit over the top side of a tube extrusion, so I was wondering if a similar section of the tube can be heated and stretched on to make this partial sleeve. I am thinking that the strength isn't that important, but am willing to be corrected. I hope this graphic explains my question a little clearer.





    Fwd beam and a frame.JPG
    Hi Perrycas,

    Could be easy or hard depending on how much expansion you need.

    Use a steel mandrel that will fit closely inside your tube make sure that it can be solidly held and then using a flat faced hammer just go around the tube tapping firmly until you have expanded it to the size you require.

    The only other way that I know of expanding a tube is to use a quite expensive expander ! This basically consists of three or more steel balls inside a steel tube that are forced outwards by a tapered shaft as the tube containing the balls is rotated inside the tube you want to expand.
    Best Regards:
    Baron J.

  5. #5
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    Quote Originally Posted by BaronJ View Post
    The only other way that I know of expanding a tube is to use a quite expensive expander ! This basically consists of three or more steel balls inside a steel tube that are forced outwards by a tapered shaft as the tube containing the balls is rotated inside the tube you want to expand.
    A place that does truck exhausts might be able to expand the tube but the problem I see is that I think the OP wants a snug/ secure fit on the Al tube underneath. Expanding the tube just enough so that it does that would be quite tricky.

    Michael

  6. #6
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    Default

    I take it this is a forward beam of a cat, is the beam round or a mast/ boom section ?
    If it is a mast section phone a mast maker and get the size to fit over it, maybe.
    I have seen external and internal sleeves before on yacht masts.

  7. #7
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    Default

    Don't forget that marine = salt water = corrosion wherever salt can enter, so any sleeve had better be sealed tighter than a little fishie's behind or one day you could find yourself with an unexpected and catastrophic failure.

  8. #8
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    Default good information, thanks

    Quote Originally Posted by Somedayplumbing View Post
    I take it this is a forward beam of a cat, is the beam round or a mast/ boom section ?
    If it is a mast section phone a mast maker and get the size to fit over it, maybe.
    I have seen external and internal sleeves before on yacht masts.
    >> yes thats what it is. It's a round section. I take the the other members comment about corrosion seriously, but this seems to be the way its done, I've seen a few before but never thought too much about it. Perhaps they were on production boats that had custom extrusion made for the sleeves? You can't really weld bits on to a cross beam for the obvious reason - it'll weaken it. The alternative is to get parts made in SS and seal, bolt them on. There's been bit of this done on the boat and I have to check it as the previous owner had some interesting ideas about it, seemed not to have had a worrying lack of understanding of the concept of electrolysis.
    I will go and chat with a spar maker, but at the moment the boat is not near me and in a really remote location so I was trawling for information so I know what to ask next. Thanks all for your input. Valuable.
    Perry

  9. #9
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    Default

    Hi perrycas,

    Welcome to the MetalWork forums.

    You will find yourself in good company here.
    To see what on offer in the rest of the forum/s do this:

    Goto the FORUM box in the top left hand cnr of the page and click the down arrow. This will bring up a pull down menu that has Forum Home at the top

    Click Forum Home which will present a scroll down page.

    Our rules, the Terms of Service are right at the top ,we ask that our members read them.

    Below that are all the various areas and sub forums that make up our MetalWork forums.

    Since your time in the Woodwork side you will see the metalwork has taken on its independent forum.
    I hope you will post a lot more than you have over there and join in our discussions.


    Welcome

    Grahame

  10. #10
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    Default

    Hi Perry,

    I had a cat with similar setup of the front crossbeam, made from oval mast section.
    From memory the doublers were simply cut from the same section, then cut lengthways into two halves, stretched (bashed?) a little to fit around, then riveted into place with rivets.
    No need to heat the sections when reshaping them because not much movement is required in relation to the wall thickness. The doublers reduce localised stresses on the main beam tube where there are fasteners etc so if well placed they should not need to completely enclose the original beam - even one longways cut down the added section of tubing should allow it to be re-shaped to a suitable radius, possibly with sheet metal bending rolls.
    Provided you use similar aluminium spar material for the doublers corrosion is not a problem - no need for special arrangements, tho' some tefgel or similar anticorrosion stuff between the layers is a simple precaution. Monel or aluminium rivets are best. I once built an 8 metre mast from a kit, and the sparmaker who sold me the kit said to use aluminium rivets with aluminium stems, not the usual steel stems that are mostly used.
    In my experience stainless sheet fixed to Al parts can be a great little electrolytic corrosion cell, tho' as mentioned tefgel or other anticorrosion compound may manage that.

    Talking to a spar maker is a good idea.

    Bill
    Last edited by WCD; 10th Oct 2020 at 08:02 PM. Reason: re-wording

  11. #11
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    Default Thanks.

    Quote Originally Posted by WCD View Post
    Bill
    Yes that was interesting Bill. I rather assumed that the same section wouldn't fit that well that it would have to be the next one up. I was wanting to go and have a chat in person with a spar maker, but there aren't any in Sydneys east so, haven't got there yet. The electrolysis issue is always one to watch I agree, particularly with this one as the previous owner told me how he felt that bolts into a spar 'would corrode in place'. Bit of a worry. I want to replace the A frame and was thinking of using the image I put up as an example with spreaders as the uprights. As I notice you are also in Sydney do have any ideas as to where I might find some used spreaders? When I lived in Fremantle years ago Tasker's was just around the corner from me, they always seemed to have old rigs around the side of the building.
    The boat is in the Azores. I looked at it in February, just before the fun started. There is a good fabricator on the island, but I will have to supply the spreaders. When I get back there. Whenever that is.
    I've put a picture here of the A frame to amuse you. The piece of garden hose is the insulation for the nav light cable. It snakes back through the tramp lacings to the pilot house. I don't think the previous owner put the A frame on so theres a chance there was some barrier grease on the bolts. Theres a lot of his DIY bodge on the boat but mostly its benign and just requires tidy up. Lots of it. The secure points for the Martingale ends appear to be original as I have an original drawing. Bit nasty.
    Perry
    Attached Images Attached Images

  12. #12
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    Default

    Perry,

    It's hard to comment on the A frame other than to say it lacks neatness, but it may well be plenty strong. There seem to be load-spreading pads of some sort at the base of the A frame which is good, tho' how the frame is fastened to the beam is not clear. Also the stainless strap with loop eye at the centre of the crossbeam looks like a corrosion risk -if you can't remove it to apply the good stuff at least spray some Lanotec under the edges to slow down unwanted activity.

    Re advice for A frame spar parts, in the east it seems to be concentrated in the Manly - northern beaches area, but possibly not the bit of east you want.
    Sheerline in West St Brookvale, who supplied my kit mast in 1989 seem to have contracted and moved on to flagpoles/goalposts, as has Goldspar at Mona Vale, but I did phone Goldspar recently and they still do mast work. Spunspar were in Mona Vale and may still be around. Even if these well established operations now concentrae on more profitable work, I suspect they still have tabs on doing the work/advice you want, or who can do it.

    Off topic - I couldn't help noticing that big Bruce anchor hanging off the beam. I have a genuine one of those on a dinghy, it's the 1 kg version, a far cry from the originals designed to stabilise North Sea oil rigs.
    Also there is a lot of sag in that front trampoline. My cat was set up like that, and I fitted a centreline beam between the mast beam and the centre of the fore beam, which seemed to stiffen up the rig, gave me a place to fit a solid anchor cleat and made the tramp into a more stable work surface.

    Bill

  13. #13
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    [QUOTE=WCD;1975961]Perry,

    Yes I agree, probably strong enough, but its a bit unattractive. When it comes time to selling it it'd be better if it was a different unit. From what can gather there is a fabricator on the island who does good work and isn't expensive so its probably the time and place to do it. I'm pretty sure I am going to get him to make me a tabernacle as well. I have had several boats with them and its pretty good to get access to the higher parts of the mast not to mention being able to go up rivers and under bridges.

    That bit of stainless in the centre of the beam is a worry but it does seem to have a bit of rubber under it. Its bolted on. Don't worry its coming off.

    Yeah the tramp hasn't been tensioned for some time I'd say. My suspicion is that its nearing its last days. I had thought of doing something like what you suggest. Its not possible to get something directly from the Centre beam to the fwd beam, theres a locker in the way. So leaning towards putting a catwalk in there. Probably reinforce it with some tube which would help getting tension on the tramp. At the moment its laced to holes in the, duh what do you call it, the seam where the hull molding meets the deck molding. Not exactly a low friction surface. Toying with the idea of putting a bit more tube around the the edges of the tramp to be able to get more tension on it.

    The Bruce is a copy. I have never had one before, I have heard some favourable comments on them. I hope this one works.

    Uploaded a few more images to show what I'm talking about. Its up on the hard and has been for a year. Smells pretty unique inside. Its covered with the previous owners DIY bodge, most of it is just going to be time consuming to rectify. But I am going to have a bit of a wait to get back there.

    Thanks for the info on potential spar people, I will have to make a northern pilgrimage.

    Which cat did you have Bill?

    This one is Norwegian designed by a guy called Ulv Tolsen. The design is based on the Havkatt 31 (which is Norwegian for Seawolf, rather than 'I have a catamaran'), which were fast boats, but this is supposed to be an improvement. We'll see. Somehow I doubt it. More comfortable than fast I suspect.
    Perry
    Attached Images Attached Images

  14. #14
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    Perry,

    I see what you mean about the front tramp to hull flange lacing. The tramp netting looks to be fine mesh but hopefully open enough to allow a tall crest to drop through easily. I only copped that once but all it did was to thoroughly rinse the blokes sunning themselves on the front tramp.
    My cat was littleand light by comparison: 8.5m GBE (Great Barrier Express) fibreglass designed in NZ by Malcolm Tennant (originally designed for cold moulded plywood) - skinny hulls less than 1 metre max beam, and definitely not an ocean cruiser.

    Bill

  15. #15
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    Default more on the A Frame

    got my contact to have a better look at the A frame and he confirmed my thoughts - that the thing was a real mess, uprights repurposed sort of alloy box section riveted/attached to SS footings, screwed and riveted to the beam. It's 'offal'. So yes will start this week talking to those contacts you mentioned to acquire some spreaders of sufficient meat. Talked to a friend of mine I hadn't seem for a while who is a blacksmith about the issue of heating and fitting the half sleeves on the X beam and he says it's not an issue. Yes the tramp in higher res images is a reasonably loose mesh and waves would drain through it. Getting to it is a bit of a problem. It isn't going to be soon.
    P

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