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  1. #1
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    Oct 2010
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    Default Routing Aluminium

    Hi,

    I posted this thread on the metal forum as well, hopefully someone can give me some advice.


    I'm trying to bend 1" stainless tubing and have made a diy bender out wood similar to this one found on youtube.

    DIY tube bender.JPG



    Trouble is, it doesn't work. The wooden formers, which have grooves routed in them, are too soft to withstand the strain, particularly at the centre bolthole where the most strain occurs. I thought of using aluminium instead of wood but the expense would be too great for my project. It got me wondering though, is it possible to rout a groove into aluminium using a woodwork router?

    And can anyone suggest a way of strengthening the pictured setup to make it work? I fitted some bronze bushes to the centre holes but they made little difference. the plywood is just too soft I think.

    redx

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  3. #2
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    moonbi nsw Aus
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    Default

    There is a bit of dynamics going on here that should be looked at.
    What thickness is the SS tubing?
    What diameter is the bolts you are using for the pivot points?

    By the pictures it looks like you have used ply for the "formers". Really they should be OK for a "disposable former". They will work fine but they will not stand up to hundreds of bends.

    The bolts/pivots need to be 13mm or even 16mm. The tubing will exert an awful lot of force as you follow the curve. If the tube is quite thin you may find that your bends will just crush the tube. A way round this is to fill the tube with sand packed in tight with the ends plugged up well. The sand, being contained, will with stand the crushing of the tube.
    Just do it!

    Kind regards Rod

  4. #3
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    Default

    It is possible to route ali, but rains large, hot, and sharp ali chips everywhere. Full protective clothing, cap, eyes, ears, face shield, gloves, heavy duty overalls, fully enclosed boots, sock protectors etc virtually essential. Hot metal chips into a woodwork dusty not a good idea, tends to start fires, have seen it start metal dust smouldering in a metalwork dusty. From our experience, general grades of ali (non heat treated) would deform before bending stainless tubing.

    You haven't said what wall thickness stainless you are working with. We used to do bent 25mm x 1.6 wall thickness furniture leg assemblies, using a 5 ton hydraulic bender with machined cast iron forms about 60mm deep which have to be very accurately profiled to avoid the tube flattenning at the bends. The profiled section of the form has to match bend radius you require, so a range of forms for different sized sections and bend radiuses quickly becomes expensive, bulky and heavy.

    Your plywood bender would not have a hope with any of the hard tubes, and would probably struggle with softer materials in 25mm thin wall sections. Might work with small section, thin wall soft materials or thin sheet or flat bar. What sort of bend radius are you looking for and what angle do you need to bend through?
    I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.

  5. #4
    Join Date
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    Default

    Redx
    Another possibility for bending tube with out it forming wrinkles on the inside diameter.
    Is to weld a plug on one end or multiple folds it must be extremely tight.
    Then fill the tube with a fine dry( must be very dry)sand.
    U then need to stuff the sand in hard.
    Place a plug on the other end ensuring there are no air gaps.
    And again weld or fold it over tight
    U do not want room on the inside for the sand to shift .
    Now if you bend the tube around a form or what ever your bending system is the tube should stay wrinkle free.
    The sand will move but not shift.
    Hopefully resulting in a wrinkle free curve

  6. #5
    Join Date
    Oct 2010
    Location
    Victoria, Australia
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    Default

    Thanks for the replies. What I'm trying to is build a new s/steel bowrail for my boat. I got the idea of making the formers out of plywood from a Youtube video. The guy who posted the video said the system worked well for him but he was only bending 7/8" s/s tubing. My stainless tube is 1" OD, not sure of wall thickness but it's more than 1mm so it's probably 1.6mm. I modified the design of the youtube bender after I found it wasn't going to work for me. The picture below shows what I came up with using the scrap steel I had laying around. It did bend the tubing ok as you can see in the photo and the groove for the tubing seems to be able to cope but the strain is too great for the plywood at the centre bolthole. The hole becomes larger and elongated as the wood compresses. I've fitted bronze bushes to try to overcome that problem but it was to no avail.

    My DIY Tube Bender (10).jpg

    My next plan is to sandwich the wooden formers between two circular 1/8" steel plates, The bolt will then pass through the steel plates as well as the wooden former and hopefully this will stop the distortion of the centrebolt hole. I'll also have to go up a couple of sizes with the centrebolt diameter. I was using 1/2" centrebolts but they're not strong enough.

    I heard about filling the tube with sand but haven't tried it yet, can't figure out how to pack sand into a 6m length of tube.

    Cheers,
    redx.

  7. #6
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    6m tube
    If the sand is very dry I've used a BQ before to dry the sand out
    It needs to be bone try.
    if maybe you can fill the tube from a height that might work !!!

  8. #7
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    Block one end of the tube. You then find a 2 or 3 story house with balcony and get a funnel and a bag of sand and a 6m steel rod a bit smaller than the side diameter of your SS tube - say 16mm. Then pour in a bit and ram it, pour some more - etc. Then block the top end too. Done.
    Cheers,
    Joe
    9"thicknesser/planer, 12" bench saw, 2Hp Dusty, 5/8" Drill press, 10" Makita drop saw, 2Hp Makita outer, the usual power tools and carpentry hand tools...

  9. #8
    Join Date
    Nov 2006
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    Default

    Quote Originally Posted by redx View Post
    It did bend the tubing ok as you can see in the photo and the groove for the tubing seems to be able to cope but the strain is too great for the plywood at the centre bolthole. The hole becomes larger and elongated as the wood compresses. I've fitted bronze bushes to try to overcome that problem but it was to no avail.

    My DIY Tube Bender (10).jpg

    My next plan is to sandwich the wooden formers between two circular 1/8" steel plates, The bolt will then pass through the steel plates as well as the wooden former and hopefully this will stop the distortion of the centrebolt hole. I'll also have to go up a couple of sizes with the centrebolt diameter. I was using 1/2" centrebolts but they're not strong enough.
    Cheers,
    redx.
    It sounds like a mat'l failure as a result of the load at the center, (the wood is not strong enough) to reduce the stress on the material (the wood) you need to increase the area of the wood (spreading the load) the brass bush is the right thinking (at a guess the brass bush didn't fail (unless it was thin walled) the brass bush deformed the wood) again, make the bush larger or make the former thicker or remove the stress from the wood and transfer it to the steel plates like you are thinking of doing, if you do that make sure there are plenty of bolts around the perimeter of the former, I'd suggest epoxy/PU glue the plates to the former as well as bolting it all together.

    I would have thought that 1/2" bolts would have been plenty strong enough, I'd suggest give the plates a try with the 1/2" bolts

    Let us know how you go with it.



    Pete

    PS
    You may need to think about increasing the depth of the groove in the former, can't quite see from the pic but it needs to come up to at least the center of the tube to help stop it squashing, with that design you can really only make it half the dia. deep alternatively, to help stop it squashing make the diameter of the groove in the former a little less than the diameter of the tube.

  10. #9
    Join Date
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    Location
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    Default

    Hi,

    To those interested. I have posted a couple of updates to this thread (with pics) on the Metal Working forum

    https://www.woodworkforums.com/showth...=1#post1761343

    Thanks,
    redx.

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