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How do I bend aluminum without it fracturing?

Discussion in 'Maintenance, Tinkering & Embellishment' started by lerner, Feb 21, 2009.

  1. lerner


    Sep 1, 2008
    Let me clarify:
    The aluminum is the jaw-tips of my Lansky Clamp. I dremeled a groove in the knife-spine. Now the Clamp must grip into the groove by means of a "claw" shape. (Without this procedure, the clamp slips off too easily.)

    I already tried bending the outer 1/16" around a nail. I just hammered it to shape while the nail was clamped in the jaws. But the aluminum fractured (cracked) at the outer corner of the bend.

    Now, I ground all that off the Clamp, reground a handsome Clamp-edge, and am ready to start anew. So the question is: How do I bend the edge over, this time without weakening the bend?

    My guess is just heat it; but I have little knowledge of heat-treating/tempering, or even if aluminum even acts like steel in that way. Must I get the aluminum red-hot for it to become "malleable". I know aluminum turns to white powder when heated to much. Assuming there was no fracturing, would the resulting "forged" bend be stronger or weaker?

    Please ask me to clarify, if this whole description doesnt sound clear.
  2. Haze


    Aug 2, 2004
    Heating it will soften the metal enough to bend it, Aluminium dosnt behave like steel so you wont be doing much if any damage.

    Some Aluminium aloys can be "hardned" by heating but I dont suppose that would make any difference in your case any way.
  3. wnease


    Apr 22, 2004
    uh oh, no way to know without knowing the exact alloy. aluminum alloys, forging, heat treatments, aging, all incredibly complex
  4. 65535


    Mar 14, 2007
    If I were you I would focus on making a knew knife grip out of some aluminum and grinding in the little "tooth" on the edge that you want.

    Like wnease said aluminum alloys are very complex if it crumbled then it was probably a cheap alloy because most alloys like 6061 which is very common tend to bend before breaking, although it sounds like you where bending it quite a bit.
  5. knarfeng

    knarfeng senex morosus moderator Staff Member Super Mod Moderator

    Jul 30, 2006
    How hot you would need to get it depends on the alloy. But, if it is a heat treated grade, if you heat it enough to bend it you will ruin the temper. Then it won't hold the knife properly anyway. Best guess at a generic temperature for being able to bend is ~500F. But I really don't recommend this.

    I think you would be better off modifying the grip by bonding something to the grip ends. You might try getting some aluminum shim stock or other thin metal, cutting it to shape, then bonding it to the ends of the clamp with high strength epoxy adhesive as sold in the local hardware. Much more likely to succeed.
  6. Hawkings


    Mar 31, 2006
    Aluminium does not behave like steel when you heat it.
    One major difference is that inner metal will melt before the the outer shell. This means that if you are not careful it will leave you with a big hole in a blink of an eye.

    The outer shell is made when aluminium makes contact with the air.

    One way to know the right temperature is to touch it really really quick with your finger tip, when it feel like "Fizzling / bubbling " under your fingertip it has the right tempeture.

    I have had succses with this method. BUT if you do it wrong, you can hurt yourself. so use with care.
  7. me2


    Oct 11, 2003
    Also, aluminum doesnt glow when heated like steel and iron do. Makes it interesting working around an extrusion plant, where the hot and cold pieces look the same.
  8. lerner


    Sep 1, 2008
    Oh great, a bunch of differing opinions.:confused:;)

    Has anybody else pimped their lansky to grip the knife?
    I ground a "tooth" into my Gatco clamp; worked great with one knife so far.
    Does anybody know the grade of aluminum in their Lansky, or Gatco, clamp?
    Can you tell from the clamps' construction if they were forged, ground, cast, or what?
    Last edited: Feb 21, 2009
  9. JatMat


    Aug 26, 2006
    Small amounts of aluminum will actually oxidize and burn up before melting. You have to have large quantities to melt and what is left after melting is considered toxic. Some of the largest dumps of that dross were declared major EPA disasters and cost millions upon millions to clean up. Though in the amounts you are working with, I doubt anyone would notice. I use to smelt aluminum until I started trying to figure out what to do with the dross.
  10. sceva

    sceva Gold Member Gold Member

    Sep 18, 2002
    When bending sheet metal, especially aluminum, you have to watch out that you do not make a tighter bend than what is called the minimum bend radius. If you try to make a smaller bend it will crack along the bend line.
    Each alloy, temper and thickness has its own min. bend radius.

    Do a search under minimum bend radius for aluminum and you will find charts.

    Find a piece of tubing that is the right diameter and bend your shaat metal over it to get the ptoper bend radius. ( 1/8" radius = 1/4" diameter tube)

    Aluminum is normally bent in the O condition (soft) so you may have to heat it but if you can get by with a larger bend radius you can probably get it done. Another thing to remember is that once bent the rule of thumb is that you can bend it further but you can not straighten it if you bend it too far or it will weaken and crack. ( One way bends only)
  11. 4ever3


    Mar 28, 2007

    Aluminum will give you no indication as to how hot it is (it will not change color like steel) until it's to late then it will be molten !!!
  12. Roger999


    Mar 22, 2008
    Then what method do you suggest for bending it?
  13. SOLEIL

    SOLEIL Platinum Member Platinum Member

    Mar 20, 2006
    6061 is the common grade for conduit and other types of malleable aluminum structures. They are usually bent with machines or on a jig. 7075 is the common grade for structural or aluminum parts, such as the Lansky clamps, and is not made to be easily bent or worn. As mentioned there are many grades of aluminum, 20k+ IIRC, and very few if any respond easily or well to bending by heating. Adhering something to the clamps to hold the blade may be your best bet.
  14. Tripton


    May 26, 2008
    Wait a minute...

    Did you say that you dremeled a groove into the spine of the knife blade??

    AND, now you are trying to curl the clamp around so that it bites perfectly into the groove that you dremeled into the blade?

    If I am picturing this correctly, I cannot see how this would work very well...

    I have never had a problem with a Gatco clamping a blade, though it is a bit of a pain in the butt...

    Might I ask why you do not just leave the clamp as is, adjust the angle of the clamps to fit the blade (if sharpening a flat ground knife) and snug it down until it is sufficiently tight?
  15. flipit


    Sep 21, 2006
    Ice water get a big pitcher half ice half water put it in a bench vice duck tape your hammer head poor almost all water ware you want the bend tap it SLOW works well up to 7005 series.when aluminum heats the molecules expand that's why it cracks when you try to bend it.
  16. Tinbasher


    Jan 24, 2007
    As a aircraft sheet metal worker bending Aluminium is part of my trade, most of the extrusions used in the clamping systems are 6061-T6. I would not try and bend T6 at a sharp angle even in T3 state you must use at least 3 times the metal thickness as your bend radius and polish the ends first (no sharp edges). We heat treat T3 to 495f in the oven for 20min then quench in cold water, it starts to get hard after 2 hrs and gets to T42 after three days.If you want T6 further aging in a ramp down oven is required.
    locally heating the Aluminium will leave it in W condition (unstable) not much good for anything.

    Chart http://www.tpub.com/content/aviationandaccessories/TM-43-0106/css/TM-43-0106_318.htm
    Last edited: Feb 21, 2009
  17. 4ever3


    Mar 28, 2007
    Aluminum is bent on a sheet metal break and the harder the aluminum the larger radius dies you have to use. All I'm saying is if you stick a propane or O/A torch to a piece of aluminum, you won't know it's to hot until it's to late and when the blob of melted Aluminum hits the floor it will splatter like water and your burnt... Bad idea

    I realize the flange for the angle guides on the Lansky are bent in a break, and as small as the radius is my guess is it is done pre heat treat in the annealed or O state then heat treated to a T6 or T651 (depending on the grade of Aluminum) and theres no way to bend it after heat treat.

    The main thing I am trying to get across is DO NOT heat it to bend it
  18. lerner


    Sep 1, 2008
    So this is the info I'm going to rely on:
    1) I wont heat the Al anywhere near melting. Just enough to decrease the min. bend radius (i.e. increase malleability?). Butane lighter or gas stove for couple minutes.
    2) One expert said the clamp is probably 6061. Another expert said 7075. Both recommended against bending.
    3) Correct me if I'm wrong, but the clamp definately doesnt compare to Al sheet-metal.
    4) there is no glue/epoxy/adhesive as strong as the Al itself; and Al cant easily be soldered/brazed.
    5) The discussion is rather academic now; Any method will be hit-or-miss; I will probably ruin this clamp, buy another, ruin with different method...

    What I'm still interested in is this:
    the terms O condition (soft), T3 state, W condition (unstable)...
    What scale or series are they members of that I can google?
  19. Tinbasher


    Jan 24, 2007
    The clamping foot is quite thick, could you not just drill and tap a few small holes near the edge then let the screws extend thru enough to locate the bottom of the groove.
  20. Tinbasher


    Jan 24, 2007
    6061 can be bought in "O" "T3" "T6" and I think "T8"

    unlike 6061 7075 can be heat treated but remains in the "W" condition until aged in a ramp down oven .
    7075 is more prone to corrosion than 6061 we see it all the time on older aircraft, just to confuse a bit more a lot of aircraft parts ie: skins and extrusions, are now made from 2024-T3 also heat treatable. Have a read here.

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