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Corner Brackets?

Discussion in 'General Talk' started by Balu, Apr 14, 2016.

  1. Balu

    Balu Veteran
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    Since I'm not used to building with extrusion, I am a little overwhelmed with all the parts and possible combinations. :)

    Right now I'm thinking about differences in the corner brackets. When do you go for what bracket?

    The difference between Cast and Black Angle Corner brackets seem to be the price mostly, but they seem to work equally good.

    The Inside Hidden Corner Bracket and the L Bracket seem to be similar in that way too, with one having the advantage of being "hidden".

    Then there are the Joining Plates - especially the 90 Degree one :).

    What are the mechanical differences between all these options? Besides connections where one bracket requires more space and might get in the way of something...

    Is one connection stronger than the others?

    Is it easier to get 90┬░ corners right (or to square a build) with one of them?

    What else didn't I think about?
     
  2. Jonathon Duerig

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    The cast corner bracket is cheaper, so use it when possible instead of the black corner bracket. But the black corner bracket does not have little homing tabs on the bottom. So use it where you need to connect extrusion to something that must be flush with the bracket (plate, mounting point, etc.) or where you want to stairstep parallel extrusions (the brackets prevent a corner bracket from being used at a right angle to the direction of the slot).

    The L-brackets are individually more flimsy than the cast corner or black brackets. But you can use the two-wide and three-wide ones to connect the wider extrusions fairly solidly. And it can also be used to mount extrusion or where things need to be flush.

    I have never used the inside corner brackets.

    The joining plates provide a much sturdier connection than the corner brackets. Partly because they provide a bigger gusset. And partly because you they provide multiple connection points to each piece. If you have two pieces connected via a corner bracket, they can rotate around one another around the screw connections. With the joining plates, this is no longer the case.

    It is easiest to get 90 degree angles with the joining plates because you can individually line each extrusion flush with the edge of a joining plate.

    Strip plates are what you didn't think about. They are nice for a lot of uses. For example, if you want a crossbar to turn a large rectangle into two triangle trusses, you can use two three-hole joining plates at the ends of the the cross beam. Then you secure it at an arbitrary angle to each side to make a truss and a sturdy square.

    So overall:

    - Use cast brackets over black corner brackets when possible. But black brackets are a bit more capable.
    - Use corner brackets where possible since they are cheaper. Where they aren't strong enough, use joining plates.
    - Strip plates can also be super-useful.

    Screw guide:

    - L-Brackets, Cast Corner Brackets, and Black Corner Brackets should all be used with 8mm screws.
    - For joining plates, I use 10mm screws with a washer. They technically work with 8mm screws, but I always end up sad when I try it that way because 8mm is too short. You need the washer because 10mm is too long.

    -D
     
    #2 Jonathon Duerig, Apr 14, 2016
    Last edited: Apr 14, 2016
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  3. Ronald van Arkel

    Staff Member Resident Builder Builder

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    To comment on Jonathon,

    If 8mm screws are to short and 10mm screws to long, flip the T-nut 180┬║ so the bevel points outwards the V-Slot/C-Beam, this will give you an extra mm.

    And, you can use a file to knock off the "homing" tabs and use it everywhere. Still, the black corners are much more square and solid, if money isn't a concern than use the black ones. Also, the black corners go flush with the end of a V-Slot/C-Beam for better looks and stability.

    -Ronald
     
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  4. Jonathon Duerig

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    Ronald, I'll have to try that. I've always consistently used T-nuts with the bumpy side towards the center of the beam since I thought that was the only way it would work.

    But it may be too late for me. I already have a bin with 7500 M5 washers. :)

    -D
     
  5. Balu

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    Thanks for that detailed explanation, Jonathon.

    The description for the Cast Corner Brackets says:
    So I'd guess you need both length of screws for those?
     
  6. Ronald van Arkel

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    If you leave the "stand off teeth" on, you need 10mm screws, but it's better in most cases to take a file to it and flatten the sides of the brackets. When you flatten the sides you need to use 8mm screws and forget about the 10mm.

    -Ronald
     
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  7. Jonathon Duerig

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    @Balu, I have only ever used the cast corner brackets in a situation where 8mm screws work for both ends because you have a corner like the one pictured on the product page. Whenever I might have been tempted to file off the teeth or use a longer screw, I have chosen to use a black corner bracket instead.

    @Ronald van Arkel, The reversed T-Nut seems to fit in the slot. I had been using them bumpy-side down religiously since the instructions on the very first extrusion project I built explicitly said to do it this way. Does it matter which way you put the T-Nut? Is there an advantage to doing it bumpy side up vs down in typical usage (when the screw is long enough for either way)? Which way do you do it?

    -D
     
  8. Ronald van Arkel

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    @Jonathon Duerig, I just make sure that the screw grabs as much T-nut as it can, there isn't any advantage other than not having to use a 1mm shim, o like you a washer, between plate and screw-head. When fixing a timing belt it is a must to have them reversed else you will have a hard time getting everything together. For the rest, I can't come up with anything in particular .

    -Ronald
     

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