Tutorial - DIY Inside Corner Bracket

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Senior member Navig has graced the our forums with another detailed how-to. This time he tells us how to make a corner bracket for connecting aluminum square tube together. There is even a bonus how-to make endplugs for the open end of the square tube you’re left with.

Navig’s thread will be merged into this article’s comments thread so the tutorial will be in the Comments section below. If the photos don’t load properly, just click this link and head straight to the forum post to read his superb tutorial.

Thanks for sharing your craft with us Navig!

– Jeremy Vaughan (hokiealumnus)

About Jeremy Vaughan 197 Articles
I'm an editor and writer here at Overclockers.com as well as a moderator at our beloved forums. I've been around the overclocking community for several years and just love to sink my teeth into any hardware I can get my paws on!


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  1. I started with ¾” angle brass, 1/16” thickness.
    Why brass? It’s solid, machinable, inexpensive, can be powdercoated, comes in standard sizes like 1/16” thick. Aluminum would be ideal, but you just can’t easily solder it, and welding it would require some fairly expensive specialized equipment. Steel would work great, but I only found ⅛” thick angle, which is probably overkill for our purposes.

    Each bracket of mine is composed of 2 pieces of the angle brass, one 4” in length and one 2 1/16” in length

    I use a cutting bandsaw:

    Alternatives: chopsaw, cutt-off saw, dremel with a cutoff wheel, standard bandsaw, handsaw with a miterbox, tablesaw with a sled, scrollsaw, sawzall.
    I also use a sanding disk to finish the edges:

    I suggest making a quick marking jig to make your holes consistent from bracket to bracket:

    Then use a center punch to create divots for your drill:

    Weapon of choice: springloaded center punch
    Drill all your holes:

    Be careful here! I’ve noticed brass has what I call pull-thru. When standard drill bits exit the far side of the material, they will catch on the under-surface and cause the material to jump up towards the chuck. You can hold it down easily, but just be ready for the jump.
    Weapon of choice: drill press.
    Alternate tools: drill

    First mark a midline slot:

    Next cut the slot out (I’ve also added a pencil line for the next step):

    I use my bandsaw:

    Alternate tools: dremel with cutoff, hand miter box.

    Clamp the 4” piece in a vise, with just about 1/64” addition from the previously scored bend line to accommodate the bend radius.
    Then I apply some gentle heat, and pound the bend in with a hammer.

    Video (click to view)

    Tools: vice, hammer, butane plumber's torch

    Some people feel that prepping is a good but not essential step. Surface preparation is CRUCIAL for welding and soldering. If you don’t take time and prep, the solder will NOT hold and you might as well not do any of this.
    Prep the interface surface:

    I used an 80 grit sanding triangle on a Dremel Multimax followed by 220 grit by hand, then cleaning with a paper towl.
    Alternates: plumber’s cleaning cloth, sandpaper by hand.

    I’ve got my brass pieces ready to solder together, but it is best to do so while they are attached to a jig. So I put together 3 pieces of ¾” square tube together to a corner, held by external L brackets. This is important so that you know your bracket will come out shaped properly.

    Next, I secured the inside corner bracket to the jig with some screws and tape.

    We are going to make a butt joint, where the ends of the folded 4” piece will meet the surface of the 2” piece. This is why the 2” piece is actually 2 1/16” in length because it sits down losing 1/16” of its length to make the joint.

    We’ve got for soldering:
    1) Small butane lighter
    2) Larger propane torch (not necessary but makes it faster)
    3) Flux and brush
    All available at any hardware store in the aisle for copper plumbing.
    4) Solder--I’m using standard Radioshack solder (it’s leaded, so remember, wear mask).
    5) Forceps or tweezers for handing hot items, maybe some hot mitts
    1) N95 mask, especially if you are using leaded solder
    2) Gloves
    3) Something to torch on, in this case an old aluminum motherboard tray
    4) Squirt bottle of water
    5) Fire extinguisher

    Make sure you surfaces are sanded and clean bare metal.
    Then add flux. Flux will dictate where the solder will go, 2 important things to remember:
    1) Work the flux down into the surfaces of the actual joint (especially on the edge of the folded piece--in fact its probably better to flux this surface before mounting it to the jig).
    2) Only put flux where you want solder to go--in fact I will mask off areas to lay down my flux:

    This is actually my first time doing this sort of thing, but this was the method I worked out.
    1) Use large propane torch to heat the targeted joint for about 10 seconds. I found the large propane torch too unwieldy to work with actually laying down solder simultaneously.
    Video (click to view)

    2) Then use the small butane torch to deposit small blobs of solder along the joint:

    Video (click to view)

    3) After depositing them, I heat them for another 10 seconds with the small butane torch to stick them to the metal (otherwise they will actually move around).
    4) Next, I use the large propane torch and just blast the solder deposits. In about 10 seconds they will liquefy, coalesce, then spread along the area of flux. This is not a subtle transformation. The picture below is literally the exactly the same pic as above just after application of nothing more than propane heat:

    Video (click to view)

    5) Repeat steps #2 thru #4 until you get a nice distribution of solder across the length of the joint:

    6) Repeat steps #2 thru #4 for the other joint:

    Video (click to view)--Whole second bead start to finish.

    1) Make sure the solder bead makes a nice gusseted joint and fills in the gap between the pieces:

    2) Turn the piece over and make sure solder has filled in the gap between the 2 pieces:
    1) I use a standard b*stard (fill in "a") and round file to shape the bead to a nice smooth concave bead:

    2) Finished:

    3) If you want to really smooth the solder bead out, you can apply JB Weld:

    4) Piece is now ready for paint or powdercoating!
    However, I’ve got other plans for these brackets....so bare brass for me.

    As a corollary project to my DIY Inside Corner Bracket, I will also include some instructions for fabricating my DIY End Plugs.
    As you can see from the above picture, once you’ve got your corners secured with the bracket, if you do standard straight cutting of your square tubes, you will end up with exposed tube inside.
    So let’s close it up with an end cap.

    I start with some strip ¾” wide, 1/16” thick bar aluminum.
    Then I cut off a ¾”+ piece (use: bandsaw, cutoff, hand miter box). Make it just slightly larger than ¾” because you can plan on sanding it down. Getting an exact ¾” square piece is too difficult without robotic aid.
    I also start with some ⅝” plastic cubes, available for very cheap at various plastic suppliers.
    You can also start with some ⅝” aluminum square bar and cut off lengths (I recommend from ½” to ⅝”).
    Finally, have a small piece of de-burred ¾” aluminum square tube (1/16” thick walls), approximately ½” length--this is going to be our jig.