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I have 36" of Aluminum 6061 square bar (5/8"x5/8") that I am trying to cut into uniform I-shapes shown below where two parallel 2" x 1/8" x 5/8" sections are cut from the long sides of each 2.5" piece. enter image description here

I have read online that the most accurate method would be to have a long bar that matches the wider dimensions (2.5" x 5/8") and running it through a CNC mill to cut it in to the uniform shape, then cutting it in to 5/8" sections. Unfortunately I do not have access to such a large section of aluminum nor a CNC mill.

I have access to:

  • Vertical bandsaw
  • Drill Press
  • Hand drill
  • Miter Saw
  • Bench Grinder

I was thinking the most straightforward albeit lengthy (and inaccurate) process would be making four cuts from the outside towards the center, then drilling four holes into the side using the drill press with a 7/64" diameter bit then making another cut to remove any remainder material as shown below: enter image description here

I would need to follow up with either diagonal cuts into the grooves because my bandsaw blade is 0.5" wide from teeth to flat side, so it wouldn't fit flush against the inner plane yet to do cut the long dimension. I think I would have to do additional cuts to get more material out of the way to cut it flat. At this point the drilled holes seem sorta unnecessary, but I wouldn't want to risk cutting deep into the finished product right at a corner (stress concentration point) with the diagonal cuts (mainly cut #2). That would result in something like below:

enter image description here

I could try to clean away that last triangle to get a flat surface with additional cuts or a file then I could make the long cut along the length of the bar.

This process seems extremely tedious and probably illustrates my inexperience really well-- is there anything else I can do with the tools I have to make this more efficient and repeatable? I will need to process at least 20 of these for the parts I need. Unfortunately there are no metal shops for small jobs where I live, and purchasing from another state costs almost as much in shipping and handling as the parts themselves cost in material and labor, both of which are in the hundreds of dollars range.

Ideally I would like very flat and parallel surfaces, but with the steps outlined so far each side is going to have at least one triangular lump that is difficult to file down. Would a jigsaw with a metal cutting blade help with cutting straighter down into the aluminum? Or maybe a compact angle grinder with a very small diamond blade to start the cut from the top? Even after reading about tools for different metal cutting applications I can't find any that really suit this particular cutting job besides a CNC mill which is thousands of dollars at a minimum.

1. How can I improve/change this process?

2. Would I need additional tools for this project?

I would be willing to spend $200-$300 on a new tool/bit set.

Thank you in advance for any advice and input!

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  • There probably are machine shops that would take this on, even in quite small places, but they can be very hard to track down. It's possible they have no online presence at all
    – Chris H
    Jun 27 at 12:12
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    With limited facilities, I tend to consider this sort of thing at the design stage. So for example make it out of 3 pieces bolted together; each piece is then a cuboid. Without knowing your application I don't know whether that would be suitable, but it's as well to consider manufacturability up front
    – Chris H
    Jun 27 at 12:16
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    You wouldn't need or necessarily want a CNC mill, a simple manual mill would make short work of this. The machinist could clamp a number of bars together and mill them off in one operation, flip and do the other side. Jun 27 at 18:14
  • Might want to specify the acceptable radii for the inside corners. Jun 27 at 23:41

1 Answer 1

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Don't overestimate the difficulty involved in filing aluminum. One can nearly sculpt aluminum into any shape in a very short time, using a sharp file and a file card. It is even practical to use only a file to create a single unit, but not 20, of course.

An angle grinder will either break the cutting disk or clog nearly immediately; reject that option.

I have a hobbyist mini-mill, not CNC. It would be somewhat tedious to cut 20 pieces, but not overly so, as your requirements are straightforward. There's no user-to-user communications on this resource, but this is something I'd take on at hobby prices. You may want to broaden your search into mini-mill forums in which you'll find agreeable hobbyists willing to take on your project as a lower cost option. If you do so, you'd want to specify tolerance of the dimensions. For example: do you need 1/8" (0.125 inches) to plus/minus 0.001 inch tolerance? Would you provide the raw material, as you've noted that you have the bar? Less expensive to ship if it's cut to length, even if slightly oversize, using a hacksaw. Aspects of this sort also apply to your own work efforts.

I believe that you could use a hacksaw with a new/sharp blade, (lubricate the blade when in use), an equally sharp file with a file card (I'll have to research lubing a file) and perhaps the drilling as you've suggested. I reference the lubrication, as a file will quickly clog with aluminum, reducing effectiveness. The file card may not keep the teeth as clean as desired. WD-40 and kerosene are common lubes for aluminum machining.

Your miter saw (electric?) is a good choice for cutting pieces to length, as it will provide more squareness to the cuts. If you have access to a sliding miter saw, you can also set depth-of-cut to your requirements. Additionally, creating the depth-of-cut at the edge of the piece as noted and sliding the work to cause adjacent cuts will remove the triangle of concern.

Note, however that the precision available on a sliding miter saw is limited by the flex of the depth-of-cut mechanism. You could mitigate this by applying "excessive" downward force to achieve the desired depth. Once completed, filing could return a uniform depth over the surface.

The vertical bandsaw also provides the equivalent capability, as long as you can be certain to limit the depth of cut and to provide appropriate guide on the outside cuts. Making cuts that leaves the appearance of a comb, then cutting away more and filing away the remainder is common in the hobby world, at least my hobby world.

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    Incredible, thank you for such a detailed, insightful answer! Thank you for the warning on the angle grinder, I will not go that route. I will try to search for local hobbyist forums, but unfortunately since the population of my state overall is relatively low compared to others I haven't been able to find one so far. If I may ask, what was the cost of your mini-mill including necessary accessories? Understood, I will use my miter saw for the 2.5" sectioning cuts. Ah, I have seen that technique used for woodworking. Thank you for the reminder, I did not think of applying it! Jun 27 at 1:17
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    I've forgotten the cost, but there are many variations of this mini-mill from mid-level distributors to the warehouse type (HF) with prices around both sides of US$1000, depending on accessories. I purchased a turnkey system with clamps, collets, mills, etc, while a bare system would be less. I suggest the forums, as shipping from a hobbyist isn't going to be problematic. Finding a hobbyist to help wouldn't be regional.
    – fred_dot_u
    Jun 27 at 8:18
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    One resource you may find useful is groups.io/g/Mini-Mills/topics which also allows peer-to-peer communications. Note that my username there is identical to this one.
    – fred_dot_u
    Jun 27 at 8:24

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