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Thread: Help machining holes in aluminum

  1. #1
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    Help machining holes in aluminum

    I can machine aluminum with my CNC without issues, but anytime I try to create any hole smaller than ~.25 my bit breaks? I am using Fusion 360 and these are helical plunges, so I'm not sure what I'm doing wrong. Should I be using peck drilling? I do not have a lot of experience with aluminum, so I need advice before I break all of my .125 bits :-)

    Thanks!

  2. #2
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    How many holes, size hole, material thickness? Are you using a mister?
    I always use peck drilling, not sure why you’d want to use a helical TP.
    Another consideration is material temper/hardness. T-6 machines nicely, (harder) T-0 not so much. (gummy)
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  3. #3
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    My understanding is that you need to take very, very light cuts with each pass of the tooling and find the optimal movement speed that cuts without over-stressing the bit laterally with aluminum...the holes are going to take longer, but should turn out really clean, too. Be sure you are using cutters designed for aluminum, too, for best results. Bruce makes some good points.

    One question...these "helical plunges'...do they remove material from the center like would happen in a normal pocketing operation, or are you cutting just the perimeter? (I don't know Fusion360...Vectric user here) 'Just curious
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    The most expensive tool is the one you buy "cheaply" and often...

  4. #4
    Squirting denatured alcohol helps, makes the shaving less gummy.

  5. #5
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    Thanks for the replies everyone! .25" thick 6061 aluminum plate. It only breaks on small holes. I have done .5" and larger holes just fine. I am making(trying) to make a drag knife and the holes that I need to make are very small, the smallest is .139" diameter and I am using Pocket tool path. Like I said, I know next to nothing about machining aluminum, but I know it can be done on my CNC. I am not using a mister, but am spritzing WD40 every few seconds. Has worked perfectly on everything except the small holes. As soon as it starts plunging the bit naps. Goes down maybe .125"

    I did do research on this and have feeds and speeds that seem to work, except for the holes. I am using a 1 flute carbide up spiral bit. would peck drilling work with this bit? This is something I've never done before.

    Thanks,

    Screen Shot 2018-12-23 at 3.29.57 PM.jpg
    Last edited by David Justice; 12-23-2018 at 3:45 PM.

  6. #6
    Denatured alcohol. I learned that in a pattern shop many years ago. We sometimes had to alter aluminum match plates.
    Again: it changes the gumyness to crispness. I'm sorry it didn't get any votes ...because it works.

  7. #7
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    1.39mm or .139 decimal? .061Ø or .139Ø, either way I would use a 1/16 or 9/64 drill and a peck routine.
    This is how prototype work done every day in machine shops. If your reasoning is to helical plunge several different diameters in one setup with one cutter you are causing yourself unnecessary headache.

    Edit: I see you clarified the diameter, (lunch time for me )
    Last edited by Bruce Page; 12-23-2018 at 5:20 PM.
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  8. #8
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    As soon as it starts plunging the bit naps. Goes down maybe .125"


    Plunging .125 for a pocketing operation in aluminum is way, way too deep of a pass, especially with a very small cutter. You need to take it off in very thin passes...a few thou each, IMHO.
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    The most expensive tool is the one you buy "cheaply" and often...

  9. #9
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    So, dumb question about peck drilling, it's called Deep Drilling in Fusion, I have found out. Does the bit have to be the same size of the hole being drilled? Normally in wood, using pocketing, I can drill a large hole with a smaller diameter bit, but the drilling tool path doesn't look like it moves any direction but up and down while making the cut? And do I use and actual drill bit for this or some other type of bit?

    Thanks!

  10. #10
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    If your using a spindle and can adjust the speed I would use a drill bit the proper size. I purchased some cheap collets off Amazon to use. I got exactly what I paid for meaning cheap but it was an assortment of sizes from 1/8 to 1/2 inch. They would be great for holding drill bits just for drilling.
    Yes I have purchased some good collets, but at least I have found a use for the others!
    Retired Guy- Central Iowa.HVAC/R , Cloudray Galvo Fiber , -Windows 10

  11. #11
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    A drilling tool path is going to expect that the cutter is the size you want the hole to be. The "pecking" refers to the action where the bit/drill will enter the material a short way and then retract to remove debris before re-entering to a deeper level. Rinse...repeat...

    Bill is correct that you'll want to adjust the speed downward when using a drill tool path with a drill.
    --

    The most expensive tool is the one you buy "cheaply" and often...

  12. #12
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    I have drilled aluminum on my CNC router. In Fusion the drill toolpath is straight up and down and the “bore” toolpath is the spiral in one. If you are using a pocket toolpath, make sure you are using a bit capable of plunging, not all can (I am not sure a single flute would). Or ramping in is an option on a pocket. Usually I just chuck up a center drill and just spot drill all the locations and finish on a drill press. I can set my spindle to low rpms, but it has little torque at the low speeds (below 6000). Get the accuracy and repeatability of the CNC, combined with the high torque, lower speeds and deep hole capability of the drill press.
    Colorado Woodworkers Guild
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  13. #13
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    @Richard, that sounds like the perfect plan, don't know why I never thought of that before. Also, I have a 2.2KW spindle, but 6000 is about as low as it will go and I know my drill press will drill those holes very easily. Marking them with the CNC and drilling them with the press is a great idea.

    Thanks for the advice everyone!

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