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Thread: What drill speeds for steel and aluminum?

  1. #1

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    What drill speeds for steel and aluminum?

    What are the recommended drill speeds for steel and aluminum? The holes are 1/4" or less and its .063 4130 steel and up to .125 aluminum. Also some 4130 tubing.

  2. #2

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    I run the slowest speed in my drill press - I think 300 RPM. You can Google to get the best speeds for those drill sizes but the exact speed is not critical. For steel, most important is to use cutting oil. Second, as mentioned in a recent EAA magazine, drill a small hole first, then enlarge it in steps. That allows you to be more precise in the location of the hole and avoid over stressing the bit.

    Best of luck,

    Wes
    N78S

  3. #3

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    Quote Originally Posted by jtrom View Post
    What are the recommended drill speeds for steel and aluminum? The holes are 1/4" or less and its .063 4130 steel and up to .125 aluminum. Also some 4130 tubing.
    The cutting speed for mild steel is ~80-100 FMP. To figure how many RPM's to turn your drill, simply multiply the cutting speed x 4 then divide by the diameter of the drill. So for a 1/4" hole in mild steel, 80 x 4 /.250 = 1280 RPM. Small drills need lots of RPM's or they end up getting broken or damaged from too much feed pressure.

    Cutting speed for aluminum is ~ 300-700 FPM.

    I don't agree with the recent article in SA. Drilling a hole with a bunch of incremental drills is a waste of time. If you want a true hole, use a properly sharpened drill and the proper speed/feed rates. If you are drilling a large hole, for example, 1" or larger then you may need a pilot hole that is the the same size as the drill web at the point. Otherwise, it's takes too much feed pressure.

  4. #4
    Quote Originally Posted by martymayes View Post
    The cutting speed for mild steel is ~80-100 FMP. To figure how many RPM's to turn your drill, simply multiply the cutting speed x 4 then divide by the diameter of the drill. So for a 1/4" hole in mild steel, 80 x 4 /.250 = 1280 RPM. Small drills need lots of RPM's or they end up getting broken or damaged from too much feed pressure.

    Cutting speed for aluminum is ~ 300-700 FPM.

    I don't agree with the recent article in SA. Drilling a hole with a bunch of incremental drills is a waste of time. If you want a true hole, use a properly sharpened drill and the proper speed/feed rates. If you are drilling a large hole, for example, 1" or larger then you may need a pilot hole that is the the same size as the drill web at the point. Otherwise, it's takes too much feed pressure.
    Reply: If you are drilling with a drill press you may have the ability to control the speed and have some idea what you are doing. With a hand held drill its just a shot in the dark...fast,slow, or somewhere in between. As a rule of thumb, aluminum and other soft materials usually work well with higher speeds, but as the drill bits get larger you may need to slow the drills rpms. Steel is harder and takes slower rpms, and even slower rpms as the drill bit size increases. Stainless steel usually takes a slow rpm but more feed pressure. Most drill bits get dull fast because they are rubbing instead of cutting because of high rpms. Personally I feel that pilot holes work well on all but very small holes. A centerdrill will help you start in the correct location. One thing to watch for is the shape of the flute at the cutting end of the bit. There are different angles, and wider webs which cause a bit to obviate more (especially on thin material). The width of the web at the point of a bit has a lot to do with how much pressure is needed. Its sometimes difficult to apply sufficient pressure when drilling thin metals with no support behind the metal, so you use less pressure.......and the bit rubs because the metal itself cannot sustain more pressure without deforming. Drilling rivet holes is usually high speed work, so keep some sharp drills handy.

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