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the best way to mill a slot?

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  • the best way to mill a slot?

    Is it better to mill a slot in 6mm thick flat steel using an end mill by first plunging all the way through and then milling the length of the slot in one pass slowly. Or to take shallow cuts the length of the slot multiple times?
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  • #2
    6 mm is pretty thin, do it in one pass. Not if using a 1 mm end mill though

    If you do not have a center cutting end mill, drill a starter hole, much faster than multiple passes ramping down....

    Sides will need to be cleaned up by climb cutting to size if any accuracy, or fine finish is needed.

    The end mill will cut oversize, so go down a size on cutter to leave some for side cleanup passes....

    I only make multiple passes, if work is much thicker than diameter of end mill.

    A roughing end mill, really speeds up the job,
    Last edited by Bguns; 04-24-2010, 05:38 PM.

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    • #3
      How do you hold something that thin while you are working on it, sandwich it?
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      • #4
        Drill a series of holes to remove most of the material first is often faster. You probably should drill a pilot hole on one end of the slot anyway so just step over and drill a few more.

        Milling shallow cuts back and forth you will recut lots of chips unless you have flood coolant or vacuum to pull them out of the slot. If you have enough rigidity, milling full depth allows chips to fall through and won't wear out the tip of your endmill.

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        • #5
          Depends how wide the slot is.

          It is fastest to punch though and "chain drill" with the end mill every 1/2 diameter of the mill, then keep the mill down and transverse the slot again to clean it up.

          This is how I was taught by an old shop guy.

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          • #6
            AFAIK endmills are not for drilling, thats what drills are for.

            My endmills usally whine at me if I try and drill with them.
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            • #7
              You can plunge an endmill (i.e. drill with it). They don't dislike it that much and provided it is centercutting, there usually is not much drama involved. Take your normal feedrate and divide by number of flutes to get a good plunge feedrate.

              When slotting like this, I like to ramp, just like the CNC'ers do, rather than plunge. With a manual machine, you can feel in the handwheels what a difference in cutting forces it makes. Much less drama ramping down.

              So I would ramp down to full cut depth, finish to the end of the slot, and then crank back to the beginning of the slot. One hand on the X or Y feed, one on the Z feed handwheel.

              Depending on how much the material is making the machine struggle, I would cut up to 1 x diameter per pass in depth.

              Cheers,

              BW
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              • #8
                Chop Milling

                Originally posted by gda
                Depends how wide the slot is.

                It is fastest to punch though and "chain drill" with the end mill every 1/2 diameter of the mill, then keep the mill down and transverse the slot again to clean it up.

                This is how I was taught by an old shop guy.
                This way works for me. We call this Chop Milling. It's fast and easy.
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                • #9
                  Originally posted by BobWarfield
                  When slotting like this, I like to ramp, just like the CNC'ers do, rather than plunge. With a manual machine, you can feel in the handwheels what a difference in cutting forces it makes. Much less drama ramping down.
                  I'd like to see a video of that. I've seen it done often with CNC but it seems like patting your head and rubbing your stomach to try it with the hand wheels.

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                  • #10
                    Originally posted by dp
                    I'd like to see a video of that. I've seen it done often with CNC but it seems like patting your head and rubbing your stomach to try it with the hand wheels.
                    ROFL, it feels a little bit like it too!

                    I first tried it almost at a lark, but discovered it was easy and worked well.

                    BW
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                    http://www.cnccookbook.com/index.htm
                    Try G-Wizard Machinist's Calculator for free:
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                    • #11
                      I tried the ramp aproach

                      I am making three inch long slots in 8mm steel. I used a 12mm end mill. Center cutting. But I didn't feed it manually. I used both the Z and X power feed until I pierced the steel and then just the X power feed. When I was through I milled to the end of the slot and then reversed X and cut the ramp out. The next piece I just plunged the end mill and cut the whole length. Both worked just fine. I am doing this on a horizontal mill with plenty power. I used 1400 rpm for the spindle and it cut fine. These parts don't have to be really exact so I didn't use a smaller diameter end mill first.
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